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RCE Volume I

PRODUCTION Second Edition EDITED BY

Bor S. Luh University of California, Davis

Springer Science+Business Media, LLC

Copyright © 1991 by Springer Science+Business Media New York Originally published by V an N ostrand Reinhold in 1991 Softcover reprint of the hardcover 2nd edition 1991 Library of Congress Catalog Card Number 90-21387 ISBN 978-1-4899-3754-4 (eBook) ISBN 978-1-4899-3756-8 DOI 10.1007/978-1-4899-3754-4 Ali rights reserved. No part of this work covered by the copyright hereon may be reproduced or used in any form by any means-graphic, electronic, or mechanical, including photocopying, recording, taping, or information storage and retrieval systems-without written permis sion of the publisher.

16 15 14 13 12 Il 10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data Rice/edited by Bor S. Luh.-2nd ed. p. cm. Rev. ed. of: Rice-production and utilization. cl980 (1 v.) "An AVI book." Includes bibliographical references and index. Contents: v. 1. Production-v. 2. Utilization. ISBN 978-1-4899-3756-8 1. Rice. 2. Rice-Utilization. 1. Luh, Bor Shiun, 191611. Rice-production and utilization. 90-21387 SB19l.R5R443 1991 CIP 633' .18-dc20

CONTRIBUTORS

D. E. BAYER, Ph.D., Professor, Department of Botany, University of California, Davis, California C. C. BOWLING, M. S. Professor of Entomology, Emeritus, Texas Agricultural Research and Extension Center, The Texas A & M University, Beaumont, Texas TE-TZU CHANG, Ph.D., Geneticist and Leader, Genetic Resources Program, International Rice Research Institute, Los Bafios, Laguna, Philippines ROBERT R. COGBURN, M.S., Research Entomologist, Rice Research Center, South Region, U.S. Department of Agriculture, Beaumont, Texas SURAJIT K. DE DATTA, Ph.D., Agronomist and Head, Agronomy Department, International Rice Research Institute, Los Bafios, Laguna, Philippines CHENG-CHANG LI, Ph.D., Professor, Department of Agronomy, National Chung-Hsing University, Taichung, Taiwan, R.O.C. SHIN L U, Ph.D., Professor, Department of Food Science, Cereal Laboratory, National Chung-Hsing University, Taichung, Taiwan, R.O.C. BOR S. LUH, Ph.D., Food Technologist, Department of Food Science and Technology, University of California, Davis, California iii

iv

CONTRIBUTORS

T. W. MEW, Ph.D., Head, Plant Pathology Department, International Rice Research Institute, Los Bafios, Laguna, Philippines DUANE S. MIKKELSEN, Ph.D., Professor of Agronomy, Department of Agronomy and Range Science, University of California, Davis, California BENITO S. VERGARA, Ph.D., Plant Physiologist, Plant Physiology Department, International Rice Research Institute, Los Banos, Laguna, Philippines JAMES I. WADSWORTH, Ph.D., Chemical Engineer, Food Products Research, Engineering and Development Laboratory, Southern Regional Research Center, U.S. Department of Agriculture, New Orleans, Louisiana C. Y. WANG, Ph.D., Nabisco Brands, Inc., 100 Deforest Avenue East, Hanover, New Jersey M. 0. WAY, Ph.D., Texas Agricultural Research and Extension Center, The Texas A & M University, Beaumont, Texas

PREFACE

Rice is one of the principal cereals used by the world's inhabitants. The hope for improved nourishment of the world's population depends on the development of better rice varieties and improved methods for rice production and utilization. During the past four decades, interest in rice research and production has increased in many countries. The development of new and better varieties by the International Rice Research Institute in the Philippines and other rice research institutes has stimulated numerous research stations to test the performance of these varieties in many countries under different climates, soil properties, cultural practices, and environmental conditions. The methods of harvesting, handling, drying, and milling rough rice have improved as a result of research efforts by the engineers and the rice milling industries. The first edition of Rice: Production and Utilization was published in 1980. This second edition presents the recent developments and progress made by the researchers, the industries, and various experiment stations. Because of the large amounts of literature available in recent years on rice production and utilization, this edition is divided into two volumes, Volume 1: Production and Volume II: Utilization. It is hoped that the books will be useful to rice researchers, processors, and people interested in rice production and utilization. Those studying v

vi

PREFACE

the agronomy of rice plants, especially the genetics, breeding, cultivation, diseases, and insects that attack both the rice plant and the stored grain, will find this edition helpful in their search for new knowledge. A new chapter on weed management, written by Dr. Davis E. Bayer, presents useful information in dealing with the weed problem in rice production. Harvesting, drying, and milling of rough rice are important procedures for successful handling of rice grains. Methods related to these procedures are presented in Chapter 9 of Volume I. Dr. James I. Wadsworth of the Southern Regional Research Center, USDA-ARS, has contributed an excellent Chapter 10 on rice milling. The physical and chemical properties of rice caryopsis are presented in Chapter 11 of Volume I. The utilization aspects of the rice cereals are presented in Volume II. I acknowledge the excellent cooperation of the contributors to this edition, who have generously provided their knowledge, experience, and time to the readers. Many friends have provided information and offered assistance in preparing and editing the contents. I wish to thank them all for their kindness and assistance. The California Rice Growers Association of Sacramento, California, and colleagues in the University of California-Davis Departments of Food Science and Technology and of Agronomy and Range Science helped greatly in completing the editing of this edition. I appreciate the assistance of Geyun Tang, Dr. Mei C. Huang, Dr. GinguoHu, Dr. Pran N. Vohra, ProfessorWu Wang, Patricia I. Bailey, Mary Miranda, Diane King, Susan Torguson, Karen Jo Hunter, Carol Cooper, Clara Robison, and Arlene Hamamoto who have worked tirelessly in editing, proofreading, and preparing the manuscripts. The encouragment and advice of Dr. R. L. Merson and Dr. Duane S. Mikkelsen in revising Rice are greatly appreciated. Davis, California

B.S. Luh

CONTENTS

Preface

v

1 Overview and Prospects of Rice Production Te-Tzu Chang and Bor S. Luh

1

2 Rice Plant Growth and Development Benito S. Vergara

13

3 Genetics and Breeding Te-Tzu Chang and Cheng-Chang Li

23

4 Rice Culture Duane S. Mikkelsen and Surajit K. De Datta

103

5 Rice Diseases T. W. Mew

187

6 Insect Pests of Rice M. 0. Way and C. C. Bowling

237 vii

viii

I

CONTENTS

7 Insect Pests of Stored Rice Robert R. Cogburn

269

8 Weed Management D. E. Bayer

287

9 Harvest, Drying, and Storage of Rough Rice C. Y. Wang and Bor S. Luh

311

10 Milling James I. Wadsworth

347

11 Properties of the Rice Caryopsis Shin Lu and Bor S. Luh

389

Index

421

RICE Volume II

UTILIZATION

RCE Volume II

UTILIZATION Second Edition EDITED BY

Bor S. Luh University of California, Davis

Springer Science+Business Media, LLC

CONTRIBUTORS

S. BARBER, Ph.D., Director, Instituto de Agroquimica y Tecnologia de Alimentos, CSIC, Valencia 46010, Spain C. BENEDITO DE BARBER, Ph.D., Cereal and Proteaginous Laboratory, Instituto de Agroquimica y Tecnologia de Alimentos, CSIC, Valencia 46010, Spain HELEN CHOW, M.S., Department of Plant Biology, University of California, Berkeley, California BENITO 0. DE LUMEN, Ph.D., Associate Professor, Department of Nutritional Science, University of California, Berkeley, California F. HSIEH, Ph.D., Associate Professor, Department of Agricultural Engineering, University of Missouri, Columbia, Missouri EDWARD J. HSU, Ph.D., Professor, Department of Biology, University of Missouri, Kansas City, Missouri CHUAN KAO, Ph.D., Chemist, USDA-FGIS, P. 0. Box 20285, Kansas City, Missouri YUAN-KU ANG LIU, Ph.D., Research Enzymologist, RJR Nabisco Inc., Del Monte Corporation Research Center, 205 N. Wiget Lane, Walnut Creek, California BOR S. LUH, Ph.D., Food Technologist, Department of Food Science and Technology, University of California, Davis, California v

vi

CONTRIBUTORS

ROBERT R. MICKUS, Director, Research and Product Development, Rice Growers Association of California, P.O. Box 958, Sacramento, California H. H. WANG, Ph.D., Professor, Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan, R.O.C. B. D. WEBB, Ph.D., Research Chemist, Rice Quality Laboratory, South Region, Rice Research Center, U.S. Department of Agriculture, Texas A & M University, Beaumont, Texas

PREFACE

During the 10 years that have passed since the first edition of Rice: Production and Utilization was published in 1980, much new information on processing and utilization of rice cereal has appeared in the literature. There is an urgent need for revision of the Rice book, especially since the first edition is out of print. The objective of the revision is to update the book and present pertinent, useful information to the readers. Because of the large volume of literature on the subject, the new edition will be split into two separate volumes: Volume I: Production and Volume II: Utilization. The contributors to both volumes have worked in their respective fields of study for 10 to 35 years. They are thoroughly experienced and productive in their research work. Volume I emphasizes plant growth, genetics and breeding, culture, rice plant diseases, insect pests of rice, weed management, harvest, drying and storage, milling, and properties of rice caryopsis. The 15 chapters of Volume II cover rice flours in baking, rice enrichment, parboiled rice, rice quality and grades, quick-cooking rice, canning, freezing and freeze-drying, rice breakfast cereals and baby foods, fermented rice products, rice snack foods, rice vinegar, rice hulls, rice oil, and rice bran. A chapter on the nutritional quality of rice endosperm is also presented. vii

viii

PREFACE

Persons interested in the production and utilization of rice cereal will find the new edition helpful and informative. Those in the rice-processing industries will find new ideas for developing rice products, convenience foods, breakfast cereals, baby foods, and new extrusion technology as applied to rice products. By-products from rice milling, such as rice bran, rice oil, and rice hulls, will bring greater returns to rice growers and processors. Chemical and physical properties of rice kernels, as well as their nutritive values, are presented in detail. These will be of great value to researchers, food and cereal scientists, and those in new product development. I thank Dr. R. L. Merson of the Department of Food Science and Technology; Dr. Charles V. Moore, of the Davis-based University of California Center for Cooperatives; and Robert R. Mickus, of the Rice Growers Association of California, for their valuable suggestions in the revision of this book. I am indebted to Dr. Duane S. Mikkelsen, of the University of California at Davis Department of Agronomy and Range Science; Dr. David E. Bayer, of the University of California Davis Department of Botany; Dr. B. D. Webb, of the Rice Research Center, Beaumont, Texas; Dr. B. 0. de Lumen, of the University of California at Berkeley; Maura M. Bean, of USDA-ARS; Dr. Te T. Chang, of IRRI, Manila, Philippines; Professor Wu Wang, of Wuxi Institute of Light Industry, Wuxi, China; and Dr. J. I. Wadsworth, of USDA-ARS, New Orleans, Louisiana, for their many kinds of encouragement and help. The assistance of Geyun Tang, Dr. Mei C. Huang, Dr. Ginguo Hu, Dr. Pran N. Vohra, P. J. Bailey, Mary Miranda, Diane King, Karen Jo Hunter, and Arlene Hamamoto in preparing and proofreading the manuscripts is greatly appreciated. Davis, California

B.S. Luh

CONTENTS

Preface

1 Introduction Bor S. Luh

1

2

9

Ri~e

Flours in Baking

Bor S. Luh and Yuan-Kuang Liu

3 Rice Enrichment with Vitamins and Amino Acids Robert R. Mickus and Bor S. Luh

35

4 Parboiled Rice

51

Bor S. Luh and Robert R. Mickus

5 Rice Quality and Grades

89

B. D. Webb 6 Quick-Cooking Rice Bor S. Luh

121

7 Canning, Freezing, and Freeze-Drying Bor S. Luh

147 ix

I

X

CONTENTS

8 Breakfast Rice Cereals and Baby Foods F. Hsieh and Bor S. Luh

1n

9 Fermented Rice Products H. H. Wang

195

10 Rice Snack Foods

225

F. Hsieh and Bor S. Luh

11

Vinegar Through Acetification of Rice Wine Edward J. Hsu Ric~

251

12 Rice Hulls

269

Bor S. Luh

13 Rice Oil

295

Chuan Kao and Bor S. Luh

14 Rice Bran: Chemistry and Technology

313

Bor S. Luh, S. Barber, and C. Benedito de Barber

15 Nutritional Quality of Rice Endosperm

363

Benito 0. de Lumen and Helen Chow Index

397

1 Overview and Prospects of Rice Production Te-Tzu Chang International Rice Research Institute

Bor S. Luh University of California, Davis

The first chapter in the 1980 edition of this book, entitled "Rice in its temporal and spatial perspectives" (Lu and Chang 1980) has provided considerable detail on crop history, world production, and supply and demand up to 1978. Subsequent years saw a continuing trend in the spread of the high-yielding varieties (HYVs), rise in grain yield, increase in world production, and expansion in consumption and international trade. This chapter highlights such changes during the past decade. Rice statistics were based mainly on the Food and Agriculture Organization's World Crop and Livestock Statistics (F AO 1987), Quarterly Bulletins of Statistics (FAO 1988 and 1989), and the World Rice Statistics 1987 of the International Rice Research Institute (IRRI 1988).

RICE PRODUCTION

World Production

Global rice production hovered between a high of 484.9 million tons of rough rice in 1988 and 377.3 million tons in 1979. The production trend from 1979 to 1988 was marked by three distinct periods: a relatively steady climb from 1979 through 1986, a marked decline in 1987, and a marked

2

RICE: PRODUCTION

Paddy production ( MUiion tons) Yield (t /ha) GOOr---------------------,3.5 480

3

Yield

.... ······

~--···· ..... ··

2.5

·······......·· .········

Area (Million ho) 160

·-·-·-·-·-·-·-·-·-·-.,.---·-·-·-·--

2 1.5

Area

0.5

260 240

~o~~~~~~~~~~~~~~~~~-~o

1965

1970

1975

1980

1985

1988

Year Figure 1-1. Trends in world paddy production, area, and yield, 1965-88. (Reprinted with permission from FAO 1987, 1988, and IRRI 1988.)

increase in 1988. The rate of increase in production during this decade (2.8% per year) was slightly lower than that of the previous decade (about 3.1% annually), even though the harvested area increased by 3.47 million ha from 1979 to 1988. The decline during 1987 was mainly attributable to adverse weather conditions in many rice-growing countries-a spattering of drought and flood over wide areas. Asia experienced a drought in 1982 as well, but the impact was smaller (Fig. 1-1). Production in Southern and Southeastern Asia

Production in southern and southeastern Asia showed three distinct climbs: 1980 and 1981, 1983 to 1985, and 1988 (Fig. 1-2). Growth rate over the decade averaged 4.1% yearly. Meanwhile, the harvested area leveled off at about 83.4 million ha. Among major producing countries in the region, Thailand maintained a steady growth of about 4.3% per year from 1979 to 1985. India posted an even more impressive gain of 7.1% in the same period, but production dropped significantly in 1987. Burma has shown a significant and steady rise since 1980. Indonesia steadily grew by more than 5.2% yearly from

OVERVIEW AND PROSPECTS OF RICE PRODUCTION

3

Milon tons

260

14·n..--.,__-.....IOO'---_.__ ___._ _.......__......_ _...._______.._ _....__.......... 1979

'eo

'al

'82

'83 Year

'84

'85

'86

1988

Figure 1-2. Paddy production in world, south-southeast Asia, and China, 1979-88. (Reprinted with permission from IRRI 1988.)

1979 onward, following increased government subsidies and improved production practices. Bangladesh averaged a 2% annual growth rate. Nepal showed gains of slightly above 3%. Pakistan grew at 0.4%. The Philippines attained self-sufficiency in 1978 but production declined during 1982-84 due to drought spells and other economic factors. Production rose again in 1985 following a recovery in harvested area. Production in Eastern Asia

Production in China began to rise significantly after 1970 and climbed more steeply during 1982-84. The marked growth was achieved mainly through higher grain yields stemming from the increased use of quick-acting nitrogen fertilizers, widespread use of hybrid rice, and changes in the commune system. Japan showed a decline in production during 1980-82. A small recovery to mid-1970 levels followed. The Republic of Korea (South Korea) made dramatic gains in 1976 when the semidwarf Tong-il variety and other interracial hybrid varieties

4

RICE: PRODUCTION

were released. The trend was sustained until 1979. Production was severely cut in 1980 when cool weather and blast epidemics pushed the production level back to that of the 1960s.

Production of North and Central America The United States remains the principal producer in this region, contributing more than 70% of the crop. Production in the United States has been on a continuous rise since postwar years, reaching an all-time high of 8.3 million metric tons in 1981. Production then declined, stabilizing at a level around six million metric tons.

Production of South America South America ranks third in the world as a rice-producing region. Brazil remained the largest producer in South America and showed an annual gain of about 5%, mainly from its vast upland areas. Colombia ranks as the second largest producer, though its production leveled off after 1978. Peru ranks as the third largest producer, having made a large jump in 1981 and maintained the gains in subsequent years.

Production in Other Regions Africa produced 8.5 million metric tons in 1979 and attained 10.1 million metric tons in 1987. Madagascar and Egypt are the ranking producers, contributing 2.3 million metric tons each in 1987. Australia produced between 0.6 and 0.7 million metric tons per year. The total production remained rather stable during the 1980s. The U.S.S.R. produced between 2.4 and 2.9 million metric tons during the period. Significant growth was made during the mid-1970s and maintained in the following decade.

The Balance Sheet Between 1951 and 1988 the broad regions of Asia, Africa, and South America tripled their rice production. However, a rapid growth in human population and increased per capita rice consumption have canceled most of the real gains. Other factors contributing to the fluctuations in production are weather, governmental price policies, import/export control, national agricultural research, and fertilizer prices. The major rice-producing countries may be grouped into four categories: 1. traditional importers, such as Bangladesh, Malaysia, Madagascar, Sri Lanka, and many African countries

OVERVIEW AND PROSPECTS OF RICE PRODUCTION

5

2. shifters, such as Indonesia, South Korea, the Philippines, and Vietnam 3. self-sufficient since the mid 1960s, such as Brazil, China (up to 1988), India (since 1978), and Pakistan. 4. net exporters, such as Australia, Burma, Thailand, and the United States

RICE ECOSYSTEMS AND GRAIN YIELD

The peak in world rice production of about 484.9 million metric tons attained in 1988 was largely achieved by Asian countries (91.29%) where 44% of the ricelands belongs to the irrigated-wetland (lowland) ecosystem, either fully or partially irrigated. The cultivars were mainly the semidwarf varieties and hybrid rices (grown only in China) which filled more than 70 million ha of Asian riceland. Another 27% belong to the shallow rainfedwetland category, where water supply and drainage range from nearly adequate (as in Indonesia and the Philippines) to highly variable and haphazardous (east India, Bangladesh, Indochina, and Thailand). Deepwater rice culture (exceeding 0.5 m in depth) and tidal wetland occupied about 9% of the Asian riceland, while rainfed-dryland (upland) rice culture followed closely at 8%. Table 1-1 shows the relative importance of the five ecosystems in 1985 with projections for 2000. The regional distribution of world rice production is depicted in Fig. 1-3. The United States produced about 1.4% of the world's rice but exclusively under irrigation. South America produced 3.9%, of which dryland culture (62%) was more important than irrigated and rainfed-wetland

Table 1-1. HaNested Area, Rough Rice Production, and Yield in 37 Major RiceProducing Developing Countries, by Ecosystem: 1985 and Projections for 2000 AREA

Ecosystem Irrigated wetland Rainfed-wetland Dryland (upland) Deepwater/tidal wetland

TOTAL

Million ha 67 40 18 13 138

(1985) % 49 29 13 9 100

PRODUCTION

(1985)

Million

313 84 21 19 437

Source: International Rice Research Institute (1989). t/ha = metric tons per hectare

%

72 19 5 4 100

YIELD (T/HA)

1985

2000

4.7 2.1 2.2 1.5 3.2

5.8 2.9 1.6 2.1

Contribution to Production in 2000 (%)

57 29 4 10

6

RICE: PRODUCTION

Africa _ __ (2.2%)

South Asia

East Asia

(23.5%)

(45.4%)

Sou1heast Asia (22.2%)

Figure 1-3. Regional distribution of rice production (c. 300 million MT milled rice), 1987. (Reprinted with permission from IRRI 1989.)

cultures (38%). Likewise, dryland culture in Africa (46%) shared a nearly equal importance with wetland cultures (51%) in production, although the dryland rice area was larger (about 60% in western Africa) but yielded less (about 0.9 t/ha). The annual growth rates in grain yield varied greatly from country to country. Much of the growth was related to (1) the expansion in irrigated areas planted to the HYVs (Dalrymple 1986), (2) governmental subsidy and pricing policy (Herdt and Capule 1983; Barker et al. 1985; IRRI 1985, 1987; Chang 1988), and (3) weather and pest incidences (Chang 1988). On the world average, the growth rate in grain yield during 1979-88 (2.6%) was slightly higher than that of 1969-78 (2.0%). During years unaffected by adverse weather or serious pest epidemics, rice yield in a given area of irrigated culture was largely determined by price incentive and the availability of chemical fertilizers. High yields were sustained when government support of varying forms was provided. Examples may be found in Japan, northern India, the United States, the Philippines (1973-83), and Indonesia (1980-88). On the other hand,

OVERVIEW AND PROSPECTS OF RICE PRODUCTION

I

7

t/ha

Ctm 3

A\lpplnes

...····

... ·········

······

.... .. ....

o~~~~~

1960

1970

~

197!5

~

1980

~~~

1985 1988

Year

Figure 1·4. Yield trends in north India, east India, Indonesia, the Philippines, and China, 1960-88. (Reprinted with permission from T. T. Chang 1988.)

extreme excesses or deficits in water regimes suppress grain yields. Instances may be found in the waterlogged east of Indi~. the deepwater areas of Bangladesh and Thailand, and the dryland areas of the world (Chang 1988). The yield trends in Fig. 1-4 show such contrasts. INTERNATIONAL TRADE

The rice traded in international markets during the decade (about 4% of world production) ranged between 11.8 and 12.7 million metric tons, which may appear relatively small when compared to wheat. However, the total volume represented more than a 20% increase over the previous decade and nearly doubled th~ volume of the late 1950s. Asia remained the largest

8

RICE: PRODUCTION

importing region, followed by Africa (over three million metric tons in 1985-86), Europe (two million metric tons in 1980-84), and South America (1.6 million metric tons in 1986). Africa showed the most striking rise in imports-the 1985-86 figures tripled those of the early 1970s and scored a 60% increase over that of 1978. Thailand remained as the number one exporter during the decade (2.8-4.8 million metric tons), followed by the United States (2.3-3.1 million metric tons), China (0.7-1.4 million metric tons), Pakistan (0.7-1.3 million metric tons), Burma and Italy (between 0.5 and 0.8 million metric tons), and Australia, Uruguay, and Japan (between 0.1 and 0.7 million metric tons). Among importing countries, Indonesia ranked first (1979-83), followed by Saudi Arabia, Nigeria, the U.S.S.R., Senegal, and the Ivory Coast. Brazil showed highly variable imports during the period. The Republic of Korea made the largest import in a single year: 2.58 million metric tons in 1981. Saudi Arabia has been a major importer since 1981. Several African nations sharply cut back their imports after 1985. The international market price showed a rapid drop following the 1974 peak (U.S.$542 for 5% broken Thai white rice) and was stable during 1978-81. A sharp decline began in 1982 and continued until the second half of 1987 when rice price rallied. The average real price was slightly over U.S.$200 in 1988 (Fig.1-5). During 1986-87, when there was a surplus on the world market and the price was at an all-time low, trade relationships among the exporting countries (United States, Thailand, and Australia) became strained, and a trade war between the United States on one side, and several Asian countries, on the other, loomed. However, the widespread drought of 1987 in southern and southeastern Asia and the erratic monsoon weather of 1988 in Bangladesh and parts of India and China have greatly reduced the reserve stocks to an all-time low, and world rice price rallied. Such is the volatility of the international rice market. UTILIZATION

The world's 5 billion people of today are generally better fed than the 4 billion in 1974: world population grew 1. 75% a year while the agricultural production index and cereal yield grew 2.20 and 2.50%, respectively (WRI 1986). However, because rice can support more people per hectare of land (Lu and Chang 1980), expansion in rice cultivation is usually accompanied by a higher rate of population growth (Chang 1987). The human population in the developing world has grown from 2.305

OVERVIEW AND PROSPECTS OF RICE PRODUCTION

9

1000 /······· ..;/,. ...

......

400

/':......

800

·-.../ ..,i

600

t . .· 200

I

,...····r : l

/ .....

..··

l

100

~ 200

1971

1989

Year

Figure 1-5. Trends in world rough rice (paddy) production al')d real price of rice, 1951-89. (Reprinted with permission from FAO 1988; IRRI 1988.)

billion in 1965 to 3.836 billion in 1988. About 40% of the masses depends on rice as the primary caloric source. As population increases at a faster rate in the developing countries than in the developed world, the share of rice for meeting future food needs in the developing world will continue to increase. OUTLOOK FOR THE FUTURE

While world rice production has been rising at a rate nearly parallel to that of the human population and no serious food shortage or famine was experienced in the producing countries, the foundations of a sound and stable rice economy have yet to be established in terms of (1) a higher potential yield on rice farms, (2) lower production costs, (3) government action in pricing policy, subsidy, land reform and infrastructure development, and (4) a cushion against the short-term effects in surplus/deficit. Since only 4% of the rice produced is traded on the international market,

10

RICE: PRODUCTION

factors such as domestic consumption and fluctuations in production and price exert a vast influence on consumers, both within and outside a producing country. Stability in production and an equitable price are equally important in raising the supply to meet an increasing demand. The importance of rice as the number one staple in the developing countries will grow as the human population increases at a higher rate in such countries as compared to the developed world. By the year 2000 rice will be the chief source of energy for about 40% of the world's people, thereby surpassing wheat. With a projected world population of more than 6 billion by the year 2000, 100 million metric tons of grain will be needed to meet the demand. The need to produce an additional 1. 7% per year on a worldwide basis and 2.1% per year by Asian countries up to year 2020, with a limited growth in riceland area, will pose the greatest challenge for rice researchers and allied workers in this century. Meanwhile, the sustainability ofriceland to provide stable production is equally imperative (Chang 1988; IRRI 1989). Meanwhile, the improvement in human nutrition and equity in food distribution remain as two unresolved problems in many developing countries. Uncontrolled expansion or mismanagement in rice cultivation also present hazards to environmental quality. The combined efforts of all sectors of society will be needed to meet the great challenges lying ahead (Chang 1988). REFERENCES

Barker, R., R. W. Herdt, and B. Rose. 1985. The Rice Economy ofAsia. Resources for the Future, Washington, D.C. Chang, T. T. 1987. The impact of rice on human civilization and population expansion. Interdisciplinary Sci. Rev., 12(1):63-9. Chang, T. T. 1988. Sharing the benefits of bioproduction with the developing world. Paper presented at the Int. Union of Biological Sci. 23rd General Assembly, Oct. 18-20, 1988, Canberra, Australia. Dalrymple, D. G. 1986. Development and Spread of High-Yielding Rice Varieties in Developing Countries. USAID, Washington, D.C. Food and Agriculture Organization (F AO). 1987. World Crop and Livestock Statistics, 1948-85. Rome, Italy. Food and Agriculture Organization (FAO). 1988. Quart. Bull. Statistics 1(3). Food and Agriculture Organization (FAO). 1989. Quart. Bull. Statistics 2(1). Herdt, R. W., and C. Capule. 1983. Adoption, Spread and Production Impact of Modern Rice Varieties in Asia. Int. Rice Res. Inst. (IRRI), Los Banos, Philippines. Int. Rice Res. In st. (IRRI). 1985. International Rice Research: 25 Years ofPartnership. IRRI, Los Banos, Philippines.

OVERVIEW AND PROSPECTS OF RICE PRODUCTION

11

IRRI. 1987. IRRI Strategic Planning Committee Report. IRRI, Los Banos, Philippines. IRRI. 1988. World Rice Statistics 1987. IRRI, Los Banos, Philippines. IRRI. 1989. IRRI Toward 2000 and Beyond. IRRI, Los Banos, Philippines. Lu, J. J., and T. T. Chang. 1980. Rice in its temporal and spatial perspectives. In Rice: Production and Utilization, edited by B.S. Luh, l-74. Westport, CT: AVI. World Res. Inst. (WRI). 1986. New York: Basic Books.

2 Rice Plant Growth and Development Benito S. Vergara International Rice Research Institute

The life cycle of the rice plant is generally 100 to 210 days; the mode falls between 110 and 150 days. In temperate climates, the average duration from sowing to harvest is about 130 to 150 days. Cultivars with growth duration of 150 to 210 days are usually photoperiod sensitive and planted in the deepwater areas. Temperature and day length are the two environmental factors affecting the development of the rice plant, which can be divided into three main phases (Vergara 1970): vegetative phase-from seed germination to panicle initiation reproductive phase-from panicle initiation to anthesis ripening phase-from anthesis to full maturity These main phases overlap each other within a rice hill or a rice crop. Physiologically, ripening does not begin until 3 weeks after fertilization. Figure 2-1 illustrates the growth behavior in the tropics of a cultivar (IRS) maturing in 120 days compared with one (Peta) maturing in 150 days. Reproductive (35 days) and ripening phases (25-35 days) are fairly constant for these cultivars in the tropics. The difference in total growth duration is in the vegetative phase, whose length may be inherent or dependent on the sensitivity of the cultivar to day length and temperature (Vergara 1970; Vergara and Chang 1976). 13

14

RICE: PRODUCTION

120- Day var iety

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RICE PlANT GROWTH AND DEVELOPMENT

15

The growth duration ofiR8 may extend to 180 to 200 days in temperate areas or at high altitudes in the tropics. Low temperature affects mainly the vegetative and ripening phases. Ripening may be prolonged from 25 to 30 days in the tropics to as long as 60 days in temperate regions.

VEGETATIVE PHASE

Seedling growth varies from 0 to 90 days, depending upon the method of sowing. Rice can be sown directly onto dry land or broadcast onto puddled soil or soil prepared dry but flooded with 10 em of water. It can be sown on a dry or wet bed nursery and then transplanted 20 to 70 days later, or grown in a special dapog nursery and transplanted after 11 days. Sometimes rice is sown on a wet bed nursery, transplanted to a bigger wet bed nursery a month later, and retransplanted to the main field after another month (double transplanting). Transplanting is still common in Asia although direct seeding, commonly practiced in the United States is becoming popular. Tillering

The production of tillers and leaves are the main visible changes during the vegetative phase. In the tropics, the maximum tiller number is reached 40 to 60 days after transplanting, depending on the cultivar, plant spacing, and fertility level. In temperate areas, where seeds are drilled or broadcast densely, tillering ability is not as important, and the maximum tiller number stage (one or three tillers) is reached within 30 days after seedling emergence. The maximum tiller stage is usually followed by a decrease in tillers per unit area. The tiller number may decrease as much as 60% in some tropical cultivars or as low as 10% in the high-yielding temperate and tropical culti vars. Tiller number and the resulting panicle number per unit area are the main components of grain yield. Leafing

Leaves are produced on the main culm at an average of one per week but can be modified by environmental factors. The interval between leaf production is shorter during early growth stage (4-5 days) and longer at later stages (8-9 days). Cultivars differ in the number of leaves on the

16

RICE: PRODUCTION

IRS PETA Figure 2-2. Variation in number of leaves on main culm.

main culm (Fig. 2-2). High yielding cultivars in the tropics have 14 to 18 leaves, similar to most of the temperate cultivars. Low temperature and long days increase the number ofleaves produced before panicle initiation. The longest leaf on the main culm is the fifth leaf from the top (Fig. 23); it develops before panicle initiation. Succeeding leaves are generally smaller. Upper leaves have a longer life than lower leaves.

REPRODUCTIVE PHASE

Panicle Initiation

The reproductive phase may begin before, at about the same time as, or after the maximum tiller number is reached. The reproductive phase is marked by the initiation of the panicle primordium and its development. In the tropics, panicle initiation occurs approximately 70 to 75 days

RICE PLANT GROWTH AND DEVELOPMENT

60

Days .after SOWing

t

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Panicle formation

17

Flowering 80

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6

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12

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14

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Figure 2-3. Leaf development.

before maturity. This period varies more in temperate areas where low temperature can lengthen the ripening period. For photoperiod-sensitive cultivars planted during the regular season, panicle initiation, panicle emergence, and anthesis occur uniformly. Within 5 days after initial heading, exsertion of panicles is complete. Photoperiod-insensitive cultivars take longer to reach 100% heading. The young panicle becomes visible to the unaided eye 10 to 13 days after initiation. At this stage, it is 1 to 2 mm long with a fuzzy or spongy tip. This marks the beginning of the booting stage as the developing panicle causes the flag leaf sheath to swell. As panicle development continues, the spikelets become distinguishable. Internode Elongation

The internode elongation stage differs by cultivar. With the early-maturing cultivars, elongation usually begins after panicle initiation. Panicle emergence, however, will not proceed until the internode elongates. In latematuring cultivars (more than 150 days), internode elongation may begin before the reproductive phase.

18

RICE: PRODUCTION

Figure 2-4. Spikelet anthesis.

Heading Stage

Complete emergence of the panicle from the flag leaf sheath occurs within 24 h. Some panicles exsert earlier than others, so 5 to 15 days may be required for heading of most of the tillers in transplanted rice. In densely broadcast rice, 100% heading may occur in a shorter time. Low temperature may result in incomplete exsertion of the panicle, especially in tropical lowland cultivars, because the last internode fails to elongate. Anthesis occurs a day after panicle emergence, with the protrusion of the first dehiscing anthers in the terminal spikelets on the panicle branches. Anthesis of all the spikelets on a panicle may be completed in 7 days (Fig. 2-4). An thesis usually starts at the top of the panicle. Cultivars with large panicles show the highest percentage of unfilled spikelets on the lower third of the panicle.

RICE PlANT GRO\IVTH AND DEVELOPMENT

19

On a clear day, anthesis starts between 1000 and 1400 h, or even earlier on warm days. Cold or humid days will delay anthesis for several days. Rice is generally self-pollinated. RIPENING PHASE

Ripening is the phase from heading to maturity. It may take 25 to 35 days in the tropics or 30 to 60 days in temperate areas. Grain development is a continuous process, and the grain undergoes distinct changes before it matures fully (Fig. 2-5). The consistency of the caryopsis (the starchy portion of the grain) is at first watery; later it turns milky, then into soft dough, and finally, into hard dough. The individual grain is mature when the caryopsis is fully developed and is hard, clear, and free from greenish tint. The crop is considered ripe when more than 90% of the grains in the panicles are fully ripened. Seven days are needed for all the spikelets in a panicle to open; full maturity for the whole panicle does not occur until30 days after anthesis. Again, several extra days are needed for all grains to ripen because panicle exsertion occurs over several days. As the grain ripens, the bottom leaves senesce and turn yellow. In

Anther Opening

2

3

4

5

6

8 Milk Stage

9

10

12

14 Dough Stage

21

Figure 2-5. Grain development.

7

30 Days Fully Ripe

20

RICE: PRODUCTION

some cultivars, the culm and upper leaves may remain green even after the grains have ripened. Low temperature increases the ripening period of rice grain and is thought to be partially responsible for the heavier and more fully filled grains of rice crops in temperate areas. Under favorable moisture and fertility, new tillers, which constitute the ratoon crop, may grow from the stubble of harvested plants. Ratooning is not popular in the tropics because virus disease often occurs. EFFECT OF TEMPERATURE ON GROWTH AND DEVELOPMENT

Rice is classified into indica,japonica, andjavanica types. Japonica-cultivars from the United States, Korea, Japan, and some European countries-generally tolerate low temperature. In the mountainous regions of the tropics, indica types with some degree of cold tolerance are also planted. The adverse effects of low temperature are low germination, leaf discoloration, stunting, incomplete panicle exsertion, increased degenerated spikelets, failure in anthesis, increased spikelet sterility, increased grain shattering, and delayed heading. Low temperature at the panicle initiation stage and at anthesis is most damaging to grain yields. Low temperatures generally reported in the literature range from 13 to 2l°C. High day temperatures (35-40°C) experienced in rice areas in Iran, Egypt, and India, can also harm the rice plant. High temperatures during the vegetative stage can result in reduced tillering and degeneration of young leaf tips. During panicle initiation and formation, high temperature can reduce the number of spikelets and degenerate those that are formed. High temperature at flowering causes high spikelet sterility and is most damaging to rice. Attempts to determine optimum temperatures for germination, seedling growth, tillering, panicle initiation and development, anther dehiscence, and ripening have generally not been especially useful. Optimum temperatures vary not only by cultivar but with the plant status before the temperature regime. Having the optimum temperature for certain growth phases of the rice plant probably is not necessary for obtaining high grain yields. For example, the optimum temperature for leaf area production may result in heavy mutual shading at an early stage of growth and actually reduce grain yields. Although low temperature slows the translocation of carbohydrates, it lowers respiratory consumption of carbohydrates, and the prolonged ripening phase results in more filled spikelets. Temperatures lower than

RICE PLANT GROWTH AND DEVELOPMENT

21

the critical 20°C, however, may result in imperfect grains; a "notched belly" develops (Nagata and Kobayashi 1957). Generally, rice grains shatter easily from the panicle and grain dormancy is shorter when the temperatures during ripening are low (Vergara and Visperas 1971). The better rice cultivars have a higher harvest index (grain yield/total dry matter produced). At lower temperatures, the higher harvest index could account for higher yields in temperate areas. In the tropics, the rice plant produces more straw than grain. High temperature accelerates grain ripening, resulting in prematurity. The main result is the inability of the spikelet to serve as a sink (Aimi et al. 1959; Nagata et al. 1966; Bhattacharya 1970). Prematurity may result in partially chalky and milk-white kernels and thicker bran and aleurone layers (Nagata and Ebata 1960; Nagata et al. 1961, 1966). EFFECT OF PHOTOPERIOD ON DEVELOPMENT

The main effect of day length on the rice plant is on panicle initiation and development. Traditional cultivars are generally photoperiod-sensitive and are classified as short-day plants. Most recent tropical cultivars have been bred to be photoperiodinsensitive. Their growth duration remains nearly constant when they are planted. Photoperiod insensitivity also increases adaptability. These cultivars can be planted at different latitudes without much change in growth duration unless temperature becomes a limiting factor. Photoperiod-sensitive cultivars are still grown in areas where water remains on the field for long periods because of natural flooding. The rice plant does not initiate the panicle primordium until the floodwater recedes, insuring harvest when the water level is low or the field is almost dry. Photoperiod sensitivity gives these cultivars their necessary growth duration of 150 to 200 days. REFERENCES Aimi, R., H. Sawamura, and S. Konno. 1959. Physiological studies on the mechanism of crop plants. The effect of the temperature upon the behavior of carbohydrates and some related enzymes during the ripening of the rice plant. Proc. Crop Sci. Soc. Japan. 27: 405-7. (Japanese with English summary.) Bhattacharya, B. 1970. Effects of various ranges of day and night temperatures at the ripening period on the grain production in rice plants. J. Faculty Agriculture Kyushu Univ. 16: 85-140. Nagato, K., and M. Ebata. 1960. Effects of temperature in the ripening periods

22

RICE: PRODUCTION

upon the development and qualities of lowland rice kernels. Proc. Crop Sci. Soc. Japan. 28:275-8. (Japanese with English summary.) Nagato, K., M. Ebata, and Y. Kishi. 1966. Effects of high temperature during ripening period on the qualities of Indica rice. Proc. Crop Sci. Soc. Japan. 35:239-44. (Japanese with English summary.) Nagato, K., M. Ebata, andY. Kono. 1961. On the adaptability of rice cultivars to high temperature in the ripening periods. Proc. Crop Sci. Soc. Japan. 29:337-40. (Japanese with English summary.) Nagato, K., andY. Kobayashi. 1957. Studies on the occurrence of notched-belly kernels (Dogire-mai) in rice plants. Proc. Crop Sci. Soc. Japan. 26:13-14. Vergara, B.S. 1970. Plant growth and development. In Rice Production Manual. Univ. of the Philippines, Laguna. Vergara, B.S., and T. T. Chang. 1976. The flowering response of the rice plant to photoperiod: A review of the literature. Int. Rice Res. lnst. Tech. Bull. 8. Los Banos, Philippines. Vergara, B. S., and R. M. Visperas. 1971. Effect of temperature on the physiology and morphology of the rice plant. Int. Rice Res. In st., Los Banos, Philippines.

3 Genetics and Breeding Te-Tzu Chang International Rice Research Institute

Cheng-Chang Li National Chung-Hsing University

The spectacular rise in rice production in the years following World War II, mainly in Asia, stemmed from expanded irrigation areas, the increased use of fertilizers, effective control of pests, double rice cropping, and the widespread adoption of improved genetic materials. The combined use of high-yielding varieties (HYVs) and nitrogen fertilizers has made possible the expression of high yield in irrigated areas. These two components have contributed about one-half of the increased rice production in southern and southeastern Asia since the late 1960s. Varieties of short growth duration that are insensitive to the photoperiod have allowed year-round planting and multiple cropping. During the same period, the United States tripled its rice production. The adoption of semidwarf HYV s triggered the beginning of the ''Green Revolution" among rice farmers in tropical Asia beginning in 1967-68. China also turned to the semidwarfs. The development of hybrid rice in China since the early 1970s has set off a second Green Revolution in that country. GENETICS

Genetic diversity and genetic information provide the foundation for all sound and efficient plant breeding programs. The first genetical study on 23

24

RICE: PRODUCTION

rice was probably made by Van der Stok (c. 1908). Since then, over a thousand publications on inheritance studies have appeared in the rice literature, dealing largely with Mendelian analyses. Only a relatively small proportion of the papers dealt with traits of economic importance (see Chang 1966). It remained for the simply inherited recessive gene (sd 1) in the Chinese semidwarfs to provide rice breeders with the impetus to achieve unprecedented progress in rice breeding. The cytoplasmic male sterility found in a Chinese wild rice plant fueled further yield increases. Among the cereals, the diverse and rich rice germplasm has seen the greatest exploitation by man. Morphologic Traits Pigmentation of plant parts

The most frequently studied subject has been the inheritance of anthocyanin pigments on different plant parts, although the color manifestations are of secondary economic importance. Rice cultivars vary greatly in pigmentation, distribution, and intensity, thus providing a fascinating array of materials for taxonomic or genetical studies. Anthocyanin pigments can be found in all the vegetative organs and several floral parts but not in the embryo or endosperm. The genetic control of anthocyanin pigments consists of a complementary gene system of three basic genes (C, A, and P-) and the occasional participation of an inhibitor gene. In tropical varieties other modifying genes may also operate. In the C-A-P- gene system, Cis the basic gene for chromogen production, A controls the conversion of chromogen into anthocyanin, and P- (to be specified asP, Pau, Pg, Pin, PI, Pta, Pig, Pr, Prp, Ps, Psh, Pu, Px, or Pw) determines the site or sites at which the pigments will appear. Multiple alleles and different dominance levels have been found in the C, A, and PI loci. Inhibitors for P, PI, and Pta have been identified. The gene for apiculus color (P) has been helpful in analyzing the inheritance of pigmentation in other vegetative organs (Nagao 1951). The complexity of pigmentation patterns in Japanese testers has been described in the earlier edition of this chapter (Chang and Li 1980) and updated by Kinoshita (1986). The pleiotropic effect is shown by the P and PI genes. For instance, PI also affects pigment distribution in the leaf sheath, pulvinus, auricles, ligule, internode, node, and rachis. The color of the different layers of seedcoat can be affected by different genes or sets of genes: Rc and Rd in complementary fashion; C, A, and Prp; p[w and C. The probable number of genes controlling the pigmentation expression in the various organs may vary from two to seven. Among the morphologi-

GENETICS AND BREEDING

25

cally diverse varieties of India, as many as 11 genes may be involved in the color segregation of three crosses (see Chang 1964). Several nonanthocyanin pigments control hull colors. A gold hull is inherited as a simple recessive (gh), a white hull as a single dominant (Wh). In the presence of Gh, the Hm, Hi, Hg, and Hf alleles confer other dark hull colors. Brown furrows on glumes are controlled by a single dominant, Bf; brown spots on glumes are due to Bf; and a black hull by complementary genes, Bha and Bhb (USDA 1963). Pubescence

Pubescence on the surface of leaf blades and hull is dominant to glabrous (gl) (Ramiah and Rao 1953; Jodon 1955). However, some varieties may have hairs on the blade surface, while the glume surfaces are smooth. A smooth hull is a desirable trait in mechanically harvested and processed rice. It has been incorporated into all varieties grown in the southern United States (Adair et al. 1973). Dwarfs and semidwarfs

Dwarfs characterized by shortened internodes and undersized grains are generally controlled by single recessive genes (d), but independent genes (d 1, d2 , etc.) govern different types (Jones 1933; Nagao 1951). Double dwarfs or intermediate types may be obtained from dwarf x dwarf crosses (Akemine 1925). In one case, a single dominant controls the dwarf character (Sugimoto 1923). Most dwarfs respond to gibberellic acid. The discrete monogenic inheritance of the Japanese dwarfs was expressed when they were crossed with Japanese cultivars (cvs.) of intermediate height, but such segregation may not be found in crosses with tall varieties of the tropics (Loresto and Chang 1978). From crosses of tall indica x Japanese dwarfs and of tall indica cvs. x Japanese cvs., it appears that the dwarfs carried another recessive inhibitor for short height (i-1) which was also present in the background of the Japanese cultivars (Loresto and Chang 1978). On the other hand, an intermediate statured tropical variety such as Baok may also carry a dominant inhibitor to tall height, I-T (Balakrishna Rao et al. 1972). Intermediate statured dwarfs with normal panicles and grains were frequently found in irradiated progenies, mostly under monogenic control. The genetic control of agronomically useful semidwarfs will be discussed in the section on quantitative traits in this chapter. Updated lists of dwarfs and semidwarfs may be found in the Rice Genetics Newsletter (vol. 3, 1986).

26

RICE: PRODUCTION

Awning

Different genetic postulates have been made to interpret the inheritance of awning when parents not only differ in awn length but on the presence of awns on different parts of the panicle. In Japanese varieties, from one to three genes (An 1, An 2 , and An 3) with cumulative effect could be involved in varying degrees of awning (Nagao and Takahashi 1942), as follows: long or full awn medium awn short awn tip awn awnless

An 1 An 2 An 3 or An 1 An 2 an 3 An 1 an 2 An 3 or An 1 an 2 an 3 an 1 An 2 An 3 or an 1 An 2 an 3 an 1 An 2 An 3 or an 1 An 2 an 3 an 1 an 2 an 3

In Chinese varieties, F 2 ratibs of 3 : 1, 9 : 7, and 15 : 1 have been reported (Kuang et al. 1946). Panicles

Compact or dense panicles behaved as a single dominant (Dn) over lax or normal panicles, while in other studies lax panicles (Lx) were dominant over normal panicles (USDA 1963). In some studies, F 2 ratios of9: 7, with the dense panicle either dominant or recessive, have been reported (Ghose et al. 1960). Spreading panicle branches (spr) behaved as a recessive to the nonspreading type (USDA 1963). Grains

A round or extremely short spikelet (Rk) has been reported to be dominant over the slightly longer oval type (Ramiah and Rao 1953) involving one gene (Chao 1928) or as many as four complementary genes (Kadam and D'Cruz 1960). A large-grained mutant behaved as a simple recessive to the normal (Ramiah and Rao 1953). Extreme variants such as minute (Mi) and long grains (Lk-f) are inherited in a Mendelian manner (Takeda in IRRI 1990c). Wide and continuous variations in the grain dimensions of commercial varieties suggest that grain size and shape are complex quantitative traits. Other traits controlled by Mendelian genes

Genetic information on many other morphologic mutants or variants of largely academic interest were summarized in Table 3.1 of the earlier edition of this work (Chang and Li 1980). Descriptions of such mutant traits are given by Chang and Bardenas (1965). Periodic updatings of

GENETICS AND BREEDING

27

gene symbols and related genetic stocks are given in the Rice Genetics Newsletter (1984 and onward). Quantitative Traits Plant stature

Evidence of quantitative inheritance may be detected in nearly all of the traits that have economic importance. However, traits of a quantitative nature have not received sufficient attention from rice researchers. On the other hand, several truly quantitative traits have been oversimplified as qualitative or oligogenic cases of inheritance. Ikeno (1919; see Ramiah 1933) was probably the first rice worker to recognize the quantitative nature of plant height in one of his crosses. Ramiah (1933) also found both oligogenic and continuous segregations for plant height from different crosses. Genetical studies after the 1950s were aided by biometrical techniques in the interpretation of quantitative data. Plant stature is such an important trait because it is related to the harvest index, growth duration, nitrogen responsiveness, and lodging resistance. The short culm length of the Chinese semidwarfs (elm in the tropics) is primarily controlled by one pair of recessive alleles (sd 1) which expresses potently in crosses with tall tropical varieties such as Peta (Chang et al. 1965; Shen et al. 1965; Aquino and Jennings 1966). The quantitative and rather complex nature of semidwarfism is indicated by: 1. an incomplete dominance of tallness in the F 1 hybrid, 2. a varying number of modifiers (minor genes of extremely unequal or oppositional effect) affecting the expression of the major recessive gene in sister selections homozygous for the sd 1 alleles, 3. some other crosses involving moderately tall and semidwarf parents which have failed to produce the F 2 ratio of3 tall: I semidwarf, indicating the interaction between sd 1 and other genes in the background of the tall parents. The recessive gene in the Peta/1-geo-tze cross, however, showed a high heritability estimate of 71 to 84% (Chang et al. 1965). The recessive nature of the semidwarfing gene not only facilitates the selection for true breeding F 2 plants, but also aids in recovering the desired combination of semidwarfism with erect leaves, high tillering, and early maturity (see Chang and Tagumpay 1970). Intercrosses of hundreds of short-statured accessions in the IRRI germ plasm collection and the analysis of parental, F 1, and F 2 data have led to the following findings:

28

RICE: PRODUCTION

1. A great majority of the semidwarfs share the sd 1 locus. A high proportion of induced mutants also involved this readily mutable locus. 2. The sd 1 gene is a compound-complex locus and shows fine structure of pseudo-alleles, i.e., certain semidwarf/semidwarf crosses may yield a small number of tall or intermediate-statured F2 recombinants. The F 2 data suggest that when the sd 1 alleles are in the trans arrangement, they may result in tall progenies (Chang et al. 1985). Between parents that do not differ markedly in height, polymeric genes or polygenes determine the differences in plant height. In such crosses, tall height generally showed partial dominance to short stature. Plant height and growth duration are positively correlated in intermediate to tall genotypes (see Chang and Li 1980 for citations). Lodging resistance

Path analysis of lodging resistance in different vanettes and crosses showed the significant contributions to straw strength from plant height, leafsheath wrapping of the lower internodes, the length of the two basal internodes, and the cross-sectional area of culm tissue at the basal internodes. Plant height ranks as the primary causal factor. In a tall/dwarf cross, height was negatively correlated with the lodging resistance factor (cLr) of the culms (r = -0. 71); however, in a tall/intermediate-tall cross, the correlation between height and cLr decreased to an r value of -0.58 (Chang 1967). Information on character association in the above crosses was summarized by Chang and Vergara (1972). Plant type

The component traits that make up a plant type are culm length, tiller number, culm angle, culm stiffness, leaf dimensions and angles at various growth stages, and panicle characteristics (length, weight, density, etc.). These traits affect the stand geometry under different spacing and fertilizer levels and determine nitrogen responsiveness, harvest index, and grain yield. The HYVs of the tropics combine 100-cm height (or slightly less), high tillering capacity, erect and sturdy culms, moderately short and erect leaves of medium width, moderately heavy grains (3 g/100 or over) and a high harvest index (c. 0.5). See Chandler (1969) and Yoshida et al. (1972) for detailed discussion. The plant type of tall traditional varieties is contrasted with that of the HYV s in Fig. 3-1. The angle of the lower leaves in crosses involving parents of contrasting plant types turns out to be a dynamic trait in that the angles of F 1

GENETICS AND BREEDING

I

29

I'

Figure 3-1. Contrasting plant 1ypes. Lett: Traditional varie1y with long and droopy leaves, tall weak stems, late maturrty, susceptibili1y to lodging when heavily fertilized, and low yield potential. Right: Semidwart varie1y with high tillering abili1y, short erect leaves, early maturi1y, stiff culms, responsiveness to high nitrogen rates. and high yield potential.

plants are predominantly droopy at the juvenile stage, but the leaf angles of F 2 plants attain a nearly normal distribution at heading, with slightly more erect leaf progenies in the F 2 populations (see Chang and Vergara 1972). In several crosses, the horizontal flag leaves show partial dominance to erect ones (Chang and Vergara 1972). In the progenies of a tall/semidwarf cross, erect flag leaves in semidwarf lines show the largest correlation value with grain yield; in intermediate and tall lines , erect leaves below the flag leaf are associated with higher yield levels (Chang and Tagumpay 1970). Leaf length, leaf width, and total leaf area show nearly normal distribution in some crosses but also indicate complex gene interactions in other crosses (Kawano and Takahashi 1969; Chang and Vergara 1972). Tiller number and panicle number are positively correlated, although the ratio of panicles to tillers may vary among cultivars and is subject to

30

RICE: PRODUCTION

environmental influence. The quantitative nature of tillering ability was indicated by the early studies of Ramiah and Rao (1953). The number of panicles per plant has been shown to be largely controlled by additive gene action. High panicle number is partially dominant to a low count (Wu 1968; Li and Chang 1970; Li 1975). Maternal effect on panicle number has been reported by Wu (1968). In diallel crosses, the panicle number is controlled by both additive and dominance effects. High panicle number is partially dominant to a low count. However, different parental arrays vary in the order of dominance and different parents carry unequal proportions of dominant and recessive alleles (Wu 1968; Li and Chang 1970; Li 1975). Differences in panicle length are largely controlled by additive gene action with dominance at some loci. Long panicles are partially dominant to short ones (Wu 1968; Li and Chang 1970; Li, 1975). Panicle length shows positive correlation with plant height and growth duration (Chandraratna 1964; Chang et al. 1973). The number of primary branches on a panicle appears to be partly controlled by additive genes, but it is also affected by complex gene interactions (Wu 1968). The number of spikelets on a panicle partly determines the density of the panicle. The additive effect and partial dominance confers a high spikelet number in diallel crosses. The direction of dominance varies from cross to cross (Li and Chang 1970; Li 1975). In some Indian varieties, lax panicles are monogenically dominant to compact ones (Parnell et al. 1922; Ramiah 1930), while other crosses show F 2 ratios of 9 lax:7 compact and 7 lax:9 compact (Ghose et al. 1960). Panicle exsertion varies from completely enclosed to partly enclosed and from exserted to fully exserted (see Chang and Bardenas 1965). The extreme types of poor exsertion may be controlled by three recessive genes (Sethie et al. 1937). Continuous variation due to polygenes appears more plausible in other crosses (Ramiah 1932). Grain characteristics

Grain dimensions are traits of economic importance, but genetical studies related to size and shape are rather limited in number and scope. Genetic postulates on grain length vary from monogenic (Chao 1928; Ramiah and Parthasarathy 1933), digenic (Bollich 1957), trigenic (Ramiah and Parthasarathy 1933), to essentially polygenic inheritance (Jones et al. 1935; Morinaga et al. 1943; Mitra 1962; Somrith et al. 1979). Dave (1939) obtained the following order of dominance when discrete segregation patterns were observed: long > medium > short > very short, although in other cases,

GENETICS AND BREEDING

31

short was dominant to long (USDA 1963). In the case of polygenic inheritance, both additive and dominance effects are detected (Somrith et a!. 1979), although the direction of dominance varies from one cross to another (Jones et a!. 1935; Somrith et a!. 1979). Grain width shows polygenic (Ramiah and Parthasarathy 1933; Jones et a!. 1935) or polymeric (three to five genes) inheritance with narrow spikelet partially dominant over broad spikelet (Bollich 1957). Grain shape is expressed by the ratio of length to width. The ratio showed essentially normal distribution in three crosses (Nakata and Jackson 1973; Somrith eta!. 1979). Long grain and slender shape are frequently correlated (Ramiah and Parthasarathy 1933; Somrith eta!. 1979), although exceptions are also known (Sakai and Pinto 1959). Grain thickness also appear to be under polygenic control (Nakata and Jackson 1973). Grain weight (estimated by the total weight of 100 grains) shows an essentially normal distribution in the F 2 generation (Chandraratna and Sakai 1960; Somrith eta!. 1979) and partial dominance with both unequal potency and additive effect (Li and Chou 1986), although some degree of nonallelic interaction effect has been detected (Somrith eta!. 1979; Li and Chou 1986). The maternal influence on grain weight has been reported (Chandraratna and Sakai 1960; Somrith et a!. 1979). Large grain size is positively correlated with seedling vigor, alpha amylase activity, and seedling respiration rate (Lee eta!. 1986; Chen et a!. 1986). Heritability estimates and character associations

Heritability estimates of economic traits based on F 2 or subsequent generations show the following decreasing order in magnitude: number of days from seeding to heading (range: 53-95%), spikelet length (7-91%), plant height (32-93%), panicle length (25-84%), spikelet width (8-69%), grain weight (40-60%), number of grains per panicle (24-33%), panicle weight (18-35%), panicles per plant (9-72%), tillers per plant (10-35%), and grain yield per plant (8-22%) (see Chang and Li 1980 for citations). An increasing number of research papers dealing with heritability estimates and character associations has recently appeared. The findings vary considerably among experiments. It may be cautioned here that, for estimating heritability, the data should come from crosses evaluated in replicated trials and not from cultivars alone, so that the environmental impact can also be assessed. Some of the reported character associations were poorly chosen because the function of one trait was physiologically related to that of the other. Moreover, the findings vary considerably from one cross to another because of divergent genetic backgrounds of the

32

RICE: PRODUCTION

parents. The researcher should select the parents for crossing with a thorough understanding of the contributing factors, and the reader should approach all papers with this caution in mind. Growth Characteristics and Ecological Adaptation Growth duration

Rice cultivars vary greatly in their growth duration and reactions to changes in day length and temperature. The growth duration of a cultivar not only determines its suitability in a particular crop season at a given location but also affects its range of adaptiveness at different locations. The description of earliness or lateness is not as biologically meaningful as the characterization of the components of growth duration: the basic vegetative phase (BVP), the photoperiod-sensitive phase (PSP), and the optimum photoperiod at which the shortest growth duration in a photoperiod-sensitive genotype is obtained (see Chandraratna 1964; Vergara and Chang 1985). By studying diverse germplasm under controlled photoperiods, varieties may be categorized as completely insensitive, essentially insensitive, weakly sensitive, and strongly sensitive (see Chang and Vergara 1971; Vergara and Chang 1985). In crosses between insensitive parents differing markedly in BVP, the F 1 plants frequently show dominance or overdominance of earliness because a series of dominant Ef genes control short BVP. The polymeric Ef series may range from one gene to several genes and are cumulative but unequal in effect (Chang et al. 1969). They belong to the anisomeric class of Grant (1964) which shows cumulative action and differential strength. The Efgenes may explain the monogenic (Hector 1922; Ramiah 1933) or multigenic control of heading date with earliness partially dominant to lateness (Jones 1928; Kudo 1968; Khaleque and Eunus 1975). By using isogenic lines, the Ef(or E) locus is found to be complex, involving the dominant E allele, its recessive alleles, and other recessive alleles of contrasting effect (If) (Tsai 1986). The anisomeric Ef genes may also account for some of the continuous distribution in the F 2 population which is markedly skewed toward the early-maturing parent. In crosses involving parents differing little in growth duration, the F 2 distributions appear essentially normal, indicating additive gene action of many minor genes or polygenes (see Chang and Li 1980 for references). In other crosses where photoperiodic reactions of the parents were not determined, lateness is dominant to earliness. The F 2 distribution may be 3late:l early or 9late:7 early (Ramiah 1933; Jones 1933). Although the late flowering (Lf) gene or genes have been postulated to explain such F 2

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segregation, the probable role of the photoperiod-sensitive gene (Se) or genes cannot be entirely ignored. Strong photoperiod sensitivity is controlled by one (Se) or two (Se 1 and Se 2) dominant genes (Chandraratna 1955; Kuriyama 1965; Chang et al. 1969). TheSe genes have potent expression in that panicle initiation is completely suppressed under long day length in spite of a short BVP as long as the prevailing day length has not reached the critical photoperiod (the lower limit of photoperiod at which panicle initiation will be triggered); i.e., Se is epistatic to the Efgenes under a long photoperiod. Moreover, an inhibitor (i-Se) may suppress the action of Se and produce an F 2 ratio of9 sensitive:? insensitive (Chang et al. 1969). In crosses between sensitive parents, a short critical photoperiod is dominant to a long one. Likewise, a short optimum photoperiod appears to be dominant to a long one (Li 1970). An association between a long PSP and a short BVP and between a short optimum photoperiod and a short critical photoperiod showed up in several F 2 populations (Chang et al. 1969; Li 1970). In other crosses involving distantly related parents, the F 2 ratios were reversed as 1 (sensitive):3 (insensitive) or 1:15 in several crosses, suggesting the recessive nature of photoperiod sensitivity. The complicating effects of temperature response (Sampath and Seshu 1961) and different seeding dates may have been involved in these crosses. The difficulty of studying photoperiod reaction under a changing natural day length has been pointed out by Chang et al. (1969). In strongly sensitive/weakly sensitive crosses, the strong photoperiod response appears to be dominant to the weak reaction in the F 1 and F 2 plants. In the F 2 populations, the strong photoperiodicity behaves as a single dominant to the weak response. A few insensitive F 2 plants have also been found, however (IRRI 1975). Variable F 2 segregation patterns appear in weakly sensitive/insensitive crosses. Although the distribution is continuous and the short-PSP plants predominate in all four crosses, transgressive segregation for long PSP is obtained in all crosses. A few strongly sensitive progenies were recovered in one cross (Lin 1972; Chang and Oka 1976). On the other hand, the segregation for BVP essentially follows the anisomeric type of Ef gene action (Lin 1972).

Response to temperatures While the partitioning of the growth duration into BVP and PSP under controlled photoperiods can account for the diverse array of previous findings on growth duration (Chang et al. 1969), the complicating effect of temperature responses cannot be ignored. It is known that tropical varieties can be retarded during the vegetative growth phase or during panicle

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initiation if cool temperatures prevail. Varieties of the temperate zone may show a greatly shortened vegetative growth phase and a shorter panicle development phase if high temperatures occur at the juvenile stage. A complex of six genes was proposed by Puke (1955) to explain the segregation for photoperiod and temperature responses in Japanese varieties. Late-maturing varieties have all six pairs of dominant alleles, medium-late ones have five, and early ones have four. One of the photoperiod-sensitive genes appears to be linked with a gene for red apiculus. However, Puke did not demonstrate the specific effect of the individual genes. Controlled environments are needed to elucidate photoperiod by temperature interactions (Chang and Oka 1976). From an early-maturing variety of northern China, a modifier gene rna is found to promote flower initiation under low temperatures in the first crop season in Taiwan. Under higher temperatures in the second crop season, this gene interacts with a basic gene for earliness (E) in further reducing the vegetative growth period. Another modifier rnb (at the same locus as rna) found in an early-maturing variety of northern Japan shows almost the same effect on flower initiation. That rna and rnb are isoalleles with slightly different effects is demonstrated by comparing isogenic lines carrying those genes. The E locus could be a compound locus located on the eighth linkage group of the Japanese testers (Tsai 1976). The growth responses of rice varieties to low temperatures at specific growth stages and the adverse effects are I. the period from germination to seedling establishment-poor germination and stunted seedlings 2. the period from seedling establishment to panicle initiation-slow seedling growth or reduced vigor and leaf discoloration 3. the period from panicle initiation to ripening-stunting, poor tillering, partial panicle exsertion, degenerated panicle tips, and spikelet sterility; or delayed heading with irregular maturity (see IRRI 1976; IRRI, 1979b) Germinability under cool temperature (15°C, 59°F) is governed by four or more dominant genes. These genes are linked with wx, d2, d6 , and 1-Bf (Sasaki et al. 1973). In Japanese varieties, two or more dominant genes control tolerance to low air temperatures (19°C, 66.2°F, or slightly below) at the meiotic phase (Sakai and Shimazaki 1948). Tolerance to cool water temperatures (18°C, 64.4°F, or slightly below) is controlled by four or more dominant genes that have unequal potencies and unequal additive effect (Toriyama and Futsuhara 1960; Li and Rutger 1980). Genetic correlation of seedling vigor under cool temperatures with earliness and large seed size has been indicated, but these traits were not correlated with adult

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plant height (Li and Rutger 1980). Heritability estimates of cool tolerance both at seedling stage (Erickson 1968; Li and Rutger 1980) and at panicle initiation period (Futsuhara and Toriyama 1971) are high. Growth habit

The lazy or ageotropic growth habit is inherited as a single recessive, Ia (Jones and Adair 1938; Ramiah and Rao 1953). In other crosses, the erect habit (er) is recessive to spreading (USDA 1963). Again, a continuous range of variation in the culm angle and the growth stage at which the prostration of the lower internodes begins to occur may be found among cultivars and their hybrid progenies. Grain shattering

The shattering of grains from the panicle is more pronounced in the wild species, the indica race of 0. sativa, and the African rices (0. glaberrima) than in the upland varieties,javanica and sinica (or japonica) races of 0. sativa. In crosses between a wild strain and a cultivar, shattering was controlled by one or two dominant genes, Sh (Ramiah and Rao 1953). Because the degree of shattering varies continuously among cultivars, it is not surprising to find that one report by Jones (1933) indicated the monogenic and dominant nature of shattering in one cross, while in another cross, difficult threshing (Th) in Japanese varieties was dominant over easy shattering. A multigenic interpretation appears more plausible (Sethi et al. 1937; Sakai and Niles 1957; Takahashi 1964). The shedding character is associated with the relative degree of development of the abscission layer between the spikelet and the pedicel. Shedding appeared to be inversely associated with the thickness of cell walls in the abscission layer (Nagai 1958). Shattering is generally more serious in the dry season than in the wet season or when lowland varieties are grown in upland culture. Grain dormancy

Grain dormancy is essential to cultivars that mature during the raining season. Dormancy in Japanese varieties is reported to be controlled by two complementary genes, and high permeability of testa to water by another gene, Sg (Takahashi 1962). In other studies, seed dormancy in Indian varieties appears to be a dominant trait governed by a number of genes. Determination of grain dormancy at several intervals following harvest led to the finding that a varying number of anisomeric genes (Sdr) control the strength and duration of dormancy (Chang and Yen 1969; Chang and Tagumpay 1973). The contribution of the hull component to

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dormancy appears to be controlled by one dominant gene or two complementary genes; modifiers may also be involved. The effect of pericarp dormancy may be independent of the hull factor in tropical varieties (Seshu and Sorrells 1986). Grain dormancy is not genetically correlated with growth duration, although superficial character association in diverse cultivars has led to the postulate that early-maturing rices have no dormancy (see Chang and Tagumpay 1973). Diffusible inhibitors from the hull of tropical varieties that confer dormancy have been identified, consisting mainly of nonanoic acid, or in combination with other short-chained saturated fatty acids (IRRI 1988a). Tolerance to excess water

Adaptation to deepwater or floating ability is essentially the ability of the submerged internodes of a cultivar to elongate rapidly or to produce tillers at the higher nodes or both. Earlier studies in India led to the postulate that two complementary recessive genes, dw 1 and dw 2 , conferred floating ability (Ramiah and Ramaswami 1941). Studies in Thailand also indicated that floating ability is a recessive trait. Strong elongation ability is associated with tall plant stature but not with photoperiod sensitivity (Prechachart and Jackson, 1975). A recent study using 20-day-old seedlings indicates the action of a dominant gene (E[) for the floating characteristic. When El is combined with the tall height gene (Sd 1) for adult plants in a complementary manner, the trait is fully expressed in the tall and elongating varieties (Thakur and HilleRisLambers 1989). Tolerance to plant submergence under floodwater is also a desirable trait in monsoonal Asia. Varieties tolerant to submergence do not necessarily have good elongation ability. The two traits appear to be independent of each other (IRRI 1976a). Both internode elongation ability and submergence tolerance appear to be complex traits (see IRRI 1982). In an 8 x 8 diallel cross, tolerance to submergence was marked by additive and dominance effects (Haque et al. 1989). Resistance to water deficit

Drought resistance in dryland (upland) culture has been identified as a complex and growth stage-specific trait largely associated with a deep and thick root system, enhanced ability to retain tissue turgor under water stress, high cuticular resistance and stomatal resistance to water loss, plasticity in leaf rolling and unrolling, and early maturity (Chang and Loresto 1986). In the roots of mature plants, high root number is generally dominant to low; thick roots behave as a dominant trait in some crosses and a recessive trait in others. Maximum root length is a dominant trait in crosses

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between dryland varieties but shows recessiveness when a semidwarf parent is involved. All the root characters indicate multigenic control. Positive correlation is obtained between the deep-and-thick root system and the tall height, low tillering, and long-panicle plant type (see Chang et al. 1986). A larger number of xylem vessels and greater xylem vessel areas are associated with thicker roots. A high xylem vessel number is a dominant trait with moderately high heritability and is positively associated with root length (Bashar et al. 1990). The root pulling resistance (the vertical force required to pull a plant from the soil) is also an expression of a strong root system and is related to field drought resistance. Genetic studies indicate F 1 heterosis in all three crosses involving high/high, low/high, or intermediate/intermediate combination. Dominant and additive alleles generally govern root pulling resistance. Heritability was rather low (39-47%), however (Ekanayake et al. 1985). Disease Resistance

Disease problems have been greatly increased by the recent practice of intensive rice cultivation in irrigated areas and compounded by continuous multiple cropping. Padwick's 1950 book on rice diseases listed 24 parasitic diseases and did not include a single virus disease. The roster of diseases grew to 65 in the mid-1980s and included five viruses (see Chang 1984). Under the tropical climate, pathogens do not necessarily go through the primary and secondary cycles of infection and, therefore, inoculum builds up rapidly. Because of the large number of research publications, the known genes for host resistance to major diseases are summarized below in genic formulas. Recent reviews have been provided by Khush and Virmani (1985) and Ou (1985). 1. Bacterial blight: Xa-1, Xa-2, Xa-3, and Xa-kg in Japanese varieties; Xa-3, Xa-4, xa-5, Xa-6 (allelic to Xa-3), Xa-7, xa-8, xa-9(?), Xa-10, Xa-11, Xa-12, xa-13, Xa-14, Xa-16, Xa-17, and Xa-18 in

tropical varieties (also see Sidhu et al. 1978; Ogawa and Yamamoto 1986; Rice Genetics Newsletter 1989). 2. Bacterial leaf streak: one to three genes. 3. Blast: Pi 1, Pi2 , Pi 11 , Pi 12 , and Pi 13 with additive effect; Pi-a, Pi-b, Pi-i, Pi-k, Pi-t, Pi-ta, and Pi-z in Japanese varieties; Pi22 , Pi 25 for seedling reactions; one to three dominant genes for neck reaction, two of which also control seedling resistance; one major gene and minor genes or additive genes for field resistance (see Kiyosawa et al. 1975; IRRI 1979). Field resistance (partial resistance) indicated polygenic control (Lin 1986; Wang et al. 1989).

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4. Cercospora leaf spots: Ce; duplicate genes (Ce 1, Ce 2). 5. Grassy stunt virus biotype 1: Gsv (from 0. nivara). 6. Brown spot (Helminthosporium oryzae): He or he. 7. Hoja blanca virus: one dominant gene (Hbv). 8. Sheath blight: one dominant gene (probably multigenic). 9. Stem rot: Sc 1 and/or Sc 2• 10. Stripe virus: two complementary genes (St 1 and St 2) or St3 • 11. Tungro virus: probably multigenic. 12. Black streak dwarf virus: Bsv. 13. Yellow dwarf virus: Ydv. The foregoing information is based largely on host reactions and, therefore, only indicates the varietal genotypes. Little is known about the gene or genes for pathogenecity in the pathogen. The situation in rice is rather unfortunate because the gene-for-gene hypothesis of pathogen-host interaction (Flor 1956) has been demonstrated to have wide application in crop plants. Until recently, only Japanese plant pathologists have probed into the frequency of virulence genes in the blast fungus by postulating on the gene-for-gene scheme (see Kiyosawa et al. 1984). Now two loci for virulence (Pos-3 and -4) have been identified in the blast fungus (Leung et al. 1988). An a virulence gene (avr-1 0) corresponding to the Xa-10 resistance gene to bacterial blight in the host has been cloned (Kelemu and Leach 1990). The spherical form of the rice tungro virus is now known to contain single-stranded RNA; the bacilliform virus consists of double-stranded DNA. The spherical form serves as a carrier for the bacilliform (IRRI 1989a). Such a phenomenon further complicates genetic studies of tungro resistance, because plant response to the virus is confounded with host reaction to the insect vector. The disease resistance genes enumerated above are mostly major genes (oligogenes) that confer the vertical type of resistance. Therefore, it is not surprising that, when the pathogen is inherently diverse in composition and given the opportunity of being selected by the resistance genes in the host, a new pathotype will readily emerge, predominate, and become virulent on the formerly resistant host. The breakdown of the blast resistance genes under the vertical category ("true resistance") has been well documented in Japan (see Ezuka 1979). The contrasting type of resistance, horizontal resistance, has been much discussed but not yet found in rice. Rice pathologists are now searching for a more durable type of resistance, called "field" or "partial" resistance (Ezuka 1979; Bonman and Mackill 1988). Field resistance is largely under polygenic control. The two types of resistance may be combined (see Ezuka 1979). To cope with the rapid shifts in pathogenic populations following the

GENETICS AND BREEDING

39

sequential release of resistant varieties based on major genes and of related parentage, various remedial schemes have been proposed: pyramiding of major genes, gene deployment, varietal mixtures, multiline varieties, and composite varieties. Additional information on these approaches may be found in IRRI (1979a) and Buddenhagen (1983). The approaches may also apply to the brown planthopper (Saxena 1989) and other genetically variable insects. Insect Resistance

In parallel to the diseases, destructive insects have also proliferated in both number and incidence under intensive cultivation and continuous monoculture of rice in irrigated areas. Insects that were little known 20 to 30 years ago, such as the brown planthopper and the whitebacked planthopper, have evolved into major threats. The leaf-sucking insects of this group are also vectors of destructive virus diseases. On the other hand, the striped stemborer has become less prevalent with the widespread adoption of the semidwarfs. The research on insect resistance in rice cultivars is an exciting area of scientific progress. The genetic findings based on Mendelian analysis of genes in the host are again summarized by the insect pests involved. Recent reviews are provided by Pathak (1977), Khush (1984a), papers in the Rice Genetics Newsletter (1986, 1988), and Kaneda (1988). 1. Brown planthopper: Bph-1, 1-Bph-1, bph-2, Bph-3, bph-4, bph-5, Bph-6, bph-7, bph-8, and Bph-9 for the respective biotypes 2. Gall midge: one dominant gene (Gm-1, Gm-2); three recessive

genes 3. Green leafhopper: Glh-1, Glh-2, Glh-3, glh-4, Glh-5, Glh-6, Glh-7, and Glh-8 4. Stemborers: one dominant or a few genes (Sb); a single recessive gene; complex inheritance 5. Stem maggots: a single gene without dominance 6. White backed planthopper: Wbph-1, Wbph-2, Wbph-3, wbph-4, and Wbph-5.

7. Zigzag planthopper: Zlh-1, Zlh-2, and Zlh-3. An understanding of host resistance to insect pests requires a knowledge of the biochemical and physiologic mechanisms involved. Helpful reviews have been provided by Pathak and Saxena (1980), Heinrichs et al. (1985), and Saxena and Barrion (1988). Because the vertical resistance is largely involved in rice breeding and resistant varieties are sequential releases of relateq parentage, varietal

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breakdown to either disease or insect has been repeatedly experienced in rice (see Chang 1984, 1990; Hibino 1987; Dahal et al. 1990). Grain Quality and Nutritive Value

The physical aspects of grain quality have been discussed under morphologic and quantitative traits. The milling and cooking characteristics are complex and have not been sufficiently researched in relation to their economic importance. Background information may be found in a recent monograph, Rice: Chemistry and Technology (Juliano 1985). The proportion of the two starch fractions in the endosperm starch is a principal component of the cohesiveness (stickiness vs. dryness) of the cooked rice. The linear amylose fraction varies from zero to 30% or above, while the remainder is the branched amylopectin. Glutinous or waxy starch having zero or negligible amylose is generally interpreted as under the control of a recessive gene (wx), but the locus has been shown to have ultra-fine structure (Li et al. 1965). Two mutant alleles (Wxa and Wxb) have been identified, and they act in the cis arrangement (Sano 1984). Wxa appears to be more efficient than Wxb in producing Wx protein. The wild relatives of 0. sativa have Wxa only (Sano et al. 1986). Because the endosperm is triploid, a range of amylose contents could be found in hybrids according to the dosage effect of the wx alleles (Okuno 1978). In crosses between nonwaxy parents (15-30% amylose), high amylose content is generally postulated as under the control of a major dominant gene and several modifiers (Seetharaman 1959; Bollich and Webb 1973; Somrith et al. 1979). However, different crosses yielded variable results, partly because the parents themselves showed a continuous variation in amylose content. An environmental effect on amylose content has also been observed (see Juliano 1985). Chalkiness of the endosperm, expressed as white belly, white center, or white back, affects the percentage of whole milled kernels (head rice) and the physical appearance and quality of the milled rice. The maternal influence on chalkiness has been reported (Xu and Shen 1988). White belly and white center are generally attributed to a single recessive gene, wb and we, respectively. However, in other studies, white belly is reported to be a dominant character. Later studies suggest that multiple genes and genotype-environment interaction were more likely the controlling factors (see Chang and Li 1980). Chalky spots are more frequently associated with bold grains rather than slender kernels. Among F 2 plants, additive effects appear to be a major genetic component (Somrith et al. 1979). Endosperm mutations such as dull (du), floury (flo), shrunken (shr),

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41

and sugary (su) have been described (see Satoh and Amana 1987). Their direct use in rice processing remains to be determined. Aroma in cooked rice adds market value to the product. The scent may also be detected in leaf tissues around heading time. Scent is generally inherited as a single dominant (Sk) (see USDA 1963), although the complementary action of two dominant genes has been proposed (Tripathi and Rao 1979). The volatile aromatic component has been identified as 2acetyl-1-pyrroline (Buttery et al. 1982), which was not detected in earlier studies. Leaf aroma has been ascribed to the complementary action of three dominant genes (Singh and Mani 1987). Cooking temperature and duration are indicated by the gelatinizing temperature of the starch fraction, which is in turn assessed by the spreading of the milled rice kernel in a weak alkali solution. The inheritance of gelatinizing temperatures presents an intriguing picture: high values often predominate among hybrid progenies in high/low and high/intermediate crosses. Intermediate values might not breed true in F3 lines. Low values are not found in high/intermediate crosses. Interpretations for such segregating behavior range from a few major genes and modifiers to additive gene action and complex gene interactions (Kahlon 1965; Stansel 1966; Somrith et al. 1979). Genotypic association between high amylose and high gelatinization temperature has been observed in several instances (Kudo 1968; Ghose and Govindaswamy 1972; McKenzie and Rutger 1983). Another aspect of cooking quality, the softness of cooked rice, is also indirectly assessed by the gel consistency (or viscosity) of cooked starch powder. In hard/soft gel crosses, F 2 segregation indicates the role of a dominant gene and several modifiers in conferring hard consistency (see Chang and Li 1980). Another study indicated an additive gene effect (Zaman et al. 1985). When all three types (hard, medium, and soft gel) are involved, the order of dominance is hard> medium> soft, and the difference between two adjacent classes is largely under monogenic control. The genetic control of brown rice protein content has received considerable attention. Low protein content appears to be dominant to high (Erickson 1969; HilleRisLambers et al. 1973; Chang and Lin 1974). Diallel analysis indicates dominance at some loci, epistasis expressed as overdominance or complementary gene action, and an unequal distribution of dominant and recessive alleles. The maternal effect and metaxenia were observed in the triploid endosperm. Both dominance and additive effects are noted in F 2 and F 3 data (Chang and Lin 1974). The triploid nature of endosperm starch prohibits a precise genetic interpretation. The heritability estimates for protein content are rather low, probably resulting from genotype x environment interactions. High protein content tends to be

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associated with early heading and light grains (HilleRisLambers et al. 1973) and a darker color in milled rice. Protein content and grain yield tend to be negatively correlated (see Juliano, 1985).

Linkage Groups During the 1940s and 1950s, Indian, Japanese, and U.S. geneticists worked independently on the linkage groups of rice, and information from three sources was summarized by Jodon (USDA 1963). However, the groups were mostly incomplete and not integrated. The first trial to develop the 12linkage groups in Japanese rices Gaponica race) was published by Nagao and Takahashi (1963) and Takahashi (1964), although some groups were represented by only two genes. Misro et al. (1966) later presented linkage maps for indica testers. Further efforts were made by Kinoshita (1976) and, cytologically, by Iwata and Omura (1984) and Iwata et al. (1984). Due to differences in the gene complexes of the two ecogeographic races and the scarcity of identical marker genes in the two races, it was not possible to establish 12 groups common to both races. A side-by-side comparison of the two schemes and including three sources was illustrated by Chang and Li (1980). The contrast in pigmentation genes between Indian and Japanese interpretations was given by Kinoshita (1986). The most recent version of Japanese efforts is shown by Kinoshita (1986, 1987). With the aid of primary trisomies and reciprocal translocations of Nishimura (1961), Khush et al. (1984) were able to reconcile to a large extent the relationship among various systems of numbering chromosomes, trisomies, linkage groups, and marker genes and arrive at a revised scheme of 12 linkage groups (also see Khush and Singh 1986). The 12 linkage groups of Nagao and Takahashi (1963) were assigned to nine chromosomes. However, Japanese workers have disputed the ''complete'' correspondence between the linkage groups of indica andjaponica marker genes on the grounds of incomplete cytological agreement (Kinoshita 1986; Iwata 1986). Uncertainties still exist in relating the extra chromosome in several Triplo lines to numbered chromosomes and variable descendants of the primary trisomies in Khush's Triplo series have given rise to tertiary trisomies (Wu and Chung 1988; Kurata 1988). At the 1990 Rice Genetics Symposium, a committee met and agreed on a new system of numbering chromosome numbers and related these numbers to the linkage groups (see Rice Genetics Newsletter 1990). CYTOGENETICS

Cytogenetical studies on the rice plant had a late start. The 24-chromosome complement of 0. sativa was first reported by Kuwada in 1909. Because of their small size and a deficiency of distinct morphologic markers, rice

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chromosomes did not appeal to many cytogeneticists. As a result, cytological studies were rather few and are unrelated to genetic markers. It became the area of genome analysis that interested several teams of rice cytogeneticists for nearly two decades after World War II (see Chang 1964). In recent years, only a few rice cytogeneticists have remained active. Chromosome Number and Karyotype Chromosome number

Diploid species in the genus Oryza have 24 chromosomes while the other group has the tetraploid complement. The 22 species are divided as follows (see Chang 1985a): 1. diploid species (2n = 2x = 24): australiensis, barthii, brachyantha, eichingeri, glaberrima, granulata, glumaepatula, longistaminata, meridionalis, meyeriana, nivara, officina/is, rufipogon, and sativa 2. tetraploid species (2n = 4x = 48): alta, grandiglumis, latifolia, longiglumis, minuta, punctata, and ridleyi

The chromosome number of 0. schlecteri is unknown since seeds or plants of this taxon are not available. 0. eichingeri has been reported as a tetraploid, probably on a mistaken specimen; similarly, diploid punctata is not likely. Karyotype

The karyotype of 0. sativa has been more frequently studied than that of other species in the genus. Pathak (1940) first described the morphology of 24 chromosomes as eight median and 16 submedian or subterminal. Varying descriptions based on haploid plants of different varieties were given by Japanese and Chinese workers (see Chang 1964). Hu (1964) reported the chromosomes of Taichung 65 distributed as three median, seven submedian, and two subterminal. Shastry et al. (1960) and Dolores et al. (1979) also described three median, seven submedian, and two subtelocentric chromosomes. Kurata (1986) interpreted the karyotype as five median (metacentric), five submedian, and two subtelocentric. While Shastry (1964) and Kurata (1986) described similar karyotypes for different species, other workers have reported considerable variation among Asian cultivars in the distribution of different chromosome types (see Hu 1964; Dolores et al. 1979; Rice Genetics Newsletter 1988). Chromosome arms of the cultivated species tend to be more symmetrical than those of the wild species (Shastry 1964).

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Aberrant meiotic behavior

Asynaptic plants have been found in nature and among X-rayed progenies. Meiosis is marked by a failure of the homologous chromosomes to synapse at prophase or metaphase, formation of univalents, and irregular distribution of chromosomes at anaphase. Chiamata per bivalent are reduced; univalents split to form laggards; supernumery spindles appear; and the gametes abort. Highly sterile panicles are found in asynaptic plants. The aberrant behavior is inherited as a single recessive (as) or controlled by one of two duplicate genes (see Chang 1964). Desynapsis is also found in irradiated material. The separation of chromosomes begins at diplotene, and univalents appear at diakinesis and metaphase. The high seed sterility associated with desynapsis is inherited as a single recessive gene, ds (see Chang 1964). Chromosome aberrants

Among the many forms of chromosome aberrants, chromosome interchanges appearing as semisterile plants are the most common form. Quadrivalent formation, "pairs" ofbivalents, and rod- or ring-shaped bivalents are frequently found. "Open" (adjacent) or "zigzag" (alternate) forms of ring configuration are observed. Pollen fertility is lowered in a ring of six chromosomes or two rings of four chromosomes each (see Chang 1964). Reciprocal translocation homozygotes were isolated by test crosses between fertile progenies of translocation heterozygotes and the untreated original variety (Nishimura and Kurakami 1952; Oka et al. 1953; Hsieh 1961). Such translocation homozygotes do not differ markedly in phenotypic appearance from their original strain and appear homogeneous in various agronomic traits (Hsieh et al. 1962). Intercrosses between reciprocal translocation homozygotes would yield information on the different chromosomes involved in various translocation lines (Nishimura 1961; Hsieh 1961). By treating single translocation homozygotes with X-rays, followed by test crosses, double translocation homozygotes have been obtained (Huang 1961). Genome Analysis

Intense studies on the pairing behavior of interspecific hybrids during meiosis were made by workers in Japan, Taiwan, and the United States from the mid-1950s to the next decade. These studies led to the identification of six basic genomes and several subgenomes in the genus Oryza, as follows: 1. Genome A: AA for sativa, nivara, ru.fipogon and their weed race, 0. sativa f. spontanea; A 1A 1 (formerly AbAb) for longistaminata

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2. 3. 4. 5. 6.

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(formerly barthii); NN for glaberrima and barthii (formerly breviligulata) and their weed race (0. stapfii);and AgPNP for glumaepatula (formerly AcuAcu for 0. cubensis). Thus, the A, N, Ag, and NP subgenomes form the different primary gene-pools of Harlan and de Wet (1971). Crosses between subgenomes and gene transfer can be made but with some difficulty. Genome C: CC for officina/is and eichingeri. Genomes Band C: BBCC for minuta and punctata. Genomes C and D: CCDD for alta, grandiglumis, and latifolia. Genome E: EE for australiensis. Genome F: FF for brachyantha.

The transfer of genes from the above genomes to the cultivars is possible but with difficulty because these are in the secondary gene pool of Harlan and de Wet (1971). Resumes on genome analysis of a classic nature may be found in Rice Genetics and Cytogenetics (IRRI 1964) and Chang (1964). Summaries on the chromosome pairing and fertility of interspecific hybrids were compiled by Chang (1964). The reader should watch out for various synonyms given to the wild species by different authors over a period of time. Repetitive DNA sequences have shown promise in studying genomes and their diversification. Sequences specific to the AA, CC, EE, and FF genomes have been reported by Zhao et al. (1989). Variations in Chromosome Numbers and Meiotic Behavior Haploids

Haploid plants appear spontaneously in nature, in X-rayed progenies, or in the progenies of hybrids. The haploid plants are reduced in the size of every part in varying proportions. Tiller number, leaf blade, plant height, spikelet number, panicle length, and pollen mother cells are also affected. Haploid plants are completely sterile unless pollinated by normal pollen from diploid plants (see Chang 1964). Haploids have recently assumed a new role as the initial product of anther or pollen calli raised from tissue culture. By doubling the chromosomes with colchicine treatment, a homozygous diploid plant is readily obtained by regeneration. Triploids

Autotriploid plants are found in nature or from irradiated progenies. The triploid plant is more vigorous than a normal diploid, producing broad leaves, stout tillers, and large floral plants. Their fertility is generally low

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(0-24%). Progenies of autotriploid plants often carry 2n + 1 and 2n + 2 chromosomes (see Khush 1975). Allotriploids can be obtained with difficulty by crossing a diploid with a tetraploid. Crosses in a reciprocal manner can produce some triploids. The pairing behavior in triploids shows a mode of ten trivalents, two bivalents, and two univalents. Other forms of nonhomologous pairing led to 8III + 6II or lOIII + 3II (Ramanujam 1937; Hu and Ho 1963). Tetraploids

Autotetraploid plants either occur in nature or result from artificial induction of chromosome doubling. High temperature treatment is also used to produce tetraploids. Tetraploid plants show gigas effects but a concurrent reduction in plant stature, rachis length, and spikelet number per panicle. Seed fertility is generally low (less than 35%). The plants are more tolerant to gamma-ray radiation (see Chang 1964). Meiosis in autotetraploids shows eight to nine tetravalents and the remaining chromosomes are bivalents or univalents (Morinaga and Fukushima 1937). Allotetraploids can be readily obtained and show heterosis. During meiosis, the F 1 hybrids produce fewer quadrivalents and univalents, and the anaphasic movement of chromosomes is more regular than in autotetraploids. The hybrids are generally more fertile, but fertility and quadrivalent/univalent frequency show no correlation (Oka et al. 1954). The tetraploid plants and hybrids show typical tetragenic segregation of Mendelian characters but are inferior to the diploids in agronomic aspects (see Chang 1964). Aneup/oids

Aneuploid plants also appear spontaneously in nature. By crossing triploids with diploids, aneuploids of 24 + x types have been obtained. Primary trisomies are thus obtained, and they have been studied by many workers. The first set of 12 primary trisomies was obtained by Hu (1968). The trisomic plants are marked by short stature, delays in heading, variation in panicle and spikelet size, and low seedset. All the trisomies can be transmitted to the next generation by selfing at an average rate of 36.7% on the female side (Khush et al. 1984; Misra et al. 1986). Other workers such as Iwata et al. (1970), Khan and Rutger (1973), and Khush and Misra (1983) also produced complete sets of primary trisomies but it remained for Khush et al. (1984) to use the whole set for linkage analysis. Monosomics have been reported from a chimera] plant and from crosses. However, monosomics are rarely transmitted to the progenies

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47

because rice is basically a diploid plant. Monosomics can be tolerated only in the sporophyte but not in the gametophyte (see Khush 1975). Chromosome Maps

The 12 linkage groups of Nagao and Takahashi (1963) agreed with the haploid chromosome number of rice plants. Trisomies and reciprocal translocations have been used to establish the relationship between the chromosomes and the linkage groups and complete association was elucidated in Japanese testers (Iwata and Omura 1984; Iwata et al. 1984) at about the same time as in Indica markers (Khush et al. 1984). The relationship among chromosomes (via reciprocal translocations), trisomies, and linkage groups was summarized by Iwata (1986). However, the three approaches were independent of one another. While rice workers present at the 1985 Rice Genetics Symposium agreed to follow the karyotype analysis proposed by Shastry et al. (1960) and obtained from pachytene chromosomes, the numbering systems for the 12 chromosomes by different workers are based on different criteria: reciprocal translocations, trisomies, and somatic chromosomes. Five of the chromosomes bear few markers. Iwata et al. (1984) and Khush and Singh (1986) attempted to associate the linkage groups with the numbering of chromosomes. However, a committee was formed to arrive at a common scheme (Rice Genetics Newsletter 1986, 1988). It was even difficult to reconcile chromosome measurements by different workers (Oka and Wu 1988). Some of the indica and japonica testers appear to differ in their respective linkage groups which adds to the problem of consolidating chromosome maps and linkage groups. Finally, at the 1990 Rice Genetics Symposium a uniform system of numbering rice chromosomes was agreed on, and the association between chromosome and linkage group was provided (see Rice Genetics Newsletter 1990). lntervarietal Hybrid Sterility

When plants of different ecogeographic races, or even within a race but rather distantly related, are crossed, the F 1 hybrids and subsequent progenies often show varying degrees of pollen and embryo sac sterility. Such a lack of sexual affinity among varieties also produces a host of other expressions: hybrid inviability, F 1 weakness, aberrant segregation, and restricted recombinations. To the breeders, intervarietal hybrid sterility poses a serious restriction in making wide crosses. It is also the phenomenon of hybrid sterility that led Japanese workers (Kato et al. 1928; Kato et al. 1930) to propose the existence of two subspecies, indica andjaponica, in common rice. Three interpretations have been offered by various workers to explain

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the variable phenomena: chromosomal, genic, and cytoplasmic-genic. Because pairing in the F 1 hybrids is essentially normal, cytologists generally ascribed sterility to small structural differences in the chromosomes of the parents. "Cryptic structural hybridity" was a term often used to explain incomplete pairing or univalents, quadrivalent formation, bridges with or without fragments, and heteromorphic bivalents which were indicative of deletions, translocations, and inversions (Hsieh 1957; Yao et al. 1958; Henderson et al. 1959; Shastry and Misra 1961). However, later studies involving many crosses showed that, while such chromosomal aberrations were observed in partial or highly sterile hybrids and F 2 plants, the frequencies were too low and often disproportional to the degree of sterility. Moreover, many parents themselves also showed a variety of such aberrations. The evidence did not rule out the chromosomal differences, but the probable role of genic imbalance appeared predominant (see Engle et al. 1969; Dolores et al. 1979). Moreover, the genic control of chromosomal behavior is also well-known in cereals. The genic hypothesis on F 1 sterility is largely the duplicate gametic development genes (s 1 and s2) which cause gametic death when both recessives alleles are present (Oka 1957). Backcrossing experiments confirmed the action of such duplicate gametic lethals (Oka 1974). A series of genes (s 1 to s5) that contributes to the sterility in interspecific crosses between 0. sativa and 0. glaberrima has been identified. These represent sporo-gametophytic interactions (Sano 1984; Sato et al. 1987). Other genic hypotheses were related to the sporophytic development of the hybrids: hybrid inviability and weakness. Dominant lethals were proposed to account for the weakness of certain F 1 plants. Either duplicate genes in certain recessive combinations or complementary recessive lethals were suggested by Oka and coworkers (see Oka 1964) to explain vegetative breakdowns in F 2 plants. Lines breeding true for semisterility can be obtained (see Chang 1964). Several varieties of diverse origin (bulu, aus, and indica/japonica hybrids) were found to produce high F 1 fertility with both indica andjaponica varieties and these were called widely compatible varieties (WCVs) by Ikehashi and Araki (1987). Studies on one of the WCVs, Penuh Baru II, suggest that multiple alleles at the wide-compatibility locus, S-5n, control female gamete fertility in the F 1 hybrids rather than the duplicate gametic lethal genes (Ikehashi and Araki 1987). Differences in fertility between reciprocal crosses of intervarietal or interspecific hybrids have been observed in many instances. A lower fertility is often found when a wild relative such as 0. sativa f. spontanea is used as the female parent (see Chang 1964). In the case of cultivars, the first usable cytoplasmic male-sterile (ems) source was obtained from

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Chinsurah Boro II!Taichung 65 (Shinjo and Omura 1966). Four other boro varieties also have ems cytoplasm. Fertility restoring genes are found in many slender-grained varieties (Shinjo 1972). The economically significant Wild Abortive (W A) ems cytoplasm of China comes from a wild source (0. sativa f. spontanea) found on Hainan Island. A large number of restorers for theW A type have been found. The commercially important source in China consists of two sporophytic restorers, but F 2 segregations suggests a variable gene effect of different restorer parents (Li and Yuan 1986; Virmani et al. 1986). An updated listing of ems sources can be found in the Rice Genetics Newsletter (1988). Cytoplasmic Inheritance

Traits under the control of cytoplasmic elements have not received their share of attention and critical analysis in rice research. Other than a small number of maternally affected traits discussed under grain weight (Chandraratna and Sakai 1960), plant height in interspecific crosses (Dolores, unpublished) and protein content (Chang and Lin 1974), the only notable activities have been focused on the ems sources and fertilityrestoring genes. In addition to the Chinsurah Boro II and WA sterile cytoplasms, other sources have been identified: Gambiaca, Taichung Native 1, Lead, 0. rujipogon, 0. sativa f. spontanea, ARC 13829-26, and others (see Virmani et al. 1986; Virmani and Shinjyo 1988). To isolate a purely cytoplasmic effect, a long series of backcrosses to both parents should be made to develop substitution (of chromosomes) lines in an alien cytoplasm, as it was done in wheat. However, the diploid nature of 0. sativa does not tolerate such drastic manipulation. Recent attempts in determining gene sequences have led to a better understanding of chloroplast genes and mitochondrial genes (Wu et al. 1986; Hirai and Ishibashi 1986). The structure of chloroplast DNA and its physical map have been characterized (Hirai and Sugiura 1988). The chloroplast DNA contains the genetic code for some enzymes involved in photosynthesis, but the cytoplasmic components remain to be explored. Plasmidlike mitochondrial (mt) DNA associated with ems have been reported (Yamaguchi and Kakiuchi 1983; Wang et al. 1987; Kadowaki et al. 1988); the DNAs differ between sativa and glaberrima cytoplasms (Sakamoto et al. 1990). A biometrical treatment of cytoplasmic inheritance in autogamous plants has been provided by Sakai et al. (1961) which was related to the study on grain weight (Chandraratna and Sakai 1960). Occasional biparental inheritance of chloroplast DNA has been reported (Second et al. 1989).

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Molecular Cytogenetics

Molecular genetics in rice had a late start. DNA sequencing of rice genes has been mainly carried out by Wu et al. (1986), whose focus is on nuclear, chloroplast, and mitochondrial genes. The study includes wild species. Genome-specific sequences have been characterized and cloned (Zhao et al. 1989). These genome-type-specific repetitive sequences are useful as hybridization probes in classifying unknown species of wild or domesticated rice and in studying genome evolution at the molecular level (Zhao et al. 1989). At IRRI, molecular techniques have been applied to transfer and isolate disease resistance genes (mainly blast and bacterial blight) from wild rices (see IRRI 1990a). Under a Rockefeller Foundation Project on rice biotechnology, a number of laboratories in both developed and developing countries are actively pursuing the gene sequencing, genome characterization, and molecular techniques. Meanwhile, a team at Cornell University is developing an RFLP map in rice to measure and partition genetic variations and to link RFLP markers with known genes (see McCouch et al. 1988; IRRI 1990c).

BREEDING

Recorded history may not mention man's earliest efforts to improve the rice plant. However, long before the advent of science, men (or, more likely, women) undoubtedly had made good use of natural variousness in the crop and its wild relatives, spontaneous mutations, natural hybrids, and introductions from foreign lands. Historical notes on rice breeding may be found in the earlier edition (Chang and Li 1980). Expansion of the rice growing area and increase in grain yield are frequently accompanied by a concurrent growth in human population and migration (Chang 1987). Significant increases in rice yield through the adoption of improved varieties were invariably associated with improved irrigation facilities, use of chemical fertilizers and other agricultural chemicals, better cultural practices and pest management, and favorable prices. Instances of such a combined package of technological improvements have been documented by Shen (1964), Herdt and Capule (1983), Barker et al. (1985), and Chang (1988). Breeding for higher yield has been the common goal in all national agricultural research systems (NARS) of major rice-growing countries. The most dramatic advances in national yield during the past decade were made in China and Indonesia (see Chapter 1). According to recent Food and Agriculture Organization (FAO) statistics, the high-yielding countries of the world continue to be Australia,

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Japan, the Republic of Korea, Democratic People's Republic of Korea, Spain, and the United States. The high yields attained in southern Europe, Australia, and northern California may be partly attributed to the oasislike environment of the crop season: intense solar radiation, long day length in summer months, moderately low night temperatures, abundance of irrigation water, low relative humidity, and minimum incidence of diseases and insects. Another common feature is the long grain-filling period of the predominant cultivars which leads to heavy grains. On the other hand, yields in most Asian countries in the tropics still average less than 3 t/ha in spite of the rapid diffusion of the HYVs. The causes for the low yield during the monsoon season in this region of great genetic diversity are high proportion of rainfed land, fickleness of the monsoon weather, poor water control (deficit or excess), poor or adverse soils, low inputs of agricultural chemicals, poor control of biotic stresses (insects, diseases, weeds, rats, and birds), and inadequate postharvest operations. Chang (1988) has recently provided a detailed assessment of the impact of the new technology on rice production in the developing countries. Conservation, Evaluation, and Use of Rice Germplasm

The success of improving a major crop inevitably rests on the breadth and depth of the genetic basis from which research and breeding emanate. The recent Green Revolution in rice and wheat production is a unique example of exploiting diverse germplasm. The genetic resources of rice are remarkably rich, comprising about 120,000 cultivars in the two cultigens (0. sativa and 0. glaberrima) and numerous populations of20 wild species. The 22 valid species in the genus Oryza are widely scattered over Africa, Asia, Australia, major islands of Oceania, and Central and South America. Their great antiquity may be traced back to the Gondwana supercontinent which fractured during the early Cretaceous period about 130 million years ago. So far, six genomes (sets of homologous chromosomes) have been identified from 16 species studied. Both diploid and tetraploid species coexist in Africa, Asia, and South America (see Chang 1985a). The numerous cultivars of 0. sativa may be grouped into three ecogeographic races: indica of the tropics and subtropics, sinica (or japonica) of the temperate zone, and javanica of Indonesia and dryland areas of Southeast Asia. Varying degrees of incompatibility exists in crosses between races and within a race (see Chang and Li 1980; Chang 1989d). The genetic diversity found in 0. sativa is unusually rich because (1) its cultivation in India and China dates back more than 7000 years, (2) its diversification was aided by wide dispersal following human migration and

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cultivation, which covers an unparalleled ecogeographic spread from 53°N to 40°S latitude, and (3) further differentiation resulted from natural and artificial selection following dispersal in diverse water-soil regimes (wetland, deepwater, tidal swamps, and dryland) and by human preference and selection for grain quality (see Chang 1976a, 1976b, 1985a, 1989a). Much of the rich spectrum of genetic variability could still be found in farmers' fields until the rapid spread of the HYVs in the early 1970s. However, the bulk of the rice germplasm had been collected by the NARS before the 1960s, followed by a massive collection campaign coordinated by IRRI during 1972-83. Nearly 50,000 seed samples were collectedjointly in Asia and Africa by the national centers concerned, one or more of the international agricultural research centers (International Rice Research Institute [IRRI] IITA, WARDA, and IBPGR) and other centers with outreach programs (Food and Agriculture Organization of the United Nations, IRAT, ORSTOM, and agencies in Japan). IRRI's recent collection efforts have been directed to the exploration and acquisition of primitive cultivars and wild species in hitherto inaccessible areas (see Chang 1989b). The base collection of85,000 accessions is housed at IRRI, while other large collections of partly duplicated composition are preserved in China, India, Japan, and the United States, and at the IITA (see Chang et al. 1989). National genebanks such as those in Bangladesh, Indonesia, Republic of Korea, Malaysia, Myanmar (formerly Burma), Pakistan, Sri Lanka, Taiwan, and Thailand also hold sizeable collections of their indigenous germplasm. Among the major crops of the world, rice has the strongest network of germplasm conservation and exchange (see Chang et al. 1982; Chang et al. 1989). Systematic evaluation of the rich and unimproved germplasm began at IRRI in 1962 (see Chang et al. 1975) and was intensified and accelerated under the Genetic Evaluation and Utilization (GEU) Program of IRRI beginning in 1974 (see Brady 1975). Evaluation is an essential bridge between conservation and use. The wide dissemination of both unimproved and improved germ plasm from IRRI to major producing countries started in the early 1960s (see Chang 1972; Beachell et al. 1972). A worldwide scheme of exchanging and evaluating elite germplasm began in 1975 with the establishment of the International Rice Testing Program (IRTP) which expanded from yield nurseries to specialized nurseries dealing with specific ecoedaphic or biotic stresses. During a 14-year period, more than 77 entries have been named and released in other countries (Seshu et al. 1989). Under the multi- and interdisciplinary evaluation and research program, numerous sources of resistance to pests and tolerance to ecological stresses have been identified (see Chang et al. 1982; Ou 1985; Heinrichs et al. 1985; Chang 1985b; annual reports ofiRRI). These useful traits have

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been extensively used in the IRRI breeding program (see Khush 1984a) and in national programs (see Harahap et al. 1982; Chang 1985a; Hargrove et al. 1988; IRRI 1989b). Among different geographic areas of the world, India has furnished the most significant sources of resistance to diseases and insects. Tolerance to adverse soil factors came from West Africa, southern Asia, and South America. Some of the wild rices have been shown to have resistance to multiple pests (see Chang 1989c). In economic terms, the returns from conserving, evaluating, and using the diverse germplasm have been multiplied many times by the benefits derived from the useful genes in the collections (Chang et al. 1975; Chang et al. 1982a; Chang 1984, 1985a). Outstanding examples of such benefits are the control of grassy stunt virus biotype 1 by the Gsv gene in 0. nivara, the control of brown planthopper biotypes by the Bph and bph genes, the suppression of the striped stemborer by many semidwarf varieties, and partial control of the tungro virus by the resistance gene to its vector (Glh 1), the green leafhopper (see Khush 1984a; Khush and Virmani 1985; Chang 1989c). Indian germplasm has also provided local breeders with sources of useful genes (see Sharma et al. 1988). On the other hand, the genes for pest resistance were largely of the vertical type and are prone to being overcome by new or different biotypes or pathotypes (see the sections on disease resistance and insect resistance). The benefits of systematic evaluation are not confined to dramatic progress in rice breeding. By working with exotic or large segments of germplasm, rice researchers were able to advance the scope of their research which led to exciting findings and even more refined research (Chang 1985c, 1989b). A fuller elucidation of the physiological mechanisms involved in drought resistance and their genetical control has been derived from in-depth studies with a broad spectrum of germ plasm (see Chang et al. 1982; Chang and Loresto 1986b). These advances have certainly brought research on tropical rice problems to new heights. However, breeding for the more complex traits, which are under multi- or polygenic control, is a longer and more torturous undertaking than dealing with simply inherited traits. Over the past three decades, the International Rice Germplasm Center (IRGC) at IRRI has supplied rice researchers all over the world with more than 700,000 seed samples and frequently with related technical information. The free supply of seed has fueled rice research and breeding in all the major producing countries and stimulated collaborative projects. Among major food crops, the rice germ plasm is indeed the most intensively and extensively exploited gene pool for economic use. The IRGC has also returned entire national collections to several Asian countries and one African nation when the local collection was lost or no longer viable. Moreover, the IRGC staff also serve as consultants toN ARS on gene bank

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design and provide training courses to genebank staff. These efforts have demonstrated the usefulness of a large base collection (Chang 1989c) and won the recognition of IRGC as a model for other genebanks (Frankel 1975; IBPGR 1978; Anon. 1987). The free provision of seed to all kinds of users has affirmed the IRGC's custodial role in making available the enormous genetic potential in the rice germplasm as a common biological heritage of mankind. Breeding for High Yield and Wide Adaptiveness

The early efforts in breeding for high yield and wide adaptiveness across crop seasons in both the sinica ("keng" or Ponlai) type and the indica (' 'hsien' ') type had their beginnings in Taiwan. Information on this approach, which not only confers nitrogen responsiveness but also adaptiveness across crop seasons and wide geographic areas, has been described by Chang (1961, 1967), Huang et al. (1972), and Dalrymple (1986). The high-yielding plant type for the tropics was first envisaged in the Ponlai varieties of Taiwan (Jennings 1964; Tanaka 1965; Beachell and Jennings 1965), but it turned out to be the semidwarf indicas (derivatives of Deegeo-woo-gen such as Taichung Native 1 and IRS) that set the pace for the Green Revolution to begin in the Asian tropics (see Chandler 1968; Pal 1972; Chang 1979a). The semidwarfs are better adapted to the tropics because of their vegetative vigor, strong roots, high tillering ability, short and stiff culms, easy threshability, and weak grain dormancy, whereas the Ponlai varieties are deficient in grain dormancy, moderate in tillering ability, and highly susceptible to virus diseases. Discussions on the genetic basis of wide adaptiveness were provided by Chang (1967) and Chang and Vergara (1972), and the contributory factors of photoperiod insensitivity, long basic vegetative phase, and low thermo-sensitivity were later reconfirmed in international adaptation trials (Kikuchi et al. 1975), regional trials inside India (Seshu et al. 1974), and international nursery trials (IRRI, 1980; Seshu et al. 1989). Physiological traits that confer high yield were discussed by Yoshida et al. (1972). The physiological and genetical interpretations were combined in Table 3-1 (Chang and Li 1980). During the past two decades, the preceding interpretations have stood the test of time and remained valid. Dramatic advances attained in China and the United States also revolved around the semidwarf plant type. On the other hand, as rice cultivation gradually turns from transplanting to direct seeding and from manual cutting and threshing to combine harvesting, cultivars of basically similar plant type but with lower tillering ability may be more advantageous in providing uniform maturation among panicles within a plant. The matter oflarge panicles and heavy grains vs. many

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Table 3-1. Plant Characteristics Associated with High Yielding Potential in Wetland Rice

Plant Part

Desirable Characteristics

Leaf

Erect

Short, small

Thick

Physiological, Ecological Contribution

Increases sun-lit leaf area, permitting even distribution of incident light; decreases the load of raindrops on leaf surface Associated with erectness; even distribution of leaves in a canopy Associated with erectness, higher photosynthetic rate Provide lodging resistance, nitrogen responsiveness

Culm, leafsheath

Short, thick culms; tight leafsheaths

Tiller

Upright, compact

Permits light penetration into canopy

High tillering

Adaptive to various spacings; compensating for missing hills; permits faster leaf expansion in transplanted crop Allow high doses of nitrogen responsiveness

Panicle

High fertility at high nitrogen rates

High harvest index

Associated with high grain yield

Genetical Control, Correlations

Erectness recessive to droopiness, but erectness largely associated with semidwarfism; erect leaves correlated with high yields Polygenic control of leaf length, leaf area; broad leaf dominant to narrow

One recessive gene, modifiers control shortness; culm length correlated with panicle length Multigenic control in most crosses; upright tillers associated with semidwarfism High tillering a dominant trait; largely additive effect; some dominance effect; associated with semidwarfism Associated with semidwarfism, relatively short panicles Multigenic control; negatively correlated with growth duration; associated with early and sustained growth vigor

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panicles and medium-sized grains is also an area being re-examined by plant physiologists and rice breeders. Breeding for Unfavorable Ralnfed Environments

Discussions in Chapter 1 and this chapter amply show that the past accomplishments in production and yield increases have been largely derived from irrigated areas and, to a much less extent, more favorable rainfedwetland areas where the improved production technology also applies well. The relative contributions of the irrigated ecosystem and the three rainfed ecosystems (wetland, dry- or upland, and deepwater/tidal swamps) to total rice production in the past and IRRI's projections for year 2000 are briefly discussed in Chapter 1. Details may be found in IRRI (1989c). The yield constraints in the rainfed ecosystems are 1. low soil fertility, often combined with one or more adverse soil factors, such as high acidity in dryland soils and tidal swamps and salinity in swamps 2. damages due to serious deficit or excess of water or one alternating with the other under fickle monsoon weather 3. chronic diseases and insects peculiar to the ecosystem concerned, such as blast in upland rice and stemborers and stem nematode in deepwater rice 4. heavy weed infestation in rainfed-wetland and upland cultures 5. low solar radiation intensity in the wet season 6. a lack of rice varieties that have an improved yield potential but require low production inputs A combination of these constraints has long depressed rice yields in rainfed areas. Alternate choice of food crops for the deepwater or waterlogged areas is ruled out by the lack of other flood-tolerant food crops. Rice farmers have been obliged to grow rice at a subsistence level. Although rice is a poor man's crop, the plant's aerenchyma tissues in the leaf sheath and culm transport air into the roots and root zone, making microbial nitrogen-fixation in a flooded soil possible. Such a unique situation has helped rice farmers to obtain about one ton of yield without nitrogen fertilizers. On the other hand, many traditional dryland rices of Southeast Asia and West Africa combine deep, thick roots with plasticity in leaf rolling and unrolling which confer the avoidance mechanism of drought resistance (Chang et al. 1982). Such features are indeed remarkable for a semiaquatic plant species. Breeding for tolerance to adverse environments is complicated by a

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number of character associations, the co-adapted complexes, which confer high levels of tolerance but are difficult to manipulate genetically by hybridization and selection. These tightly linked traits are probably products of millenia of natural and artificial selection in special ecological niches. Examples are 1. Tall plant stature and tolerances to low temperatures, drought (through deep and thick roots), or deepwater (through internode elongation ability) 2. Long growth duration or photoperiod sensitivity with tolerance to deepwater and the ability to recover from drought or adverse soil factors in waterlogged areas 3. Extremely short growth duration and the escape mechanism of drought resistance 4. A low-yielding potential contributed by long and weak culms, low tillering, or low grain number per square meter of land correlated with the foregoing tolerance mechanisms or attributes. A low harvest index (below 0.4) is common to these cultivars. Therefore, past efforts to improve the rice cultivars in perennially depressed production areas have made little impact on rice yields. The traditional germ plasm having the co-adapted complexes continues to dominate the riceland. Moreover, rice experiment stations in these areas are usually poorly designed, inadequately supported, and understaffed (see Chang et al. 1982). Breeding and agronomic evaluation are limited to one cycle a year in most rainfed areas. To have an impact on unfavorable environments, rice research will require better characterization and fuller understanding of the ecosystems concerned in both biological and socioeconomic terms, more intensive interdisciplinary collaboration, broader evaluation and use of germplasm, more in-depth research on physiogenetic mechanisms with assistance from advanced laboratories in the developed countries, and station and staff development. Countries having similar abiotic stresses should collaborate closely by sharing genetic materials, scientific findings, and training opportunities. It is imperative to have a regional research consortium to make full use of the limited resources available in the stressed production areas. It is encouraging that rice breeders have recently organized periodic workshops to strengthen the collaboration in each of the unfavorable environments: deepwater, dryland, and problem soils. The desirable plant type that will fit in a particular environment for each of the six ecosystems has been outlined by IRRI scientists (IRRI 1989c). For upland areas, a weedcompetitive plant type featuring droopy lower leaves and erect upper leaves has been identified (IRRI 1988a).

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IRRI's future efforts are aimed at strengthening the collaborative research among NARS and international centers and maximizing the outputs in areas where the stresses exist. Long-term land sustainability and environmental conservation will be included as a part of the crop improvement package (see IRRI 1989c). Rice researchers at IRRI and elsewhere recognize that attaining the target in harsh environments will be a slow and difficult process with low efficiency in terms of returns. However, it is also a matter of equity to improve the livelihood of the rice farmers in the unfavorable areasespecially the women, who will likely handle the bulk of the manual chores. Breeding in High-Yield Countries

The historical developments in Italy, Spain, Japan, Republic of Korea, and the United States prior to 1979 were described in the 1980 version of this chapter. The focus here will be on the developments in six selected countries after 1980. China

Among the Asian countries, mainland China has made the most impressive gains in yield during the past decade: from 4.1 t/ha (1978-79) to 5.3 t/ha (1984-87). With a continuous expansion in irrigated rice areas (25.70 million ha in 1949 to 31.75 million ha in 1986) and in double cropping, a 3.5-fold increase in production has been realized. Quick-acting nitrogen fertilizers and pest management were two of the contributory factors, while hybrid rices, which are now widely grown in the southern provinces of Sichuan, Guangdong, Hunan, and Fujian, provided the potential for higher yields. Hybrid rices surpassed the best semidwarf varieties of hybrid origin by as much as 20 to 30%. Since hybrid rice was released in 1976, the area planted to hybrid rice rose from 5 million ha in 1979 to about 13 million ha in 1988-89 (out of a total of 32.9 million ha). The highest yield obtained from hybrid rice in Jiangsu Province was 14.4 t/ha in contrast to 10.4 t/ha from an improved variety (Yuan et al. 1989). An economic study conducted in southern Jiangsu Province revealed that hybrid rices yielded 7.8 t/ha on 90 farms vs. 6.8 t/ha for improved keng (sinica race) varieties. The yield difference was 15% for both the southern and northern districts. However, the profitability amounted to about the same because the keng rices command a higher market price than the hybrid rice having the indica type of cooking quality (He and Flinn 1989). A number of hybrid rices have been developed to suit different climatic and soil conditions in various regions of China (Yuan and Virmani 1988). Details on hybrid rice research and development are discussed in a separate section.

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Descriptions of rice breeding activities and their progress from the 1930s up to 1981 may be found in Shen (1980) and CAAS (1986). In the conventional process of hybridization and selection, increasing emphasis has been given to disease resistance, insect resistance, tolerance to salinity, drought resistance, and low temperature tolerance (CAAS 1986). Improved grain quality is a common objective among many breeders. China was among the pioneers in developing improved varieties by anther culture. Several varieties were released since the 1970s, but most of them did not command large-scale adoption or possess unique features. The methodology is described under Innovative Approaches. Colombia

Among the countries outside Asia, Colombia has shown the most dramatic rise in rice yield in recent decades: the national average was slightly under 2 t/ha in the mid-1960s; it rose to nearly 5 t/ha in 1987. Rice yields began to climb in the early 1970s when seeds ofiR8 and IR22 were obtained from IRRI. CICA 4 and CICA 6, both selected from IRRI lines, were released by the Centro Internacional de Agricultura Tropical (CIAT) and the national center, Instituto Columbiano Agropecuaria (ICA). CICA 7 and CICA 9 were released in 1978, followed by Metica 1 and Oryzica 1 and 2 in the 1980s. By 1975, all the irrigated riceland was planted to the semidwarfs, amounting to about 235,000 ha. Two production constraints, blast and the Hoja blanca virus disease, continue to restrain yield, although the virus problem was largely resolved by developing the resistant varieties, Metica 1 and Oryzica 1 (see Dalrymple 1986). Japan

The dramatic rise in rice yield in the postwar years stemmed partly from an improved plant type that is similar to the semidwarf type in having a reduced plant stature, erect, thick, and dark green leaves, stiff culms, and well-filled grains (see Tsunoda 1965). Improved varieties such as Hoyoku, Kokumasari, and Shiranui have a shorter plant type stature than their predecessors because of their common lineage from Jikkoku/Zensho 26. Jikkoku has the sd 1 gene in thejaponica background (Kikuchi 1986). These transformations took place during the late 1950s and the 1960s. Meanwhile, breeding methods and materials were diversified (see Chang and Li 1980). Improved cultural practices also substantially contributed to the yield increase. While the average national yield continued to rise after the mid-1960s, overproduction has led to shifts in breeding objectives: (1) appropriate grain quality for various domestic uses receives increasing attention; (2)

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tolerance to adverse weather condition, especially cold water tolerance, is widely screened; (3) yield stability is ensured by breeding for disease and insect resistance; (4) grain threshability is tuned to suit combine harvesting; (5) earliness is desired in the warm regions of southern Japan; and (6) certain high-yielding rices may be diverted to animal feeds. Research institutions have been reorganized to increase efficiency and coordination (see Kaneda 1986). Since 1981, the Ministry of Agriculture, Forestry, and Fisheries has embarked on a three-phase coordinated research program aimed at increasing the yield by 50% over a 15-year period by using japonica/indica hybrids. The first phase of three years was devoted to the selection of local parents and crossing them with alien germplasm. During the second phase, three high-yielding cultivars were developed and registered on a national level. Hoshiyutaka, bred by the Chugoku National Agricultural Experiment Station (earlier called Chugoku 96) has medium-slender grain and high amylose-the first Japanese variety having such a grain type. Habataki (Hokuriku 129) is another indica grain type selected from a cross between two South Korean varieties (Milyang 42/ Milyang 25) which are also of interracial origin. Oochikara (Hokuriku 130) came from BGl/Shu 3116. BGl (Big Grain 1) has large and heavy grains. The drier (less sticky) condition of cooked rice is now preferred in preparing fried rice and other processed forms of rice (Kushibuchi 1988). Among the diseases, blast still ranks as a major threat. Other diseases receiving increased attention are bacterial blight and the stripe virus disease. Sheath blight became more prevalent following heavy nitrogen fertilization. Breeding efforts for this fungus disease have not been rewarding because varietal resistance is unstable and low in heritability. The brown planthopper has increased its damage to Japan's rice crop because the insect is annually transported by the air stream into Japan from east China, and the insect's prevalence has also been on the rise in China and neighboring Vietnam (see Kisimoto 1979). Each of the four Bph (or bph) genes has been successfully introduced into Japanese germplasm during a 15-year period (Ikeda and Kaneda 1986; Nemoto et al. 1989). High standards of grain quality were set by popular varieties such as Koshihikari and Sasanishiki which were bred by the Ministry-designated prefectural stations three decades ago. They are tall in stature and susceptible to lodging, however. Successful developments in this important area consisted of the release of (1) Akita-Komachi, (2) Kikara 397 derived from a dull endosperm mutant, and (3) Kinuhikari of the Hokuriku Station which combines the taste of Koshihikari and stiff culms contributed by the IRS parent. Kanto 154, bred from Basmati 370/Nipponbare, carries the strong aroma and soft cooked kernels. Hybrid rice is an area of renewed and intense activity: the first usable

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cytoplasmic male-sterile source was identified by Shinjo and Omura (1966) (see the section on hybrid rice). Stimulated by the recent developments in China, Japanese breeders are exploiting the yield potential offered by F 1 hybrids. Workers at the National Agriculture Research Center (NARC) have identified a thermosensitive genic male-sterile source which may replace the fertility-restorer genes or the need to maintain the male-sterile source. NARC scientists have succeeded in developing abundant regenerated seedlings by the artificial seed method-28 million seedlings from one gram of cultured F 1 embryos (Kaneda personal communication). In the search for more distantly related cultivars for interracial crosses, several tropical varieties and one U.S. breeding line have been identified as widely compatible with Japanese varieties. These are Dular, CP231SL017 selection, Calotoc and Ketan Nangka (Ikehashi and Araki 1987). Chinese breeders are also interested in such materials in their effort to broaden the base of their hybrid rices. Recently, several Japanese companies have entered the area of rice breeding, especially in applying techniques from cellular and molecular biology. Advances in these areas will be mentioned in the section on innovative approaches. Korea

Both countries of the Korean peninsular have attained outstanding advances in yield level through breeding. The use of the tropical semidwarf varieties in the Republic of Korea (South Korea) has led to a jump in the national yield from 4.6 t/ha in 1971-72 to 6.8 t/ha in 1977-78. However, widespread planting of the genetically similar semidwarfs together with cool weather led to serious cold injury and blast incidence in 1979 and subsequent years which resulted in a sharp drop in the HYV area. Rice production slumped in 1980. Taste preference and price differential led many farmers to revert to the traditional varieties. The current focus is directed to cold tolerance and blast resistance (RDA 1985). North Korea made equally impressive advances in yield level via interracial crosses. Breeding efforts are focused on tolerance to both high and low temperatures, drought and flood tolerance to typhoon damage, and tolerance to salinity in coastal area. The most popular variety Pyongyang 15 is grown on 60% of the riceland. United States

The historical aspects of rice breeding in the United States have been described by Jones (1936) and Adair et al. (1973). Since the breeding programs were initiated in each of the four major producing states (Arkansas, Louisiana, Texas, and California), the primary objectives were for

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high field and mill yields and stable production of a range of grain types (short, medium, and long) for domestic and foreign markets. Initially, disease resistance received more attention in the southern states than in California, where cool tolerance, especially tolerance to cold irrigation water, is more critical. However, with use of high levels of nitrogen fertilizer (up to 225 kg/ha) problems with stem rot have greatly increased in California. Milling, cooking, and processing qualities are also prime criteria in the evaluation of hybrid progenies. During the period from 1951 to 1961, the grain yields of 18 selected varieties grown at six locations have shown markedincreases over the check varieties, ranging from 5 to 8% (Adair et al. 1973). The increases ranged from 2 to 31% for five locations during the 1961-69 period (Adair et al. 1973). A list of principal varieties developed between 1917 and 1971 was provided by Johnston et al. (1972). Since the mid-1950s, U.S. breeders have devoted much attention to developing an improved plant type that would combine short plant stature, nitrogen responsiveness, lodging resistance, early maturity, and high head rice yields with the desired grain quality (Johnston et al. 1972). Important factors making possible the major shift to shorter and earlier maturing varieties in the United States, which started in 1968 with the release of Starbonnet, were the development of (1) satisfactory chemical methods of weed control, and (2) variety-specific rate and timing of nitrogen fertilization. After Taichung Native 1 (TNl) had established a record yield at the Beaumont Center in Texas, and recognizing IRRI's success with the semidwarfs and their impact on rice yields in tropical Asia, U.S. breeders also turned to the semidwarfs for enhancing nitrogen responsiveness, lodging resistance, and yield performance. A second source of semidwarfism involving the sd1 locus was developed from induced mutants of CalroseCalrose 76 was the first California semidwarfwith ajaponica background (Rutger et al. 1977). Improved sd 1-derivatives which greatly contributed to yield increases in recent years may be exemplified by (1) M9, M201, M202, L201, and L202 in California and Lemont and Gulfmont from Texas which have TN1 or IR8 parentage, and (2) M7, M101, M301, M302, and S201 which have Calrose 76 parentage. More than two-thirds of the semidwarf ancestry came from TN1 or IR materials (Dalrymple 1980, 1986). By 1984, about 22% of the U.S. ricelands were seeded to the semidwarfs, with California at 96%, leading the other states. In 1989, about 50% of the U.S. rice hectarage was seeded to semidwarfs. Because of their very high susceptibility to blast, the high-yielding California semidwarf varieties are not suitable for growing in the more humid southern states. About one-half of the southern U.S. hectarage is in Arkansas, and even the progressive farmers have hesitated to accept present semi dwarf varieties because of difficulty in obtaining good stands

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and increased competition by weeds. Moreover, the inherently high susceptibility of the semi dwarfs to sheath blight requires increased chemical control. Several nonsemidwarfs-high-yielding, short-statured, and lodging resistant varieties including Starbonnet and, more recently Mars, Newbonnet, and Tebonnet-have served the Arkansas farmers well. Each of these had improved plant type with more erect leaves, increased disease resistance, and grain yields 10 to 15% higher than its respective predecessor. The conventional varieties Labelle and Lebonnet which formerly occupied major acreage in Texas and Louisiana were replaced by the Texas-developed semidwarfs Lemont and Gulfmont. The latter varieties are also widely grown in Mississippi and to some extent in Arkansas. Hectarage of the very high-yielding and widely-grown (in Arkansas and Mississippi) N ewbonnet has declined because of two severe outbreaks of blast due to the buildup of two previously minor races of the fungus. Newbonnet was grown on over one million hectares in Arkansas and Mississippi in 1986 (Huey et al. 1989). Rice yields in the United States have increased 20% in the past 20 years to an average of 6330 kg/ha (Arkansas Agricultural Statistical Service 1989). In recent years rice researchers have paid increasing attention to sheath blight in the southern states and stem rot in California. Blast remains the number one disease problem because of its potential for destroying the rice crop in the southern United States. Progress in breeding for blast resistance is evidenced by the recent release from the cooperative Arkansas program of the new long-grained variety Katy which possesses high resistance to the eight predominant races of blast common in the region. Consumers' increased interest in fancy types has led the southern states to release an aromatic IRRI line (IR841) as Jasmine. Other diseases receiving attention in the breeding programs include brown spot, kernel smut, water mold complex, sheath rot, narrow brown leaf spot, aggregate sheath spot, and straighthead (a physiological disorder). The virus disease hoja blanca also has received attention (Rice Technical Working Group 1982, 1986). The major insects being emphasized are water weevil, stemborers, and stink bugs. So far, insect damage has been small, but other insects have the potential of damaging the rice crop (Rice Technical Working Group 1982, 1984, 1986, 1988). Research on anther culture, somaculture, mutation breeding, and genetic engineering has increased considerably, but major emphasis is still placed on improving methods and conventional breeding. Research also is being conducted on hybrid rice, including the search for apomixis (Rice Technical Working Group 1986, 1988). The major varieties of the four rice-producing states since the 1930s

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were based on 39 introductions and parents, which reflects a narrow genetic base. U.S. breeders have recently devoted more time to germ plasm acquisition, conservation, and use by exploring South America for wild species, rejuvenating the world rice collection of the U.S. Department of Agriculture (USDA), and holding annual committee meetings on germplasm use (Rice Technical Working Group 1986; Dilday 1990). In recent years private seed companies have entered the realm of rice improvement. N.F. Davis Drier and Elevator, Inc. in California (see Hu 1983) has produced rices of special grain quality: California Belle (long grain) and Calpearl (short grain). Several seed companies are working on hybrid rice development. Two companies have obtained license from China to develop hybrid rices outside China. The strength of the breeding programs in the United States stems from cooperative federal and state efforts, acquisition and use of diverse germ plasm, and collaborative research with rice researchers in other disciplines. The increased and more efficient use of nitrogen fertilizers through growth-stage-specific timing, improved chemical control of weeds, and ratoon cropping of early maturing varieties have contributed greatly to the sustained increase in rice yields (Evatt and Beachell 1962; Johnston eta!. 1972).

Breeding in Tropical and Subtropical Asia

The past decade saw sustained national efforts in using the semidwarfing gene (sd 1) for raising yields in irrigated areas. Varietal improvement has been achieved by three means: (1) local breeding programs drawing on introduced materials mainly from IRRI-c. 50%, (2) testing and adopting introduced genetic materials or named IR varieties-c. 35%, and (3) elite materials from other countries' programs supplied by the International Rice Testing Program, coordinated by IRRI-c. 15% (Hargrove et a!. 1988). The international exchange of elite germplasm reached a new height during the decade, with IRRI serving as the hub (see Chang eta!. 1988). The multidisciplinary approach exemplified by IRRI's GEU Program became widely practiced in several countries (see Harahap eta!. 1982). Asian rice breeders also made extensive use of IRRI materials in breeding for insect resistance (46% of the parents), disease resistance (39%), short growth duration (38%), and grain quality (23%). For insect and disease resistance, donors from other Asian countries were heavily used: 25% and 18%, respectively. Of 71 widely grown varieties in 1984, 60% were semidwarf, 11% intermediate, and 21% tall (see Hargrove eta!. 1988). The objectives common to most national breeding programs are high yield, locally preferred grain quality, resistance to diseases and insects,

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and wide adaptiveness. Increased emphasis was placed on drought resistance, tolerance to adverse soil factors, ability to withstand excess water (deepwater or submergence due to flash floods) and tolerance to cool temperatures. These needs were reflected in IRRI' s new strategy for the year 2000 and beyond (IRRI 19S9c) and the organization of international teams to work together on a common ecosystem of the unfavorable category (IRRI 19S4a, 19SSb, 1990b). Progress in rice breeding during the decade from 1979 to 19SS for selected Asian countries is enumerated below. India

The major breakthrough in rice breeding during a food crisis in India was the widespread use of the semidwarfparents (Taichung Native 1 and IRS) in many state and national stations, following their successful introduction in the mid 1960s. Indian breeders have also used induced mutations to shorten the height of tall traditional varieties that are tolerant of ecoedaphic stresses. An example is Jagganath which was selected from mutants of T141. Many foreign introductions, both from IRRI and other sources, became established in certain ecologic niches, such as Pankaj (selected from IR5), the early-maturing Palman 579 (IR579-4S-1) in north India, and Mahsuri of Malaysia in soils oflow fertility and poor drainage. Meanwhile, a large number of farmers' varieties grown in pest-endemic areas were identified, purified, and released. Some of these were verified to have high levels of pest resistance to multiple pests in IRRI's GEU Program and were later incorporated into IR varieties. Examples are the ARC varieties of Assam State, the CO series, the PTB series, and Chempun of Kerala State. Similarly, FR13A was reconfirmed to have the highest tolerance to submergence by flood waters (see IRRI 19S2b; Sharma et al. 19SS; Seshu et al. 19S9). Locally bred varieties of some impact were Jaya, Sana, Ratna, Annapuma, and CR1014 (Gangadharan 19S5). IRRI-supplied materials were extensively used by local breeders (Hargrove et al. 19SS). The extent of HYV adoption during 19S3-S4 was 54.1% which included several IR varieties such as IRS, IR20, IR36 and IR42 (Dalrymple 19S6). On the other hand, rice yields remained low in the unfavorable environments, such as east India (the Bengal Bay States) and the northeast states. Recently, improved varieties for the upland areas have been released: Birsa Dhan 191 and Annada (MW10). For waterlogged soils of shallow depth, Mahsuri remains popular. A package approach to raise the low-yield ceilings needs to be developed on a multidisciplinary basis.

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Indonesia

An interesting combination of breeding efforts, monitoring of pests, government subsidy, and community collaboration in plant protection led Indonesia to raise its rice yields dramatically. The extent of HYV use was 85% in the early 1980s. The elite germplasm came mainly from IRRI, though a local multidisciplinary breeding program, similar to IRRI's Genetic Evaluation and Utilization (GEU) Program, also went into action (Harahap et al. 1982). The continuous cultivation of a single pest-resistant IR variety under a double-cropping system involving staggered planting dates soon led to serious outbreaks of the brown planthopper when a new biotype of the pest emerged from vast tracts of the earlier resistant variety. Then, another variety containing a major gene resistant to the new biotype was introduced to replace the old cultivars, though not for long. Overuse of insecticides led to a resurgence of the pest following repeated applications. This kind of boom-and-bust cycles recurred in north Sumatra and parts of Java during 1975-76, 1982-83, and 1985-86. Then, the plant protection workers helped rice farmers to synchronize planting dates, monitor pest developments and practice community pest control. Pest incidence became markedly reduced, and bumper harvests continued from 1983 through 1989. Varietal rotation was successfully used to control the once-rampant tungro virus disease. The most important locally developed varieties in the 1980s were Cisdane (from Pelita I-1//IR789/IR1527) and Krueng Aceh (from Pelita II/IR2709). They have replaced IR36 in areas where the brown planthopper incidence was low. Myanmar (Burma)

Myanmar has had an interesting journey in varietal improvement. While improved varieties such as IR8 and C4 were introduced into the country about 20 years ago, the HYVs did not gain widespread acceptance. Up to 1979-80, only 27% of the riceland was planted to HYVs, while exportquality rices kept their dominance in the irrigated areas. The HYVs rose to 49% in 1983-84. However, since the early 1980s, three varieties, which did not come from local breeding programs quickly gained acceptance: a mutant of IR5, Mahsuri (of Malaysia), and a nameless variety selected by a Burmese farmer. These varieties now occupy about 80% of the ricelands (Win and Win 1990). Taiwan

The earlier history of rice breeding in Taiwan has been covered in the previous edition (Chang and Li 1980) and in the section on breeding for high yield and wide adaptiveness. Because of the intensive cultiva-

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tion practices and double cropping, breeding efforts continued to focus on: 1. resistance to blast, bacterial blight, sheath blight, stripe virus, brown planthopper, whitebacked planthopper, the small brown planthopper 2. a higher yield in the second crop 3. grain quality with preference toward the low amylose Ponlai type More significant advances have been attained in improving the resistance to insect pests than in the other areas. Since the mid-1980s, the rice breeding programs of different stations have been reorganized to have the hybridization operations centralized at the Taiwan Agricultural Research Institute and the subsequent selection and testing at designated district agricultural improvement stations. The most important commercial variety grown during a 10-year period was Tainung 67, although it is susceptible to blast. A new release, Tainung 69, has multiple resistance to brown planthopper and the whitebacked planthopper. Tainung 70 has good quality. Because of the use of indica semidwarf parents in the crossing program, the amylose content of many Ponlai varieties has been raised to a nearly intermediate level of about 20%. Tai-Keng 2 and Tai-Sen 1 have a slightly higher yield potential than Tainung 67 (5% increase). Among the indica varieties, Taichung Sen 10 is the most promising successor to Taichung Native 1. With the multidisciplinary approach, Taiwan breeders and affiliated scientists have developed a number of varieties that are early-maturing and outstanding in the international nurseries. These are Taichung Sen Yu 285, Tainung Sen Glutinous 2, Chianung Sen Yu 26, and Si-Pi 692033. Recently added breeding objectives are adaptiveness to direct seeding or mechanized transplanting and combine harvesting, strong rooting ability, and large grains. The development of hybrid rice is progressing well, more so in the indica group. Efforts to equalize yields between the first season (average 5 t/ha) and the second season (average 4.2 t/ha) have shown less progress. Sri Lanka

Sri Lanka is an island similar in size to Taiwan, but its diverse ecosystems and rich genetic variability among landraces make it a microcosm of varietal diversity. Breeding efforts in the 1940s led to improved varieties of the H series which had both improved yield potential and resistance to blast. The introduction of the semidwarfing gene sd 1 to local varieties lent new impetus to the varietal improvement efforts by recombining early-

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maturity, high yield, and biotic and abiotic tolerances. The BG series of improved varieties pushed the yield level to 10 t/ha. Brown planthopper resistance was another breeding objective since it flared up in the mid1970s. Other improved varieties include the BW and LD series. Adoption of the new varieties reached 80% of the ricelands in the early 1980s. However, diverse soil and climatic constraints have prevented greater expansion of the modern varieties. Many BG and BW varieties have shown outstanding performance in the international nurseries, espe·· cially for their short duration, intermediate height, vigorous seedling growth, and resistance to blast, and are adapted to adverse environments of high soil acidity and iron toxicity. Grain quality remains an area where local preference for the small roundish grains and a red pericarp have impaired wide acceptance of the Sri Lankan varieties outside their home territories. Thailand

Thailand maintained its lead in rice export through breeding efforts, maintenance of genetic diversity among major cultivars, coordinated research, and a favorable pricing policy. During the dry season, the semidwarf RD1 predominates in the irrigated areas. In the wet season, thousands of traditional varieties are grown, providing security through diversity. Therefore, Thailand has experienced only light outbreaks of diseases and insects except for a brown planthopper epidemic in 1974. Meanwhile, breeders have developed improved types to suit different ecosystems. For instance, RD8, an induced mutant from the famous quality rice, Khao Dawk Mali 105, finds acceptance in the unfavorable environment of the northeast. RD19 is adapted to water depth of about 1 m. Breeding at IRRI

Breeding at IRRI began in 1961-62 when 256 widely grown varieties of Asia and the United States were planted and observed. About 80 of the better entries were tested for yield performance in late 1962. Continued varietal evaluation led to the use of about 30 varieties which were hybridized in 1963 under two categories: tropical indica x semidwarf indica (from Taiwan) and tropical indica x Ponlai (from Taiwan). Soon after, U.S. varieties and lines were crossed with tall tropical indicas, and backcrosses were added. From the first group of crosses, the eighth cross (IR8: Peta/Dee-geo-woo-gen), the ninth cross (IR9: Peta/1-geo-tze), and the fifth cross (IR5: Peta/Tangkai Rotan) produced some of the more promising hybrid progenies, and the selected ones were yield-tested in late 1964 and twice in 1965. Extensive testing of these lines at multiple sites in the Philippines, Bangladesh, India, Mexico, Pakistan, and Thailand during

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1966 fully demonstrated the high yield performance under heavy nitrogen fertilization and wide adaptiveness ofthe IRS-2SS-3line; it was named IRS in late 1966 (see IRRI 1967). IR5-47-2 was named a year later, and it found wide acceptance in less favorable environments. IRS set the pace for other tropical semidwarfs bred by IRRI and NARS of tropical Asia (see Chandler 196S), and its planted area quickly expanded (see Dalrymple 1976). The next phase was to improve the grain quality and to incorporate the necessary resistance to major diseases and insects. Meanwhile, cooperative efforts on testing and exchange with NARS was intensified (Beachell et al. 1972). IR20, IR26, IR36, and IR42 represented widely grown products of the second decade (Khush 19S4b). The planted area of IR36 reached about 10 million ha in the early 19SOs. IR42 produced high yields in the wet season at moderate nitrogen levels. However, their top yield levels were below that of IRS. Implementation of the multidisciplinary GEU Program since 1974 intensified the search for resistance to biotic factors (diseases and insects) and tolerance to abiotic stresses (drought, deepwater, salinity, low temperatures). The program also broadened the scope ofiRRI's breeding efforts for different environments (see Brady 1975). The GEU approach was also adopted by several Asian countries (Harahap et al. 19S2). Extension of the GEU approach on an international scale led to the initiation in 1974 of the International Rice Testing Program (IRTP) coordinated by IRRI (IRRI 19SO). More than SOO rice scientists in 75 countries have joined the network. Together with the seed exchanges provided by IRRI's germplasm bank and the breeding program, exchange and collaborative testing of rice germplasm, both unimproved and improved, reached an unprecedented scale. Since 1975, IRRI has stopped naming varieties from its crosses, thus encouraging breeders in NARS to exchange widely and use the international pool of genetic materials-about 160 varieties named by NARS were bred at IRRI and 40 more were named from entries in IRTP nurseries. During 19S1-S2, about 36 million ha ofriceland in southern and southeastern Asia were planted to the high-yielding (or modern) varieties, the bulk of which was IR varieties. The widespread use of the pest resistance genes in IR varieties and lines by Asian breeders was also sustained (see Hargrove et al. 19SS). Since the mid-1970s, efforts were also directed toward developing early-maturing (100-110 days) types that fit better in multiple-cropping systems. IR36 and IR56 have 110-d maturity, while IR50 and IR58 were five to 10 days shorter in growth duration. The incorporation of additional disease and insect resistance to the earlier IR varieties was another major thrust (see Khush 19S4a, 19S4b; Khush and Virmani 19S5). However, the reliance on major genes of the vertical resistance type and the sequential release of such related varieties have accelerated breakdowns in varietal

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resistance to the brown planthopper (Bph and bph genes), grassy stunt virus biotype 1 (Gsv), and tungro virus resistance. The breakdowns were largely due to shifts in insect population structure which responded to changes in host resistance to the insect vector (see Saxena and Barrion 1985; Hibino 1988; Chang 1988). Since the early 1980s, IRRI has collaborated with several Asian countries in testing hybrid rices based on the WA ems of Chinese origin and in developing better adapted hybrids for the tropics. Research on fertility restoration and the physiological aspects of hybrid vigor has made good progress. However, the development of superior hybrids for on-farm use and the technology of hybrid seed production for tropical areas are still at the developmental phase (see IRRI 1988c). In the early years of its operations, IRRI breeders collaborated with young rice breeders of NARS, who were studying at IRRI, in developing, crossing, and testing projects for the countries involved by making the desired crosses at IRRI and testing them in the home country of the trainees. Such assistance was extended to Colombia, Mexico, the Republic of Korea, Thailand, Indonesia, and later to China. In the late 1970s, a GEU training program for young breeders and affiliated disciplines in the NARS was instituted. Each trainee was required to make a large number of crosses at IRRI and bring F 1 seeds back to the home station. Such arrangements help both manpower development and the generation of specifically tailored breeding materials. Under NARS-IRRI collaborating schemes, IRRI-generated crosses provided to NARS have encompassed the irrigated, rainfed-wetland, upland, and deepwater regimes, as well as adverse soils. An expanded version of collaboration, termed shuttle breeding, was developed between IRRI on the one hand and the Republic of Korea and China on the other, in which the crosses were made by national workers at IRRI. F 1 hybrids were advanced to F2 populations in the winter months at IRRI, segregating materials were selected in the national center during the summer months, and another generation was grown at IRRI during the ensuing winter. Korean breeders regularly made large-scale seed increases of promising lines at IRRI during the cool months and the breeder's seeds were airshipped to Korea for further increase and multiplication. Such an effective process was illustrated by the development of Tong-il (IR667-98) which spearheaded the advent of semi dwarf interracial varieties in Korea. Innovative techniques of cellular and molecular biology have been used recently by IRRI researchers to augment the tools offered by conventional breeding programs. Techniques of anther culture, pollen culture, embryo culture, and protoplast fusion have been successfully adapted for use in rice. Interspecific hybrids involving officina/is, minuta, brachyan-

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tha, and others have been obtained through tissue culture of the F 1 embryos, thus providing an avenue for the use of multiple pest resistance or novel source present in the distantly related wild species (see IRRI 1990a). Under Rockefeller Foundation funding, researchers in advanced laboratories and IRRI researchers and breeders are collaborating closely in using the new tools to overcome genetic barriers in breeding and in understanding the physiogenetic bases of host-pest interactions. Some of the recent advances made by Cocking et al., McCouch et al., and Wu et al. are described in this section on innovative approaches. All these efforts will certainly expand and accelerate the use of novel genes in the expanded genetic pool available to rice breeders (see Chang and Vaughan 1991). Breeding efforts for the adverse environrpe11ts under rainfed culture (wetland, upland, deepwater, and adverse soils) were initiated in the mid1970s by different research teams in the GEU program. Workshops dealing with upland, deepwater, cool temperatures, and adverse soils have been held periodically to sustain collaborative efforts among NARS and IRRI (for the latest publications, see IRRI 1979, 1984b, 1986; 1988b, 1990a; Juo and Lowe 1986). While the research findings on various environmental stresses have steadily added the essential knowledge in dealing with hitherto little-known ecosystems and genetic resources, varietal development has been slow in coming, partly because the IRRI site is not representative of the difficult environments and therefore poorly suited for testing and selecting breeding materials. In spite of the slow progress, workers in NARS have taken steps to form working groups by region or the stress factor concerned (see IRRI 1984b, 1986, 1988b, 1990b). Beginning in 1990, IRRI's research program will become ecosystemoriented in order to pool existing resources and focus more closely on the different research needs of a particular ecosystem. Greater emphasis will be paid to NARS-IRRI collaboration in the major production areas of each one of the ecosystems: irrigated, rainfed-lowland, upland, and deepwater and tidal wetlands. A cross-ecosystem research thrust will deal with broad needs common to two or more ecosystems. The restructured research ftpproaches aim to increase research efficiency ~nd productivity and to ensure long-term sustainability of ricelands (IRRI 1989c, 1989d).

Current Breeding Methods

A wide array of methods has been used by rice breeders to develop improved germplasm. The simplest approach consists of selecting panicles or plants in an unimproved variety grown by the farmers. One of the widely grown varieties in Myanmar (formerly Burma) was selected by a farmer from his field in such a manner (Win and Win 1990). Many experiment stations continue to collect and evaluate local varie-

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ties. Mass selection or individual plant selection, followed by comparative trials, has led to the identification of superior germ plasm. Several varieties possessing multiple resistance to insect pests under field conditions were thus developed at the Pattambi and Coimbatore Rice Experiment Stations in southern India. Releases such as PTB-18, PTB-33, C0-43, and C0-44 in India were products of this simple and effective method (Sharma et al. 1988). For breeding materials following controlled hybridization, the pedigree method of selection among the F 2-derived progenies is the most popular method. Concurrent testing of progenies in early generations from F 3 onward for pest resistance and grain quality is a distinct advantage of this method. During the process of testing advanced lines, phenotypically similar sister plants of a line are usually bulked to provide sufficient seedstock for large-scale testing and for further seed increase. Therefore, most named varieties do not qualify as pure lines by Johansen's definition. When grown in a different environment, an improved variety may reveal variants within the population. Such a phenomenon has been termed "environmental segregation" (see Chang 1976c). The bulk population breeding method is sometimes used by rice breeders, but more often in a combination with the pedigree method, also known as the modified bulk method (see Jennings et al. 1979). In IRRI's upland rice improvement program, the hybrid progenies were often carried as bulked populations for two to three generations until the prevailing environmental conditions permitted an effective selection of individual plants (IRRI 1987). For lowland rice breeding programs, plant competition is more intense, especially in heavily fertilized fields in the tropics. The breeder needs to take the proper measures so that the short statured plants would not be suppressed by competition from tall plants (see Jennings et al. 1979). The backcross method is used in some instances to incorporate a simply inherited trait quickly into a preferred agronomic background. Its effective use can be illustrated in the transfer of the Gsv gene for grassy stunt virus resistance from 0. nivara into IR lines (see Khush 1984b). It is also a helpful technique in building up pest resistance by pyramiding the resistance genes. Another application has been made in developing ems lines (Shinjo 1975). However, the backcross method is not so widely used as it may merit. The single-seed descent approach has been used at IRRI to advance the hybrid generations rapidly in the phytotron or glasshouse. The method is well-suited for photoperiod-sensitive materials that can be shortened in life span by short-day treatment (see Ikehashi and HilleRisLambers 1979). However, the successful application of this method has yet to be realized. Composite populations with the help of a male-sterile gene (ms) have

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been attempted (see Ikehashi and Fujimaki 1980). However, such a practice has not been carried out long and broadly enough to allow an assessment of its usefulness. Mutation breeding has been widely practiced by rice workers in the 1960s, often as a means to accelerate improvement efforts with small populations and limited objectives. A large spectrum of mutations was produced, particularly in the areas of reduced plant stature and earlier maturity, but rather few mutants had a proper mix of economic traits to qualify as improved germplasm. Reviews of past attempts have been provided by Gregory (1972), Mikaelsen (1980), and Micke et al. (1987). The notable successes were several superior varieties, namely, Reimei of Japan, Jagannath of India, RD6 and RD15 of Thailand, and Calrose 76 which supplied the sd 1 locus in a japonica background (see Mikaelsen 1980; Micke et al. 1987). Recurrent selection for population improvement involves repeated intercrossing and testing of hybrids. The successive cycles of selection with selected recombinations permit an accumulation of desired genes. The method can be combined with a diallel-cross composite base under the diallel selective mating system. Such a selection embodies intermating among hybrids to enhance the breaking of linkages (see Jensen 1988 for details). In spite of the potential advantages offered by these methods, practically none of the rice breeders has gone beyond selection under selffertilization following initial crossing in the quest for yield improvement and stabilization. Another method of developing a pure diploid from a haploid of hybrid origin is by means of tissue culture. The technique of making use of a doubled haploid is described in the section on innovative approaches. The use of F 1 hybrids in commercial production is described in the next section. Hybrid Rice

Heterosis in intervarietal crosses was first reported by Jones (1926). A great many papers have appeared since, either describing the phenomenon of hybrid vigor or proposing means to produce F 1 hybrids for commercial use. However, a stable source of cytoplasmic male-sterility, as was found in maize and onion, was not available in rice to facilitate hybrid seed production until the 1960s (see Yuan and Virmani 1988). Reciprocal crosses involving the Asian cultivars and their weed race (spontanea) showed differences in F 1 pollen sterility. Workers in Japan (Katsuo and Mizushima 1958) ascribed the sterility to an interaction of the nuclear genes in the cultivars with the cytoplasm of the wild relative. Later, a source of cms-bo was found in Chinsurah Boro II/Taichung 65

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hybrids (Shinjo and Omura 1966), however, it was not used until the 1970s by rice breeders in northern China. A pollen-sterile wild rice (Wild Abortive or WA) found on Hainan Island in China in 1970 paved the way for widespread use of this ems- WA source in the indica(' 'hsien' ')varieties of China which began in 1974 (see Chang 1979c for earlier reports of Chinese workers). It heralded a second Green Revolution of rice in China. The cytogenetic mechanism underlying successful hybrid rice seed production is the same as that of maize and onion: a pollen-sterile cytoplasm in the Wild Abortive female parent interacts< with nonrestoring gene(s) in the male parent to produce a useful maintainer line (A) which can be agronomically upgraded by backcrossing to any nonrestoring parents. The male-sterile (A) plants are grown side by side with a parent (B) line capable of restoring the fertility and when cross pollination between the two parents is effected, F 1 hybrid seeds are produced in quantity. When certain crosses produce sufficient hybrid vigor (heterobeltiosis-superiority over the high parent) in yield and possess desirable agronomic characteristics, such F 1 hybrids can be exploited to commercial advantage. The scheme of producing hybrid seeds under the three-line system is shown in Fig. 3-2. Chinese workers experimented with a large variety of cultural practices and manipulations to maximize seed production and reduce seed cost. Manipulations such as adjusting the ratio of pollinator plants to the sterile plants, increasing the planting density of the sterile parent, stripping the flag leaves of the female parent, shaking the panicles of the male parent to increase pollen dispersal, and spraying of growth hormones to regulate plant height were helpful in making hybrid seed production practical on a large scale. Seed production has increased from 0.75 t/ha before 1981 to 1.6 t/ha in 1986 (see Yuan and Virmani 1988). The planted area dramatically rose from 8.670 ha in 1976 to about 13 million ha in 1988 and 1989 and is likely to grow further. The yield advantage of superior F 1 hybrids over the best improved varieties ranged between 10 and 30% in the early years, and it has been raised to 20-30%. Yields over 8 t/ha were frequently obtained. The use of pest-resistant IR varieties and lines have helped to sustain hybrid rice yields in China when new biotypes of insects or pathotypes began to attack the widely grown hybrids (Yuan and Virmani 1988). The yield superiority of the F 1 hybrid has been studied and ascribed to a higher crop growth rate up to heading, increased spikelets per panicle, higher spikelet fertility percentage, grain weight, and greater vigor of the root system in some cases (see IRRI 1988c). Genes that can restore pollen fertility of Wild Abortive ems lines have been found in Chinese varieties as well as IR varieties such as IR24 and

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X maintainer

multiplication of ems lines

maintainer

ems

line

restorer

hybrid seed production field

restorer

Figure 3-2. Process of hybrid rice production involving continuous supply of agronomically improved cytoplasmic male-sterile line, maintainer line, and fertility restorer line in system. Maintainer and restorer lines are maintained by selfing (@),while ems line and F1 seeds are produced with efforts to enhance cross pollination ( x) in field. F and S refer to fertile and sterile cytoplasm; Rf and rf are fertility-restoring and -nonrestoring genes, respectively.

IR36. Two such genes (Rf1 and Rfz) are needed for fertility restoration. For the Chinsurah Boro II cytoplasm, only one gene is needed (see Virmani and Shinjyo 1988). In the seed production fields, the ratio of the areas planted to the three lines is 1 male-sterile line:50 hybrid seed production field:5000 commercial production field. The near monopoly of Wild Abortive ems in the southern provinces of China has caused concern to many rice workers. A number of other

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ems sources has been reported: Gambiaca, Dissi, Chinsurah Boro II (LiMing), and others of minor importance. The Wild Abortive cytoplasm remains as the most stable source of pollen sterility in the southern provinces of China, as well as in tropical Asia. Recent research activities in China have been directed toward shortening the growth duration, improving grain quality, and increasing the level of resistance to diseases and insects. To simplify the seed production process, a two-line approach, using a photoperiod- or temperature-sensitive maintainer (B) line is being tested to replace the traditional three-line method. Such a maintainer line is male-sterile under long day length, but it becomes male-fertile when days become short. However, hybrids of the two-line scheme have lower yields than the traditional hybrids and require more refined work to link ecogeographic adaptation of the male-sterile lines with specific sites (Lu et al. 1989). Outside China, both public institutions and private seed companies began their hybrid rice research in the early 1980s. Among international institutions, IRRI has collaborated with China on hybrid rice research and organized a network of national centers in tropical Asia that share the same interest. Most of the research activities focused on the extent of heterosis obtainable from hybrids, combining ability tests, comparison of different ems sources and restorers, tests of fertility restoration by local parents, extent of natural outcrossing, and grain quality of hybrids (see IRRI 1988c). Private seed companies in the United States have concentrated on the developmental processes of identifying commercially viable hybrids, but the grain quality of such hybrids is below market demand. Progress to date has indicated that the ems-WA is the most stable source in tropical environments, and the extent of heterosis is impressive. The main constraints for hybrid rice use in the tropics are the high technology needed in seed production, high cost of seed, necessity of changing seed every crop season, and farmers' dependence on outside sources for the supply of seed. The use of hybrid seed is also affected by the local pricing policy, which will determine if the increased yield is economically viable (see IRRI 1988c). The Yield Ceiling and Future Potential

Since the late 1960s, rice yields on experimental stations have not gone beyond the records established earlier (see Chang 1990). This constraint is of serious concern to all rice researchers. The highest yield obtained on the IRRI farm was 10.3 t/ha from IRS and 11.0 t/ha from IR24 in the dry seasons. The highest yield reported from farms was 13.2 t/ha from Japan, 14.4 t/ha from Jiangsu Province of China, and 17.8 t/ha from India. Climatic conditions and pest incidence

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greatly influence rice yields. The highest yields are generally obtained in the temperate zone where oasislike weather prevails such as California and Australia. A higher potential yield may be realized if both biomass and the harvest index can be raised. It appears feasible to raise the harvest index from the present 0.5 to 0.6. Several rice physiologists and breeders had opted for sink size with large grains and high spikelet number, but the efforts were not particularly rewarding because of compensatory interactions among the yield components. Enriching the growing plants with C0 2 could add 2 t/ha to the harvest (Yoshida 19Sl). Other approaches proposed by rice physiologists are to improve the partitioning of energy for sink formation with less total dry matter at heading, more erect leaves, and medium growth duration. Attainable yield targets are 15 t/ha in the tropics and 1S t/ha in the temperate region. Hybrid rice appears to offer such an avenue (Akita 19S9). Meanwhile, grain production per hectare per day has been raised by reducing the growth duration of the HYV s. Some of the recently developed IR varieties have not surpassed IRS or IR2S in yield per hectare, but they produce more grains per hectare per day (see Yoshida 19Sl). Reinstating Genetic Diversity in Major Cultivars

Paradoxically, success in plant breeding soon leads to genetic uniformity and a narrowing of the genetic base. This trend is common to other major cereals, especially wheat and maize. During 19S2-S3, the HYV s were planted on more than 73 million ha of riceland (Dalrymple 19S6) which can be partitioned into: • noncommunist Asian countries: 36.37 million ha (44.9% of total area) • communist Asian countries*: 33.3S million ha (Sl.O% of total area) • Latin American countries: 2.29 million ha (26.0% of total area) • African countries: 0.20 million ha (4.7% of total area) • Near East countries: 0.10 million ha (8.4% of total area) • United States: nearly 0.5 million ha (50% of total area) Most of the HYVs are semidwarfs, and they share the sd 1 locus (see Chang et al. 19S5). Many of the HYVs bred in the 1970s have the cytoplasm of Cina (Tjina) which was present in IRS and several other IR varieties. Moreover, most of the 13 million ha hybrid rice grown in China share the Wild Abortive cytoplasm and the sd 1 gene. Genetic uniformity in such *Incomplete for China; North Korea not included.

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vast areas is a matter of concern to several rice workers (Chang 1976c, 1979a, 1979b, 1984; Hargrove et al. 1979, 1988; Dilday 1990). For the near future, the trend of decreasing diversity among forthcoming releases may not be readily corrected because rice breeders in tropical Asia continue to involve IR varieties, other semidwarfs, and similar sources of pest resistance as parents in their crosses (see Hargrove et al. 1988). While the spectre of a major disaster like the 1970-71 southern leaf blight epidemic of maize in the United States may not happen in rice, the situation in rice warrants a critical review of past events to devise preventive measures for the future. The rice crop is more vulnerable than temper·· ate-zone crops because continuous multiple cropping of rice is practiced in the hot and humid tropics. In addition to a single variety or similar varieties being planted in close succession over large contiguous areas, staggered plantings in irrigated areas have further increased pest incidence (see Chang 1988). Adding to the misuse of an improved variety in successive plantings over a large area, the gene or genes conferring pest resistance are major genes of the vertical type which is prone to being overcome by the emergence of a new pathotype or insect biotype. A number of serious pest outbreaks are enumerated below to show the wrong use of a technology package comprising pest-resistant HYVs in multiple cropping that led to the "boom and bust" cycles described by Robinson (1976). 1. IR26 was widely planted in Mindanao Province of the Philippines, northern Sumatra in Indonesia, and South Vietnam as a brown planthopperresistant variety during the early 1970s. Under intensive and double cropping, however, the Bph-1 gene in IR26 soon lost its protective value as brown planthopper biotype 2 emerged as the predominant fraction in the insect population after three to four years. IR32, IR36, and IR42, all carrying the bph-2 gene, were substituted to cope with brown planthopper biotype 2. In about five years in the same areas, biotype 3 or a different biotype emerged in 1982. IR56, IR60, and other later releases were offered as replacements. Epidemics broke out again during 1985-86. 2. The Gsv gene conferring resistance to the grassy stunt virus lost its effectiveness when a new biotype of the virus emerged. 3. The tungro virus persists as another major destabilizer to rice production in the Philippines and other Southeast Asian countries because the assumed varietal resistance was not true resistance to the virus but a protection provided by resistance to the green leafhopper which is the insect vector for the virus. Subtle shifts in the insect population, especially when insects continuously feed on a resistant variety, became accelerated. The new population of insects also gain efficiency in virus transmission (see Chang 1984, 1988; Hibino et al. 1987 for citations). On the other hand, farmers of Thailand continue to grow traditional

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varieties of diverse composition in the monsoon season, while semidwarf HYV s are grown in the dry season under irrigation. Thailand is one of the few major producing countries in the Asian tropics that have not been affected by serious insect and disease outbreaks for decades, except for a brown planthopper epidemic in the 1974 dry season (Chang 1984). In the temperate zone, South Korea saw a sharp rise in rice yield during the mid 1970s when interracial hybrids were bred and widely grown. In 1978, about 76% of the rice area was planted to the new varieties carrying sd 1 gene. However, these varieties were susceptible to cool temperatures at maturation and to the blast disease as well. A cool season and blast epiphytotics in 1980 severely damaged the HYVs, and heavy yield losses resulted. Many farmers returned to the use of the traditional varieties, and the HYV hectarage dropped to 20% in 1988. After attaining selfsufficiency in 1978, Korea imported one million tons of rice in 1981, and the national economy suffered (see Chang 1988 for sources of information). Although other misapplications of technology such as the improper use of insecticides, which could lead to a resurgence of the brown planthopper, have also contributed to serious pest problems, some of the problems associated with a narrow genetic base can be alleviated by other approaches. Among those measures successfully used in Indonesia are varietal rotation, synchronized time of planting, and the monitoring of pest incidence followed by communitywide control (see Chang 1988). In the long run, reinstating genetic diversity in the major cultivars will prove to be one of the essential requisites in stabilizing crop production. In a related manner, the expansion in planting rice and wheat in close succession will also present problems, as the two cereals are affected by certain pathogenic fungi that are closely related (see Chang 1988). Innovative Approaches Offered by Cellular and Molecular Biology

The advent of biotechnological techniques that can make use of novel genes and cytoplasm from distantly related plants has raised the horizon for future improvements. The potentials are a two-way traffic, i.e., both to and from rice. The expanding gene-pool to supplement the rice germplasm has been discussed by Chang and Vaughan (1991). Past achievements and future possibilities are discussed under the following six headings. Wide hybridization

The first cultivated/wild interspecific cross made for a practical purpose was made by Ting (1933) in the late 1920s. From a sativa/spontanea cross, Yatsen I was selected. Other crosses involving an Indian wild rice gave several progenies which have a higher level of insect resistance than most

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other Chinese cultivars. Bao-tai-ai and Bao-xuan 2 were the outstanding examples (Chang et al. 1982). The first interspecific hybrid involving different genomes was made between sativa (A) and australiensis (E) by Li et al. (1963), but no useful progeny was obtained. The hybrid rice of China was also based on the spontanea (Wild Abortive) and sativa cross (Lin and Yuan 1980). IRRI breeders, entomologists, and pathologists have made crosses with several wild species in an attempt to transfer into sativa the multiple insect resistance in 0. officina/is (CC genome), blast resistance in 0. minuta (BBCC genome), yellow stemborer resistance in 0. brachyantha (FF genome) and other biotic and abiotic stress tolerances in other wild taxa of unknown genomes. Tissue culture was extensively used to produce F 1 plants from the otherwise incompatible crosses (Bajaj 1980; IRRI 1990a). Intergeneric hybrids involving rice, sorghum, bamboo, reed, corn, wheat, and other grasses were reported from China, but none of the reputed hybrids led to useful progenies (see Chang et al. 1982). Recently, hybrids between Porteresia coarctata (formerly 0. coarctatum) and 0. sativa have been obtained (see Finch in IRRI 1990c). P. coarctatum is a salt-tolerant wild relative found in coastal mangrove swamps. Its seed is collected as a food supplement, but the seeds do not germinate readily under laboratory conditions. Anther, pollen, and ovary culture

Anther culture has been used by Chinese scientists since the 1960s to accelerate breeding progress. Haploid tissue of an F 1 hybrid was cultured, the chromosomes doubled, and the plant regenerated to provide a homozygous line. Several varieties produced by anther culture-derived doubled haploids have been released in China, but the scope of genetic improvement was no greater than those produced by conventional hybridization of selection and are largely confined to the readily cultured sinica race (see Bajaj 1980; Hu 1985; Raina 1989). For traits that do not readily recombine, this technique may offer advantages, however. A scheme to produce alien addition and substitution lines from interspecific crosses through anther culture has been proposed by Chu (1982). Anther culture has been pursued at IRRI for a variety of objectives which included cold tolerance and salt tolerance (Zapata et al. 1986, 1989). A discussion on pollen and ovary culture may be found in Cho and Zapata (1988) and Raina (1989). Another use of cell/tissue culture is to facilitate genetic manipulations in distantly related hybrids: alien chromosome addition and substitution,

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induction of homologous pairing, induction of amphidiploidy, and induction of translocations (see Raina 1989). Somatic cell culture

Somatic cell culture can be used to rescue hybrid embryos, poorly viable seed, and in vitro storage of recalcitrant germplasm. Another potential application is large-scale plant regeneration, which would aid rapid propagation of desired genotypes and quick screening for variants at the cellular level. Variants that appear during the regeneration of cultured cells are called somaclonal variants and comprise another means of producing novel variability, probably through mutations and chromosomal interchanges. Mutations obtained in rice were related to culm length, flowering date, grain shape, and spikelet fertility, and the variants became fixed in the R2 generation. Somaclonal variants for tolerance to salt and aluminum were screened at IRRI and mutants with higher tolerance levels were obtained. Similarly, variants having enhanced resistance to Helminthosporium oryzae toxin were found in a Chinese study (Raina, 1989). The potential scope offered by this method for crop improvement appears to be less than those involving alien germplasm, however. Protoplast fusion

Protoplasts can be isolated, cultured, and regenerated from single cells in a culture. In the absence of a cell wall, the protoplasts are amenable to genetic transformation through the incorporation of foreign DNA, cell organelles, and other genetic components. When the naked cells fuse, somatic hybridization and mitochondrial recombination could take place. Amphidiploid protoplasts can be directly generated. Thus, this method offers more possibilities for genetic manipulation than other kinds of cell cultures by bypassing zygotic barriers. Recent experiments have demonstrated that rice protoplasts can be isolated, cultured, and fused first within a sinica variety and then a whole plant regenerated (as by Yamada et al. 1985; Fujimura et al. 1985; Coulibaly and Demarly 1986; and Abdullah et al. 1987). Protoplast fusion and plant regeneration have also been attained in indica varieties (Kyozuka et al. 1988; Peng and Hodges 1989; IRRI 1989). Somatic hybrids have been obtained in the following crosses: 0. sativa and Glycine sp. (Niizeki et al. 1984), 0. sativa and Echinochloa oryzicola (Terada et al. 1987), between 0. sativa cvs. (Toriyama and Hinata 1988) and between sativa and a wild species with a different genome (Hayashi et al. 1988). Hybrids have been

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obtained from ems and fertile lines in which cytoplasmic male sterility was transferred (Akagi et al. 1989; Yang et al. 1988). Protoplasmic DNA uptake

Molecular manipulations using DNA offer one of the most powerful means of gene transfer. The first step consists offractionizing and isolating donor DNA from an alien source. Direct plant transformation by microinjection of DNA into ovules or embryos and by protoplast fusion with bacterial spheroplasts have been attempted by Gerlach et al. (1985) and Cocking and Davey (1987). Fertile transgenic plants regenerated from transformed protoplasts have been obtained (Shimamoto et al. 1989). Recombinant DNA

The DNA fragment is first fractionized and confirmed to carry the desired genetic information as the vector. The fragment can be transferred when mediated by a T 1 plasmid. Such a transfer has been achieved (Lorz and Gobel 1986). · The foregoing summary represents to date largely experimental approaches that are indispensable to applying the techniques. Although no successful transfer of an agriculturally important gene into rice for commercial use has been achieved, the potentials appear highly promising, partly because rice is more readily regenerated than wheat or barley. On the other hand, the incomplete status of rice genetics will continue to affect rapid advances in genetic engineering. Several agricultural scientists have pointed out that genetic engineering alone will not lead to improved cultivars nor replace conventional plant breeding. The combined input of plant breeders, biotech workers, and other disciplines will be needed to attain the expanded goals (see Sprague et al. 1980; Carlson 1983; Borlaug 1983). Sustained training of competent plant breeders is crucial to the team approach in delivering usable products.

AREAS FOR FUTURE ENDEAVOR

The world's human population passed the 5 billion mark in August 1988 and will well exceed 6 billion by 2000. The rate of increase is higher in the rice-growing regions than other regions. The estimated requirement for rice by the turn of this century will be around 556 million tons which represents a 100-million metric ton increase over the present level of 458.

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The increased need will have to come mainly from improved yield because the prospects for expanding riceland are limited (see IRRI 1989c). This presents a great challenge to all rice workers, especially those involved in crop improvement, as rice farmers may not be able to increase their input at a sustained rate in the face of diminishing natural and related resources (see Chang 1988). One of the avenues to higher rice yields is to increase concurrently the total biomass and the harvest index (HI), the ratio of grain to biomass. For presently grown HYVs in irrigated fields, the HI ranges between 0.4 and 0.5. The HI needs to be elevated to 0.6 in order to reach a 15-22 t/ha yield level (Akita 1989). A high rate of dark respiration in the tropics has been often described as one of the factors leading to low yields, but it is also a necessary step in the accumulation ofphotosynthates. On the other hand, yield-enhancing genetic interactions in cultivated/wild crosses have not been explored, while it was shown in oats to be a promising approach (see Frey 1983). The yield destabilizing effects of unfavorable weather and heavy pest incidence need to be reduced in extent and frequency. As the global warming trend is likely to intensify, and weather disturbances such as the El Nino phenomenon continue, the monsoon will be pushed northward. Drought will be more frequent and serious in the middle latitude countries such as China and India (see Bryson 1974; World Climate Research Program 1990). Meanwhile, a rise in seawater level will aggravate flooding in coastal and low-lying areas. Expansion in intensive multiple cropping will increase pest epidemics. On the other hand, unique genes in the rich rice germplasm will enable breeders and allied scientists in plant protection to make a fuller use of genetic tolerances and render them more durable. Germplasm collection in remote areas and of the wild relatives must be completed and the materials fully evaluated. Further advances in genetic manipulations and their combined use will facilitate the incorporation of genes from a broader array of germplasm even beyond the genus Oryza. Related genera such as Leersia, Porteresia, Zizania, and others-each possess unique characteristics that can be exploited to improve the rice plant-should be explored (see Chang and Vaughan 1991). Meanwhile, a fuller understanding of the genetic system of rice is indispensable to more refined genetic manipulations and enhancement (see Flavell 1985). Further efforts to meet the impending food needs will not only involve greater collaboration among the various scientific disciplines of many nations working on rice but also different sectors of society: rice farmers, food processors, rice consumers, agricultural engineers, decisionmakers, educators, mass media, and the public (see Chang 1988). It will be an allout war for human survival that cannot be circumvented.

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REFERENCES

Abdullah, R., E. C. Cocking, and J. A. Thompson. 1986. Efficient plant regeneration from rice protoplasts through somatic embryogenesis. Bio/Technology 4:1087-90. Adair, C. R., eta!. 1973. Rice in the United States: Varieties and Production. Agric. Handbook 289 (revised edition). Washington, DC: U.S. Dept. of Agriculture. Akagi eta!. 1989. Construction of rice hybrid plants. Mol. Gen. Genet. 215:5016. Akemine, M. 1925. On the inheritance of dwarf habits in rice. Proc. Japan. Assoc. Adv. Sci. 1:308-14. Akita, S. 1989. "Improving rice yield potential in tropical rice." In Progress in Irrigated Rice Research, 41-73. Los Banos, Philippines: IRRI. Anon. 1987. A report on the security of the world's major gene banks. Rural Advancement Fund International Communique. Aquino, R. C., and P.R. Jennings. 1966. Inheritance and significance of dwarfism in an indica rice variety. Crop Sci. 6:551-4. Arkansas Agricultural Statistical Service. 1989. Crop Production Report, Oct. 13. Bajaj, Y. P. S. 1980. "Implications and prospects of protoplast, cell, and tissue culture in rice improvement programs." In Innovative Approaches to Rice Breeding, 103-34. Los Banos, Philippines: IRRI. Balakrishna Rao, M. J., K. Srinivasulu, and D. Choudhury. 1972. Inheritance of dwarfing in crosses involving rice variety Baok. Current Sci. 41:306. Barker, R., R. W. Herdt, and B. Rose. 1985. The Rice Economy ofAsia. Washington, D.C.: Resources for the Future. Bashar, K., T. T. Chang, and G. C. Loresto. 1990. Variability of root xylem vessels in selected rice varieties at different ages. SABRAO J. 22(1):11-16. Beachell, H. M., and P. R. Jennings. 1965. "Need for modification of plant type." In The Mineral Nutrition of the Rice Plant, 29-35. Baltimore, MD: Johns Hopkins Press. Beachell, H. M., G. S. Khush, and R. C. Aquino. 1972. "IRRI's international breeding program." In Rice Breeding, 89-106. Los Banos, Philippines: IRRI. Bollich, C. N. 1957. Inheritance of several economic quantitative characters in rice. Diss. Abst. 17:1638. Bollich, C. N., and B. D. Webb. 1973. Inheritance of amylose in two hybrid populations of rice. Cereal Chern. 50:631-6. Bonman, J. M., and D. J. Mackill. 1988. Durable resistance to rice blast disease. Oryza 25:103-10. Borlaug, N. E. 1983. Contributions of conventional plant breeding to food production. Science 219:689-93. Brady, N. C. 1975. "Rice responds to science." In Crop Productivity-Research Imperatives, edited by A. W. A. Brown et al., 62-96. Yellow Spring and East Lansing, Ml: Michigan Agricultural Experiment Station and C. F. Kettering Foundation. Bryson, R. A. 1974. A perspective on climatic change. Science 184:753-60.

GENETICS AND BREEDING

85

Buddenhagen, I. W. 1983. Breeding strategies for stress and disease resistance in developing countries. Ann. Rev. Phytopath. 21:385-409. Buttery, R. G., L. C. Ling, and B. 0. Juliano. 1982. 2-acetyl-1-pyrroline: an important aroma component of cooked rice. Chern. Ind. 23:958-9. Carlson, P. S. 1983. "Beyond haploids." In Cell and Tissue Culture Techniques for Cereal Crop Improvement, 407-417. Beijing: Science Press (also Los Banos, Philippines: Int. Rice Res. Inst.). Chandler, R. F., Jr. 1968. Dwarf rice-A giant in tropical Asia. In Science for Better Living. Yearbook ofAgriculture, 252-5. Washington, D.C.: U.S. Dept. of Agriculture. Chandler, R. F., Jr. 1969. "Plant morphology and stand geometry in relation to nitrogen." In Physiological Aspects of Crop Yield, edited by R. C. Dinauer, 265-85. Madison, WI: Amer. Soc. of Agronomy/Crop Sci. Soc. of Amer. Chandraratna, M. F. 1955. Genetics of photoperiod sensitivity in rice. J. Genet. 53:215-23. Chandraratna, M. F. 1964. Genetics and Breeding of Rice. London: Longman, Green, and Co. Chandraratna, M. F., and K. I. Sakai. 1960. A biometrical analysis of matroclinous inheritance of grain weight in rice. Heredity 14:365-73. Chang, T. T. 1961. Recent advances in rice breeding in Taiwan. In Crop and Seed Improvement in Taiwan, R.O.C., May 1959-January 1961. Taipei, Taiwan: Jt. Comm. Rural Reconstr. Pl. Ind. Ser. 22. Chang, T. T. 1964. Present knowledge of rice genetics and cytogenetics. Int. Rice Res. Inst. Tech. Bull. 1. Los Banos, Philippines: IRRI. Chang, T. T. 1966. The need for genetical investigations to assist rice breeders in tropical Asia. Indian J. Genet. Pl. Breeding 26A:206-16. Chang, T. T. 1967. The genetic basis of wide adaptability and yielding ability of rice varieties in the tropics. Int. Rice Comm. Newslett. 16(4):4-12. Chang, T. T. 1972. "International cooperation in conserving and evaluating rice germplasm resources." In Rice Breeding, 177-85. Los Banos, Philippines: IRRI. Chang, T. T. 1976a. The rice cultures. Phil. Trans. Roy. Soc. London, The Early History of Agriculture, B275:143-57. Chang, T. T. 1976b. The origin, evolution, cultivation, dissemination and diversification of Asian and African rices. Euphytica 25:425-41. Chang, T. T. 1976c. Manual on the Genetic Conservation of Rice Germplasmfor Evaluation and Utilization. Los Banos, Philippines: IRRI. Chang, T. T. 1979a. "Genetics and evolution of the Green Revolution." In Replies from Biological Research, Proc. UNESCO-CSIC Symp. on Biology and Ethics, edited by R. de Vicente, 187-209. Madrid: Consejo Superior de Investi-

gaciones Cientificas. Chang, T. T. 1979b. "Crop genetic resources." In Plant Breeding Perspectives, edited by J. Sneep, A. J. T. Hendriksen, and 0. Holbek, 83-103. Wageningen: PUDOC. Chang, T. T. 1979c. "Hybrid rice." In Plant Breeding Perspectives, edited by J. Sneep, A. J. T. Hendriksen, and 0. Holbek, 173-4. Wageningen: PUDOC.

86

RICE: PRODUCTION

Chang, T. T. 1984. Conservation of rice genetic resources: luxury or necessity? Science 224:251-6. Chang, T. T. 1985a. Crop history and genetic conservation: rice-A case study. Iowa State J. Res. 59:425-56. Chang, T. T. 1985b. Evaluation and documentation of crop germplasm. Iowa State J. Res. 59:379-98. Chang, T. T. 1985c. "Evaluation of exotic germplasm for crop improvement." In Proc. Int. Symp. on Southeast Asian Plant Genetic Resources, edited by K. L. Mehra and S. Sastrapradja, 95-103. Bogor: LBN/LIPI. Chang, T. T. 1987. The impact of rice on human civilization and population expansion. Interdisciplinary Sci. Rev. 12(1):63-9. Chang, T. T. 1988. Sharing the benefits of bioproduction with the developing world. Report presented at the Int. Union of Biological Sci. 23rd General Assembly, Oct. 18-20, 1988, Canberra, Australia. Chang, T. T. 1989a. "Domestication and the spread of the cultivated rices." In Foraging and Farming-The Evolution of Plant Exploitation, edited by D. R. Harris and G. C. Hillman, 408-17. London: Unwin and Hyman. Chang, T. T. 1989b. The management of rice genetic resources. Genome 31(2):825-31. Chang, T. T. 1989c. "The case for large collections." In The Use of Plant Genetic Resources, edited by A. H. D. Brown et al., 123-56. Cambridge: Cambridge Univ. Press. Chang, T. T. 1989d. The ethnobotany of rice in island Southeast Asia. Asian Perspectives 26(1):69-76. Chang, T. T., and E. A. Bardenas. 1965. The morphology and varietal characteristics of the rice plant. Int. Rice Res. Inst. Tech. Bull. 4. Los Banos, Philippines: IRRI. Chang, T. T., and S. T. Yen. 1969. Inheritance of grain dormancy in four rice crosses. Bot. Bull. Acad. Sin. 10:1-9. Chang, T. T., and 0. Tagumpay. 1970. Genotypic association between grain yield and six agronomic traits in a cross between rice varieties of contrasting plant type. Euphytica 19:356-63. Chang, T. T., and B. S. Vergara. 1971. Ecological and genetic aspects of photoperiod-sensitivity and thermosensitivity in relation to the regional adaptability of rice varieties. Int. Rice Comm. Newslett. 20(2):1-10. Chang, T. T., and B. S. Vergara. 1972. "Ecologic and genetic information on adaptability and yielding ability in tropical rice varieties." In Rice Breeding, 431-53. Los Banos, Philippines: IRRI. Chang, T. T., and 0. Tagumpay. 1973. Inheritance of grain dormancy in relation to growth duration in 10 rice crosses. SABRAO Newslett. 5(2):87-94. Chang, T. T., and F. H. Lin. 1974. Diallel analysis of protein content in rice. Agron. Abst. 1974:65. Chang, T. T., and H. I. Oka. 1976. Genetic variousness on the climatic adaptation of rice cultivars. In Climate and Rice, 87-lll. Los Banos, Philippines: IRRI. Chang, T. T., and C. C. Li. 1980. "Genetics and breeding." In Rice: Production and Utilization, edited by B. S. Luh, 87-146. Westport, CT: AVI. Chang, T. T., and G. C. Loresto. 1986a. "Screening techniques for drought

GENETICS AND BREEDING

87

resistance in rice." In Approaches for Incorporating Drought and Salinity Resistance in Crop Plants, edited by V. L. Chopra and R. S. Paroda, 108-29. New Delhi: Oxford and IBH. Chang, T. T., and G. C. Loresto. 1986b. "Germplasm resources and breeding for drought resistance." In Progress in Upland Rice Research, 199-212. Los Banos, Philippines: IRRI. Chang, T. T., and D. A. Vaughan. 1991. "Conservation and potentials of rice genetic resources." In Biotechnology in Agriculture and Forestry, edited by V.P.S. Bajaj, 531-52. Heidelberg: Springer-Verlag. Chang, T. T., C. C. Li, and B. S. Vergara. 1969. Component analysis of duration from seeding to heading in rice by the basic vegetative phase and the photoperiod-sensitive phase. Euphytica 18:79-91. Chang, T. T., C. C. Li, and 0. Tagumpay. 1973. Genotypic correlation, heterosis, inbreeding depression and transgressive segregation of agronomic traits in a diallel cross of rice cultivars. Bot. Bull. Acad. Sinica 14:83-93. Chang, T. T., C. R. Adair, and T. H. Johnston. 1982. The conservation and use of rice genetic resources. Adv. Agron. 35:37-91. Chang, T. T., D. V. Seshu, and G. S. Khush. 1988. "The rice seed exchange and evaluation programs of IRRI." In Rice Seed Health, 21-32. Los Banos, Philippines: IRRI. Chang, T. T., S.M. Dietz, and M. N. Westwood. 1989. "Management and utilization of plant germplasm collections." In Biotic Diversity and Germplasm-Global Imperatives, edited by L. Knutson and A. K. Stoner, 127-159. Dordrecht: Kluwer. Chang, T. T., et al. 1965. Genetic analysis of plant height, maturity and other quantitative traits in the cross of Peta X I-geo-tze. J. Agric. Assoc. China 51:1-8. Chang, T. T., et al. 1975. "The search for disease and insect resistance in rice germplasm." In Crop Genetic Resources for Today and Tomorrow, edited by 0. H. Frankel and J. G. Hawkes, 183-200. Cambridge: Cambridge Univ. Press. Chang, T. T., et al. 1982. Strategy and methodology of breeding rice for droughtprone areas. In Drought Resistance in Crops with Emphasis in Rice, 217-44. Los Banos, Philippines: IRRI. Chang, T. T., et al. 1985. Semidwarfs in rice germplasm collections and their potentials in rice improvement. Phytobreedon 1(1): 1-9. Chang, T. T., J. L. Armenta-Soto, C. X. Mao, R. Peiris, and G. C. Loresto. 1986. "Genetic studies on the components of drought resistance in rice (Oryza sativa L.)." In Rice Genetics, 387-98. Los Banos, Philippines: IRRI. Chang, T. T., et al. 1989. "International collaboration on conservation, sharing, and use of rice germplasm." In Progress in Irrigated Rice Research, 325-37. Los Banos, Philippines: IRRI. Chao, L. F. 1928. Linkage studies in rice. Genetics 13:133-69. Chen, C. C., F. J. M. Sung, and C. C. Li. 1986. Physiological and genetic studies on seedling vigor in rice. I. Relations between seed weight, seedling respiration rate, and growth of rice seedlings. J. Agric. Assoc. China 135:916.

88

RICE: PRODUCTION

Chinese Acad. of Agricultural Sci. (CAAS). 1986. Chinese Rice Culture (in Chinese). Beijing: Agriculture Publ. Soc. Cho, M. S., and F. J. Zapata. 1988. Callus formation and plant regeneration in isolated pollen culture of rice (Oryza sativa L. cv. Taipei 309). Plant Sci. 58:239-44.

Chu, C. C. 1982. "Anther culture of rice and its significance in distant hybridization." In Rice Tissue Culture Planning Conference, 47. Los Banos, Philippines: IRRI. Cocking, E. C., and M. R. Davey. 1987. Gene transfer in cereals. Science 236:1259-62.

Coulibaly, M. Y., andY. De marly. 1986. Regeneration of plantlets from protoplasts of rice, Oryza sativa L. Z. P.flanzenzuchtg. 96:79-81. Dahal, G., H. Hibino, and R. C. Saxena. 1990. Changes in cultivar reactions to tungro due to changes in "virulence" of leafhopper vector. Phytopathology 80:371-7.

Dalrymple, D. G. 1976. Development and spread of high-yielding varieties of wheat and rice in the less developed nations. For. Agric. Econ. Rept. No. 95. Washington, D. C.: USDA-USAID. Dalrymple, D. G. 1980. Development and spread of semidwarf varieties of wheat and rice in the United States. Agric. Econ. Rept. 455. Washington, D.C.: USDA-USAID. Dalrymple, D. G. 1986. Development and Spread of High Yielding Rice Varieties in Developing Countries. Washington, DC: USAID. Dave, B. B. 1939. Annual Report Rice Research Station for 1938. Raipur, Central Provinces, India. Dilday, R. H. 1990. Contribution of ancestral lines in the development of new cultivars of rice. Crop Sci. (in press). Dolores, R. C., T. T. Chang, and D. A. Ramirez. 1979. The cytogenetics of F 1 hybrids from Oryza nivara Sharma et Shastry x 0. sativa L. Cytologia 44:527-540.

Ekanayake, I. J., et al. 1985. Inheritance of root characters and their relations to drought resistance in rice. Crop Sci. 25:927-33. Engle, L. M., D. A. Ramirez, and T. T. Chang. 1969. The cytology of sterility in F 2 , F 3 and F 4 hybrids of Indica x Japonica crosses of rice (Oryza sativa L.). Cytologia 34:572-85. Erickson, J. R. 1968. Rice Genetic Investigations. U.S. Dept. Agric. Ann. Rep. Biggs, CA: Rice Experiment Station. Erickson, J. R. 1969. Rice Genetic Investigations. U.S. Dept. Agric. Ann. Rep. Biggs, CA: Rice Experiment Station. Evatt, N. S., and H. M. Beachell. 1962. Second-crop rice production in Texas. Texas Agric. Prog. 8(6):25-8. Ezuka, A. 1979. "Breeding for and genetics of blast resistance in Japan." In Proc. Rice Blast Workshop, 27-48. Los Banos, Philippines: IRRI. Flavell, R. B. 1985. "Molecular and biochemical techniques in plant breeding." In Biotechnology in International Agricultural Research, 247-55. Los Banos, Philippines: IRRI. Flor, H. H. 1946. The complementary genic systems in flax and flax rust. Adv. Genetics 8:29-54.

GENETICS AND BREEDING

89

Frankel, 0. H. 1975. ''Genetic resources centres-A cooperative global network.'' In Crop Genetic Resources for Today and Tomorrow, edited by 0. H. Frankel and J. G. Hawkes, 473-81. Cambridge: Cambridge Univ. Press. Frey, K. J. 1983. "Genes from wild relatives for improving plants." In Crop Improvement Research, Proc. 4th Int. SABRAO Congr., edited by T. C. Yap, K. M. Graham, and J. Sukaimi, 1-20. Bangi, Selangor, Malaysia: SABRAO. Fujimura, T., eta!. 1985. Regeneration of rice plants from protoplasts. Plant Tissue Culture Lett. 2:74-5. Fuke, Y. 1955. On the genes controlling the heading time of leading rice varieties in Japan and their specific responses to daylength and temperature. Bull. Nat. Inst. Agric. Sci. D5:1-71 (Japanese with English summary). Futsuhara, Y., and K. Toriyama. 1971. Genetic studies on cool tolerance in rice. IV. Effectiveness of individual and line selection for cool tolerance. Japan. J. Breed. 21:181-8. Gangadharan, C. 1985. "Breeding." In Rice Research in India, 73-105. New Delhi: Indian Council of Agricultural Res. Gerlach, W. L., E. S. Dennis, and W. J. Peacock. 1985. "Approaches to the transformation of crop plants.'' In Biotechnology in International Agricultural Research, 257-67. Los Banos, Philippines: IRRI. Ghose, A. K., and S. Govindaswamy. 1972. Inheritance of starch iodine blue value and alkali digestion value in rice and their genetic association. Riso 21:12332. Ghose, R. L. M., M. B. Ghatge, and V. Subrahmanyan. 1960. Rice in India. New Delhi: Indian Council of Agricultural Res. Grant, V. 1964. The Architecture of the Germplasm. New York: Wiley. Gregory, W. C. 1972. ''Mutation breeding in rice improvement.'' In Rice Breeding, 551-72. Los Banos, Philippines: IRRI. Haque, Q. A., eta!. 1989. Inheritance of submergence tolerance in rice. Euphytica 41:247-51. Harahap, Z., M. D. Pathak, and H. M. Beachell. 1982. "Genetic evaluation and utilization-A multidisciplinary strategy." In Rice Research Strategies for the Future, 81-96. Los Banos, Philippines: IRRI. Hargrove, T. R., W. R. Coffman, and V. L. Cabanilla. 1979. Genetic interrelationships of improved rice varieties in Asia. IRRI Res. Paper Ser. 23. Los Banos, Philippines: IRRI. Hargrove, T. R., V. L. Cabanilla, and W. R. Coffman. 1988. Twenty years of rice breeding. BioScience 38:675-81. Harlan, J. R., and J. M. J. de Wet. 1971. Toward a rational classification of cultivated plants. Taxon 20:509-17. Hayashi, Y., J. Kyozuka, and K. Shimamoto. 1988. Hybrids of rice (Oryza sativa L.) and wild Oryza species obtained by cell fusion. Mol. Gen. Genet. 214:6-10. He, G., and J. C. Flinn. 1989. "Economic efficiency of hybrid and conventional rice production in Jiangsu Province, China." In Progress in Irrigated Rice Research, 270. Los Banos, Philippines: IRRI. Hector, G. P. 1922. Ann. Rep. of Bengal Dept. of Agriculture for 1921-23. Heinrichs, E. A., F. G. Medrano, and H. R. Rapusas. 1985. Genetic Evaluation for Insect Resistance in Rice. Los Banos, Philippines: IRRI. Henderson, M. T., B. P. Yeh, and B. Exner. 1959. Further evidence of structural

90

RICE: PRODUCTION

differentiation in the chromosomes as a cause of sterility in intervarietal hybrids of rice, Oryza sativa L. Cytologia 24:415-22. Herdt, R. W., and C. Capule. 1983. Adoption, Spread and Production Impact of Modern Rice Varieties in Asia. Los Banos, Philippines: IRRI. Hibino, H. 1987. Towards stable resistance to rice viruses. Paper presented at the Symp., Crop Protection in the Tropics, 11th Int. Congr. of Plant Prot. 4-9 Oct. Manila, Philippines. Hibino, H., et a!. 1987. Resistance to rice tungro-associated viruses in rice under experimental and naturalconditions. Phytopa.thology 77(6):871-5. HilleRisLambers, D., eta!. 1973. Genetic and environmental variation in protein content of rice (Oryza sativa L.). Euphytica 22:264-73. Hirai, A., and T. Ishibashi. 1986. "Structure of rice chloroplast DNA." In Ria Genetics, 877-85. Los Ihnos, Philippines: IRRI. Hirai, A., and M. Sugiura. 1988. Structure of chloroplast DNA isolated from rice. Rice Genet. Newslett. 5:137-8. Hsieh, S. C. 1957. Studies on hybrid sterility in rice. I. Cytological investigation of the hybrid sterility between Indica and Japonica varieties of rice. Oryza sativa L. Agric. Res. (Taiwan) 7(3):51-61 (in Chinese, with English summary). Hsieh, S. C. 1961. Mutation in rice induced by X-rays. V. Analysis of reciprocal translocations in rice: Bot. Bull. Acad. Sinica 2:111-7, pl. I. Hsieh, S.C., W. T. Chang, and T. M. Chang. 1962. Studies on agronomic characters in reciprocal translocation homo zygotes of rice. Japan. J. Breed. 12:45-8. Hu, C. H. 1964. "Further studies on the chromosome morphology of Oryza sativa L." In Rice Genetics and Cytogenetics, 51-6l.Amsterdam: Elsevier. Hu, C. H. 1968. Studies on the development of twelve types of trisomies in rice with reference to genetic study and breeding program. J. Agric. Assoc. China 63:53-71. Hu, C. H. 1983. Breeding of California long grain and pearl rice varieties with high yields and good grain quality. Japan. J. Breed. 33:195-207. Hu, C. H., and K. M. Ho. 1963. Karyological studies of triploid rice plants. I. Chromosome pairing in autot~;:iploid of Oryza sativa L. Bot. Bull. A cad. Sinica 4:30-6. Hu, H. 1985. "Use of haploids in crop improvement." In Biotechnology in International Agricultural Research, 75-84. Los Banos, Philippines: IRRI. Huang, C. H. 1961. "Induction of mutations for rice improvement in Taiwan." In Crop and Seed Improvement in Taiwan, Republic of China, May 1959January 1961, Plant Ind. Ser. 22:59-76. Taipei, Taiwan: Chinese-Amer. Joint Comm. Rural Reconstr. Huang, C. H., W. L. Chang, and T. T. Chang. 1972. "Ponlai varieties and Taichung Native I." In Rice Breeding, 31-46. Los Banos, Philippines: IRRI. Huey, B. A., K. K. Moldenhaver, and R. S. Helms. 1989. Rice Varieties in Arkansas, Univ. Arkansas Ext. Service Leaflet 518. Fayetteville, AR: Univ. of Arkansas. Int. Board for Plant Genetic Resources (IBPGR). 1978. Address by the IBPGR to the Workshop on Rice Germplasm Conservation. In Proc. Workshop on Genetic Conservation of Rice, 39-41. Los Banos, Philippines: IRRI. Ikeda, R., and C. Kaneda. 1986. "Genetic analysis of resistance to brown planthopper in rice." In Rice Genetics, 505-12. Los Banos, Philippines: IRRI.

GENETICS AND BREEDING

91

Ikehashi, H., and H. Araki. 1987. Screening and genetic analysis of wide compatibility in F 1 hybrids of distant crosses in rice, Oryza sativa L. Trap. Agr. Res. Center Japan Tech. Bull. 23. Tsukuba, Japan: TARC. Ikehashi, H., and H. Fujimaki. 1980. "Modified bulk population method for rice breeding." In Innovative Approaches to Rice Breeding, 163-82. Los Banos, Philippines: IRRI. Ikehashi, H., and D. HilleRisLambers. 1979. "Integrated international collaborative program in the use of rapid generation advance in rice." In Proc. 1978 Int. Deepwater Rice Workshop, 261-76. Los Banos, Philippines: IRRI. IRRI. 1964. Rice Genetics and Cytogenetics. Amsterdam: Elsevier. IRRI. 1967. Annual Rep. for 1966. Los Banos, Philippines: IRRI. IRRI. 1972. Annual Rep. for 1971. Los Banos, Philippines: IRRI. IRRI. 1975. Annual Rep. for 1974. Los Banos, Philippines: IRRI. IRRI. 1976a. Annual Rep. for 1975. Los Banos, Philippines: IRRI. IRRI. 1976b. Climate and Rice. Los Banos, Philippines: IRRI. IRRI. 1979a. Proc. of the Rice Blast Workshop. Los Banos, Philippines: IRRI. IRRI. 1979b. Rep. of a Rice Cold Tolerance Workshop. Los Banos, Philippines: IRRI. IRRI. 1980. Five Years ofthe IRTP; A Global Rice Exchange and Testing Network. Los Banos, Philippines: IRRI. IRRI. 1982a. Annual Rep. for 1981. Los Banos, Philippines: IRRI. IRRI. 1982b. Proc. of the 1981 Int. Deepwater Rice Workshop. Los Banos, Philippines: IRRI. IRRI. 1984. An Overview of Upland Rice Research. Los Banos, Philippines: IRRI. IRRI. 1986. Progress in Upland Rice Research. Los Banos, Philippines: IRRI. IRRI. 1987. Annual Rep.for 1986. Los Banos, Philippines: IRRI. IRRI. 1988a. Annual Rep. for 1987. Los Banos, Philippines: IRRI. IRRI. 1988b. 1987 Int. Deepwater Rice Workshop. Los Banos, Philippines: IRRI. IRRI. 1988c. Hybrid Rice. Los Banos, Philippines: IRRI. IRRI. 1989a. Annual Rep. for 1988. Los Banos, Philippines: IRRI. IRRI. 1989b. Progress in Irrigated Rice Research. Los Banos, Philippines: IRRI. IRRI. 1989c. IRRI Toward 2000 and Beyond. Los Banos, Philippines: IRRI. IRRI. 1989d. Implementing the Strategy-Workplan for 1990-94. Los Banos, Philippines: IRRI. IRRI. 1990a. Annual Rep. for 1989. Los Banos, Philippines: IRRI. IRRI. 1990b. Problem Soils Workshop. Los Banos, Philippines: IRRI. IRRI. 1990c. 2nd Int. Rice Genetics Symp. (Abstracts). Los Banos, Philippines: IRRI. Iwata, N. 1986. "The relationship between cytologically identified chromosomes and linkage groups in rice." In Rice Genetics, 229-38. Los Banos, Philippines: IRRI. Iwata, N., and T. Omura. 1984. Studies on the trisomies in rice plants. VI. An accomplishment of a trisomic series in Japonica rice plants. Japan. J. Genet. 59(3): 199-204. Iwata, N., T. Omura, and M. Nakagahra. 1970. Studies on the trisomies in rice plants (0. sativa L.). 1. Morphological classification of trisomies. Japan. J. Breed. 20:230-6. Iwata, N., H. Satoh, and T. Omura. 1984. Studies on trisomies in rice plants. V.

92

RICE: PRODUCTION

Relationship between the twelve chromosomes and the linkage groups. Japan. J. Breed. 34(3):314-21. Jennings, P. R. 1964. Plant type as a rice breeding objective. Crop Sci. 4:13-5. Jennings, P.R., W. R. Coffman, and H. E. Kauffman. 1979. Rice Improvement. Los Banos, Philippines: IRRI. Jensen, N. F. 1988. Plant Breeding Methodology. New York: Wiley. Jodon, N. E. 1955. Present status of rice genetics. J. Agric. Assoc. China 10(N.S.):5-21. Johnston, T. H., N. E. Jodon, C. N. Bollich, J. N. Rutger, et al. 1972. "The development of early maturing and nitrogen-responsive rice varieties in the United States." In Rice Breeding, 61-75. Los Banos, Philippines: IRRI. Jones, J. W. 1926. Hybrid vigor in rice. J. Amer. Soc. Agron. 18:423-8. Jones, J. W. 1928. Inheritance of earliness and other agronomic characters in rice. J. Agric. Res. (U.S.) 36:581-601. Jones, J. W. 1933. Inheritance of characters in rice. J. Agric. Res. 47:771-82. Jones, J. W. 1936. "Improvement in rice." In U.S. Dept. Agric. Yearbook 1936, 415-54. Washington, DC: Government Printing Office. Jones, J. W., and C. R. Adair. 1938. A "lazy" mutation in rice. J. Hered. 29:315-18. Jones, J. W., C. R. Adair, and H. M. Beachell. 1935. Inheritance of earliness and length of kernel in rice. J. Amer. Soc. Agron. 27:910-21. Juliano, B. 0., Ed. 1985. Rice: Chemistry and Technology. St. Paul, MN: Amer. Assoc. of Cereal Chemists. Juo, A. S. R., and J. A. Lowe, Eds. 1986. The Wetlands and Rice in Subsaharan Africa. Ibadan, Nigeria: Int. Inst. of Tropical Agriculture. Kadam, B. S., and R. D'Cruz. 1960. Genic analysis in rice. III. Inheritance of some characters in two clustered varieties of rice. Indian J. Genet. Plant Breed. 20:79-84. Kadowaki, K., T. Osumi, H. Nemoto, K. Harada, and C. Shinjyo. 1988. Mitochondrial DNA polymorphism in male-sterile cytoplasm of rice. Theor. Appl. Genet. 75:234-6. Kahlon, P. S. 1965. Inheritance of alkali digestion index and iodine value in rice. Diss. Abst. B25:5512-3. Kaneda, C. 1986. Rice breeding for extremely higher yielding ability by japonica-indica hybridization. JARQ 19:235-40. Kaneda, C. 1988. Genetics and breeding of rice for insect resistance-A brief review. Gamma Field Symp. 27:71-89. Ibaraki, Japan: Inst. of Radiation Breeding. Kato, S., H. Kosaka, and S. Hara. 1928. On the affinity of rice varieties as shown by the fertility of hybrid plants. B. Sci. Fakult. Terkult Kyushu Imp. U. 3:132-47. Kato, S., et al. 1930. On the affinity of the cultivated varieties of rice plants, Oryza sativa L. J. Dept. Agr. Kyushu Imperial Univ. 2(9):241-76. Katsuo, K., and U. Mizushima. 1958. Studies on cytoplasmic differences in rice. I. On the fertility of hybrids obtained reciprocally between cultivated and wild varieties. Japan. J. Breed. 8:1-5 (in Japanese with English summary). Kawano, K., and M. E. Takahashi. 1969. Inheritance modes of quantitative traits in two rice crosses. J. Fac. Agric. Hokkaido Univ. 56(2):225-40.

GENETICS AND BREEDING

93

Kelemu, S., and J. E. Leach. 1990. Cloning and characterization of an avirulence gene from Xanthomonas campestris pv. oryzae. Molecular Plant-Microbe Interactions 3(2):59-65. Khaleque, M.A., and A.M. Eunus. 1975. Inheritance of some quantitative characters in a diallel experiment of six rice strains. SABRAO J. 7:217-24. Khush, G. S. 1975. "Rice." In Handbook of Genetics, vol. 2, edited by R. C. King, 31-58. New York: Plenum Press. Khush, G. S. 1984a. Breeding rice for resistance to insects. Prot. Ecol. 7:147-65. Khush, G. S. 1984b. "IRRI breeding program and its worldwide impact on increasing rice production." In Gene Manipulation in Plant Improvement, edited by J. P. Gustafson, 61-94. New York: Plenum. Khush, G. S., and R.N. Misra. 1983. "Identification of primary trisomies of rice." In XV Int. Congress ofGenetics, New Delhi, Abstracts ofContributedPapers, pt. I, 668. Khush, G. S., and R. J. Singh. 1986. "Relationships between linkage groups and cytologically identifiable chromosomes of rice." In Rice Genetics, 239-48. Los Banos, Philippines: IRRI. Khush, G. S., and S. S. Virmani. 1985. "Breeding rice for disease resistance." In Progress in Plant Breeding I, edited by G. E. Russell, 239-79. London: Butterworths. Khush, G. S., R. J. Singh, S.C. Sur, and A. L. Librojo. 1984. Primary trisomies of rice: origin, morphology, cytology and use in linkage mapping. Genetics 107:141-63. Kikuchi, F. 1986. Semidwarfing genes of high yielding rice varieties in Japan. In Rice Genetics, 285-96. Los Banos, Philippines: IRRI. Kikuchi, F., K. Kumagai, and S. Suzuki. 1975. "Evaluation of adaptability by Finlay and Wilkinson's method." In Adaptability in Plants, edited by T. Matsuo, JIBP Synthesis, vol. 6. Tokyo: Japanese Comm. for the Int. Bioi. Program. Kinoshita, T. 1976. Difference and similarity of linkage groups between Japonica and Indica types of rice. Recent Adv. Breed. 17:19-34 (in Japanese). Kinoshita, T. 1986. "Standardization of gene symbols and linkage maps in rice." In Rice Genetics, 215-28. Los Banos, Philippines: IRRI. Kinoshita, T. 1987. Report of the Committee on Gene Symbolization, Nomenclature, and Linkage Groups. Rice Genetics Newslett. 4:3-37. Kisimoto, R. 1979. "Brown planthopper migration." In Brown Planthopper: Threat to Rice Production in Asia, 113-24. Los Banos, Philippines: IRRI. Kiyosawa, S., K. Kushibuchi, and S. Watanabe. 1975. Recent trends and problems in breeding for blast resistant varieties and its investigation (in Japanese). Nogyo Oyobi Engei (Agric. Hortic.) 50:25-30, 258-62, 377-80, 629-35. Kiyosawa, S., Y. Orimoto, and S. Iida. 1984. Relationship between frequencies of resistance gene in the host and corresponding virulence gene in the pathogen in rice blast disease. Japan. J. Breed. 34:322-34. Kuang, H. H., D. S. Tu, and Y. H. Chang. 1946. Linkage studies of awn in cultivated rice (Oryza sativa L.). J. Genet. 47:249-59. Kudo, M. 1968. Genetical and thermotological studies of characters, physiological or ecological in the hybrids between ecological rice groups. Bull. Nat. Inst. Agric. Sci. 19D: 1-84 (in Japanese, with English summary).

94

RICE: PRODUCTION

Kurata, N. 1986. "Chromosome analysis of mitosis and meiosis in rice." In Rice Genetics, 143-52. Los Banos, Philippines: IRRI. Kurata, N. 1988. Identification of trivalent chromosomes of IR36 Triplo plants. Rice Genet. Newslett. 5:54-8. Kuriyama, H. 1965. Studies on the ear-emergence in rice. Bull. Nat. Inst. Agric. Sci. 13D:273-353 (in Japanese with English summary). Kushibuchi, K. 1988. Rice Cultivation in Japan-Present Conditions and Prospects. Tsukuba, Japan: Nat. Agriculture Res. Center. Kyozuka, J., E. Etoo, and K. Shimamoto. 1988. Plant regeneration from protoplasts of indica rice: genotypic differences in culture response. Theor. Appl. Genet. 76:887-90. Lee, C. C., C. C. Li, and F. J. M. Sung. 1986. Physiological and genetic studies on seedling vigor in rice. II. Inheritances of alpha-amylase activity and seedling vigor in rice. J. Agric. Assoc. China 135:17-24. Leung, H., E. S. Broromeo, M.A. Bernardo, and J. L. Notteghem. 1988. Genetic analysis of virulence in the rice blast fungus Magnaporthe grisea. Phytopathology 78(9): 1227-33. Li, C. C. 1970. Inheritance of the optimum photoperiod and critical photoperiod in tropical rices. Bot. Bull. Acad. Sin. 11:1-15. Li, C. C. 1975. Diallel analysis of yield and its components traits in rice (Oryza sativa L.). 1. Agric. Assoc. China 92:41-56. Li, C. C., and T. T. Chang. 1970. Diallel analysis of agronomic traits in rice (Oryza sativa L.). Bot. Bull. Acad. Sin. 11:61-78. Li, C. C., and J. N. Rutger. 1980. Inheritance of cool-temperature seedling vigor in rice and its relationship with other agronomic characters. Crop Sci. 20:295-8. Li, C. C., and W. Y. Chou. 1986. Studies on inheritance of grain size in rice. Nat. Chung Hsing Univ. Agron. Bull. 9:1-16. Li, Y. C., and L. P. Yuan. 1986. "Genetic analysis of fertility restoration in male sterile lines of rice." In Rice Genetics, 617-32. Los Banos, Philippines: IRRI. Li, H. W. 1963. Cytogenetical studies of Oryza sativa L. and its related species. 4. Interspecific crosses involving 0. australiensis with 0. sativa and 0. minuta. Bot. Bull. Acad. Sin. 4:65-74. Li, H. W., S. Wang, and P. Z. Yeh. 1965. A preliminary note on the fine structure analysis of glutinous gene in rice. Bot. Bull. Acad. Sin. 6:101-5. Lin, F. H. 1972. Inheritance of photoperiod sensitivity in the crosses between indica and japonica varieties of rice. Taiwan Agric. Q. 8:168-75 (in Chinese with English summary). Lin, S. C. 1986. "Genetic analysis of minor gene resistance to blast in japonica rice." In Rice Genetics, 451-70. Los Banos, Philippines: IRRI. Lin, S. C., and L. P. Yuan. 1980. "Hybrid rice breeding in China." In Innovative Approaches to Rice Breeding, 35-52. Los Banos, Philippines: IRRI. Loresto, G. C., and T. T. Chang. 1978. Half-diallel and F 2 analysis of culm length in dwarf, semidwarf and tall strains of rice (Oryza sativa L.). Bot. Bull. Acad. Sin. 19:87-106. Lorz, H., and E. Gobel. 1986. "In vitro culture of rice and direct gene transfer to cereal cells." In Rice Genetics, 849-57. Los Banos, Philippines: IRRI. Lu, X. G., et al. 1989. "Application of photoperiod-sensitive genic male sterility

GENETICS AND BREEDING

95

in hybrid rice breeding." In Progress in Irrigated Rice Research, 270. Los Banos, Philippines: IRRI. McCouch, S. R., G. Kochert, Z. H. Yu, Z. Y. Wang, G. S. Khush, W. R. Coffman, and S. D. Tanksley. 1988. Molecular mapping of rice chromosomes. Theor. Appl. Genet. 76:815-29. McKenzie, K. S., and J. N. Rutger. 1983. Genetic analysis of amylose content, alkali spreading score, and grain dimensions in rice. Crop Sci. 23:30613. Micke, A., B. Donini, and M. Maluszynski. 1987. Induced mutations for crop improvement-A review. Trop. Agric. (Trinidad) 64(4):259-78. Mikaelsen, K. 1980. "Mutation breeding in rice." In Innovative Approaches to Rice Breeding, 67-79. Los Banos, Philippines: IRRI. Misra, R.N., K. K. Jena, and P. Sen. 1986. "Cytogenetics oftrisomics in indica rice." In Rice Genetics, 173-84. Los Banos, Philippines: IRRI. Misro, B., R. H. Richharia, and R. Thakur. 1966. Linkage studies in rice (Oryza sativa L.). VII. Indentification of linkage groups in indica rice. Oryza 3(1):96-105. Mitra, G. N. 1962. Inheritance of grain size in rice. Current Sci. 31:105-6. Morinaga, T., and E. Fukushima. 1937. Cytogenetical studies on Oryza sativa L. III. Spontaneous autotetraploid mutants in Oryza sativa L. Japan. J. Bot. 9:71-94. Morinaga, T., and H. Kuriyama. 1948. Linkage between the genes for sparse caryopsis and depressed palea of 0. sativa L. Japan. J. Genet. 23:33-4. Nagai, I. 1958. Japonica Rice: Its Breeding and Culture. Tokyo: Yokendo. Nagao, S. 1951. Genic analysis and linkage relationship of characters in rice. Adv. Genet. 4:181-212. Nagao, S., and M. Takahashi. 1942. Type and inheritance of awnedness in rice. J. Soc. Agric. and For. Sapporo 34(3):36-43. Nagao, S., and M. Takahashi. 1963. Trial construction of twelve linkage groups in Japanese rice. J. Fac. Agric. Hokkaido Univ. 53(1):72-130. Nakata, S., and B. R. Jackson. 1973. Inheritance of some physical grain quality characteristics in a cross between a Thai and Taiwanese rice. Thai J. Agric. Sci. 6:223-35. Nemoto, H., E. Shimura, and C. Kaneda. 1989. Registration of brown planthopper (BPH)-resistant germplasm lines in Japan. Int. Rice Res. Newslett. 14(2): 16. Niizeki, M., K. Saito, and M. E. Takahashi. 1984. Selection of somatic hybrid cell lines of rice, Oryza sativa L. and soybean, Glycine max (L.) Merr. Bull. Fac. Agric. Hirosaki Univ. 42:34-9. Nishimura Y. 1961. Studies on the reciprocal translocations in rice and barley. Bull. Nat. Inst. Agr. Sci. D9:171-235. Nishimura, Y., and H. Kurakami. 1952. Mutations in rice induced by X-rays. Japan. J. Breed. 2:65-71 (in Japanese with English summary). Ogawa, T., and T. Yamamoto. 1986. "Inheritance of resistance to bacterial blight in rice." In Rice Genetics, 471-9. Los Banos, Philippines: IRRI. Oka, H. I. 1957. Genic analysis for the sterility of hybrids between distantly related varieties of cultivated rice. J. Genet. 55:397-409. Oka, H. I. 1964. "Considerations on the genetic basis of intervarietal sterility

96

RICE: PRODUCTION

in Oryza sativa." In Rice Genetics and Cytogenetics, 158-74. Amsterdam: Elsevier. Oka, H. I. 1974. Experimental studies on the origin of cultivated rice. Genetics 78:475-86. Oka, H. 1., and H. K. Wu. 1988. Comparison of data on rice chromosomes presented by different authors. Rice Genetics Newslett. 5:34-40. Oka, H. 1., T. D. Chang, and M.S. Huang. 1953. Reciprocal translocation in rice. Japan. J. Genet. 28(3):87-91. Oka, H. 1., S.C. Hsieh, and T. S. Huang. 1954. Studies on tetraploid rice. V. The behavior of chromosomes in the meiosis of tetraploid rice varieties and their hybrids. Japan. J. Genet. 29:205-14 (in Japanese with English summary). Okuno, K. 1978. Gene dosage effect of waxy alleles on amylose content in endosperm starch of rice. Japan. J. Genet. 53(3):219-22. Ou, S. H. 1985. Rice Diseases. Kew, Surrey, England: Commonwealth Mycological lost. Pal, B. P. 1972. "Modern rice research in India and its impact." In Rice Science and Man, 89-104. Los Banos, Philippines: IRRI. Parnell, F. R., eta!. 1922. The inheritance of characters in rice. II. Mem. Dept. Agric. Ind. Bot. Ser. II: 185-208. Pathak, G. N. 1940. Studies in the cytology of cereals. J. Genet. 39:437-67. Pathak, M.D. 1977. Defense of the rice crop against insect pests. Ann. N.Y. A cad. Sci. 287:287-95. Pathak, M.D., and R. C. Saxena. 1980. ''Breeding approaches in rice.'' In Breeding Plants Resistant to Insects, edited by F. G. Maxwell and P.R. Jennings, 421-55. New York: Wiley. Peng, J., and T. K. Hodges. 1989. Genetic analysis of plant regeneration in rice (Oryza sativa L.). In Vitro Cell Dev. Bioi. 25:91-4. Prechachart, C., and B. R. Jackson. 1975. "Floating and deepwater rice varieties in Thailand." In Proc. Int. Sem. on Deepwater Rice, 1974. Dacca, Bangladesh: Bangladesh Rice Res. lost. Raina, S. K. 1989. Tissue culture in rice improvement: status and potential. Adv. Agron. 42:339-98. Ramanujam, S. 1937. Male sterility in rice. Madras Agr. J. 23:190. Ramiah, K. 1930. The inheritance of characters in rice. Part 3. Mem. Dept. Agric. Ind. Bot. Ser. B:2ll-7. Ramiah, K. 1932. Madras Agricultural Station Reports, Paddy Breeding Section for 1931-32. Coimbatore: Madras Dept. Agric. Ramiah, K. 1933. Inheritance of flowering duration. Indian J. Agric. Sci. 3:377-410. Ramiah, K., and N. Parthasarathy. 1933. Inheritance of grain length in rice (Oryza sativa L.). Indian J. Agric. Sci. 3(Pt. 5):808-19. Ramiah, K., and K. Ramaswami. 1941. Floating habit in rice. Indian J. Agric. Sci. ll:l-8. Ramiah, K., and M. V. Rao. 1953. Rice Breeding and Genetics. ICAR Sci. Monog. 19. New Delhi: Indian Council for Agricultural Res. Rice Genetics Newsletter. 1984. List of genes and genetic stocks. Rice Genet. Newslett. I :28-57.

GENETICS AND BREEDING

97

Rice Genetics Newsletter. 1986. Gene symbols for dwarfness. Rice Genet. Newslett. 3:8-10. Rice Genetics Newsletter. 1987. Gene symbols for resistance to insects. Rice Genet. Newslett. 4:43-6. Rice Genetics Newsletter. 1988. List of gene symbols. Rice Genet. Newslett. 5:7-9. Rice Genetics Newsletter. 1989. Rice Genet. Newslett. 6. Rice Genetics Newsletter. 1990. Rice Genet. Newslett. 7. Rice Technical Working Group. 1982. Proc. 19th Rice Technical Working Group. College Station, TX: Texas Agricultural Experiment Station. Rice Technical Working Group. 1984. Proc. 20th Rice Technical Working Group. College Station, TX: Texas Agricultural Experiment Station. Rice Technical Working Group. 1986. Proc. 21st Rice Technical Working Group. College Station, TX: Texas Agricultural Experiment Station. Rice Technical Working Group. 1988. Proc. 22nd Rice Technical Working Group. College Station, TX: Texas Agricultural Experiment Station. Robinson, R. A. 1976. Plant Pathosystems. Berlin: Springer-Verlag. Rural Development Administration (RDA). 1985. Rice Varietal Improvement in Korea. Suweon, Republic of Korea: Rural Development Admin. Rutger, J. N., M. L. Peterson, and C. H. Hu. 1977. Registration of Calrose 76 rice. Crop Sci. 17:978. Sakai, K. 1., and E. R. Pinto. 1959. Genetic studies on seed size in rice hybrids. Ann. Rep. Nat. Inst. Genet. (Japan) 9:72-3. Sakai, K. 1., andY. Shimazaki. 1948. Genetical studies on abnormal hypertrophy of tapetal cells in Oryza sativa L. Kanchi-Nogyo 2(2):93-5 (in Japanese). Sakai, K. 1., S. lyama, and T. Narise. 1961. Biometrical approach to the cytoplasmic inheritance in autogamous plants. Bull. Int. Stat. Inst. (Tokyo) 38(III):249-57. Sakai, K. I., and J. J. Niles. 1957. Heritability of grain shedding and other characters in rice. Trap. Agric. (Ceylon) 113:211-8. Sakamoto, W., K. Kadowaki, K. Tano, and T. Yabuno. 1990. Analysis of mitochondrial DNAs from Oryza glaberrima and its cytoplasmic substituted line for Oryza sativa associated with cytoplasmic male sterility. Japan. J. Genet. 65(1):1-6. Sampath, S., and D. V. Seshu. 1961. Genetics of photoperiod response in rice. Indian J. Genet. Pl. Breed. 21:38-42. Sano, Y. 1984. Differential regulation of waxy gene expression in rice endosperm. Theor. Appl. Genet. 68:467-73. Sano, Y., M. Katsumata, and K. Okuno. 1986. Genetic. studies of speciation in cultivated rice. 5. Inter- and intra-specific differentiation in waxy gene expression of rice. Euphytica 35:1-9. Sasaki, T., T. Kinoshita, and M. T. Takahashi. 1973. Estimation of the number of genes in germination ability at low temperature in rice-Genetical studies in rice plant. LVII. J. Fac. Agric. Hokkaido Univ. 57:301-12. Sato, Y., Y. Sano, and M. Nakagahra. 1987. Gene symbols for gametic effect, sterility and weakness. Rice Genet. Newslett. 4:46-51. Satoh, H., and E. Amano. 1987. Gene symbols for endosperm traits. Rice Genet. Newslett. 4:38-41.

98

RICE: PRODUCTION

Saxena, R. C. 1989. "Durable resistance to insect pests of irrigated rice." In Progress in Irrigated Rice Research, 111-32. Los Banos, Philippines: IRRI. Saxena, R. C., and A. A. Barrion. 1985. Biotypes of the brown planthopper Nilaparvata lugens (Stal) and strategies in deployment of host plant resistance. Insect Sci. Applic. 6(3):271-89. Second, G., A. Dally, and S. H. Zhang. 1989. Occasional biparental inheritance of chloroplast DNA in rice. Rice Genet. Newslett. 6:150-3. Seetharaman, R. 1959. The inheritance of iodine value in rice and its association with other characters. Diss. Abst. 20:856-7. Seshu, D. V., and M. E. Sorrells. 1986. "Genetic studies on seed dormancy in rice." In Rice Genetics, 369-82. Los Banos, Philippines: IRRI. Seshu, D. V., S. V. S. Shastry, and W. H. Freeman. 1974. Phenotypic stability of performance in yield of dwarf rice varieties. Indian J. Genet. 34A: 1130-9. Seshu, D. V., et al. 1989. Report ofActivities and Accomplishments of the International Rice Testing Program, 1985-89. Los Banos, Philippines: IRRI. Sethie, R. L., B. L. Sethi, and T. R. Mehta. 1937. Inheritance of sheathed ear in rice. Indian J. Agric. Sci. 7:134-48. Sharma, S.D., A. Krishnamurthy, and S. R. Dhua. 1988. Genetic diversity in rice and its utilization in India.'' In Plant Genetic Resources-Indian Perspectives, edited by R. S. Paroda, R. K. Arora, K. P. S. Chandel, 108-20. New Delhi: Nat. Bureau of Plant Genetic Resources. Shastry, S. V. S. 1964. "A new approach to the study of rice karyomorphology." In Rice Genetics and Cytogenetics, 62-7. Amsterdam: Elsevier. Shastry, S. V. S., and R. N. Misra. 1961. Pachytene analysis in Oryza. II. Sterility in japonica-indica hybrids. Chromosoma 12:248-71. Shastry, S. V. S., D. R. Ranga Rao, and R.N. Misra. 1960. Pachytene analysis in Oryza. I. Chromosome morphology in Oryza sativa. Indian J. Genet. Plant Breed. 20: 15-21. Shen, J. H. 1980. "Rice breeding in China." In Rice Improvement in China and Other Asian Countries, 9-30. Los Banos, Philippines: IRRI. Shen, T. H. 1964. Agricultural Development in Taiwan Since World War II. Ithaca, NY: Comstock Pub. Assoc. Shen, T. T., T. T. Lu, and J. S. Li. 1965. A genetical analysis of some characters in breeding early-maturing short-statured rice types. Zuowu Xuebao (Crop Sci. J.) 4:391-402 (in Chinese). Shimamoto, K., R. Terada, T. Izawa, and H. Fujimoto. 1989. Fertile transgenic rice plants regenerated from transformed protoplasts. Nature 338:274-6. Shinjo, C. 1972. Distribution of male sterility inducing cytoplasm and fertility restoring genes in rice varieties introduced from sixteen countries. Japan. J. Breed. 22:329-33. Shinjo, C. 1975. Genetical studies of cytoplasmic male sterility and fertility restoration in rice, Oryza sativa L. Sci. Bull. Coli. Agric. Univ. Ryukyus 22:1-51. Shinjo, C., and T. Omura. 1966. Cytoplasmic male sterility in cultivated rice, Oryza sativa L. I. Fertilities of F 1, F 2 and offspring obtained from their mutual reciprocal backcrosses and segregation of completely male sterile plants. Japan. J. Breed. 16(Suppl. 1): 179-80 (in Japanese). Sidhu, G. S., G. S. Khush, and T. W. Mew. 1978. Genetic analysis of bacterial

GENETICS AND BREEDING

99

blight resistance in seventy-four cultivars of rice, Oryza sativa L. The or. Appl. Genet. 53:105-11. Singh, J.P., and S. C. Mani. 1987. Inheritance of leaf aroma in rice. Rice Genet. Newslett. 4:92-3. Somrith, B., T. T. Chang, and B. R. Jackson. 1979. Genetic analysis of traits related to grain characteristics and quality in two crosses of rice. IRRI Res. Paper Ser. 35. Los Banos, Philippines: IRRI. Sprague, G. F., D. E. Alexander, and J. W. Dudley. 1980. Plant breeding and genetic engineering: a perspective. BioScience 30:17-21. Stansel, J. W. 1966. The influence of heredity and environment on endosperm characteristics of rice (Oryza sativa L.). Diss. Abst. B27:48. Sugimoto, S. 1923. Examples of the genesis of abnormal forms in rice. Japan. J. Genet. 2:71-5 (in Japanese). Takahashi, N. 1962. Physicogenetical studies on germination of rice seeds with special reference to the genetical factors governing germination. Bull. Inst. Agric. Tohoku Univ. 14(1):1-87 (in Japanese). Takahashi, M. 1964. ''Linkage group and gene sche'mes of some striking morphological characters in Japanese rice." In Rice Genetics and Cytogenetics, 215-36. Amsterdam: Elsevier. Tanaka, A. 1965. "Plant characters related to nitrogen response in rice." In The Mineral Nutrition of the Rice Plant, 419-36. Baltimore, MD: Johns Hopkins Press. Terada, R., J. Kyozuka, S. Nishibayashi, and K. Shimamoto. 1987. Plantlet regenerations from somatic hybrids of rice (Oryza sativa L.) and barnyard grass (Echinochloa oryzicola Vasing). Mol. Gen. Genet. 210:39-43. Thakur, R., and D. HilleRisLambers. 1989. Inheritance of plant elongation ability at seedling stage in rice. Euphytica 41:227-33. Ting, Y. 1933. Wild rice of Kwangtung and new variety bred from the hybrids of wild rice with cultivated rice. Sun Yatsen Univ. Agron. Bull. 3:1-22. Toriyama, K., andY. Futsuhara. 1960. Inheritance of cool tolerance. I. Japan. J. Breed. 1:143-52. Toriyama, K., and K. Hinata. 1988. Production of somatic hybrid plants between cultivars in rice through electrofusion. Japan. J. Breed. 38(Suppl. 1):76-7. Tripathi, R. S., and M. J. B. K. Rao. 1979. Inheritance and linkage relationship of scent in rice. Euphytica 28(2):319-23. Tsai, K. H. 1976. Studies on earliness genes in rice, with special reference to analysis of isoalleles at the E locus. Japan. J. Genet. 51:115-28. Tsai, K. H. 1986. "Gene loci and alleles controlling the duration of basic vegetative growth of rice." In Rice Genetics, 339-50. Los Banos, Philippines: IRRI. Tsunoda, S. 1965. "Leaf characters and nitrogen response." In Mineral Nutrition of the Rice Plant, 401-18. Baltimore, MD: Johns Hopkins Press. U.S. Dept. Agriculture (USDA). 1963. Rice gene symbolization and linkage groups. In Agric. Res Ser. ARS 34:34-8, 1-56. Vander Stok, J. E. 1908. On the inheritance of grain colour in rice. Teysmannia 65:5. Vergara, B.S., and T. T. Chang. 1985. The Flowering Response of the Rice Plant to Photoperiod-A Review of Literature. Los Banos, Philippines: IRRI. Virmani, S. S., and C. Shinjyo. 1988. Current status of analysis and symbols for

100

RICE: PRODUCTION

male-sterile cytoplasms and fertility-restoring genes. Rice Genet. Newslett. 5:9-15. Virmani, S. S., K. G. Raj, C. Casal, R. D. Dalmacio, and P. A. Aurin. 1986. "Current knowledge of and outlook on cytoplasmic-genetic male sterility and fertility restoration in rice.'' In Rice Genetics, 633-48. Los Banos, Philippines: IRRI. Wang, B., et al. 1987. Plasmid-like mitochondrial DNA associated with cytoplasmic male sterility. Rice Genet. Newslett. 4:118-20. Wang, Z., D. J. Mackill, and J. M. Bonman. 1989. Inheritance of partial resistance to blast in indica rice cultivars. Crop Sci. 29:848-53. Win, K., and K. Win. 1990. Experience in rice improvement of Burma 1830-1985. IRRI Res. Paper Series (in process). World Climate Research Program. 1990. Global Change. Geneva, Switzerland: World Meteorol. Org. and Int. Council of Scientific Unions. Wu, H. P. 1968. Studies on the quantitative inheritance of Oryza sativa L.l. Diallel analysis of heading time and plant height in F 1 progeny. Bot. Bull. Acad. Sin. 9(2):1-9. Wu, H. K., and M. C. Chung. 1988. Identification of extra chromosomes of six IR36 Triplo lines. Rice Genet. Newslett. 5:41-6. Wu, R., Z. Peng, T. Kao, E. Moon, andY. Cai. 1986. "Molecular cloning and sequencing of rice genes." In Rice Genetics, 825-38. Los Banos, Philippines: IRRI. Xu, Y. B., and Z. T. Shen. 1988. Maternal effect on chalkiness in rice kernels. Rice Genet. Newslett. 5:111-3. Yamada, Y., Z. Q. Yang, and D. T. Tang. 1985. Regeneration of rice plants from protoplasts. Rice Genet. Newslett. 2:94-5. Yamaguchi, H., and H. Kakiuchi. 1983. Electrophoretic analysis of mitochondrial DNA from normal and male-sterile cytoplasms in rice. Japan. J. Genet. 58:607-11. Yang, Z. Q., T. Shikanai, andY. Yamada. 1988. Asymmetric hybridization between cytoplasmic male-sterile (CMS) and fertile rice (Oryza sativa L.) protoplasts. Theor. Appl. Genet. 76(6):801-8. Yao, S. Y., M. T. Henderson, and N. E. Jodon. 1958. Cryptic structural hybridity as a probable cause of sterility in intervarietal hybrids of cultivated rice, Oryza sativa L. Cytologia 23:46-55. Yoshida, S. 1981. Fundamentals of Rice Crop Science. Los Banos, Philippines: IRRI. Yoshida, S., J. H. Cock, and F. T. Parao. 1972. "Physiological aspects of high yields." In Rice Breeding, 455-67. Los Banos, Philippines: IRRI. Yuan, L. P., and S. S. Virmani. 1988. "Status of hybrid rice research and development." In Hybrid Rice, 7-24. Los Banos, Philippines: IRRI. Yuan, L. P., S. S. Virmani, and C. X. Mao. 1989. "Hybrid rice: achievements and outlook." In Progress in Irrigated Rice Research, 219-35. Los Banos, Philippines: IRRI. Zaman, F. V., E. A. Siddiq, and A. B. Prasad. 1985. Genetical analysis of gel consistency in rice. Indian J. Genet. 45:111-8. Zapata, F. J., R. R. Aldemita, A. U. Novero, L. B. Torrizo, L. B. Magaling, A. M. Mazaredo, R. M. Visperais, M. S. Lim, and H. P. Moon. 1986. IRRI-

GENETICS AND BREEDING

101

Korea collaborative project for the development of cold-tolerant lines through anther culture. IRRI. Res. Paper Series 118. Los Banos, Philippines: IRRI. Zapata, F. J., M. Akbar, D. Senadhiru, and D. V. Seshu. 1989. Salt tolerance of anther culture-derived rice lines. Int. Rice Res. Newslett. 14(1):6-7. Zhao, X. P., T. Wu, Y. Xie, and R. Wu. 1989. Genome specific repetitive DNA sequence in the genus Oryza. Theor. Appl. Genet. 78(2):201-9.

4 Rice Culture Duane S. Mikkelsen University of California, Davis

Surajit K. De Datta International Rice Research Institute

Rice is unique among the world's major food crops by virtue of the extent and variety of its uses and its adaptability to a broad range of climatic, edaphic, and cultural conditions. It is usually grown under shallow flood or "wet paddy" conditions but is also cultured where floodwaters may be several meters deep and, at the opposite extreme, as an upland cereal. Although rice appears to have a high water requirement, its requirement is actually not much different from that of other field crops. Unlike most cereal crops, however, rice benefits from standing water. It is capable of anaerobic respiration and has aerenchyma tissue in the aerial organs through which oxygen diffuses to the roots. Its unique ability to grow and produce high caloric food values per unit area on all types ofland and water regimes, combined with its adaptation to a wide variety of climates and agricultural conditions, make rice the world's most important cereal crop. Thousands of cultivars are grown throughout the world, representing a wide range of plant and grain characteristics. The crop was planted on some 144,641,000 ha of land (1985-87) which produced 468,275,000 metric tons of rice with an average world yield of 3.2 t/ha. The significance of rice is shown in its widespread use as a staple food by more than half of the world's population. Millions of people in Asia subsist almost entirely on rice. Most countries rely almost entirely on domestic production to feed their populations, with only about 103

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Rest of world (2.8%)

Latin America (3.9Cfo)

South Asia (23.5%) East Asia

(45.4%)

Southeast Asia (22.2 Cfo)

Figure 4-1. Regional distribution of world rice production (298 million tons milled rice), 1987 (IRRI 1988a).

4% of the world's rice production reaching the international market (FAO 1989). More than 90% of world's rice is produced in Asia (Fig. 4-1). The estimated area and production of rice for the years 1985-87, by selected countries and regions, are shown in Table 4-1. The average yields of rough rice per hectare in each region of the world are shown as follows: Location

tlha

Asia Latin America Africa United States Rest of World World

3.3 2.3 1.9 6.2 4.8 3.2

According to Chang (1976), the two cultivated species of rice, Oryza

RICE CULTURE

105

sativa and 0. glaberrima, developed from a common progenitor, progressively from a wild perennial to a wild annual, and ultimately a cultivated annual. Through diversification accelerated by climatic changes, human dispersal and selection over a wide range of latitude and altitude, plus manipulation for cultural adaptation, many different cultivars have been developed. From its origin in ancient India, 0. sativa was dispersed to north and central China, where puddling and transplanting techniques were developed. In Southeast Asia, upland rice culture occurred first. Planting progressed from shifting cultivation to direct sowing in prepared fields, with later transplanting into bunded fields. The dispersal of 0. sativa has led to the development of three ecogeographical races: indica, japonica, and javanica, each grown with cultural practices ranging from upland to lowland and to deepwater cultures. 0. glaberrima developed somewhat later than 0. sativa and is grown largely in Africa. The tropical race, indica, has spread through the humid tropics, the Middle East, Europe, and Africa. Bold grain, tall javanica races have spread through parts of Asia and many contiguous island areas, including Indonesia, the Philippines, Taiwan, and Japan. The cool-season race, japonica, was developed in the lower Yangtze River area of China, from where it was introduced into Korea, Japan, and later to southern Europe, the U.S.S.R., the United States, and South America. With distribution of rice cultivars to the high latitudes, cultivar changes occurred in response to low temperature and short photoperiod. This was accompanied by selection for short plant stature and plants with more determinate tillering and uniform heading. In the high latitudes of the world, rice can be grown only during the warm season of the year. Great genetic diversity exists, as shown by the fact that more than 83,000 rice cultivars are currently identified at the International Rice Research Institute (IRRI) by differences in adaptability to various climates, soil and water requirements, agronomic characteristics of plant type, growth duration, photoperiodism, grain type, and quality. The main theater of rice production is found on the Asian continent and adjacent islands which lie in the tropical and subtropical regions. Much of the Asian rice is produced in the monsoon area where abundant rainfall, plus some supplementary irrigation, provides an edaphic advantage. Rice production is concentrated in areas where water management is convenient on flat lowlands, river basins, and delta areas. The continental monsoon varies from year to year, however, creating an instability in rice production which can be overcome only by adequate supplementary irrigation. Within the Asian area, regional monsoons, trade winds, typhoons, and tropical depressions create a pattern of distinct wet and dry seasons and add variability to the climatic features from year to year. The monsoon season-from June to December in the tropics north of the

0o-

Asia Afghanistan Bangladesh Cambodia China India Indonesia Iran Japan Korea, DPR Korea, Republic Laos Myanmar Nepal Pakistan Philippines Sri Lanka Thailand Turkey Vietnam

Major Rice Producing Countries, Regions, and World

129,530 211 10,229 1,717 32,798 40,991 9,889 493 2,298 858 1,229 599 4,718 1,352 2,010 3,426 851 9,378 57 5,691

1.1 5.3 2.1 4.0 3.7 6.3 7.0 6.4 2.2 3.2 1.9 2.4 2.7 2.9 2.0 4.9 2.8

3.3 2.2 2.2

428,968 468 22,350 1,933 174,934 87,335 39,474 1,841 14,379 6,000 7,824 1,342 15,012 2,508 4,754 9,135 2,498 18,887 275 15,891

Production (thousand t)

(1985-87)

Yield (t/ ha)

ROUGH RICE

Area (thousand ha)

Table 4-1. Rice Production

100 12 10 93 35 63 100 98 67 91 11 17 21 100 43 63 14 100 40

Irrigated

37 17 0 0 20 8 40 56 65 0 43 29 69 0 31

5

0 53 37

Rainfed Lowland (0-50 em) 0 15 7 0 7 3 0 0 0 0 0 9 7 0 2 I 9 0 14

Deepwater (51-100 em)

0 8

5

0 11 21 0 6 3 0 0 0 0 0 3 4 0 0 0

Floating (>199 em)

DISTRIBUTION OF RICE AREA(%)

0 9 25 2 15 14 0 2 13 I 49 15 3 0 12 7 3 0 7

Upland

40

30 17 28 58 72 12 100 60 22 15 49 36 49 87 89 13

Areas Planted to Modern Varieties

......

!::3

Latin America Argentina Brazil Colombia Cuba Dominican Republic Ecuador Guyana Mexico Peru Surinam Uruguay Venezuela Africa Ivory Coast Egypt Guinea Liberia Madagascar Nigeria Sierra Leone Tanzania Zaire United States Rest of the world World

143 5,368 418 423 560 232 1,183 717 350 318 337 972 1,165 144,641

84

7,606 108 5,457 378 156 101 173 87 189 203 75

2.3 3.7 1.8 4.8 3.4 4.0 2.7 3.7 3.4 4.7 4.0 4.7 2.6 1.9 1.3 5.9 0.8 1.2 1.9 2.0 1.4 1.6 0.9 6.2 4.8 3.2 17,733 401 9,956 1,804 528 399 653 324 644 950 299 399 365 9,924 532 2,514 466 288 2,201 1,449 483 515 303 6,029 5,621 468,275 0 0 0 3

8

53

0 23

-

-

-

-

I

0 0 3 0 4 12 70 4564617326450

0

-

90

6 100 5 0 31 16 0 10 5 100

0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0

0 6 0 0 0 50 0 0 0 0 0 0

100 18 65 100 98 40 95 41 84 100 100

13

0

90

87 0 47 94 19 55 67 26

0 76 35 0 2 10 5 59 16 0 0 10

100

85 80 100 100 85 88 95 100 94 100 100 100

108

RICE: PRODUCTION

equator and from November to April south of the equator-constitutes the area of the so-called "monsoon" rice crop. While the bulk of the rice production is centered in wet tropical climates, the crop flourishes in humid regions of the subtropics and temperate climates such as Egypt, Japan, Korea, Spain, Portugal, Italy, South, and Central America, Hungary, the U.S.S.R., the United States, France, and Australia. The highest grain yields have been recorded between 30° and 45° latitude, while the producing areas extend from about 5l 0 N to 35°S latitude. Various explanations have been suggested for the higher rice yields obtained in the higher latitudes of the world. These include longer day length and higher solar energy, varietal differences (japonica in higher latitudes), more favorable soil conditions, better water control, and fewer disease and insect problems. The rice plant is unique in that it is adaptable to a wide range of climatic and environmental conditions ranging from upland and lowland to deepwater culture. Cultivars have been developed which meet the wide range of conditions under which rice is grown as a commercial crop.

CLIMATIC FACTORS AFFECTING RICE PRODUCTION

The distribution of rice production over the world is controlled primarily by climatic variables that ideally should provide adequate water during the entire growing season, relatively high air and soil temperatures, adequate solar radiation, the absence of destructive storms, a moderately long growing season, and relatively rain-free conditions during the ripening period. Important edaphic factors include the need for relatively levelland with poor internal drainage and favorable chemical and physical properties in the soil itself. A calendar of planting and harvest times is shown in Table 4-2 for the various rice-growing countries of the world. Precipitation and Water

Water, often in the form of precipitation, is the most important factor influencing the distribution of rice in the world, and also its growth and yield potential. The growth of all rice varieties is favored by flooding, and yields have been increased as much as 53% over adequately irrigated but nonflooded culture (Senewiratne and Mikkelsen 1961). Although rice benefits from a flooded soil environment, it requires no more water than most upland field crops. The major benefits from a flooded soil are the enhanced availability of nutrients, especially N, P, Fe, and Mn, enhanced nitrogen fixation, less competition from weeds, and favorable microclimatic regulation. Nonflooded culture initially favors seedling growth but

RICE CULTURE

109

is unfavorable for tiller production, vegetative and reproductive growth, and ultimate yield. Consequently, rice is preferentially grown only in the rainy season except where water storage and irrigation facilities are available. Total seasonal precipitation, as well as its intensity and distribution, is extremely important. Under rain-fed lowland rice culture, a desirable rainfall pattern provides abundant precipitation at the beginning of the rice season to allow timely land preparation, transplanting, or broadcast seeding of the crop. Less frequent rainfall is needed during the vegetative phase, but it should be sufficient to replace losses due to evaporation, transpiration, percolation, and runoff. Ideally, during the reproductive and ripening phases, solar radiation should be high to favor photosynthesis and grain formation. Water stresses during these phases are particularly damaging to grain production. Rainy weather during the flowering period, often accompanied by a lowering of temperature, may also adversely affect normal pollination and increase the percentage of sterile spikelets. Since rice is unable to make full use of the total annual rainfall, only the precipitation occurring during the cropping period is directly beneficial. As a rule, between 70 and 90% of the total rainfall during cropping effectively benefits the crop. The intensity and distribution of the rainfall, the water retention characteristics of the soil, various field losses, and water conserving cultural practices all affect water availability. With rain-fed flooded rice culture, the major determinants of crop water requirements are surface runoff, percolation losses, and evapotranspiration. Where it is feasible, a portion of the potential surface runoff should be restricted by surrounding bunds, but when continuous precipitation exceeds 50 to 80 mm day, runoff is likely to occur. Water is also lost by percolation depending upon soil type, land preparation practices, and depth of the water table. Percolation rates may vary from I mm/day in well-puddled clay soils to 3 to 10 mm/day in coarse textured soils with deepwater tables. Studies on the role of percolation rate on productivity of lowland rice soils have reached diverse conclusions. Chinese workers observed that draining lowland rice soils for short periods during vegetative growth greatly improved soil aeration and suggested that this may be favorable for rice growth (Cheng 1981). Japanese researchers suggest that a percolation rate of 10 to 20 mm/day is essential to get high rice grain yields (De Datta 1981; Hasegawa et al. 1985). Recent results at IRRI (Sharma et al. 1989a) suggest that percolation significantly benefited rice grain yield only in acidic soils and those rich in organic matter. In silty clay loam, with 10.5% organic matter and pH of 5.2, a percolation rate of 40 mm/day increased grain yield by about 21% over that with no percolation control. In soils having less than 5.1% organic matter, grain yield remained unaf-

_,.

0

Asia Bangladesh: Aus T. aman B. aman Boro Myanmar: Main Second China: Early crop Intermediate" Late rice Northern India: Kharif: Early Main Rabi (summer) Indonesiah: Main: Java S. Sulawesi N. Sumatra S. Sumatra

Crop and Country

Sept. Aug.-Sept. Nov.-Jan. April-May March-May Aug.-Sept. Jan.-March April-June

June-July Aug.-Oct. Oct.-Nov.

June-Dec. Nov.-April March-June Feb.-June Aug.-Oct. Dec.-March Jan.-June

Feb.-May March-May June-July Mid-April to Mid-June March-May June-Oct. Nov.-Feb. Oct.-March May-June July-Nov. Oct.-Jan.

July Sept.

Dec. April

Nov.-Jan. March-May

June Nov.

July-Aug. Dec.

Bulk of Harvest

July-Sept. Nov.-Jan. Late Oct.-Dec. April-May

Harvest

April July-Aug. April Dec.

Planting

Table 4-2. Rice Crop Calendar by Country

.... ~

Iraq Japan Kampuchea: Main Second Korea DPR Korea Rep Laos Lebanon Malaysia: Main: West Sabah Sarawak Second: West Nepal: Early Late Pakistan Philippines: Main Second Third

Second: Java S. Sulawesi N. Sumatra S. Sumatra Oct.

Dec.-Feb. Jan.-Feb. Sept.

Early Nov.

Late Aug. to Mid-Nov. Sept.-Nov. Dec.-Jan. March Sept.-Oct. Oct.-Nov. Nov.-Dec. Sept.-Oct. Nov.-March Jan.-March March-April July-Oct. Aug.-Sept. Nov. Mid-Oct. to Nov. Nov.-Jan. April-June Sept.-Nov .

May April-May June-July Dec.-Jan. May-June June-July June-Aug. May Sept.-Oct. June-Aug. Oct.-Nov. April-May Late May-Aug. June-July Mid-April to Mid-July July-Sept. Jan.-Feb. May-June

Dec. May

Sept. Oct.

July-Sept. May Aug.-Sept. Sept.-Oct.

July-Oct. April-June Aug.-Sept. Sept.-Oct.

April-June Nov.-Feb. May-June June-July

...... j\j

Saudi Arabia Sri Lanka Maha (main) Yala Syria Taiwan, China: Main Second Thailand: Main: North Northeast Central South Second Turkey Vietnam lOth month (main): North Central South Winter-spring North Central South

Crop and Country

Table 4-2. Continued

Nov. Feb.-March Aug.-Sept. Mid-Sept. to Oct. May-July Sept.-Nov. Nov.-Jan. Nov.-Jan. Nov.-Feb. March-May June-Aug. Sept.-Oct. Late Sept.-Nov. Sept. to Mid-Dec. Late Nov.-Feb. May-June April-May

Oct.-Nov. April-May July-May Jan.-March May to Mid-Aug. May-June June-Aug. June-July Sept.-Nov. Jan.-May April-May May-Early Sept. May-Sept. May-Early Oct. Jan.-Early March Jan.-Early March Mid-Dec. to Early March

Harvest

July

Planting

March-May

Oct.

Nov.-Jan.

June Oct.

Oct.

Feb.

Bulk of Harvest

c;';

......

5th month spring Summer-fall: North Central South South America Argentina Bolivia Brazil: South Northeast North Chile Colombia: Summer (main) Winter Ecuador: Winter (main) Summer French Guiana: Upland Lowland Guyana: Autumn (main) Spring Paraguay Peru Surinam: First Second Aug.-Sept. Late July-Sept. July-Oct. Mid-March to Mid-June Jan.-March Feb.-May Aug.-Oct. April-June March-April June-Aug. Dec.-Feb. April-June Aug.-Dec.

April-May April-May April-June Mid-Sept. to Mid-Dec. Oct.-Nov. Aug.-Dec. March-May Nov.-Dec. Oct.-Nov. March-April Dec.-Feb. May-Aug.

Sept.-Oct. Feb.-May Jan.-March May-July Sept.-Oct. March-April

May-June Dec.-Jan. Sept.-Dec. Jan.-Feb. April-May Oct.-Nov.

March-Oct. Whole year-round

May-June

Oct.-Nov.

Oct. March-April Feb.-March July

May

March-April Oct. May April

April Feb.-March

~

.....

June-July April-May

March-April Sept.-Oct. Sept.-Oct. Dec.-Jan. Mid-Sept. to Mid-Jan. Nov.-Feb.

March-June

Oct.-Nov. April-May April-May Dec.-Jan. Mid-March to Mid-July June-July

Nov.-Dec. Aug.-Sept. Aug.-Dec. July-Dec. Jan.-Feb. Oct.-Dec. Aug.-Dec.

Sept.-Dec. March-May

April-June Oct.-Nov.

April-Aug.

Feb. Oct.

Jan.-Feb. Sept.-Nov.

April-June

Nov. Dec.

Oct.

Nov. Nov.

Oct.-Dec.

Oct.-Dec.

April-May

March-July

Oct.-Dec.

Bulk l~{ Harvest

Uruguay Venezuela: Spring Winter Central and North America Belize: Main Second Costa Rica: North South Cuba Dominican Republic: Spring (main) Winter El Salvador Guatemala Haiti: First Second Honduras Jamaica Mexico Nicaragua

Harvest

Planting

Crop and Country

Table 4-2. Continued

~

en

Panama: Main Second St. Lucia Trinidad & Tobago United States: Gulf California Africa Algeria Angola Benin Burundi Cameroon: North South' Central African Rep Chad Congo Egypt: North (main) South Ethiopia Gambia Gabon Ghana Guinea: Major Minor Ivory Coast Late Aug.-Sept. Oct.

June

Aug.-Oct. Mid-Sept. to Nov. Mid-Sept. to Mid-Oct. Mid-March to Mid-May Mid-Aug. to Mid-Dec. Mid-May to Mid-July Nov.-Dec. Dec.-Jan. Nov. Oct.-Dec. April-May Mid-Sept. to Oct. Dec.-Jan. Dec.-Jan. Oct.-Nov. Mid-May to Mid-June Mid-July to Mid-Oct. Sept.-Oct. Oct.-Jan. Mid Aug. to Mid-Dec.

April-June April-June April-May Mid-Oct. to Mid-July Mid-April to Mid-July Mid-Oct. to Mid-Dec. June-July Aug. July June-July Nov. Late April-June July-Aug. April-June June-July Mid-Nov. to Mid-Jan. Mid-March to Mid-May April-May May-Aug. March-July

Oct.

Oct.

Dec.

Nov. Nov.

June-Early Aug.

Sept.

Aug.-Oct. Dec.-Jan. Nov.-Dec. Late Oct.-Early Dec.

April-May Aug.-Sept.

......

c>

Kenya: Main Second Liberia: Upland Swamp Madagascar Mali Malawi Mauritania Mauritius Morocco Mozambique Niger Nigeria Rwanda Senegal: Casanance Fleuve Sierra Leone: Upland Inland swamp Mangrove swamp Boliland Riverain

Crop and Country

Table 4-2. Continued

Nov.-Jan. Oct.-Dec. Aug.-Oct. Sept.-Dec. Dec.-Jan. Dec.-Jan. Dec.-Jan.

Mid-July to Mid-Aug. Mid-April to May Mid-Oct. to Mid-Dec. June-July June-July May-June May-July July-Aug. May-July April-May

Nov.-Dec. June-July

Harvest

Sept. to Mid-Dec. Dec.-Jan. April-June Late Nov.-Jan. April-June Oct.-Nov. May-June July-Aug. May-June Mid-Nov. to Mid-Dec. Aug.-Sept. Mid-May to Mid-July

Mid-April to July July-Aug. Oct.-Nov. June-July Mid-Nov. to Dec. June

Planting

Nov.

Oct. June

Aug. June

Nov.

Oct.

Bulk of Harvest

...... ...... -..1

Somalia Sudan Swaziland: Main Second Tanzania: Mainland Zanzibar Togo Uganda: First crop Second crop Third crop Upper Volta Zaire: North South Western Europe France Greece Italy Portugal Spain Eastern Europe Albania Bulgaria Hungary Romania Mid-Feb. July-Aug. June-July Oct.-Nov.

Jan.-Feb. April-July June-Oct. June-Aug. Mid-Oct. to Mid-Nov. Jan.-Feb. June-July Sept.-Nov. Mid-Oct. to Mid-Nov. June Jan. Sept.-Oct. Sept.-Oct. End Aug.-Early Nov. Aug.-Oct. Sept.-Oct. Oct. July-Aug. Sept.-Oct. Sept.-Oct.

May

Mid-May to Mid-July Feb. Oct. March-April May April-May March-May May April-May March-April April-May April-May

Oct. Aug. Oct. Oct.

Oct. Sept. Sept. Sept. Sept.

Mid-Sept.

Sept. Oct.

May June

~

cP

April

March-May April-May April-May June-July

Oct. Nov. Feb.-July May-Aug. Whole year round April-May

" Includes single crop late rice. b If irrigation is available, especially in Java and Bali, rice is harvested whole year-round and in some sites a third rice crop can be harvested at least once every 2 years. Java accounts for 62% of the total rice crop. Source: USDA. 1983. Foreign Agriculture Circular. Grains. Reference Tables on Rice-Utilization for Individual Countries. Washington.

Sept.

Aug.-Sept.

April-May

Bulk of Harvest

U.S.S.R. Oceania Australia: New South Wales Western Australia Fiji Papua New Guinea Solomon Islands Tonga

Harvest

Planting

Crop and Country

Table 4-2. Continued

RICE CULTURE

119

fected by percolation rate. Possible causes were the fast degradation of organic acids and other phytotoxins at higher soil temperatures produced during the decomposition of organic matter. Another study by the same authors (Sharma et al. 1989b) reported from a field trial that rice yield and root length density remain unaffected by the addition of 6 t/ha of rice straw and by percolation rate of 9 and 123 mm/day. Evapotranspiration values vary according to local climatic conditions, cropping practices, and phase of plant development. Evapotranspiration in humid climates is fairly consistent between 3.5 and 6 mm/day where advective energy is relatively small to 8 mm/day with a high advective influence. Transpiration losses vary with temperature, humidity, wind velocity, water management practices, and plant growth stages. Generally, transpiration increases with total crop leaf area. Transpiration is relatively slow after transplanting, then increases with tillering, reaching a peak at heading and decreasing with grain ripening. Evaporation likewise varies with climatic and crop density factors but generally reaches its maximum rate during the seedling stage and decreases as the plant canopy shades the water. The net water requirement for rice grown in tropical Asia varies from 750 to 2500 mm with the average about 1250 mm. Of this amount, 40 mm is allocated for seedling nursery purposes, 210 mm for land preparation, and about 1000 for irrigation purposes. Typical water requirements in various areas include 2.5-4.5 acre-ft/season in Japan, 6.0 in Thailand, 4.0 in Indochina, and 4 to 6 in Sri Lanka, Australia, and the United States. Excessive rainfall can be a major source of crop loss where flooding cannot be controlled and crops are inundated. In parts of Asia and Africa, special deepwater or "floating rice" varieties must be grown to tolerate deep flooding. Irrigated lowland rice covers about 50% of the rice-growing area of the world. Irrigation allows complete control of water application and depth and is becoming the major system of world rice culture. In temperate Asia-China, Japan, Korea, and Pakistan-most riceland is irrigated. In the United States, Australia, and Latin America-Argentina, Columbia, Cuba, Dominican Republic, Guyana, Surinam, Uruguay, and Venezuela-and Egypt in Africa, most of the rice area is also irrigated (see Table 4-1).

Temperature

In temperate regions, temperature is a limiting factor in rice culture. In the main rice-growing season of the Asian tropics-particularly India, Myanmar, Malaysia, Vietnam, Indonesia, Thailand, and the Philippines-temperature is more or less constant and within safe limits. How-

120

RICE: PRODUCTION

ever, in rice-farming regions far from the equator, low temperatures during seedling and early vegetative phases cause slow growth of some varieties. In areas of northern India and Bangladesh, where three crops a year are grown, even a photoperiod-insensitive variety may take 20 to 40 days longer to mature when planted in December or January than it does when planted in March through June. Rice is adaptable to areas with abundant sunshine and average temperatures above 20 to 38°C (68-1 00°F). Temperatures below 15°C (59°F) retard seedling development, delay transplanting, slow tiller formation, delay reproductive growth, and consequently reduce grain yields. The lower temperature limits for germination are difficult to estimate and vary with variety, but germination proceeds only slowly at 1ooc (50°F). The optimum temperature for germination is in the range of 18 to 33°C (64-91.4°F) with seeds of most varieties germinating more rapidly at the higher temperatures than the lower ones. At 42°C (108°F), germination is arrested; at 50°C (122°F) the seed is killed. Critical air temperatures are 15 to 15.SOC (59-60°F) for transplanting seedlings from lowland nurseries, 14 to 15°C (57.2-59°F) from semi-irrigated beds, and 13 to 13.SOC (35.4-56.SOF) for seedlings from upland nurseries. Rice rooting occurs over a range of 19 to 33°C (66.2-91.4°F), 25 to 28°C optimum (77-82.4°F), with root inhibition occurring below 16°C (60.8°F) and above 35°C (95°F). Top growth is generally linear between 18 and 33°C (64.4 and 91.4°F), but above and below that range, growth notably decreases. As a rule, water temperature is more critical than air temperature because the growing meristem is usually under water. Sasaki (1927) reported that leaf elongation increases with temperature in the range of 17 to 31°C (52.6-87.8°F), but decreases and practically ceases at 45°C (113°F). The lower limit for leaf elongation is 7 to 8°C (44.6-46.4°F). Tillering is a complex relationship involving an interaction between carbohydrate metabolism, solar radiation, and temperature. Tillering is generally favorably affected in the range of 15 to 33°C (59-91.4°F). Anthesis generally begins at the same time as panicle emergence from the sheath. Morning temperatures, rather than daily mean temperatures, determine the start of flowering. Sakai (1949) states that 29 to 31 oc (84-88°F) appears to be the most favorable temperature range for the opening of spikelets and for effective pollination. Flowering is usually stimulated by high temperatures, although variations occur among cultivars. Patterns of temperature variation during each crop season and sequential changes from season to season are complex and affect plant growth and maturity in different ways. As a rule, the annual mean temperature decreases from lower to higher latitudes and altitudes. In the tropics, rice can usually be planted in any month of the year since temperature variations are only slight from season to season and day to night. Temperature

RICE CULTURE

121

differences do not usually cause yield fluctuations in the elevations near sea level in the tropics. Even so, low temperature at high altitudes may be a problem for tropical varieties, and high temperature near sea level during flowering and grain formation may cause damage. In subtropical and temperate areas, temperatures usually increase from spring to summer and decrease again in autumn, thus limiting the growing season. Air and root-zone temperatures may change considerably from night to day and from season to season, affecting nutrient uptake, vegetative, and reproductive development and grain ripening. The effects of temperature on rice plant growth can be evaluated by relating phenological data to heat summation units or day-degrees. Heat summation data for all the growing days above the baseline of a mean daily temperature show that the lower range is probably between 898 and 1206°C (1649 and 2204°F) and that most varieties need an accumulated temperature of 1639 and 1978°C (2982-3593°F). Nuttonson (1951) computed day-degree summation with a 10°C (50°F) baseline from the sown to ripe period of nontropical cultivars showing a range of 373°C (704°F) in the U.S.S.R. (lat. 43° 40'N) to over 1516°C (2760°F) in Texas (lat. 30°04'N). IRRI research (Bhattacharyya and De Datta 1971) reported that low temperatures at the early vegetative phase retarded the growth of shoots and roots. A temperature of l5°C delayed panicle initiation by 17 days and extended the time required for complete heading. Crop maturity was proportionately delayed. The rice plants were highly sensitive to cool soil and water temperatures during panicle development. Heading was delayed at low temperature and it took longer for all panicles to emerge. Grain yields were significantly decreased by a 15°C soil temperature during this period. Photoperiod

The photoperiod, or day length, the duration of the light period between sunrise and sunset, including the twilight hours, is a major factor influencing the development of the rice plant, especially its flowering characteristics (Chang and Vergara 1972). Although rice is considered a short-day plant (short days decrease their growth duration), cultivars differ widely in sensitivity. The daylight hours fluctuate during the year and vary with latitude. The day length is shortest in winter, increasing gradually toward summer, with the greatest changes occurring in the high latitude areas. In the tropics the maximum photoperiod difference is less than 3 h/day, but in the warm temperate zones, the difference in photoperiod may be as much as 5 h. Photoperiod-sensitive cultivars flower when the decreasing day length reaches a critical point. Day length also exerts a large effect on the growth duration of rice cultivars, depending upon their photoperiod sensitivity.

122

RICE: PRODUCTION

The response is seen largely through changes in the basic vegetative growth pattern, especially the duration of the reproductive phase. Photoperiod sensitivity (the critical day length required for flowering) varies greatly, some cultivars being referred to as nonseasonal or neutral, others as weakly photoperiod sensitive, and others as strongly photoperiod-sensitive. Weakly sensitive cultivars vary only slightly in growth duration from the time of planting to harvest, while those termed strongly sensitive can be planted only during seasons with long day length. Photoperiods that are longer or shorter than the optimum delay the flowering of photoperiodsensitive cultivars. The range of diversity among cultivars is very large with virtually no cultivars showing a long day response. The practical aspect of photoperiod sensitivity is that farmers must select carefully among the variety of cultivars, since the degree of sensitivity will determine the growth duration, maturity date, and potential yield of a crop as well as cultivar adaptation to double cropping. In tropical areas, photoperiod-sensitive cultivars have traditionally been selected because they could be planted when the monsoon rains begin and be harvested at a fixed time after rains cease and floodwaters recede. Such cultivars utilize the high solar radiation at the late growth stages which has a beneficial effect on yields. Solar Radiation

Solar radiation and sunshine hours are important climatic determinants in rice production. Numerous studies have shown a close correlation between solar radiation, plant growth and yield (Moomaw et al. 1967; Stansel 1975). Young seedlings have a comparatively low solar radiation requirement so shading at early stages exerts only small effects on ultimate yield. Light becomes progressively more important through the vegetative and reproductive phases, reaching maximum importance at the heading stage. The need for solar energy is most critical from panicle differentiation to about 10 days before maturity (Stansel1975). Results at IRRI (Moomaw et al. 1967) show that high grain yields were strongly correlated with total solar radiation between 30 and 45 days before harvest (De Datta and Zarate 1970). Although postflowering itradiance is clearly an important determinant of grain yield, irradiance during earlier periods of development may be at least as important and possibly more so. The greater importance of preflowering irradiance shown by shading experiments is also supported by Yoshida's (1973) results with the C02 enrichment of rice crops at various stages before and after flowering; Yoshida's study was based on the assumption that both C02 enrichment and high irradiance increase

RICE CULTURE

123

photosynthesis. Grain yield increased 30% by enrichment for 33 days before flowering, but only 10% by enrichment for 30 days after flowering (Evans and De Datta 1979). Results at IRRI (Evans and De Datta 1979) showed significant correlations between yields of all test varieties and irradiance (over 20- or 30-day intervals) during crop reproductive and ripening phases. Regardless of whether irradiance rises or falls progressively, high irradiance at any stage after panicle initiation is associated with higher yields in both older and modern varieties. Responsiveness to irradiance was greater at higher application levels of nitrogen fertilizer. The amount of sunlight a crop receives depends on solar radiation intensity, day length, cloud cover, and mutual shading by the plants in a population. Day length and solar radiation intensity are determined by geographical location and changing seasons as modified by cloud cover. Mutual shading is the shading of one plant part by others. Plant type and leaf arrangement play an important role in the energy absorption characteristics of the plant canopy. The effects of mutual shading in the tropics are most critical where days are shorter and midday intensity is high for relatively short periods. Cloudiness greatly reduces the period of energy absorption, especially during the monsoon. Many rice growing areas have distinct wet and dry seasons which greatly affect solar radiation. Mean daily solar radiation values during the main rice-growing season are lower in the tropics than in the temperate zone, which may account in part for yield differences in the two areas. Tropical Storms

Tropical storms of various types, often violent and destructive to the rice crop, include tropical cyclones that originate in the low-latitude oceanic areas and move rapidly as violent hurricanes or typhoons, cyclonic depressions developing in the middle and high latitudes; and, to a lesser extent, tornadoes. If they occur after the heading of the rice, they may cause severe lodging and shatter loss in some varieties. Strong winds just before heading may also cause a decrease in the number of spikelets per panicle. High winds during pollination will induce sterility, while continued strong winds have been shown to reduce photosynthesis and promote the spread of bacterial diseases both in temperate and tropical rice areas. Strong winds and rains that mechanically damage the leaves are responsible for grain losses through increased shatter. Rice cultivars that are susceptible to mechanical damage of leaves and the shattering of the grain produce lower grain yields than less susceptible ones (Chang and Vergara 1972).

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SOIL CHARACTERISTICS AFFECTING RICE PRODUCTION

Over the centuries, a number of systems of rice production has evolved to fit local conditions of climate, soils, water supply, economics, and social conditions. Despite wide variations in culture, two main systems of soil management have evolved: (1) dry soil management, in which the land is prepared dry and the crop is seeded in the same manner as other cereal crops (this is referred to as upland rice culture but may also be practiced in irrigated lowland rice production), and (2) wet soil management, referred to as lowland or wetland culture, in which the land is flooded and all soil preparation is done in wet or submerged soil. Upland Rice Soils

Upland rice is grown under a wide range of soil conditions, on both flat and undulating fields that are not bunded to accumulate water. The fields are prepared for seeding in dry soil and are dependent on rainfall for crop moisture. The soil characteristics found in upland rice culture are nonspecific with respect to soil texture, pH, organic matter content, and slope, and soil fertility variations encompass virtually all possible conditions (De Datta and Feuer 1975). Moorman and Dudal (1965) suggest that soil texture and topography may be the most important soil characteristics for upland rice since they profoundly affect the moisture of the soil and its tilth for seeding. The textural profile of the surface and the subsoil layers is important in optimizing water penetration and storage. Soil structure figures prominently in tillage, desirable seedbed characteristics, moisture interception and conservation, and crop management practices. According to De Datta and Feuer (1975), vertisols and alfisols are the major soil groups used in upland rice culture in Southeast Asia and in tropical rain forest areas of Central and South America. Oxisols are of less importance in Southeast Asia except in Java but are of major importance in Central and South America and parts of Africa. Hydromorphic soils with shallow ground water, seepage areas, or surface waters during part of the growing season are often used for rice production. The gleyic cambisols, humic-gley soils, and entric fluvisols represent large upland rice areas in West Africa. A surface soil with medium to fine texture overlying a subsoil of finer texture is considered most desirable overall for upland rice. Together with good soil structure, which influences soil moisture storage potential and root penetration, these soils provide good conditions for upland rice production. Soil reaction for upland rice is most favorable over the pH range of 5.5 to 6.5, although most upland rice areas are more acidic. Ponnamperuma (1975) summarizes the growth-limiting

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factors in upland rice soils as being related primarily to the variable soil moisture regimes, and a nutrient status with less soluble iron, phosphorus, and silica than in flooded soils. Most plant nutrients occur in their oxidized forms, making nitrate-nitrogen and sulfate-sulfur susceptible to leaching. Potential problems on acid upland soils are manganese and aluminum toxicities and, on alkaline soils, iron deficiency. Lowland Rice Soils

A major portion of the rice in tropical, subtropical, and warm temperate regions is grown under conditions where the soil is flooded during the greater part of the growing season. Rice is physiologically, morphologically, and anatomically adapted to grow in wet or flooded soil conditions. The flooded culture provides benefits of weed control, improved water and air microclimates, improved soil fertility and moisture relations, and a root zone environment well suited for rice culture. Soils used for lowland rice culture are usually on level terrain or on terraces where standing water can be maintained. By virtue of their physiographic position, often accentuated by inundation and soil management practices for rice, these soils usually have strong hydromorphic characteristics and poor internal drainage but can be irrigated and drained in rice culture management. Lowland soils, particularly in Southeast Asia, are frequently prepared for planting while they are covered with several centimeters of water. The objectives of wet tillage (puddling) are to reduce the power requirements for land preparation, to control weeds and incorporate crop residues, to produce a "plow sole" to reduce percolation losses, and to develop a soft soil suitable for transplanting. From a physical viewpoint, puddling destroys soil aggregates, reducing them to a slurry. Puddling decreases the volume of soil macropores, increases bulk density, and reduces internal drainage, thereby increasing the water holding capacity of the soil (Sharma and De Datta 1986). Studies have shown that the physical properties of medium- to coarsetextured soils low in active clay are hardly changeable and that tillage does not improve rice growth (Lal 1985). Moreover, the prospects of satisfactory yield with no tillage or with minimum tillage have been demonstrated (Rodriguez and Lal 1985). Recent research (Mambani et al. 1989) concluded that tillage is not required to alleviate soil physical limitations in rain-fed lowland rice production in low permeable soils under an adequate climatic water balance. Wet tillage is a prerequisite for rice productivity in medium- to coarse-textured soils in drought-prone environments, although thorough puddling showed no advantage over shallow puddling. Incorporating crop residues before transplanting rice lessens the likeli-

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hood of toxicities from anaerobic decomposition products, accelerates the onset of soil reductive processes, and enhances the availability of some plant nutrients. In some countries, rice straw is returned to the soil; in others, it is burned in piles or rows. Decomposition of the rice straw returned to the soil causes changes in soil reduction and cation exchange capacity and helps maintain a balanced nutrient reserve in the soil. Keeping the soil continuously flooded throughout the growing period is recommended for high rice yields. However due to the uncertainty of rainfall or lack of adequate irrigation in tropical countries, rice fields are often subjected to varying moisture stress. Varying the water condition is expected to modify the flooding effects on Fe and Mn and, consequently, on Fe and Mn uptake by plants (Mandai and Mitra 1982). In a greenhouse study using two high-pH soils, applying rice straw increased IR36 straw and grain yields and Fe and Mn yields at different growth stages with 0.5% rice straw; Fez+ and Mn 2 + in the soil solution peaked early, and high Fe and Mn contents were obtained (Yodkeaw and De Datta 1989). The diffusion of oxygen into water is only 10- 4 of that in soil, so the exchange of oxygen from the atmosphere to the soil is extremely small. A few millimeters of soil beneath the soil-water boundary does contain small amounts of oxygen, and it remains in an oxidative condition. Beneath this thin oxygen sink, the soil remains largely in a reduced state through the metabolic activity of aerobic and facultative anaerobic microorganisms which either act directly as electron acceptors in anaerobic dissimilation reactions or by forming various organic decomposition products. The main chemical changes occurring in flooded soils are reviewed by Patrick and Mikkelsen (1971), Ponnamperuma (1972), and De Datta (1981). These include the following: 1. Gases such as C0 2 , CH4 , Nz, and Hz from microbial dissimilation products are accumulated. 2. The pH of acid soils increases while that of calcareous and sodic soils decreases. This change in pH of acid soils occurs when Fe++ iron and Mn + + manganese begin to precipitate and equilibrate with COz and HC03 in the soil solution. In alkaline soils, the acidifying effect of COz lowers the soil pH, which is buffered by Ca and Mg carbonates. 3. The change of NO], Mn+ +++,Fe+++, and S04 to their reduced forms is controlled by an established thermodynamic redox sequence found to occur in flooded soils. 4. Increased electrical conductivity is seen, correlated with HC03,

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Fe++, and Mn + + ion concentrations in acid soils and with Ca and Mg bicarbonate concentrations in alkaline soils. 5. The supply and production of NHt -N from both the native soil nitrogen and heterotrophic and autotrophic nitrogen-fixing organisms, is increased. Biological nitrogen fixation represents direct addition of nitrogen to the soil, while organic matter is mineralized more slowly and entails less immobilization, leaving a net increase in available N. 6. Increased availability of P, Fe, Mn, Si, and Mo is a consequence of reduction, dissolution, and desorption reactions. 7. The accumulation of toxic substances and the associated anaerobic decomposition of soluble carbohydrate materials may cause the formation of gases such as C0 2, CH4, N 2, and H 2, organic acids such as acetic, butyric, propionic, and formic acids, and H 2S from reduced sulfates in flooded soils. In the rice-growing areas of the world, the full development of yield potential is often limited by soil problems of a diverse nature. Problems of salinity and alkalinity, various toxicities, and especially strong acidity where high levels of soluble iron and aluminum are most common. Some of these constraints on yield can be corrected by proper soil treatment and management, but the costs involved are often beyond the means of farmers in developing countries. Rice varieties that can tolerate adverse soils are sought in current research. Results from such research could bring vast areas of unused land into productive use. Rice is grown over a wide range of soil characteristics, often through the ameliorating effects of flooding. About 80% of the world's rice production occurs on entisols and inceptisols where seasonal drainage problems occur. Vertisols, ultisols, and alfisols are commonly used where available water is sufficient and the terrain is flat or gently sloping. Oxisols are sometimes used in rice production in the tropical and subtropical areas, although the hilly terrain usually requires terracing. Organic soils (histosols) are not used widely for rice and are quite variable in their production capability. Kalimantan in Indonesia and Florida in the United States have large areas under histosols, some of which are grown to rice. BIOTIC FACTORS AFFECTING RICE PRODUCTION

Rice, like other plants, does not live alone in nature but in association with other organisms ranging from the soil microflora to mankind itself. This section briefly discusses the major biotic influences affecting the growth and yield of rice.

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Weed Pests

Weeds are universal competitors of rice, competing for moisture, light, and plant nutrients essential to plant growth and yield. Weeds also create problems in harvesting, drying, and cleaning, and reduce the quality and marketability of the crop. Insects pests such as leafhoppers and stemborers also live on weeds as alternate hosts and directly attack the rice crop, sometimes spreading virus diseases. Water management is often impeded when weeds block irrigation systems, slowing drainage. Mechanical harvest of rice is more expensive, as are cleaning and drying, when weeds grow in competition with the crop. There are some 30,000 different weed species regarded as serious rice pests in the world. Of these, 30 species are very damaging and some 88 species are noxious. Weed control issues are extensively reviewed in Weed Control in Rice (IRRI 1983). Matsunaka (1975), commenting on the world's worst rice pests, lists Echinochloa colonum, E. crusgalli, Sphenoclea zeylanica, Ischaemum rugosum, and Fimbristylis miliacea. In Southeast Asia, the major rice weeds are reportedly Echinochloa glabrescens (formerly E. crus-galli ssp. hispidula), E. colonum, Cyperus rotundus, C. difformis, Fimbristylis miliacea I, M onochoria uaginalis, and Sphenoclea zeylanica. Species making up the total weed complex vary widely in economic importance in different rice-growing regions and often differ between adjoining fields. The species, their density, and the duration of their competition all affect rice yields (Smith 1983; De Datta 1981). Upland culture

Weeds are a major barrier to satisfactory rice production wherever they occur but are especially troublesome in upland rice where their growth is less restricted and where conservation of available moisture is critical. Weeds in upland rice consist of both annual broadleafs, sedges, and grasses, and a wide variety of perennials, including some shrub species. Since rice is grown under such a wide range of climatic conditions, soil types, and crop rotations, it is not possible to identify the most damaging species. Echinochloa crus-galli, E. colonum, Cyperus rotundus, Rottboellia cochinchinensis, and lmperata cylindrica are serious weed pests in most upland rice areas of the world (Sankaran and De Datta 1985). The most common means of weed control in tropical areas is hand weeding, usually with a short-handled hoe, requiring about 300 man-h/ha. Cultivation with animal or machine power is also practiced, as well as weed burial and intercropping. Without satisfactory weed control, upland rice yields are severely restricted. Under moderate competition, weeds alone may reduce grain yields by 40 to 50%, and severe competition may

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cause complete crop failures (De Datta 1980). Moisture levels often dictate control of some of these weeds with herbicides (Pathak et al. 1989). Weed problems in upland conditions develop to serious proportions where intensive labor input is not available. In West Africa, Moody (1975) reports that present weed control methods (both cultivation and herbicides) are unsuitable for continuous or large-scale farming. Likewise, if cultivation areas are shifted once weeds become too prevalent, it is necessary to abandon the land to forest, a means used by early man to cope with upland weed problems. An understanding of environmental factors and their interactions in relation to rice-weed competition will be an important breakthrough in weed control research. Knowledge is being sought from some ecophysiological processes that are well-studied for various crops. Recent IRRI research (Ampong-Nyarko and De Datta 1989) suggests that C4-weeds in upland rice fields gave higher net photosynthetic rates than did Crupland rice varieties under all light intensities. Interspecific differences were observed in rice and weed response to water availability. Upland rice weeds gave lower leaf conductance, lower transpiration rate, and higher water use efficiency than did upland rice. The ability of rice to recover from early season competition partly explains the existence of critical periods in rice-weed competition. Lowland culture

Conditions in lowland rice culture favor the growth and reproduction of aquatic and semi-aquatic annual and perennial weeds. The most prevalent weeds are grasses, broadleaf weeds, and sedges, but submerged aquatic weeds and algae often have an adverse effect on rice growth. Among the most damaging lowland and aquatic weeds in rice (De Datta 1988a, c) are Echinochloa spp., Eichhornia crassipes, Fimbristylis spp., Cyperus spp., Monochoria vagina/is, Sagittaria spp., Salvinia spp., Polygonum spp., Marsilea quadrifolia, Alternanthera spp., Eclipta alba, Jussiaea spp., Sphenoclea zeylanica, and lschaemum rugosum. The control of weeds in flooded lowland is facilitated by thorough land preparation before planting. When this is properly done, most weed seeds fail to germinate and weeding becomes easier and less expensive. Straight row transplanting enables farmers to use push-type rotary weeders along the rows, providing a distinct advantage over random transplanting. Hand weeding, involving pulling or trampling the weeds into the mud, is a satisfactory alternative where rotary weeders are not available (AmpongNyarko and De Datta 1991). IRRI data show that, under average field conditions, hand weeding requires 120 man-h/ha, while similar rotary weeding takes 70 h. Effective rotary weeding requires adequate floodwater

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and a soft soil condition. Hand weeders cannot eliminate weeds if floodwater is maintained too deep in the fields, since the plants float and remain alive. Water management has long been known to be an effective means of weed control in both transplanted and directly seeded rice. The germination of weeds and the kinds of weeds that emerge are closely related to soil moisture content and depth of flooding. Research at IRRI has shown that continuous soil saturation (1-2.5 em deep) up to the late dough stage of rice allows more sedges to grow than grasses or broadleaves. Flooding at depths of 15 em from 4 days after transplanting to the late dough stage suppresses grass and sedge germination. Broadleaf weeds are not controlled by flooding (De Datta 1988a). Many herbicides are effective against broadleaf weeds, sedges, grasses, and submerged aquatic weeds. The concept of preemergence weed control with herbicides such as 2,4-D, 2-methyl-4-chlorophenoxyacetic acid (MCPA), butachlor, and thiobencarb has rapidly changed weed control practices in tropical Asia (De Datta and Ampong-Nyarko 1988). Insect Pests

Rice is grown under diverse conditions of climate and culture over a wide geographical range. Because of crop adaptability to warm, humid conditions, the survival and proliferation of insects are a great problem in the tropics and semitropics, diminishing somewhat in the temperate rice areas. More than 70 species of rice pests are known and some 20 have major significance. They attack virtually all parts of the rice plant at all growth stages. Insects also serve as vectors of virus diseases that attack rice and contribute to the low rice yields obtained in the humid tropics. Continuous cropping and the favorable environment of the humid tropics allow overlapping insect populations throughout the year, with no distinct diapause or dormancy period. Among the insect pests of rice, the rice stemborers (Chilo suppressalis and Tryporyza incertulas) are generally considered the most serious in tropical rice production. Other important rice insects are green leafhoppers (Nephotettix virescens) and brown planthoppers (Nilaparvata lugens). The rice water weevil (Lissorhoptrus oryzophilus) is a common problem in the temperate zone, in addition to the rice stink bug (Oebalus pugnax), planthopper (Sogatodes orizicola), and others. Other destructive groups include grasshoppers, locusts, gall midges, rice hispa, army worms, cutworms, whorl maggots, and thrips. Current control of rice insect pests depends largely on the use of pesticides, even though many traditional and new cultivars have some

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degree of resistance to insect pests. Chemicals will no doubt continue to play an important role in rice crop protection. With tropical rice where pesticides are costly and sometimes not available, it is increasingly important to combine various compatible management practices that provide crop protection at minimum cost. Entomologists recognize that the easiest integration of pest control methods is to combine cultivar resistance, cultural practices, and the timely use of pesticides. In recent years, the Integrated Pest Management (IPM) concept has received considerable attention in both temperate and tropical countries. An example of IPM success is that from Indonesia. Since the introduction of IPM through the United Nations' Food and Agriculture Organization (FAO) program using Indonesia's and IRRI's technology, the number of insecticides used was drastically reduced in 1987-88. Rice yields not only remained stable but increased (P. Kenmore, FAO, unpublished). Diseases

Diseases of rice are caused by a variety of organisms including fungi, bacteria, viruses, and probably mycoplasma-like bodies. These will be discussed in Chapter 5. Other Rice Pests

Among several pests often localized in their economic damage are rodents, birds, snails, crabs, and sometimes a variety of large animals. Rodents, particularly rats, cause serious losses in rice and are considered as economically important as insects. Rodents damage rice by eating seeds and seedlings, gnawing off tillers, damaging plants, and feeding on ripened grain. They attack rice in the field in all growth stages. They also cause large losses of grain in storage. Rats burrow in bunds and ditches causing loss of water, decreased irrigation efficiency, and an increase in the cost of maintaining irrigation systems. Losses due to rats vary widely, but field losses vary from 3.5 to over 25% with complete crop failures occurring in some localized areas. Birds cause greater rice crop losses than do most other vertebrate pests. They may attack ripening grain in all stages from the early "milk" stage through grain maturation. Most bird pests perch on the rice panicle and feed on the ripened grain. Large quantities of rice are often shattered, fall to the ground, and are lost. Some bird species feed on rice that falls to the ground after harvest, or rice that is seeded directly on dry prepared seedbeds, planted on mud, or sown into water. The principal African bird pest is Quelea quelea, an abundant and widespread sparrow-sized weaver bird. Large flocks of this nomadic bird migrate across Africa, descending on rice, millets, and sorghum indiscrimi-

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nately, often completely destroying entire crops. Control is very difficult because of the large populations involved, their migratory characteristics, and their extremely broad feeding range. Frightening the birds by various devices provides some short-term relief, but the effort is very time-consuming. A wide variety of bird species eat seeds. This poses a problem in most areas of the world. Some are indigenous birds, omnipresent but often migratory, following the ripening of rice and various other grain crops. In tropical Asia the weaver birds of the genus Ploeus, parakeets, Munia, and sparrows destroy rice crops. Blackbirds, cowbirds, and the common grackle permanently colonize forest and swamp areas, causing great damage in Latin America. Ducks, geese, and various waterfowl damage rice in many countries, including Australia, the United States, South America, and West Africa. Varieties of mollusks and crustacea, occurring in both fresh and brackish water, attack rice in many parts of the world. Snails such as Lanistes ovum, Amulearia lineata, and A. galuca (usually growing in standing water) harm the rice crop by feeding on seeds and newly emerged seedlings. Snails are often difficult to control because of their soil-burrowing characteristics. Two types of crabs, land crabs (Gercarindal) and river crabs (Potamonidal), damage rice by burrowing in bunds and irrigation systems. Crabs also attack rice planted by transplanting as well as by direct seeding. Shrimp (Triops granarius and T. longicaudatus), often referred to as tadpole shrimp, cause damage especially in the subtropic and temperate zones of the Americas, West Indies, Hawaii, and Japan. They do not attack drilled seed or transplanted seedlings but cause damage to pregerminated seed sown directly in flooded fields. Chemicals applied directly to the floodwater have been successful in combating this. In some areas of rice production, disorders occur in rice that resemble the symptoms of fungus and virus diseases. Some of these disorders are called physiological diseases and are sometimes associated with physiological and nutritional abnormalities. These plant disorders have been called by names such as akagare, akiochi, aogare, bronzing, and straight head. SYSTEMS OF RICE CULTURE AND PRODUCTION METHODOLOGY

Despite the importance of rice as a world crop, there are no complete quantitative data classifying ricelands by water regimes and predominant plant type. Based on land and water management practices, ricelands are classified as either lowland (wetland preparation of fields) or upland (dryland preparation of fields). Based on water regimes, ricelands can be classified as upland (with no standing water), rain-fed lowland (with 5-50

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Table 4-3. HaNested Area, Yield, and Rough Rice Production in 37 Major RiceProducing Less Developed Countries, by Ecosystem, 1985 AREA

Ecosystem

PRODUCTION

million ha

Irrigated Rainfed lowland Upland Deepwater/tidal wetland Total

Yield (tlha)

%

67 40 18 13 138

49 29 13 9 100

%

million t

4.7 2.1 1.1 1.5 3.2"

313 84 21 19 437

72 19 5 4 100

"Weighted average. Source: IRRI (1988b).

em of standing water), deepwater (with > 51 em standing water), and floating (with from 101 em to 5-6 m of standing water) (De Datta 1981). These definitions differ from many of those used throughout Asia, the argument being that basic rice plant types suited to each area will differ. Furthermore, the irrigated rain-fed environment cannot be sharply divided but represents a continuum of conditions ranging from very good to poor water control (Barker et al. 1975). Regardless of how various factors combine to affect the relative contribution of each ecosystem, the irrigated areas will continue to dominate production. Irrigated land now comprises about half the total harvested area but contributes more than two-thirds of the total production (Table 4-3). In the areas of poor water control, both drought and uncontrolled flooding can be a problem. In Africa and Latin America, upland rice is the major system of rice culture. On the basis of the type of rice culture, climate, soil conditions, and technology level of agriculture, rice in Africa is divided into 14 major ecosystems (Table 4-4). All of Africa's 5.37 million ha, however, comprise only 3.7% of the world's rice area. About 6.3% of the world's rice is grown on 9.2 million ha of land in Table 4-4. Major Rice Ecosystems in Africa GUINEA SAVANNAH

MIDAL TITUDE

Rice Culture Type Upland Irrigated Shallow flooded Deep flooded

Forest

+ + +

Humid Dry

+ +

+

Sudan Savannah Pluvial Hydro.

+ + +

Source: Buddenhagen and Ter Vrugt (1977).

+

+

Pluvial

Mangrove

+ +

+

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the Americas (1988). Brazil has 5.9 million ha, of which about 3.5 million ha are upland. In several South American rice areas, rice yields have steadily increased since the introduction of modern rice varieties and irrigated culture. Six major ecosystems for rice culture are identified for Latin America and the Caribbean areas. See Table 4-5. In many rice-growing areas of the tropics, the year is divided into fairly distinct wet and dry seasons. In most areas, the bulk of the rice is produced in the wet season. The amount of rainfall received during the dry season is usually not sufficient to grow a crop of rice, so irrigation is necessary. Because of the lack of irrigation facilities in most rice-growing areas of the tropics, the hectarage planted to rice in the dry season is limited. Although many countries have increased their irrigation facilities for rice (and for other crops), rice grown in the tropics may still have to depend largely on monsoon rains. The problem of variable rainfall is further compounded by the inflexible planting times in tropical Asia. The production methodology or cultural practices that have evolved or developed for rice are both complex and unusual. Because rice is grown under both irrigated and rain-fed conditions, one set of cultural practices cannot be used effectively for all conditions. We will therefore discuss systems of rice culture separately and mention how cultural practices vary with different conditions. Rain-Fed Lowland Rice

On most unirrigated farms, rice is grown during the wet season and the land lies fallow or is planted with low input crops through the dry season. Because of the farmers' dependence on both the fickle monsoon rains and conventional late maturing rice varieties, this has been the only feasible cropping system for centuries. The potential to intensify food production exists in most of these rainfed areas, although the technology and often the markets may be lacking. The practices followed are much more complex and variable in rainfed lowland areas than in irrigated areas. Transplanted rice

The onset of the monsoon determines the planting time and thus the day length and solar radiation available during the growing period. In lowland rice culture, transplanting is the major system of rice culture. Land preparation: Effects of puddling and flooding. The traditional method of preparing land for transplanted lowland rice consists of plowing and puddling the soil. The method has been widely adopted because it greatly reduces the weed population. In addition, puddling substantially increases the amount of water retained by the soil and reduces the amount of water lost through percolation (Sanchez 1973a, b). In an experiment

w en

Source: Mikkelsen (1987a).

Irrigated Favored upland Moderately favored upland Upland nonfavored Manual or traditional Low-lying flooded areas

Ecosystem

Traditional

6.5 0.9 5.9 25.0 92.6 47.9

Tall Improved

21.9 57.4 7.8 74.2 2.0 19.7

. Dwarfs

71.6 41.7 86.3 0.8 5.4 32.4

Production %

60.7 6.0 4.9 26.2 1.2 1.0

Production (thousand ha)

10063.9 987.2 819.7 4345.9 195.5 157.4

Yield (t/ha)

4.2 2.4 2.5 1.0 1.3 2.5

Area (thousand ha)

2387.2 409.1 329.4 4146.0 156.3 63.0

PERCENTAGE DISTRIBUTION OF VARIETIES

Table 4-5. Production by Ecosystems and Rice Varieties Cultivated in Latin America and the Caribbean, 1983/84 Harvest

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Cumulative amount of water (mm)

1200r--------------, NONPUDDLED SOIL

PUDDLED SOIL

10001800 r--

Water applied-

600Percolation

400-

Water applied

200-Evapotranspiration

20

I

I

I

40

60

80

~Evapotranspiration

100 0

20

40

60

80

100

Days after planting

Figure 4-2. Comparison of cumulative water applied, evapotranspiration, and percolation loss in puddled and nonpuddled soils continually flooded at 5 em (IRRI1972 wet season). From De Datta and Kerim (1974).

conducted (Maahas clay), water lost through percolation was considerably higher in unpuddled soil than in puddled soil (Fig. 4-2), so unpuddled soil received twice as much water (1180 mm) as puddled soil (588 mm). Rice in puddled soil had 2.5 times the water use efficiency (7 .8 kg rice/ha/mm of water) of unpuddled soil (2.9 kg rice/ha/mm of water) (De Datta and Kerim 1974). Thus, in rain-fed areas, puddling lowers the chance that yield-reducing moisture stress will occur between two successive rains. The rain-fed puddled system should therefore result in better moisture conservation, and possibly higher yield, than the rain-fed unpuddled system. Puddling, however, involves more labor. From De Datta and Kerim (1974). The term puddling has several different meanings. Farmers in Asia consider it a method of soil preparation which facilitates transplanting and reduces moisture losses through percolation. Soil physicists describe puddling as the process of breaking down soil aggregates into a uniform mass when clay soils are plowed and harrowed at about soil saturation. Consequently, several changes take place in the soil structure. Puddling changes the solid and liquid phases of the soil, decreasing the respective volumes occupied by macropores by 91 and 100%. Because most gaseous elements of the soil are in macropores, tillage at the moisture equivalent

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causes a corresponding reduction in the amounts of trapped gases present. Puddling decreases the macroporosity of clay soils and increases their microporosity, thereby causing an increase in the so-called water-holding capacity of the puddled soil (Sharma and De Datta 1986). For most crops, good soil structure is beneficial because it promotes infiltration of water and aeration of the soil. Although only a small amount of air is present in the micropores of well-puddled soil, no aeration problems occur with rice. A rice plant can tolerate low soil oxygen levels because its roots receive oxygen by transfer from the aerial parts. Puddling is often accompanied by the submergence of rice soils. That increases the availability of many nutrients, particularly N, P, K, Ca, Si, and Fe (Ponnamperuma 1972; Obermueller and Mikkelsen 1974). If the soil structure is highly porous, however, nutrients will be leached from the root zone. Studies show that the large losses of water from unpuddled soil caused greater nitrogen losses and less nitrogen uptake by rice at all growth stages. As a result, rice yields were significantly lower on unpuddled soil than on puddled soil, with or without the addition of nitrogen fertilizer (De Datta and Kerim 1974). The effects of puddling on the physical properties of soil, percolation losses of water and nutrients, nutrient uptake, and grain yield were evaluated in an IRRI experiment (Sharma and De Datta 1985). Puddling decreased the bulk densities of soils in the top 0.1-m layer by about 30% but differences in bulk density between puddled and nonpuddled soil narrow with time. The concentration ofN03 -N in puddled soil was either comparable to or lower than that in nonpuddled soil. Higher percolation rates did not improve soil productivity, but increased leaching losses of water and plant nutrients. Bulk density and soil strength were the main factors that affected grain yield. Puddling is achieved by tilling the saturated (flooded) soil with animalor power-driven plows and harrows until the soil macrostructure is destroyed. In practice, the land in the rain-fed lowland areas is prepared by an animal-drawn implement, frequently with poor results. Plant spacing. In monsoon Asia, high tillering cultivars are very desirable for culture of transplanted rice. Cultivars with improved plant type and high tillering capacity can be planted at a wide range of spacings and still produce an adequate number of tillers per unit area. The tiller number per unit area in a rice population is largely a function of planting density. The tiller number is correlated with grain yield either positively or negatively, depending on the rice cultivar and crop environment. A uniform stand containing an optimum plant population is essential for proper crop development and high grain yields. Management is found to be much easier if the field is planted in straight rows, since cultural practice such as

138

RICE: PRODUCTION

weeding by hand or chemical methods, spraying insecticides, and topdressing with nitrogen fertilizers can then be done without damaging the rice plants significantly. A great deal of work has been done in Japan on the effects of plant density and spacing on rice yield, and such work has lately assumed importance in the tropics. The conclusions from these findings vary. Some suggest that closer spacings produce higher yields, whereas others report opposite effects, depending on environmental conditions. It is true that, with varieties such as IRS, plant spacings between 15 x 15 em and 30 x 30 em would not give any significant yield difference. Recent evidence indicates that a relatively short-statured variety with moderate tillering capacity must have close spacing for maximum yield, i.e., plant spacings of 15 x 15 em give significantly greater yields than 20 x 20 and 25 x 25 em (Nguu and De Datta 1979). Further, under poor or no weed control, closely spaced rice competes better with weeds. Water management and moisture-stress effects. Rice, like other crops, requires adequate water to grow and develop at its maximum potential rate. Unlike other crops, rice is usually grown in flooded soil. With an adequate water supply from rain or irrigation, continuous flooding with from 5 to 7 em of standing water is desirable on most soils for the best moisture supply. It also gives the best weed and insect control with granular chemicals and high nutrient availability with minimum loss of nutrients from fertilizer and soil. Thus, wherever possible, a flooding depth from 5 to 7 em should be maintained even in rain-fed rice. lt is imperative that levees be kept in good repair to minimize surface runoff of excess water when it rains. In rain-fed areas, the paddies often become dry and' the crop suffers from various degrees of moisture stress. Although rice can be grown under upland, lowland, and deepwater conditions, stable high yields occur only under continuous optimum flooded conditions. Moisture stress is perhaps the chief factor that limits economical and stable yields of rain-fed rice (De Datta et al. 1973). Senewiratne and Mikkelsen (1961) report that grain yield is 53% lower under nonirrigated nonflooded conditions than under flooded conditions. Unlike other crops, the upper limit of the range of available moisture for rice is not field capacity. Jana and De Datta (1971) report that the optimum soil moisture conditions for high grain yield in upland rice (which should be true for rain-fed lowland rice as well) is between the maximum water holding capacity and the field capacity. De Datta et al. (1973) indicate that soil moisture tension as low as 15 cb was enough to reduce grain yields of rain-fed lowland rice. Part of the reduction in grain yield is due to a loss of nitrogen under the alternating dry and wet conditions which

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139

prevailed in the plots subjected to various stress levels. At the same time, there is enough evidence to demonstrate marked varietal differences between the modern rices in their tolerance to high levels of moisture stress(± 30 cb). Farmers in rain-fed lowland areas have been growing varieties that fit in with the probable rainfall distribution. Early-maturing rice varieties are often preferred to avoid drought stress. Early-maturing varieties should provide good stable yields under rain-fed lowland culture. The need for drought-tolerant rice cultivars in the drought-prone areas is widely recognized. These cultivars must survive drought stress during the vegetative phase, quickly recover, and grow rapidly upon renewed availability of soil moisture. Thus, a technique that quantifies soil moisture stress for screening thousands of cultivars and breeding lines for drought tolerance during the vegetative phase has been developed (De Datta et al. 1988c). Table 4-6 shows the test entries from different crop environments that showed better drought tolerance than the tolerant check. Results suggest that farmers in rain-fed areas should grow drought-tolerant modern rice cultivars with good recovery ability. During dry spells, the visual degree of desiccation during the vegetative phase permits the farmers to estimate potential plant recovery upon relief of soil moisture stress (Malabuyoc et al. 1985). Fertilizer management. The development and dissemination of fertilizer-responsive cultivars of rice, wheat, and other cereals have encouraged a steady increase in the use of fertilizer in the developing world. Fertilizer responsiveness is a key factor in differentiating among the traditional rices and the new high-yielding cultivars. Only where the levels of fertility are at least modest do yield differences between the new and the old become significant; without fertilizer, the new cultivars yield little better than the old. With fertilizer, in contrast, the yield potential is often double or even triple that of the traditional ones (De Datta et al. 1974; Shastry et al. 1974). The efficiency of applied nutrients in rice has long been studied by soil fertility scientists. Only recently, however, has concern been expressed over possible shortages and higher prices of fertilizer, particularly nitrogen and phosphorus. Serious concern about the efficient use of these nutrients in rice production stems from the realization that the fossil fuel supplies needed for the manufacture of nitrogen fertilizer are not limitless and that adverse environmental effects may occur with improper use. Fertilizer use efficiency can be described as the output of economic produce by any crop per unit of fertilizer nutrient applied under a specific set of soil and climatic conditions. The least amount of fertilizer needed to match plant use at maximum grain yield is the most efficient rate of

g

Source: Malabuyoc et al. (1985).

96

!RAT 9 (Susceptible variety) Desiccation score Recovery score IR20 (Susceptible variety) Desiccation score Recovery score IR442-2-58 (Tolerant line) Desiccation score Recovery score Salumpikit (Tolerant variety) Desiccation score Recovery score

97

99

103

n

Variety/Line Character

0 4

0 5

0 0

0 0

I

0 30

II

0

0 0

0 0

2

4 45

0 46

0 2

0 0

3

28 14

4 24

0 20

0 2

4

I98I

49 3

10 9

63

I

0 4

5

10 0

39 3

0 18

0 9

6

I

3

I

45

41 4

8 44

7

2 0

1 0

58 2

61 33

8

0

1

0 0

3 0

27 4

9

98

94

88

101

n

0 13

0 25

0 0

9 0

I

0 2

1

0

0 0

9 0

2

SCORE FREQUENCY DISTRIBUTION

8 72

0 57

0 2

1

9

3

31 0

0

I

0 0

9 0

4

I982

51 10

7 10

0 53

9 2

5

6 0

46 0

1 2

0

1

6

0

1

I

40

40 31

1 1

7

0 0

0 0

44 0

34 1

8

Table 4-6. Frequency Distribution of Desiccation and Recovery Scores of Two Drought Susceptible Rice Varieties, a Drought Tolerant Line, and a Drought Tolerant Variety, IRRL 1981 and 1982 Dry Seasons

0 0

3 0

65 96

9

RICE CULTURE

141

fertilizer application. Bartholomew (1972) classified nitrogen needs according to plant use-good use efficiency, average use efficiency, poor use efficiency, and polluting rates. Several factors determine fertilizer efficiency in rice. At the farm level, these are soil, cultivar, season, time of planting, water management, weed control, insect and disease control, cropping sequence, sources, rate, methods, and time of fertilizer applications. For India, Mahapatra et al. (1974) summarized the fertilizer efficiency in cereals as follows: dry season rice > wet season rice > wheat > corn > millet> sorghum. Despite agronomic efforts to improve plant nitrogen use efficiency, the recovery of fertilizer nitrogen applied to transplanted rice is seldom more than 30 to 40% (De Datta 1987a) and 60% in water seeded, mechanized rice (Mikkelsen 1987b). Understanding the mechanisms and pathways of nutrient losses has helped researchers develop practices to increase the efficiency of fertilizer use in rice. Even a slight improvement in nitrogen fertilizer efficiency will save energy costs and foreign exchange in countries that import nitrogen fertilizer. Hence, the increased interest in nitrogen transformation processes in lowland rice in recent years. Ammoniacal nitrogen is subject to clay fixation and loss by volatilization, nitrification and denitrification, leaching, runoff, and seepage (Mikkelsen 1987b; De Datta 1988b). In lowland rice, 60 to 80% of the nitrogen absorbed by the crop is derived from the native nitrogen pool (Broadbent 1979). Recent results suggest that approximately 60% of the rice yield, ranging from 2 to 4 t/ha, is produced without fertilizer nitrogen. With increased study on soil nitrogen, and its management, especially fertilizer placement, substantial yield gains are possible with resources already on the land. Recently, significant differences in nitrogen use efficiency were found among rice genotypes, and the possibility of improving nitrogen use efficiency in rice through genotype selection was shown (Broadbent et al. 1987). A method has been proposed for evaluating nitrogen utilization efficiency among rice genotypes by various combinations of rice plant parameters, and for ranking their performance in the field (De Datta and Broadbent 1988). From extensive data, Watanabe et al. (1981) found that a rice crop used an average of 40 to 50 kg N/ha from the soil pool, when no nitrogen fertilizer was applied. In most instances, soil nitrogen did not decrease, indicating that the nitrogen used was compensated for by mechanisms, among which biological nitrogen fixation (BNF) was the most important. Among the gaseous losses, ammonia volatilization and denitrification are the most important (De Datta and Patrick 1986). Nitrogen loss through

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RICE: PRODUCTION

ammonia volatilization from flooded soils was reported by various researchers (Mikkelsen et al. 1978; Fillery et al. 1984; Fillery and De Datta 1986; De Datta et al. 1989). Jayaweera and Mikkelsen (1990) have shown that ammonia volatilization is dependent on water NH 4 concentration, pH, temperature, water depth, and wind speed over the flooded rice system. Summarized data of recent field studies on ammonia volatilization in lowland rice soils show a large variation (5-47%) in the amount volatilized. The magnitude of losses are sometimes due to different measurement techniques used by the researchers, the chemical nature of the fertilizer, and the varying fertilizer application methods. Nevertheless, data from these studies indicate that ammonia volatilization losses from irrigated lowland rice fields may be substantial (De Datta 1987a; De Datta et al. 1989; Jayaweera and Mikkelsen 1990). Nitrification-denitrification has long been considered an important nitrogen loss mechanism in flooded soils. However, direct field measurements of denitrification losses from puddled rice soils in the tropics were made only recently. The direct recovery of (N 2 + N20)- 15N from 15Nenriched urea has recently been measured in the Philippines, Thailand, and Indonesia. In all12 studies, recoveries of(N2 + Nz0)- 15 N ranged from 0.1 to 2.2% of the nitrogen applied (Buresh and De Datta 1990). Total gaseous nitrogen losses, estimated by 15N-balance technique, were much greater, ranging from 10 to 56% of the applied urea-nitrogen. A great deal of attention has been devoted to evaluating the relative merits of various fertilizers for lowland rice. The yield response of rice to different sources of nitrogen is affected by soil condition and management practices, particularly water management and time and method of nitrogen application (Mikkelsen and Finfrock 1957; De Datta 1986a). In most situations, ammonium-containing and ammonium-producing (urea) fertilizers are similar in effectiveness based on grain yield. Urea is likely to remain the leading nitrogen source for rice beyond the end of the century as attested by the large potential for new urea capacity in Asia, where rice is primarily grown. Most urea is produced and sold as dry prills, but recently, production shifted toward that of granular urea (Stangel 1985). The optimum integrated nitrogen management strategy would be influenced by (I) availability of native soil nitrogen, (2) the mineralization rate of organic nitrogen sources, (3) timing of chemical nitrogen applications, (4) losses of native and added nitrogen, and (5) interactive effects of organic and chemical fertilizers on nitrogen availability and loss (De Datta and Buresh 1989). In some areas, rice is produced in arid regions where the soils are high in pH and often saline. The typical water management system calls for

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143

G~i;n~y~ie~ld~(t~/~~1--------------~R=A=IN~fwE~D~------------------------, 6

JRRI form (Cloy; p/16.0; CEC45meq/100g)

Formers' field Moloyontoc (Cloy loom; pH5.8; CEC IBmeq/IOOg)

5 4

3 2

..., "'

.... ~ ~ 0 a.

00

=

Ci

"'

0

Figure 4-3. Relative grain yields of IR26 grown under rain-fed conditions. Grown without nitrogen fertilizer and with 30 kg nitrogen/ha as urea under different methods of application. IRRI and farmers' fields in Malayantoe and Nueva Ecija, Philippines, 1974 wet season. From De Datta et al. (1974).

intermittent flooding similar to rain-fed lowland rice fields in tropical Asia. The flooding-drying sequences are rather short, permitting a number of cycles during the growing period of the rice. The fields are not puddled, and water infiltration rates are sometimes high. Although nitrogen transformation processes in irrigated lowland rice under continuous flooding are fairly well understood, hardly any pertinent research has been done in rain-fed lowland rice. Rain-fed lowland conditions are more harsh and variable, so that denitrification losses may be high. Research should measure denitrification losses in relation to ammonia volatilization loss in rain-fed lowland rice using simultaneous measurement techniques. Fertilizer nitrogen placed 8 to 10 em deep is apparently less subject to volatilization and microbial oxidation than surface applied material. The loss of nitrogen is commonly more serious in rain-fed lowland conditions than in irrigated fields. Experiments in several countries have shown that deep placement of fertilizer nitrogen gave higher yields than other methods of application. Results obtained in the Philippines are given in Fig. 4-3.

144

RICE: PRODUCTION

The grain yield differences between deep placement and other methods were less at the IRRI farm because rainfall distribution was more uniform there than in farmers' fields (De Datta et al. 1974). Although research results indicate that nitrogen efficiency is higher when the fertilizer is deeply placed, most farmers usually wait until the crop is established before applying any nitrogen fertilizer. In rain-fed areas, the best time to topdress nitrogen is at tillering (20-30 days after transplanting) and at panicle initiation. Recent results suggest that even in rain-fed lowland rice fields, deep placement and basal incorporation without standing water are advantageous in minimizing nitrogen losses and increasing nitrogen use efficiency over topdressing 10 to 15 days after transplanting. Improved incorporation or placement of urea and improved urea and coatings offer considerable potential for increasing the yield response of rice to urea fertilizer application. Priority should be placed on (1) developing labor- and cost-effective methods offertilizer placement, (2) disseminating available information on the most agronomically effective timing for conventional prilled and granular urea, and (3) developing a costeffective and environmentally safe coated urea (De Datta and Buresh 1989). Sources, method, and time of application of phosphorus and potassium would not be any different for irrigated and rain-fed areas. Still, rain-fed rice generally needs more phosphorus than does irrigated rice. This is because more phosphorus is brought into solution under good water conditions, such as continuous flooding, than under rain-fed rice culture where moisture deficiency is a factor affecting nutrient availability. Weed control. In many rain-fed areas, water accumulates in the bunded field as the crop grows. In other situations, the crop starts as a lowland crop and finishes as an upland crop. With those uncontrolled water conditions, weeds generally develop in larger numbers and greater diversity of species than with rice grown in puddled soil under good irrigation. Lack of water control is a major practical management factor that increases the amount oflabor required for weeding. Precise water management with continuous flooding is ideal for a number of reasons, particularly to minimize weed growth. Since most fields in South and Southeast Asia cannot be flooded continuously, indirect and direct complementary practices are essential for effective weed control at the farm level. Like irrigated rice, many weed species in rain-fed lowland rice are annuals, such as Echinochloa crus-galli ssp. hispidula, E. glabrescens, Leptochloa chinensis, Fimbristylis littoralis, Cyperus difformis, and C. iria. The perennials Paspalum distichum and Scirpus maritimus are also a problem. The broadleaved weed Monochoria vagina/is also grows when water is standing in the field.

RICE CULTURE

145

Under the existing conditions of high weed density, relatively low labor cost, and the availability of some chemicals, the necessity of weed removal is more important than how it is achieved. In the Asian tropics, either hand weeding or use of a rotary weeder is effective in rain-fed transplanted rice fields, although both are tedious, time consuming, and somewhat expensive. In tropical Asia, either 2,4-D or MCPA effectively control annual weeds (De Datta et al. 1968). If the water control is not good, however, 2,4-D applied before emergence of the weeds (4 days after transplanting) often does not control weeds adequately. Thus, supplemental hand weeding is often necessary to control surviving weeds. Selective herbicides such as butachlor or thiobencarb are somewhat more effective against a wide spectrum of weeds, particularly under the area of relatively poor water control in rain-fed rice (De Datta 1988a, c). Insect control, harvesting, and threshing

Practices such as insect control, harvesting, and threshing do not differ between rain-fed and irrigated rice culture of a transplanted crop. These operations are discussed elsewhere in this chapter. Direct seeded lowland rice

Direct seeded lowland rice culture is an important system for the Asian tropics (De Datta 1986b). Pregerminated seeds are broadcast onto puddled fields without much standing water. Direct seeding is primarily by the broadcast method. Such is the case for most rice areas in Sri Lanka and parts of India and Bangladesh. The area under broadcast seeded flooded rice is rapidly increasing in Malaysia, Thailand, and the Philippines. Fields are prepared under wet conditions. The degree of puddling depends on the amount of moisture accumulated from the rain. Stand establishment is often poor because of poor land preparation and insufficient water control. Farmers in Java, Indonesia, often decide whether to seed rice under wet or dry soil conditions according to the amount of moisture available during the planting month. If less than 200 mm of rain falls within that month, farmers opt for dry seeding; with more than 200 mm, they seed under wet conditions (De Datta 1981). Water management. Water control is more critical for broadcast seeding than for transplanting. For better stand establishment, the field should be kept saturated but not flooded from the time of seeding to about 6 days later. Because of a lack of precise water control and use of muddy water, germinating rice seeds are often covered with a layer of silt, thereby reducing the stand. When that occurs, it is best to reseed with pregerminated seeds in the areas where germination is poor.

146

RICE: PRODUCTION

Weed control. In the direct seeding system of rice culture, weeds grow vigorously. Selective herbicides such as butachlor and thiobencarb would control weeds under rain-fed culture. Supplemental postemergence weed control, either with 2,4-D (if the predominant weeds are broadleaves and sedges) or by hand weeding, is essential to control the remaining weeds (De Datta 1989). Other cultural practices. In rain-fed areas, fertilizer application, insect control, harvesting, and threshing will not differ markedly between direct seeded and transplanted rice culture.

Dry seeded bunded rice

The greatest economic return to farmers in the rain-fed areas may not come through an increase in the yield per crop, but rather by expansion through double cropping. For many years, farmers in Bangladesh and Indonesia have grown rain-fed lowland rice seeded directly on unpuddled soil at the beginning of the rainy season. This method of rice culture is known as ''aus'' cropping in Bangladesh and "gogo-rantja" in Indonesia. By doing this, the farmer takes advantage of early rainfall and may thus manage to grow an extra crop of rice (De Datta 1981). Drought damage and weed infestation are the two most critical factors in good seedling establishment of dry sown rice on bunded fields. Good land preparation is difficult because of the power required to cultivate the hardened soil. Drought damage is severe, and weeds tend to outgrow rice under this system. Recently, early-maturing modern cultivars with good drought tolerance have minimized drought damage. Further research at IRRI and other organizations in Southeast Asian countries hopefully will develop improved technology for the direct seeding of rice. Irrigated Rice

Irrigated rice remains the keystone to global rice security. It accounts for over 50% of the world's 144 million ha planted to rice, and 70% of the 470 million tons of global rice production. In South and Southeast Asia, irrigated rice accounts for some 40% of the rice area and over 50% of rice production. In temperate Asia, such as the People's Republic of China, Japan, Korea, and Taiwan, most of the riceland is irrigated. In temperate America, Europe, and Australia, rice is entirely an irrigated crop. In those temperate countries, rice is simply not grown if irrigation water is not available. In irrigated areas of the world, rice is grown as follows: transplanted,

RICE CULTURE

147

seeded directly onto puddled soil, drill seeded into dry soil, and seeded directly into water. Cultural practices in these systems of rice culture often vary a great deal. Transplanted rice

In irrigated areas of Asia, most of the rice is transplanted. Land preparation. Land preparation for irrigated transplanted rice is no different from that for rain-fed transplanted rice discussed earlier. The water requirement for land preparation in the lowland field varies from 150 to 200 mm. Water management. Rice, like any other crop, requires adequate water to grow and develop at its maximum potential rate. Unlike other crops, rice is usually grown in flooded soil. Submergence has many advantages, such as better weed control, higher efficiency of fertilizer, and better insect and weed control with granular herbicide. Considering all factors, continuous submergence with 5 to 7 em of water is probably best for irrigated rice. The rotational method of irrigation has not been widely adopted (except in China) because it requires competent irrigation personnel as well as good cooperation among farmers. Existing conveyance systems must be modified to include measuring devices. Weeds are also more difficult to control when the fields lack standing water for a time. Fertilizer management. Much of the fertilizer nitrogen applied for a rice crop is not taken up by the rice plants. Depending upon soil type and the method and time of fertilizer application, only 20 to 60% of the fertilizer is utilized by the crop in a given growing season. Some of the remainder is combined with organic forms by soil microorganisms in the soil, and it may be released too late for crop uptake. Some is lost to the atmosphere by the biological process of denitrification. In other cases, nitrogen is directly lost to the atmosphere by ammonia volatilization. Figure 4-4 shows the fate of fertilizer nitrogen under flooded and upland conditions in the Philippines. Obviously, the challenge is to minimize the loss of fertilizer nitrogen and to increase the efficiency of usage by the crop. Fertilizer nitrogen management can be improved by (1) basal incorporation of the first nitrogen dose rather than broadcast application at 10 to 21 days after transplanting, when nitrogen losses are extremely high, and (2) application of second nitrogen dose immediately before, rather than after, panicle initiation (De Datta 1987a). Although basal incorporation of urea into drained soil can reduce nitrogen loss (De Datta et al. 1989) and frequently increase grain yield, gaseous nitrogen loss remains substantial, suggesting that considerable

148

RICE: PRODUCTION

Figure 4-4. Balance sheet of nitrogen fertilizer applied to flooded and upland

soils. Adapted from IRRI (1974).

scope for improving the efficiency of urea still exists. Implements and technologies for more thorough incorporation of prilled and granular urea merit investigation (De Datta and Buresh 1989). Coarse textured soils usually have high percolation rates and demand split applications of nitrogen (usually two or three) to avoid serious losses that would prevent maximum crop growth. More finely textured soils require fewer nitrogen applications, often only one or two, provided that water management practices are good. Yield differences do not always correlate to differences in nitrogen uptake. Proper placement of nitrogen fertilizer within the flooded system is of extreme importance. Fertilizers containing ammonium nitrogen are stable provided they are placed 8 to 10 ern below the surface of the flooded rice field. This is because microorganisms capable of oxidizing ammonium nitrogen cannot function in an oxygen-deficient zone. Fortunately, rice

RICE CULTURE

149

readily uses ammonium as well as nitrate nitrogen, but nitrate forms cannot be retained in flooded soils (Mikkelsen and Finfrock 1957). A considerable advantage appears to exist in keeping the nitrogen fertilizer concentrated rather than dispersed throughout the soil. Deep placement of urea in lowland rice fields is widely recognized as an effective management practice for irrigated rice, except in high percolation rate. Basal deep placement of urea is superior to split application of prilled urea in both transplanted and broadcast seeded flooded rice (De Datta et al. 1988a). Considerable scope exists for the development of less labor-intensive, more economical methods of deep placement. Moreover, better delineation is needed of environments where deep placement has a distinct comparative advantage over other management practices. The sources of nitrogen are no different for irrigated rice than for rain-fed transplanted rice. The topic is covered in the section on rainfed culture. Phosphorus deficiency is a widespread nutritional disorder of rice. It occurs on millions of hectares of ultisols, oxisols, vertisols, and certain inceptisols. These soils are not only low in available phosphorus but also fix fertilizer phosphorus as highly insoluble minerals. Besides, soil submergence gives only a slight increase in the availability of phosphorus in these soils. In Indonesia, about 1 million ha of soils cultivated for rice are deficient in phosphorus, while many areas in Thailand, particularly in the northeast, are also deficient in phosphorus. Phosphorus deficiency is not only quite widespread but also acute in certain areas. In acutely phosphorus-deficient areas, the response to P alone has been comparable to or even better than that to N at equal rates of application. Few significant differences have been found among the effects of various phosphorus sources in flooded rice except in extremely acidic or alkaline soils. India, Pakistan, the Philippines, Korea, and Myanmar use superphosphate as their primary sources of phosphorus on all soils, while Sri Lanka, Malaysia, Thailand, Cambodia, and Vietnam use rock phosphate. On the acidic soils of South and Southeast Asia, phosphate rocks have been applied directly as sources of phosphorus Jor rice. These sources are lower in price than acidulated phosphates and represent a means of reducing fertilizer cost where transport costs are not too great (De Datta et al. 1990). Experiments in the greenhouse at the U.S. National Fertilizer Development Center and in fields in Thailand evaluated several phosphate rocks with varied citrate solubility. A procedure has been developed that allows the choice of P source on the basis of both agronomic

150

RICE: PRODUCTION

effectiveness and price of Pas triple superphosphate (TSP) vs. phosphate rocks (Engelstad et al. 1974). In general, phosphorus is applied at planting. If needed, application can be postponed but not past the time of active tillering. It has been reported that early application of phosphorus is essential for root elongation. Phosphorus applied no later than the early tillering stage is most efficiently utilized for grain production. In general, most phosphorus applications should be made as a basal treatment. The phosphatic fertilizer needs of rice on deficient soils can be reduced if varieties that can extract phosphorus efficiently from the soil can be developed. That would be a real benefit to the poor farmers of the tropics where most of the phosphorus-deficient soils occur, especially since phosphate fertilizers have recently tripled in price (Kundu and De Datta 1988). Most rice soils have not been shown to be particularly deficient in potassium. That is because irrigation water usually contains significant amounts of potassium. The majority of rice soils in Asia responds more to N and P, than to K (De Datta and Mikkelsen 1985). In Japan, crops grown on degraded paddy soils respond well to potash fertilizers, and yield increases of 20 to 30% can be expected. Further, a response to potassium is obtained on light soils where leaching causes considerable loss of bases. Favorable responses to potassium have been demonstrated from sandy and coarse textured soils of Vietnam, Sri Lanka, and Malaysia. In Sri Lanka, about 25% of the total rice fields suffer from potassium deficiency. The average increase in yield in Taiwan from potassium application is about 50%. Responses are most significant in red and yellow earths, and the effects of potassium are generally greater in the second crop than in the first. Common sources of potassium are potassium chloride and sulfate and complete fertilizers. Potassium should be applied during the final land preparation. Results from Taiwan occasionally indicate that split application of potassium is beneficial to rice grown on coarse textured soil. Five-year data on clay soils in the Philippines showed no beneficial effects from a split application of potassium over a single application (De Datta and Gomez 1974). In response to recent fertilizer shortages, there is a move to reduce the doses of phosphorus and potassium and in some cases eliminate them altogether from recommendations for various crops in India. Results from the long-term fertility experiments indicate that, in areas where one crop per year is grown with an adequate supply of nitrogen, the response to phosphorus and/or potassium may be marginal. Response may become marked, however, under--intensive. cultivation involving more than one crop per year (De Datta et al. 1988b).

RICE CULTURE

151

Because of the current fertilizer situation, inorganic fertilizers should be supplemented with green manure, compost, and other organic manures, and rice straw. Quantitative experimental data are needed to assess the value of organic manures in realizing high yields from the modern rice varieties. In some Asian countries, straw is available in large quantities as a source of organic matter and nutrients. In other countries, rice straw is used for cattle feed and hence is not available for field use. In clay soils, straw incorporation has limited fertilizer value, but in sandy soils of low cation exchange capacity (CEC) the effects may be of some significance (FAO 1973). These organic sources alone, however, would seldom serve as substitute for chemical fertilizers if modern high-yielding rice cultivars are grown. Next to nitrogen and phosphorus, zinc deficiency is perhaps the most important nutritional factor limiting the grain yield of wetland rice. It occurs in alkaline, calcareous, wet, organic, and sandy soils. Millions of hectares of low-lying land in the humid tropics, well-supplied with water, could be brought under rice cultivation if improved cultivars with tolerance to zinc deficiency are developed. Zinc deficiency in rice has been extensively reported in India, Pakistan, the Philippines, Japan, the United States, and Brazil. In many countries, zinc deficiency is perhaps the second most important nutritional disorder limiting the yield of lowland rice. At least 13 provinces in the Philippines have large areas of zinc deficient soils (Orticio and Ponnamperuma 1977). In these zinc-deficient areas, NPK fertilizers alone will provide only a limited yield advantage unless zinc deficiencies are corrected first. The incidence of zinc deficiency has increased in recent years because of the replacement of old cultivars by modern ones with less tolerance to zinc deficiency, the removal of large amounts of zinc by the new high-yielding cultivars, the replacement of ammonium sulfate with urea, the increased use of phosphate fertilizers and concentrated fertilizers, and double and triple cropping of lowland rice (De Datta 1981). In transplanted rice, zinc deficiency is easily corrected by dipping seedlings in 2% zinc oxide suspension in water (Yoshida et al. 1970). Other methods of correcting zinc deficiency in transplanted rice include foliar sprays and soil application. Treatment of transplanted seedlings and soil treatment are the two most common methods of zinc application. Sprays are usually employed only in emergency situations when the crop is growing and shows deficiency symptoms (Mikkelsen and Kuo 1976). Cultivars with tolerance to zinc deficiency would reduce the problems of growing rice in zinc deficient soils. Results at IRRI showed

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that IR20, IR34, BG 90-2, and several IRRI elite breeding lines tolerated zinc deficiency. Cultivars tolerant to zinc deficiency should be grown on zinc-deficient neutral soils. On organic and calcareous soils, it is advisable to use a combination of tolerant cultivars and a 2% zinc oxide suspension dip (Orticio and Ponnamperuma 1977). Weed control. Weed control does not differ greatly between irrigated transplanted rice and rain-fed transplanted rice as discussed earlier. Good land preparation and good water control make weed control less difficult for irrigated transplanted rice than for rain-fed transplanted rice. Hand weeding is commonly used in almost all areas in South and Southeast Asia. Rotary weeding seems common in some Southeast Asian countries although not in others. Herbicides are used most commonly in areas of inadequate labor and high wages, particularly in eastern Asia-Taiwan, Korea, and Japan. In the Philippines and some tropical South and Southeast Asian countries, 2,4-D is the principal herbicide used because of its low cost. In the tropics, 2,4-D controls annual grasses if applied to transplanted rice four days after transplanting, before the emergence of weeds (De Datta et al. 1968). Other promising herbicides include butachlor, thiobencarb, piperophos, molinate, ftuazifop-butyl, and oxadiazon (De Datta 1988a). In most of tropical Asia, developing integrated methods of weed control (using limited quantities of low cost chemicals in combination with direct and indirect methods) may be the most attractive alternative from agronomic, economic, and ecological points of view (De Datta 1988a). Insect and disease control. Insects do far more damage to rice in the tropics than in temperate regions. In fully irrigated areas of the tropics, where year-round rice culture is practiced, pest problems became much more serious than in the cool temperate climates where only one crop can be grown each year. The control of insect pests in the tropics currently depends largely on the use of pesticides, even though many traditional cultivars have some resistance to one or more insect pests or diseases. These have played and will continue to play a major role in successful rice production. In recent years, scientists have evaluated different insecticides and application methods to learn how farmers can maximize return on insecticide investments. In biological control studies, it was found that a predator (Cyrtorhinus lividipennis) can kill an average of 0.6 brown planthopper nymphs per day, or 50 green leafhopper nymphs per day, for at least 4 consecutive days. The predator prefers to prey on nymphs rather than adults, and prefers green leafhoppers to brown planthoppers. Entomologists have recognized that integration of pest control

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methods involves combining cultivar resistance with pesticides when necessary. Plant resistance should reduce the pest population somewhat, if not considerably, and insecticides can be applied to reduce the number of these pests even further. Farmers in the tropics cannot afford the luxury of expensive plant protection measures. Crop resistance with a minimal insecticide application must be the answer if rice production in the tropics is to be economic. Promising lines are being developed continually that combine broad genetic resistance to all major insects and diseases in tropical Asia. The concept of Integrated Pest Management (IPM) is gradually becoming an important guideline for pest control in rice. For diseases of rice, resistant lines have been identified and incorporated in the elite breeding lines. Although chemical control of blast or of the vectors of virus diseases is possible, this control is neither practical nor economical. Cultivar resistance to these diseases and to the vectors of virus diseases is the only economic solution to these problems. Harvesting, threshing, drying, and storage. In the tropics, rice matures about 30 days after heading. Harvest must occur on time otherwise grain may be lost through damage caused by rats, birds, insects, shatter, and lodging. Timely harvest ensures optimum grain quality, a higher market value, and greater consumer acceptance. In the Asian tropics, harvesting is done by hand. The straw is usually cut about 15 to 25 em above the ground, although in some areas, particularly Indonesia and some upland rice areas in the Philippines, the panicles are clipped off with a sharp knife. Threshing is done by hand, by beating the rice heads on a perforated platform made of bamboo. Occasionally, threshing is done by having animals tread on the harvested rice crop. In the recent past, the axial flow thresher has gradually become popular in Thailand and other Southeast Asian countries. The grain is usually dried in the sun, although that is difficult during the wet season when clouds and rains often disrupt operations. Practical experience has shown that, in the Philippines, four days of sun drying are usually sufficient to reduce the moisture content of the grain to an acceptable level. Most farmers save only a certain amount of harvested rice (rough rice) for family consumption and store the grain in sacks or in small barrels since proper storage facilities are rare in the Asian tropics. The problem of postharvest operations, including storage, has become more serious because of the higher yields obtained with modern cultivars. The IRRI Engineering Department has designed a number of small harvester units, or threshers, and dryers for the Asian tropics, and

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widespread use of these (like any mechanical equipment) will depend on availability, pricing, and the profitability of production. Direct seeding onto puddled soils

The practical difficulties of establishing good stands of direct-seeded rice under monsoon conditions have been studied to determine whether transplanting is indeed superior to direct seeding under tropical conditions. Evidence suggests that grain yields are similar for direct-seeded and transplanted rice. This finding, along with the increasing cost of transplanting, may lead to serious consideration of direct seeding as a desirable alternative, at least in areas with controlled irrigation. Although machines are available for drilling pregerminated rice onto puddled soil, the broadcast method is most common (De Datta 1986b). Direct seeding on puddled soil is practiced in some parts of India, Bangladesh, Malaysia, Thailand, and the Philippines. In Sri Lanka, 80 to 90% of the rice acreage is broadcast. Egypt and Korea grow rice under broadcast seeded flooded conditions. Cultural practices for direct seeding onto puddled soils are similar to those for transplanted rice in some operations, and distinctly different in other operations. Land preparation. The practice of puddling in broadcast seeded rice culture, similar to the transplanted system, reduces water percolation. Puddling is also reported to aid in creating a level soil surface, incorporate uniformly added fertilizer, incorporate weeds, and hasten mineralization of organic nitrogen. Water management. Without leveling of fields, water management is difficult. The depth of water determines the success of seedling establishment. Systems of water management for direct seeding onto puddled soil vary widely. In one system, fields are flooded just before seeding and kept flooded until harvest. They may be drained soon after seeding and flooded again. In another system, pregerminated seeds are sown onto a inoist but drained field, and the field is reflooded with 3 to 5 em of water when rice is at the four-leaf stage and weeds at the three-leaf stage. Fields are often drained during the growing season. The reasons for drainage include control of aquatic weeds, algae, and water-weevil, and application of feitilizers and agricultural chemicals. Also, for basal nitrogen incorporation, puddled field should be drained first (De Datta et al. 1988a). From the literature, continuous submergence appears suitable under most situations for direct-seeded rice. Fertilizer management. Management of fertilizer does not greatly differ between direct-seeded irrigated rice and direct-seeded rain-fed lowland rice. Recent research suggests that if farmers do not wish to change their

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first topdressing of nitrogen 2 to 3 weeks after planting, switching from transplanting to broadcast seeding will minimize nitrogen losses by 9 to 10% (Obcemea et al. 1990). Furthermore, nitrogen fertilizer efficiency is greater in direct-seeded irrigated rice than in rain-fed lowland rice under a similar method of planting. Weed control. Weed control is more critical and difficult in rice grown from pregerminated seeds broadcast directly into the field than in transplanted rice. Laborers cannot move through broadcast rice to weed by hand without destroying some rice plants. Furthermore, laborers cannot distinguish between young grassy weeds and young rice seedlings. For direct-seeded flooded rice culture, the herbicides butachlor and thiobencarb, which are commercially available in several Asian countries, give excellent weed control without injuring the rice crop (De Datta and Bernasor 1971). Propanil and molinate are also effective in the production of direct-seeded rice (Smith et al. 1977). Among the new herbicides, a mixture of piperophos and dimethametryne has shown excellent selectivity and broad spectrum activity in both the tropics and temperate regions. Another new selective herbicide for direct-seeded flooded rice is butralin (De Datta and Bernasor 1973). In trials in India, Pillai (1973) compared direct seeding to drilling on dry soil, except that the seedbeds are usually left very coarse and dry before flooding. Soil clods 2 to 6 em in diameter are found in a typical good seedbed. After flooding, these practices effectively control weeds in direct-seeded rice. In the Philippines, Malaysia, and Thailand, this method of culture has become popular as new herbicides are identified and marketed (De Datta 1989). The direct-seeded flooded rice culture will become an acceptable alternative as the cost of labor rises, as less expensive selective herbicides become available, and as water control becomes better (De Datta and Flinn 1986). Insect and disease control and other cultural practices are the same for direct seeded as for transplanted rice in most tropical areas. Harvesting, threshing, and storage are also similar. Direct seeding into water

In areas where highly mechanized agriculture is justified or where the labor requirement for transplanting is excessive, direct seeding into flooded fields is practiced. The practice is ancient in parts of Asia, including India, Sri Lanka, Malaysia, and Thailand, and is now done on a wide scale in the Americas, southern Europe, the U.S.S.R., and Australia. Direct seeding saves time and labor in both land preparation and in actual sowing. More care must be exercised in the management of water sown rice than with most other methods of cultivation. Water depth, excessively

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high or low water temperatures, and muddy water are occasionally sources of problems in stand establishment. Direct seeding requires 40 to 50% more seed than transplanting; the seed must have good viability and the cultivars must possess good seedling vigor. The seed used is pre germinated by soaking in water for 18 to 24 h, draining for an additional24 h or until sprouts develop about 2 mm long. The sprouted seed is broadcast directly into the flooded field. Field flooding practices vary according to local conditions. Oxygen deficiency does not appear to be a limiting factor in stand establishment of rice in flooded soils (Chapman and Mikkelsen 1963). Adequate chemical weed control measures must be available since mechanical cultivation is not possible. Land preparation. Land preparation for rice seeded directly into water is similar to that used for drilling on dry soil except that the seedbeds are usually left very coarse and dry before flooding. Soil clods 2 to 6 em in diameter are found in a typical good seedbed. After flooding, these clods slake down to smaller aggregates, leaving an irregular surface that reduces seedling drift and helps establish root penetration. A suitable seedbed should be relatively level, devoid of low and high spots (De Datta 1981). Water may be too deep for good emergence in the low spots, and weeds (especially barnyard grass) may be favored in soil not covered with water. Fertilizer management. Fertilizer placement by band drilling nitrogen 5 to 10 em deep in dry soil or broadcast applications incorporated by dis king to the same depth have given significant yield increases and higher nitrogen use efficiency than nitrogen applied at the surface (Mikkelsen and Finfrock 1957). Surface-applied nitrogen may be nitrified and subsequently lost by denitrification or ammonia volatilized after the floodwater is applied. Ammonium nitrogen, drilled 5 to 10 em deep where reducing conditions develop within a few days of flooding, remains effective in the soil during most of the crop season. Broadcast applications to typical rice seedbeds show that ammonium nitrogen is nitrified if it is applied too far in advance of flooding. With soil temperatures that average 22°C (71.6°F), as much as 60% of the ammonical nitrogen can be converted to nitrate in 7 to 9 days (Mikkelsen and Miller 1963). The average effect of nitrogen placement at four locations was to increase rice yields by 34% over broadcast in water applications and 19% over broadcast applications on a dry seedbed (Mikkelsen and Miller 1963). Split applications of nitrogen, part as a basal application and the balance topdressed at panicle initiation, has proven effective in some parts of the world. Topdressing experiments in California have shown no superiority over adequate preplant soil applications (Mikkelsen and Miller 1963). When the basal nitrogen application is not sufficient to meet crop needs, topdressings have been effective in increasing rice yields.

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Phosphorus, potassium, and zinc are best applied to the soil before flooding. Phosphorus and potassium can be incorporated during seedbed preparation with good effectiveness. Zinc, however, should be applied to the soil surface without incorporation. Since water-sown rice has a great need for zinc during the first three weeks after planting, it is essential that it be applied in the soil surface for maximum efficiency of recovery at the lowest levels of application. Surface-applied zinc adequately meets the needs of rice during the growing season (Mikkelsen and Kuo 1976). Weed control. Weed control in water-sown rice is accomplished by proper management of water depth and the judicious use of herbicides. The same types of herbicides and methods of application described for drill-seeded rice apply with relatively few exceptions (Smith et al. 1977). Barnyard grass and other annual grasses do not survive if water is maintained between 5 and 10 em deep (De Datta 1981). Surviving grass seedlings are controlled by propanil or other appropriate herbicides applied to actively growing plants although some herbicides like propanil have no residual value. Treatments at recommended rates do not normally cause permanent injury, although propanil applied with certain seed treatments or carbamate insecticides may cause severe injury. Propanil may cause damage to sensitive crops, so spray drift must be avoided. Molinate in a granular or emulsifiable form, also used as a pre- and postemergence herbicide, is especially effective against Echinochloa spp. For maximum effectiveness, water in rice fields treated with molinate should be held for at least seven days. Phenoxy herbicides, particularly 2,4-D and MCPA, control many broadleaf weeds, sedges, and aquatic weed species. As reported for drilled rice, consideration is necessary for the proper rate and time of application. Harvesting and drying. Harvesting and drying requirements are the same as described for drill-seeded rice. Conventional harvesters are widely used where artificial systems of rice drying are available in many parts of the world. In Japan and other Asian countries, small combines are available with single row and head threshing units. Drill seeding into dry soil

Drill seeding into dry soil is widely used in the Americas, southern Europe, the U.S.S.R., and Australia, where land holdings are large and labor scarce. Typically the preplanting climate is relatively dry, land is level, and irrigation can be controlled with some precision. Drill seeding is also used in rice-producing areas of South and Southeast Asia, Africa, and South America where seeds remain in the soil until rainfall is sufficient to initiate germination and sustain seedling growth. In most drill seeding,

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however, fields are irrigated to ensure adequate moisture for stand establishment, and after an appropriate time, the fields are placed in permanent flood. Land preparation and planting. The drill seeding of rice is usually accompanied by other highly mechanized farming practices. The land is frequently plowed in the off season with a large tractor-drawn moldboard or disk plow, then disked again and harrowed before planting. When fields remain wet during the off season, the entire land preparation may be done just before planting. Harrowing is usually done with a minimum of tillage unless the soil contains large amounts of clay. A roller packer is often used to break up clods and firm the soil, helping to retain moisture. Soil preparation usually involves machine travel over the gently sloping levees which are usually rebuilt after seeding and subsequently seeded. Conventional grain drills are commonly used for drilling seed in rows spaced 15 to 20 em apart. Drills are capable of planting seed, and when equipped with a fertilizer applicator, they place the seed at a uniform depth and simultaneously place fertilizer below and to the side of the seed. In Australia, direct seeding is sometimes done into pasture sod after heavy animal grazing without previous land preparation. A planting depth of 3 to 5 em is common. Uniformity of seeding is important to uniform stand establishment and crop maturity. Water management. When soil moisture is not adequate for seed germination, fields are flushed with water. The irrigation water is drained soon after the fields are completely submerged, since seed cannot germinate and emerge if covered with both soil and water. If soil moisture becomes limiting or if crusting occurs, additional irrigation followed by drainage is used. Irrigation practices vary, but fields are usually completely submerged with 5 to 10 em of water when seedlings are 8 to 12 em tall. If the fields are weedy, water is applied to inhibit weed growth as soon as the rice has emerged. After the permanent flood is applied, the water depth is held nearly constant until several weeks before harvest. Water is usually drained only when special problems develop as with algae, water weevil, or weed. Fertilizer management. Fertilizer use on drilled rice takes on many variations, depending on variables of climate, cultivars, and crop and water management practices. The required plant nutrients, except nitrogen, are commonly either applied during land preparation or are drilled with the seed along with all or a part of the nitrogen requirement. Up to two-thirds of the nitrogen requirement is usually applied by drilling or broadcasting just before permanent flood is applied to the rice crop. Midseason nitrogen applications, broadcast into the water, are sometimes made using internode elongation or leaf analysis as a guide to proper

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timing, as reviewed by Mikkelsen and Patrick (1968). Proper timing avoids excessive plant height and increases grain yields. Zinc deficiency is a common problem on alkaline soils, causing chlorosis which affects plant survival and crop maturity. Soil applications of zinc are usually applied in combination with other fertilizer materials or applied independently by broadcasting. Applying sulfuric acid to either the soil or floodwater has provided some relief from zinc deficiency in areas where the water is derived from limestone substrate and tends to be high in dissolved calcium and bicarbonate ions (Mikkelsen and Kuo 1976). In areas of the southern United States with long growing seasons, the growth of a ratoon or "stubble" crop is possible. After the initial harvest, the ratoon crop is stimulated by applying fertilizer nitrogen. Weed control. Weed control is accomplished with judicious management of both water and herbicides. Cultivation between drill rows is difficult except with rotary weeders, and the practice is not widely used. Herbicides are an important production resource to reduce weed populations and to increase the effectiveness of other practices. The herbicides propanil and molinate, the most widely used, are applied early after seeding to control grass seedlings, sedges, and some aquatic weeds. Broadleaf weeds and sedges are usually controlled with phenoxy herbicides, especially 2,4-D and MCPA. Propanil is applied by both ground and aerial equipment as mediumfine droplets to obtain good plant coverage. Echinochloa spp. are controlled most effectively when they have from three to five leaves and are growing actively. Molinate in a granular form is applied to the water after the rice emerges. It controls Echinochloa spp. up to about 7 em tall but is not effective against broadleaf, sedges, or aquatic weeds. For effective control, water should be held on the field for at least 7 days after treatment. During cool weather or where irrigation water is to be drained, molinate is more effective against barnyard grass than is propanil. Phenoxy herbicides, including 2,4-D and MCPA, are effective against many broadleaf weeds, sedges, and aquatic plants, but are ineffective against grasses. These herbicides are usually applied about midseason when rice is in the early jointing stage. At that time, weed control is effective with minimum damage to the rice plants. A variety of new chemicals have potential for weed control in drilled rice, including thiobencarb, oxadiazon, butachlor, bifenox, and bentazon. Harvesting and drying. Self-propelled combine harvesters are used extensively in the Americas, southern Europe, the U.S.S.R., and Australia where water and mechanized drill seeding is practiced. Combines mounted on tracks or equipped with oversized pneumatic tires with large lugs for

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traction and flotation move effectively over drained fields. Harvesters are provided with the component parts necessary for cutting the crop, threshing, and separating the grain and holding it in field storage. The equipment must sometimes be specially adapted for certain harvesting conditions. Mechanical failures from working in wet soils in rainy weather sometimes make combine harvesting difficult. Since rice is usually harvested at 20 to 25% moisture content to preserve high milling yields, artificial drying must be used to reduce the grain moisture below 14% for safe storage. Deepwater and Floating Rice Areas

About 10 million ha of riceland in the world is subjected to annual floods (Table 4-1). The depth of water, duration of flooding, the rate of increase in water level, temperature, turbidity, time of occurrence, etc., vary at different locations, so that the term deepwater may have different meanings (Vergara 1977). ''Deepwater'' is a general term used to refer to a rice culture or cultivar planted where the standing water for a certain period is more than 50 em with a maximum water depth of 1 m, resulting sometimes in complete but usually partial submergence of the plant. Special selected deepwater cultivars are used in areas with uncontrolled water regimes where floodwaters annually rise from 50 em to 4 or 5 m deep. For our discussions, these areas with uncontrolled water supply are divided into deepwater and floating rice areas. Nearly half of the rice in Asia is grown in uncontrolled water regimes, with maximum water depths varying from 51 to 100 em. We would call part of this area (that with a water depth of 51-100 em) the deepwater rice area. When the water level exceeds 100 em and the water usually remains in the field for 3 to 4 months, special rice types known as "floating rice" are planted. Such conditions of uncontrolled water regimes, whether a deepwater or a floating rice area, prevail in densely populated deltas, estuaries, and river valleys of Asia in India, Bangladesh, Myanmar, Vietnam, Thailand, Cambodia, and parts of Indonesia. In Africa, deepwater rice is grown in Mali, Niger, Nigeria, Dahomey, Gambia, and Sierra Leone, and Ecuador in the Americas. Special cultivars are required since local cultivars, the semidwarf rices, cannot elongate with rising floodwater, nor can they withstand submergence; most simply drown out if grown in such deep water. The few plants that may survive will mature when the water is still high. Harvest is difficult or impossible, and panicles may rot on the stalk. It is easy to see why farmers in deepwater rice areas prefer their traditional deepwater adapted cultivars, mostly photoperiod-sensitive types, even if they yield only about 1 t/ha.

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In deepwater rice areas, dry seeding is fairly common-as well as drought stress (De Datta and O'Toole 1976). For example, in Bangladesh, sowing starts in mid-March, but with the advent and amount of rainfall as factors determining the actual date of sowing (Hasanuzzaman 1974). Further, farmers are fully constrained by uncertain rainfall during March and April and frequently sustain drought damage and poor stand establishment. In West Bengal, seed is broadcast in April through May on dry soil (Mukheijee 1974). In Thailand, deepwater rice is planted and grown under dry-season rainfall conditions until the monsoon achieves full force, any time from June to August. During this period, rice frequently suffers from severe drought (Prechachart and Jackson 1974). In Vietnam, farmers often compare deepwater rice culture to gambling. Farmers in deepwater rice areas often have to reseed once or twice if rain does not fall within several days of seeding (Xuan and Kanter 1974). Early seeding is desirable to ensure that the plants are of sufficient size to elongate when water levels rise. However, the erratic onset of the monsoon rains and the possibility of subsequent drought increase risks in early planting. If drought tolerance is bred into cultivars meant for deepwater areas, early seeding will ensure rapid establishment, thereby reducing the risk that a sudden rise of floodwater will destroy young seedlings. Another problem of deepwater rice cultivars is that they need 6 weeks of growth before their internodes elongate when submerged. Floods that occur before the plant has grown sufficiently are a major contributing factor in low plant density obtained in the deepwater rice crop. Although the rise in water level is generally 3 to 10 em/ day, in certain years and in certain places, the increase may be as much as 60 em/day during a few days of rainfall. The deepwater rices must flower after the water level has reached its peak to minimize the danger of the panicles being submerged. The traditional deepwater rices for a particular area generally flower at a time selected by farmers to ensure less crop damage and easier harvesting (Vergara 1977). Weed control is a major factor limiting the grain yields of deepwater rices. The problem of weeds usually occurs during the early stages of growth when upland conditions exist prior to flooding (De Datta et al. 1982). Although early weed competition may be decreased by heavy seeding, tall weeds that grow faster than the rice will offer competition. Farmers generally do not weed deepwater rice areas. The deepwater rices with vigorous seedling growth and spreading tillers compete better with weeds. In Bangladesh, weeding is done to a small extent under either preflooded or flooded conditions (Hasanuzzaman 1974). Except for Ipomoea aquatica, Eichhornia crassipes Salons (water hyacinth), and wild rices, weeds are not a serious problem at later stages of growth. The rise in water level eliminates most of the weeds.

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Most of the diseases in shallow water rice culture have also been reported in deepwater culture. There are very few reports on outbreaks of plant pests and diseases in deepwater rice. Salinity is another problem affecting some deepwater areas. Because most of cultivars grown in deepwater rice areas are photoperiod-sensitive, harvesting is done after floodwaters have receded. It is important that breeding, agronomic efforts, and relevant physiological studies be directed to improving the yields of deepwater rice. This effort should help a large number of subsistence farmers. It is anticipated that these breeding and research efforts will expand the area where improved cultivars can be grown. Upland Rice

Upland rice refers to rice grown on both flat and sloping fields that are not bunded, that are prepared and seeded under dry conditions, and that depend on rainfall for moisture (De Datta 1981). Upland rice is grown on three continents, mostly by small subsistence farmers in the poorest regions of the world. Grain yields are generally low: 0.5 to 1.5 t/ha in Asia, about 0.5 t/ha in Africa, and 1 to 4 t/ha in Latin America. The area planted to upland rice, however, is so large (nearly one-sixth of the world's total riceland) that even a small increase in yield would substantially influence total rice production. The following sections summarize updated information on factors that limit the grain yield of upland rice and discuss the prospects of overcoming them. Irregular rainfall

Upland rice is grown under a wide range of rainfall, from as low as 800 mm (in some years) in Uttar Pradesh, India, to 4000 mm in the Amazon Basin of Peru. Even within individual countries, the distribution of rainfall can be as diverse as the amount. For example, in the upland areas of Myanmar, rainfall from May to November can be as low as 500 mm or as high as 2000 mm; in Sri Lanka it varies from 875 to 1000 mm (De Datta and Vergara 1975). In the southern portion of West Africa, 1200 mm in two rainy seasons is separated by a short dry season (FAO Inventory Mission 1970). Some dry northern parts of West Africa have 600 mm of rain during the 4-month rainy season (Cocheme 1971). Latin American countries may have 200 mm of monthly rainfall during the growing season (Brown 1969; Sanchez 1972). These total amounts are usually adequate for growing a crop of upland rice, although they are not the most favorable for high upland rice yields. The daily rainfall is actually more critical than the monthly or annual

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total rainfall. Plants in an area that receive as much as 200 mm of precipitation in 1 day can be damaged or even killed by moisture stress if no rain falls for the next 20 days. A precipitation of 100 mm/month, distributed evenly, is preferable to 300 mm/month which all falls in 2 or 3 days (De Datta and Vergara 1975). More important than variations in the seasonal distribution of rainfall is the variability in efficiency of a given volume of precipitation which substantially depends on temperature, day length, atmospheric humidity, wind movement, and other factors determining the rate of evapotranspiration. Tropical cyclones (typhoons and hurricanes) and torrential rains also occur during the monsoon season where upland rice is planted. The strong winds may cause lodging, sterility, and grain shatter, thereby adding to the problem of too little or too much rain. The prospects for overcoming irregular rainfall with varietal development will depend on two major factors: agronomic characteristics, such as plant type and maturity group, and drought tolerance. Many upland cultivars currently grown are of the early-maturing type. Quite likely, they were bred or selected primarily for drought tolerance or drought avoidance. Nevertheless, they provide valuable material to obtain low but stable yields under upland rice culture. Major factors that often determine the partial success or failure of the crop are plant type, maturity group, and yielding ability, as well as tolerance to drought. In screening rices for drought tolerance, several techniques are available to mass screen a large number of cultivars and breeding lines (De Datta et al. 1988c). Information is meager however on practices that minimize drought damage in upland rice. Since upland rice depends on rainfall, some cultural practices have been suggested to decrease damage from water shortage (De Datta et al. 1976). Clearly, poor to imperfect drainage conditions are preferred for the growth and production of rice. All well or excessively drained soils are risky to a varying degree, but the risks may be diminished by conserving rainwater through leveling and bunding of the land as defined earlier. In low rainfall areas (800-1200 mm of annual rainfall), much of the rice area is planted to dry-seeded bunded rice, loosely termed upland rice. Similar dry seeding in bunded fields is practiced in the aus crop areas in West Bengal, India, and Bangladesh. It is also practiced in Java where a choice between a system of upland/lowland culture combination (gogo-rantja) and purely lowland rice culture will depend on the amount of rain that falls at the time of seeding. If less than 200 mm of rain is received during the planting month, the land is prepared dry and seeded dry (De Datta 1981). Fields are bunded to hold rainwater in later months. Such agronomic techniques are practiced in the "sabog-tanim" method in some parts of the Philippines to grow a direct-seeded crop in bunded dry fields. Similar

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water management was suggested on land with level topography in West Africa (Moorman et al. 1975). Bunding and leveling ofland was suggested to increase the hectarage of rain-fed riceland outside the optimum climatic zone. Very few studies have been made on the effects of mulching on moisture conservation in upland rice. Studies in Nigeria showed that moisture retention was improved by straw mulching (IITA 1972). A surface straw mulch of 4 t/ha was found to be more effective in increasing soil moisture retention than the same organic matter at 5.0 t/ha buried 10 em below the surface (liT A 1973). A well-designed windbreak often influences crop productivity and increases water use efficiency. IRRI physiologists have theorized that upland rice grown under coconut trees is less subject to drought damage primarily because the crop is shaded. It is believed that, besides providing shade, coconut trees may serve as windbreaks, reducing wind damage to the upland rice crop. Such planned tree plantings around upland rice fields may be worth considering in areas with high frequency of drought and where strong wind aggravates drought damage. This is the practice in some areas of Java, Indonesia, where a tall legume tree species is planted around upland rice fields, providing shade and serving as a windbreak for upland rice. Flowers from the legumes plants are eaten by the farmers. The leaves of the legumes are used as cattle feed and as a green manure to supplement commercial fertilizers. No matter what the annual rainfall or its distribution may be, progressive farmers sow upland rice at the onset of the rainy season and harvest it about 100 days after seeding. With the residual moisture, many farmers in Batangas Province, Philippines sow another crop that may have a high value in cash, such as onion, garlic, com or sorghum. In parts of northern India (in Uttar Pradesh), upland rice is followed by wheat. All these examples convince us that, to make upland rice economically viable, it should be considered as part of the cropping system and not as a monoculture in subsistence farming, as it is widely considered today.

Diseases and insects It is mandatory that all upland rice cultivars have a high level of blast resistance. In fact, most upland types currently grown resist blast. Sheath blight is a disease becoming serious in upland rice in the Philippines. Other diseases that may affect the growth of upland rice are Helminthosporium and Cercospora leaf spots, bacterial leaf streak, and bacterial · leaf blight.

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The picture of insect damage is less clear in upland rice than in lowland rice. Grasshoppers, stemborers, leaf folders, white-backed planthoppers, green leafhoppers, zigzag leafhoppers, and brown planthoppers are some of the pests. Considerable progress has been made in incorporating insect resistance into lowland rices. Nevertheless, many of the crosses with intermediate stature and high insect resistance should generate progenies with desirable plant type and resistance to pests and diseases. Soils on which upland rice is grown

The frequency and duration of moisture stress is affected not only by rainfall distribution but also by the capacity of the soils to retain water (De Datta and Feuer 1975). The texture of a soil affects its moisture status more than any other factor except topography. Texture is particularly important in upland rice fields that have no bunds to retain surface moisture. Rooting depth depends not only on texture of the surface soils but also on the textural profile, including the subsoil. Many upland rice soils have a sandy or loam texture and have poor moisture retention capacity. In such soils, drought stress commonly occurs unless the rainfall distribution is perfect, which is very rare. In West Africa, soils on which upland rice is grown are either freely drained or hydromorphic (with high water tables and receiving supplemental water through surface runoff). In these freely drained soils, upland rice frequently suffers from drought stress. In addition, the soils are highly weathered and generally have low nutrient content because they are derived mainly from acid rocks and are more strongly leached under the high rainfall regime of the areas in which they occur (Moorman et al. 1975). Raising a good upland rice crop on these freely drained soils requires cultivars and technology that tolerate these extremely harsh conditions. On the other hand, suitable management technology should be developed to take advantage of hydromorphic soils on which rice would suffer fewer moisture and nutrient deficiency problems. Deficiency or toxicity of elements

In general, alternate wetting and drying of the soil leads to losses of both native and applied nitrogen. It was reported that rice takes up less nitrogen under upland conditions than under lowland conditions. An upland soil has less water than has a submerged soil; iron phosphate and silica are less soluble; available nitrogen is present as a highly mobile nitrate; either soil acidity or alkalinity may be problems (Ponnamperuma 1975). Upland soils, unlike submerged soils, do not adjust their pH levels to the favorable range of 6.5 to 7 .0. This means that manganese and

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aluminum toxicities can occur in strongly acid soils and iron deficiency in alkaline soils (Ponnamperuma 1975). It seems that upland rice will do best on lower numbers of the toposequence of slightly acid soils. Sodic, calcareous, and saline soils, acid sulfate soils, and soils low in organic matter are not suitable for upland rice. It is entirely possible that interacting factors, such as lack of adequate moisture and soil problems, affect the growth and yield of rice. The need to study these factors together has been demonstrated (De Datta et al. 1975). It was reported that the reduction in grain yield caused by increased soil moisture tension may be due to either the direct effects of moisture stress or moisture stress-induced soil problems, such as iron deficiency, or to a combination of both. Therefore, moisture stress and soil problems should be considered together in evaluating the suitability of rices for upland culture. The content of water-soluble iron in most aerobic soils is too low for ready detection. The apparent iron requirement of rice is higher than that of other plants, and rice suffers from iron deficiency in well-drained upland soil. Several cultivars and breeding lines that are tolerant to iron deficiency were identified by IRRI soil chemists. These rices would perform well in most iron-deficient soils on which rice is grown. Competition from weeds and control measures

More weeds grow under upland than under lowland conditions. Sometimes, the infestation in untreated fields of upland rice is so heavy that no grains can be harvested (Sankaran and De Datta 1985). The traditional puddling and subsequent flooding which minimizes weed infestations in lowland rice is irrelevant to upland rice where flooding has been recognized as an effective weed control method for many years. Under heavy weed competition, weeds alone may reduce grain yields by as much as 80 to 100%. If perennial weeds, such as purple nutsedge (Cyperus rotundus L.), are present, competition for moisture, light, and nutrients is severe, reducing grain yields (Okafor and De Datta 1976). Much of the future expansion in riceland may have to be in upland areas, since most potential lowland areas are already under cultivation. Suitable weed control practices, including the use of herbicides, would play an important role in increasing rice production in such new areas. For example, Indonesia has 1.28 million ha under upland rice, and the upland area is gradually expanding in southern Sumatra and Borneo. If weeds such as lmperata cylindrica and C. rotundus are controlled, further increases in areas under upland rice are possible. For West Africa, reports indicate that manual weed control methods are unsuitable for continuous or large-scale farming. In areas of shifting

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cultivation, once weeds become too great a problem, the land is abandoned to forest, a cheap and effective means of control. To make upland rice culture meaningful, the highest priority should be given to research aimed at finding chemicals that are economical and effective (De Datta et al. 1986). The most feasible and economical schedule for weed control in upland rice is one which uses both chemical and mechanical methods, as well as other cultural practices. One hand-weeding often takes 350 to 600 manh/ha. However, several hand-weedings are necessary to remove weeds completely, so that chemical weed control may be essential for successful upland rice cultivation anywhere in the world. With all chemical treatments, a subsequent hand weeding is often essential to remove weeds either not controlled by the chemicals or freshly regrown (De Datta 1977a, b). The perennial nutsedge, Cyperus rotundus L., is a problem in upland rice because it germinates just before or simultaneously with upland rice; it grows with, and therefore competes with, the rice crop (De Datta and Llagas 1984). Other cultural practices

Practices such as land preparation, sowing method, seed rate, row spacing, dates of planting and fertilization affect the grain yields achieved by the upland rice farmers. Land preparation. In most of Asia, little mechanization is used to prepare land for planting. As soon as enough rain has fallen to permit initial land preparation, the field is plowed with an animal-drawn implement, and then harrowed with a comb harrow to prepare a good seedbed and to firm up the soil. Sometimes the weed seeds are allowed to germinate for a week, and then the field is harrowed for the final time, destroying all germinated seeds. Indonesian farmers generally prepare the land with animal-drawn plows during June through August. Indian farmers simply turn the soil over with country plows and pulverize it no more than 10 em deep. About 98% of the riceland in Africa is prepared manually because draft cattle are scarce, most being susceptible to the trypanosome disease. Land-preparation methods in Latin America vary greatly from country to country. In Peru's areas of shifting cultivation, for example, mature secondary forests are cut and burned during the drier months from July to September. Upland rice is then seeded by dibbling without further land preparation (Sanchez 1972). Shifting cultivation in Peru is quite similar to the slash-and-burn methods that precede planting in Malaysia, Myanmar, and Thailand.

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Sowing time, methods, seed rate, and row spacing. Upland rice farmers have learned through experience to plant early, where rainfall distribution is unimodal and the rainy season lasts about 4 months. Upland rice gives the highest grain yield and best nitrogen response if planted shortly after the first monsoon shower. · In most of the Philippines, an animal-drawn wooden plow called a "lithao" is used to open furrows. Dry seeds are then broadcast. An implement called a "kalmut" is then used to divert the seeds into rows and to cover them. In most of India, seeds are broadcast on either dry or moist soil in roughly prepared fields. Indonesian farmers seed rice broadcast on dry soils soon after the rainy season begins. In the areas of shifting cultivation in Asia, the land is cleared by the slash and burn method and seeds are then dibbled into the soil. In West Africa, rice is sown by broadcasting or dibbling. On the 40% of the upland area with annual rainfall of less than 1500 mm, seeds are dibbled into rows made with a pointed stick or a narrow-bladed hoe. On the 60% that has more than 1500 mm annual rainfall, seeds are broadcast on dry soil. Seeding methods vary greatly among Latin American countries. In Peru, eight to ten rice seeds are normally planted in holes dug with a pointed stick called a "tacarpo" at irregularly wide spacings, about 50 x 50 em. The seeds are not covered with soil. Sanchez (1972) considers this system of seeding inefficient because the rice competes poorly with weeds and ripens unevenly. In parts of Brazil, seeds are drilled with a tractordrawn seed drill, at spacing as wide as 60 em. Upland rice in Latin America, whether grown under shifting or under semimechanized cultivation, is generally spaced widely to discourage the spread of blast disease and to help the crops tolerate drought. Optimum row spacing for upland rice should be developed locally depending on two major factors: severity of drought in the area and varietal resistance to blast. To get high yields of upland rice, it is essential to plant a lodgingresistant and high-yielding cultivar. If the area suffers from annual drought or the cultivar grown is susceptible to blast, it is essential to plant at wide spacings (45-60 em), as in Brazil. Variety and fertilizer application. Most upland rices do not respond well to nitrogen; nitrogen fertilizer increases susceptibility to blast and lodging. However, considerable progress has been made through plant breeding in developing cultivars with higher levels of blast resistance. There seems to be a trade-off in plant-type requirement for drought tolerance and shading of weeds with semidroopy leaves versus lodging resistance. Many intermediate-statured cultivars with high tillering ability will lodge under heavy showers. On the other hand, they fare better than short-statured varieties under less favorable moisture status and in weedy areas. Fortunately,

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damage from lodging is less severe under upland than under lowland conditions. For this reason, the taller types are favored. Regardless of varietal type, it is better to apply nitrogen in split doses to minimize lodging and to get maximum nitrogen efficiency (De Datta et al. 1990). Results further indicate that banding the fertilizer near to the seed (10 em deep) greatly enhances nitrogen efficiency in upland rice. In phosphorus-deficient areas, banding of both nitrogen and phosphorus complements and increases the efficiency of both elements under upland rice culture. Harvesting. Many different systems of harvest have been devised for rice, depending upon environmental, cultural, religious, and economic factors. Over the world the major portion of rice is harvested by hand sickle, though various knives are also used. In highly mechanized riceproducing areas, rice is harvested entirely with high-capacity selfpropelled combine harvesters. Hand harvest is widely used because it can be done under a wide range of weather and field conditions, is adapted to small plots where rice maturity varies from plot to plot, can occur as panicles ripen, and can eliminate weeds from the harvested material. Mechanical equipment is often inoperable under these conditions. The type of equipment used in hand harvesting depends on such factors as method of planting, plant height, lodging problems, shatter losses, timeliness of harvest, method of threshing, and weather conditions during the harvest season. The shattering of ripened grain is a problem with certain cultivars, especially when the grain is too dry (below 15-20% moisture). The harvest techniques employed, including timely harvests, must minimize shatter losses. Rice subjected to excessive drying may shatter badly and may undergo "sunchecking," which causes minor cracks to develop in the kernel, favoring breakage during hulling and milling. A grain moisture value between 20 and 25% is considered satisfactory for an acceptable harvest. The sickle is used widely for harvest, although the size and design varies from country to country. Harvesting requires workers to hold the straw with one hand and cut with the other. The length of cut varies with local conditions. After cutting, the harvested portion is either dried further in the field or collected for threshing. In parts of Southeast Asia, only the panicles (plus 5-6 em of straw) are harvested. A special harvest knife, consisting of a soft metal blade set in a crescent-shaped wooden handle, is used. Individual panicles are sometimes harvested as they mature, lessening shatter losses and facilitating drying. Animal- and engine-powered reapers, windrowers, and threshers have

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been developed and are used for small plots in Europe, Japan, China, and elsewhere. Modern combine harvesters, suitable for large-scale mechanized rice production, are used in many areas, especially in the Americas, Europe, and Australia. The modern combine cuts the straw and threshes out the grain which is then separated from the straw, cleaned, and stored temporarily in self-contained bins. A high-capacity combine can harvest 6 to 12 ha/day. A part of combine harvesting essential for high milling quality is artificial drying. Threshing of hand-harvested sheaves usually requires adequate preor postthreshing drying. The sheaves may be laid on the ground, stacked, or hung on racks for drying prior to threshing or storage. Threshing involves separating the grain from the panicle by a variety of methods employing manual beating or treading, animal treading, or engine-powered threshing devices. Cleaning foreign material from the grain and drying to 13 to 16% moisture is accomplished before rice is placed in storage. FUTURE OUTLOOK IN RICE PRODUCTION TECHNOLOGY

Rice truly means life itself to the most densely populated regions of the world. About 80 to 100 million additional people must be fed each year, most of them in the poorer and less developed countries. Dependence on rice for food energy is much higher in Asia than in other regions. However, the growth rate in most irrigated area in Asia is declining (Fig. 4-5). Irrigated areas currently produce about 72% of total rice supply which may not be sustained unless the trend is reversed. Rice provides between

Growth rates (%)in net irrigated area

8....-------------, 6

Asia

Africa

11M ha

4

2 0

1970-76 1976-80 1981-85

1970-76 1976-80

1981-85

Year Figure 4-5. Limited and declining growth in irrigated area in Asia, and rapid expansion of irrigated area in Africa. From Levine et al. (1988).

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35 and 59% of the calories consumed by 2.7 billion people in Asia. In Africa and Latin America, rice provides only 8% of the food energy for almost 1 billion people. Regardless of the region, most rice-dependent economies have high population growth rates, low rice yields (except for China and Indonesia), and low GNP. To meet the projected growth in demand for rice, making allowances for the substitution of other foods in diets as incomes increase, IRRI estimates that the world's annual rough rice production must increase from the current 458 million tons to 556 million tons by 2000 and to 758 million tons by 2020-a 65% increase (1.7%/yr). For the leading ricegrowing countries in South and Southeast Asia, the need to increase rice production in 2020 is about 100% (2 .1 %/yr) (IRRI 1989). Rice is the primary or secondary staple food of nine-tenths of the lowincome people of the most densely populated regions of the world. The average annual income of those who depend primarily on rice is only $80. In spite of the impressive technological advances of the past decade, national production figures show increases that are barely high enough to meet population growth in the developing countries. The experiences of the past few years remind us that the production revolution needed to feed rice consumers has only begun. Rice output can be increased through the expansion of cultivated area or through an increase in the productivity of existing land. In South and Southeast Asia, prior to 1960, the expansion of land area provided the principal source for output growth. New lands were opened up at a pace roughly in keeping with the growth in the agricultural labor force. The gradual closing of the frontier land after 1960-more pronounced in lowland rice than in upland crops-necessitated a shift toward the use of modern yield-increasing inputs (Herdt and Barker 1977). Modern Cultivars

The most important single factor for increasing rice production has been the development of modern cultivars that respond to yield-increasing inputs. The introduction of the IRS plant type in the late 1960s generated widespread hope for coping with the chronic rice production gap that plagued many developing countries. The introduction of modern cultivars also generated improved technology to exploit the yield potential of these cultivars. More fertilizers were used for these modern cultivars than in traditional ones and the practice was termed the Green Revolution. It is still not uncommon to refer to so-called Green Revolution technology as synonymous with seed-and-fertilizer technology. Often, little emphasis is given to complementary management practices such as the control of insects and weeds and improved water management. Nevertheless, the greatest breakthrough took place in the development of modern cultivars

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that take from 120 to 125 days to mature from seed to harvest, as opposed to the 150 days required by older varieties. Shortening the growth period while obtaining a marked increase in grain yield potential was perhaps the most significant breakthrough in agriculture as a whole, and rice research in particular. These groups of modern cultivars increased rice production considerably in irrigated areas and to some extent in rain-fed areas. In the following 8 to 10 years (1967-1976), varietal development focused on two issues: (I) building up insect and disease resistance in modern cultivars, and (2) shortening the growth duration further, to around 100 days. As a result, a series of cultivars has been introduced in South and Southeast Asia which met both objectives. These cultivars provided a unique opportunity to intensify rice cropping. It is likely that future developments might generate cultivars with a still shorter growth period, such as those that would mature between 85 and 90 days. There is, however, enough evidence to indicate that shortening the growth period from 85 to 90 days sacrifices a certain amount of yield potential. Despite this shortcoming, rice with an extremely short growing period would perform a valuable role in certain environments. In many instances it would mean an extra crop instead of nothing. With the present level of technology, 100-day growth duration is perhaps the lowest limit without greatly sacrificing the grain-yield potential. Rice-Based Cropping Systems

Several terms have been used by various researchers and research administrators to explain the basic production systems of intensive cropping. For example, terminology such as double cropping, triple cropping, multiple cropping, cropping intensity, cropping patterns, continuous cropping, and cropping systems all have one thing in common: they deal with more than one-crop culture. No matter what the terminology is, increased cropping intensity will continue to play a significant role in future rice production in South and Southeast Asia. Results from agronomic research focused on crop intensification show that, under most conditions in irrigated areas and partly in favorable rain-fed lowland rice areas, at least one additional crop can be grown profitably. China has, in fact, partially met this objective by growing one additional crop in some rice-growing regions. In many areas of successful intensive cropping, the essential features are the availability of improved cropland with good irrigation and drainage, improved cultivars and management practices, the availability of farm machinery, and a high demand for farm produce. Further, a favorable ratio of labor to land must be present.

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In some parts of tropical Asia, cropping systems can be intensified by extending the growing season and by utilizing the available growing season more efficiently. Extension of the growing season can be accomplished by supplemental irrigation, early crop establishment, conservation of residual soil moisture, and growing drought-tolerant crops into the dry season. Better utilization of the growing season can be achieved by growing earlier maturing rice varieties, reducing turnaround time, harvesting at physiological maturity, and using relay cropping and intercropping. Yield increases can be partitioned between increases from irrigating a higher proportion of the area and from using more yield-increasing inputs, such as new seed and more fertilizer. In vast areas, rice is grown under rain-fed conditions. In these areas, the greatest returns may not come through an increase in yield per crop but through expansion of the area that is double-cropped. Rain-fed farms in Indonesia, Bangladesh, and northeastern India have been taking advantage of pre-monsoon rain to establish a direct-seeded rice crop. IRRI scientists have demonstrated that rain-fed lowland rice seeded directly onto nonpuddled soil at the beginning of the rainy season takes advantage of early rainfall and may allow an extra crop of rice to be grown. Continuous cropping of rice in irrigated areas and increasing rice cropping intensity in the rain-fed lowland areas are not free of problems. Evidence indicates that continuous rice cropping causes a buildup of some pests. In those intensively cropped areas, the IPM concept should be followed, minimizing pesticide use by carefully monitoring threshold levels of pests and diseases. The problems of continuous cropping are more serious and more complex, but farmers in rice-growing areas will grow rice wherever reasonable success can be achieved. The greatest challenge of the future will be to develop technology to minimize these hazards. The buildup of complex and diverse insect, disease, and weed problems could persuade us to consider cropping intensity that would include crop diversity. Modern rice cultivars mature a month or more earlier than traditional rices, leaving enough time and soil moisture to grow other crops. Residual fertilizer left in the ground after rice harvest can be converted into more food rather than be wasted. Alternate crops will use the long and warm growing season of the tropics to the fullest extent. Multiple cropping and rice-based cropping systems are not new. Farmers have grown other crops with or following rice for a thousand years, but the need to intensify cropping is far greater today than ever before. Studies are underway in most rice-growing countries to find the biological potentials of different cropping systems. The development of intensive farming schemes that are slanted to the needs of small-scale farmers rank high in priority.

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Since cropping intensity and pattern are controlled by the physical, economic, and social resources, and by the environment, a knowledge of the environments in which we work and how they limit cropping potential is important. The researcher who understands the environment and the existing and potentially available resources is equipped to design improved patterns to make more efficient use of the available physical resources. He must, at this point, have a source of improved component technology (cultivars, pest management, new crops, etc.). He puts potentially feasible cropping patterns together with socioeconomic resource requirements that can be used in his target area. These cropping patterns, together with their management and input requirements, become potential cropping systems. Potential cropping systems must be tested for their adaptation to the physical and socioeconomic environment. The testing of cropping systems thus requires farmer participation at an early stage (Garrity 1990). Improved cropping systems aim at more efficient and more complete use of farmer resources. To be successful, they must both produce more agricultural products and improve farmer welfare. The traditional practice of intercropping (growing two compatible crops, such as corn and upland rice, simultaneously in alternate rows) is highly suited to situations of limited land and surplus labor. Intercropping corn and upland rice produces as much as 1 1/3 ha to every 1 ha of corn and upland rice planted separately. Intercropping uses inputs efficiently. Besides increased food production, intercropping and multiple cropping lessen the risk of total crop failure and provide higher income and more balanced nutrition to farm families than does the monoculture of rice. A future goal, then, is to find the sequences and combinations of crops that will increase productivity and improve farmer welfare while using resources more effectively. The first task is to provide a choice of alternative cropping patterns which fit the soil type, drainage, and water availability pattern of the region. More than one alternative cropping pattern is needed, because as intensity increases, labor and power usually become limiting factors. The efficient use of both of these resources depends on diversification of farm enterprises. Diversification also compensates for the loss of stability in any given cropping pattern as intensity is increased. In the future, it will be necessary to develop sufficient component technology for crop management, such as tillage method, and control of insects, diseases, weeds, and nematodes. Further, it is necessary to develop varieties with suitable plant type, maturity, and management characteristics, and develop the know-how to manage the crops under a range of conditions of fertility, tillage, water, and cash and labor availability. In most parts of monsoonal Asia, rice is transplanted during the early

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part of July and harvested toward the middle of November, a period when a crop may not suffer from major stress problems. Crop intensification in this typical environment complex can be achieved by (1) using early crop establishment techniques, (2) using a premonsoon upland crop during the short period just before the main rice growing season, (3) introducing a second rice crop necessarily in combination with an early seeded first rice crop, (4) reducing the turnaround time between the first and second rice crops, (5) ratoon cropping of the first rice crop, (6) planting upland crops (after a single rice crop), (7) reducing the turnaround time between rice and upland crops, and (8) relay cropping or intercropping. Development of New Cultivars and Technology

We know that the areas under irrigation are increasing, so efforts to develop cultivars and technology that would produce still higher yields than those currently in use are being intensified. We also know that even under irrigated conditions, the grain yield potential of existing cultivars and technology is not achieved under field conditions. We must understand why farmers are not able to get as high a yield as the experiment stations. Are the conditions in the experiment stations so different from those in farmers' fields that variety and technology would not give similar performance? If so, we must learn what are the constraints to high yields under farm conditions. If the variety and technology are not entirely suitable under farm environments-biophysical and socioeconomic-then we must develop varieties and technology appropriate to the farmers' conditions. The problem of increasing grain yield is far greater for rain-fed farming than for irrigated farming. Constraints on high yields in rain-fed farms are innumerable. Even today, for about three rice farms out of four, there is no improved cultivar and technology that can significantly increase production beyond current levels. For these millions of subsistence farmers, the best available technology consists of hardy but low-yielding local rices and ancient farming methods. These farmers depend solely on the unpredictable monsoon rains to water their crops. Some grow upland rice and manage it like wheat. Others bund their fields to hold water on the land in paddies, but the monsoon rains often fail and drought sets in. The new short-statured rices and modern technology are not suited for hundreds of millions of farmers-those on whose fields floodwaters annually rise to depths of 50 em to 4 or 5 m. Many farmers have problem soils such as saline and alkaline soils or toxic soils with excess soluble iron and aluminum, and in mountains and hilly regions, rice suffers from cold damage. This shows that in droughtand flood-prone areas, in mountainous areas, and areas with problem soil

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the Green Revolution has not occurred. Varietal and technology development for these disadvantaged environments should be sharply focused to raise production and income for millions of poor farmers. New technology

If production in irrigated areas needs to be increased further and new cultivars are introduced into rain-fed areas, it is important to develop new technology that will encourage more efficient use of agricultural inputs. Fertilization. One area of recent concern is increasing fertilizer use efficiency. Energy-based commodities such as fertilizers and pesticides were badly hit by the unrealistic rise in prices in 1974. The era of cheap fertilizers and pesticides is probably at an end. The millions of small-scale rice farmers who have reaped the benefits of the new rice technology often do not have the capital to use high rates of agricultural chemicals. Agronomists have demonstrated that deep placement of nitrogen fertilizer increased efficiency, sometimes saving 40% of fertilizer nitrogen with no reduction in grain yield. The greatest challenge for the future is to develop a machine that will place fertilizer in the root zone where losses are minimal. This increase in fertilizer efficiency would reduce the dependence of the rice crop on petroleum-based agricultural chemicals. Cropping systems involving legume crops and crop residue management will help farmers become more self-sufficient. Mechanization. The modern technology is referred to as seed-fertilizer technology. However, throughout Asia, the concept of modernization is closely associated not only with biological and chemical technology but also with mechanical technology. The biological and chemical technology is thought of primarily as saving land and the mechanical technology as saving labor. To raise production at the farm level in rain-fed and irrigated areas, some degree of mechanization is essential. Some mechanized processes are already taking place. For example, in land preparation under the puddled system, mechanization of some form is spreading rapidly in the Philippines and some other South and Southeast Asian countries. What is needed badly is to mechanize land preparation operations to establish a dry-seeded crop in rain-fed areas. In many parts of Thailand, dryland preparation with large tractors is practiced as labor demand is shifted from farm to industrial growth. Weed control is another operation that needs to be partially mechanized, especially in the rain-fed areas under dry seeding. Threshing is another operation where mechanization would be helpful. At present,

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losses in threshing are high in most farms in tropical Asia, although axial flow threshers designed at IRRI are gaining popularity in Thailand and the Philippines. Despite some mechanization in land preparation and threshing, there has been a substantial increase in the use of hired labor, partially replacing family labor. That is because mechanization complements existing methods of land preparation, weeding, and threshing, allowing family labor to be used in other more profitable farm operations. As a result, there is a net gain of hired labor utilization in South and Southeast Asia (Cordova and Barker, 1977). It appears, then, that emphasis on mechanization in tropical Asia would help increase rice production. In the future, if the availability of labor decreases, mechanization will help minimize labor costs. In other words, the experiences in East Asia will generally be repeated in tropical Asia if alternative employment of labor is generated. With rice varieties of shorter growth duration, growing two crops where one grew before or three crops where two grew before is distinctly possible. We must not only reexamine the issue of land preparation but also relate it to seeding method, pest and disease control, and harvesting practices in order to maximize the potential of the new rice technology. In short, the changes witnessed to date in rice growing in tropical Asia are only a beginning. The future holds great prospects for increased rice production through improved technology and national efforts to minimize production constraints. In the developed countries of the world, a relatively advanced degree of rice production technology already exists. Annual rice yields are reasonably stable each year, primarily because the production resources are available and used at near-optimum levels. Extreme climatic variables do not usually occur, complete irrigation control is possible, and disease and insect pests cause fewer problems. Annual rice production in these developed countries tends to be influenced more by general national agricultural policies than production constraints. Rice production and trade policies are closely linked, usually with production-support programs that guarantee to domestic producers prices somewhat above normal world price levels. These policies have multiple objectives: to achieve certain broad social and economic gains by insuring a desired level of income and stability to farms and equitable pricing policies for consumers. Production policy is sometimes further complicated by the use of rice surpluses in world markets on concessional terms, creating irregularities in normal commercial trade channels. Rice yields per hectare in developed countries are not likely to make large short-term gains in the foreseeable future. With a high level of

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technology already in existence, future yield increases will be small and largely geared toward improved rice varieties, more careful farm management, and the skillful combination of the various production resources. Among the major objectives for improved rice production in the developed nations would be 1. Development of high-yielding cultivars with short stature and lodg-

ing resistance, earlier maturity, resistance to major insect and disease pests, better adaptability to climatic conditions, and grain qualities preferred by various consumer groups 2. Development of improved cultural practices, including seeding techniques, insect, disease and weed control, improved water management, and desirable crop rotations which effectively deal with residues from the rice crop As in developing countries, industrialized countries can look to greater prospects for increased grain yields per hectare through improved cultivars, technology, and greater national efforts to control the environment for rice production. Increasing the environmental consequences of growing rice will need to be considered in management decisions-water, fertilizers, pesticides, straw burning, etc. The worldwide rate of food production has recently been increased along with population. The Green Revolution of the late 1960s raised the hope of avoiding massive hunger. In Asia, where rice is mostly produced and consumed, the Green Revolution has been dramatic. Several developing countries now feed their own people. SUSTAINABLE RICE PRODUCTION

The Green Revolution technologies, by focusing on high-resource environments, were highly successful in addressing production problems. It has become increasingly critical, however, to generate technologies that will consider agricultural employment and still address the needs of production and environmental protection in low-resource areas. Research results have emphasized that high input use to intensify agricultural production is not always an appropriate solution. The sustainability of rice production will be a consequence of improved technical management and the inherent stability and sustainability of the entire agro-economic system. Part of the critical research agenda should include genetic diversity; germplasm collection, characterization, and utilization; developing cultural practices for efficient resource use; quantifying the effects of lowland rice culture on global climate change and

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of global climate change on rice production; fine-tuning of IPM; improving management of sloping uplands to conserve topsoils; and involving farmers' participation in cropping systems (De Datta 1990). REFERENCES

Ampong-Nyarko, K., and De Datta, S. K. 1989. "Ecophysiological studies in relation to weed management strategies in rice." In Proc. 12th Asian-Pacific Weed Sci. Soc. Conf., vol. I, 31-45. Seoul, Korea, 21-26 Aug. Ampong-Nyarko, K., and S. K. De Datta. 1991. A Handbook on Weed Control in Rice Manila, Philippines: IRRI (in press). Barker, R., H. E. Kauffman, and R. W. Herdt. 1975. Production constraints and priorities for research. IRRI Agric. Econ. Dept. Paper 75-8. Mimeo. Bartholomew, W. V. 1972. Soil nitrogen supply and space processes and crop requirements. N. Carolina State Univ. Tech. Bull. 6. Bhattacharyya, A. K., and S. K. De Datta. 1971. Effects of soil temperature regimes on growth characteristics, nutrition, and grain yield of IR22 rice. Agron. J. 63(3) 443-9. Broadbent, F. E. 1979. "Mineralization of organic nitrogen in paddy soils." In Nitrogen and Rice, edited by I. Watanabe, 105-118. Manila, Philippines: IRRI. Broadbent, F. E., S. K. De Datta, and E. V. Laureles. 1987. Measurement of nitrogen utilization efficiency in rice genotypes. Agron. J. 79:786-91. Brown, F. B. 1969. Upland rice in Latin America. Int. Rice Comm. News!. 18:15. Buddenhagen, I. W., and J. Ter Vrugt. 1977. "Rice ecosystem research and evaluation in tropical agriculture-IITA approach." In Proc. Rice in Africa Conf., Int. Inst. Trap. Agric., 7-11, March, Ibadan, Nigeria. London: Academic. Buresh, R. J., and S. K. De Datta. 1990. Denitrification losses from puddled rice soils in the tropics. Bioi. Fert. Soils 9:1-13. Chang, T. T. 1976. The origin, evolution, cultivation, dissemination and diversification of Asian and African rices. Euphytica 25:425-41. Chang, T. T., and B. S. Vergara. 1972. "Ecological and genetic information on adaptability and yielding ability in tropical rice varieties." In Rice Breeding. Los Banos, Philippines: IRRI. Chapman, A. L., and D. S. Mikkelsen. 1963. Effect of dissolved oxygen supply on seedling establishment of water-sown rice. Crop Sci. 3:392-7. Cheng, Yun-Sheng. 1981. "Drainage of paddy soils in Taihu Lake Region." In Proc. Symp., Paddy Soils., edited by Inst. of Soil Sci., Academia Sinica, 517-23. Beijing: Science Press. Cocheme J. 1971. "Notes on the ecology of rice in West Africa." In Notes on the Ecology ofRice and Soil Suitability for Rice Cultivation in West Africa. Rome: U.N. Dev. Prog., Food Agric. Org. U.N., (in French). Cordova, V. G., and R. Barker. 1977. The effect of modern technology on labor utilization in rice production. IRRI Sat. Sem. May 28. Mimeo.

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De Datta, S. K. 1977a. "Some relevant research on weed control and soil and crop management in rainfed rice at IRRI and other locations in tropical Asia.'' In Proc. Rice in Africa Conf., March 7-11, Int. Inst. Trop. Agri., Ibadan, Nigeria. London: Academic. De Datta, S. K. 1977b. Weed control in rice in Southeast Asia: Methods and trends. Philipp. Weed Sci. Bull., 4:39-65. De Datta, S. K. 1980. "Weed control in rice in South and Southeast Asia." In ASPAC Food & Fertilizer Technology Center Ext. Bull. 156. De Datta, S. K. 1981. Principles and Practices of Rice Production. New York: Wiley. De Datta, S. K. 1986a. Improving nitrogen fertilizer efficiency in lowland rice in tropical Asia. Fert. Res. 9:171-86. De Datta, S. K .. 1986b. Technology development and spread of direct-seeded flooded rice in Southeast Asia. Exp. Agric. 22:417-26. De Datta, S. K .. 1987a. "Advances in soil fertility research and nitrogen fertilizer management for lowland rice." In Efficiency of Nitrogen Fertilizers for Rice, Proc. Meeting Int. Network on Soil Fertility and Fertilizer Evaluation for Rice, Aprill0-16. Manila, Griffith, New South Wales, Australia. Los Banos, Philippines: IRRI. 27-41. De Datta, S. K. 1987b. Nitrogen transformation processes in relation to improved cultural practices for lowland rice. Plant and Soil 100:47-69. De Datta, S. K. 1988a. "Overview of rice weed management in tropical rice." In Proc. Nat. Seminar and Workshop on Rice Field Weed Management, 1-24. Malaysian Agricultural Res. & Development Inst. (MARDI) and the Malaysian Agricultural Chemicals Assoc. De Datta, S. K. 1988b. "Urea: Experience in lowland rice." In Proc. Int. Symp. Urea Technology and Utilization, edited by E. Pushparajah, A. Rusin, and A. T. Bachik, 23-37. Kuala Lumpur: Malaysia Soc. of Soil Science. De Datta, S. K. 1988c. "Progress in weed science and control technology in tropical rice." 14-35. In Proc. 2, Weed Problems and Weed Management in South and Southeast Asia. Keynote paper presented at 2nd Tropical Weed Science Conf. 6-10 December, Phuket, Thailand. De Datta, S. K. 1989. Technology and economics of weed control in small rice farms in the Asian tropics. Paper presented at Symp., Economic Weed Control, 12th Asian-Pacific Weed Science Soc. Conf. 21-26 August, Seoul, Republic of Korea. De Datta, S. K. 1990. Sustainable rice production: Challenges and opportunities. Paper presented at the 17th Session of the Int. Rice Commission (IRC), Food and Agriculture Organization of U.N. 4-9 February, Goiania, Goias, Brazil. De Datta, S. K., and K. Ampong-Nyarko. 1988. "Cost-effective integrated weed management practices for irrigated rice." In Proc. 19th Anniversary and Annu. Conv. Pest Control Council of the Philippines, Sacred Heart Center, Cebu City, 27-38. De Datta, S. K., and P. C. Bernasor. 1971. Selectivity of some new herbicides for direct-seeded flooded rice in the tropics. Weed Res. 11(1):41-6. De Datta, S. K, and P. C. Bernasor. 1973. Chemical weed control in broadcastseeded flooded tropical rice. Weed Res. 13:351-4.

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De Datta, S. K., and F. E. Broadbent. 1988. Methodology for evaluating nitrogen utilization efficiency by rice genotypes. Agron. J. 80:793-8. De Datta, S. K., and R. J. Buresh. 1989. Integrated nitrogen management in irrigated rice. Adv. Soil. Sci. 10:143-69. De Datta, S. K., and R. Feuer. 1975. "Soils on which upland rice is grown." In Major Research in Upland Rice. Los Banos, Philippines: IRRI. De Datta, S. K., and J. C. Flinn. 1986. "Technology and economics of weed control in broadcast-seeded flooded tropical rice." In Weeds and the Environment in the Tropics, Proc. lOth Asian-Pacific Weed Sci. Soc. Conf, 51-74. De Datta, S. K., and K. A. Gomez. 1974. Changes in soil fertility under intensive rice cropping with improved varieties. Soil Sci. 120(5):361-6. De Datta, S. K., and M. Z. Hoque. 1982. "Weeds, weed problems, and weed control in deepwater rice areas." In Proc. 1981 Int. Deepwater Rice Workshop, 427-42. Manila, Philippines: IRRI. De Datta, S. K., and M. S. A. A. Kerim. 1974. Water and nitrogen economy of rainfed rice as affected by soil puddling. Soil Sci. Soc. Amer. Proc. 38(3):515-8. De Datta, S. K., and M.A. Llagas. 1984. "Weed problems and weed control in upland rice in tropical Asia." In An Overview of Upland Rice Research, Proc. 1982 Upland Rice Workshop, 321-41. Philippines: IRRI. De Datta, S. K., and J. C. O'Toole. 1976. "Screening deep water rices for drought tolerance." In Proc. Deep Water Rice Workshop. Int. Rice Res. Inst., Rice Division, 8-10, Nov. Bangkok, Thailand. De Datta, S. K., and W. H. Patrick, Jr. 1986. Nitrogen Economy of Flooded Rice Soils. The Netherlands: Martinus Nijhoff. De Datta, S. K., and B.S. Vergara. 1975. "Climates of upland rice regions." In Major Research in Upland Rice. Los Banos, Philippines: IRRI. De Datta, S. K., and P.M. Zarate. 1970. Environmental conditions affecting the growth characteristics, nitrogen response and grain yield of tropical rice. Biometeorol. 4:71-89. De Datta, S. K., W. P. Abilay, and G. N. Kalwar. 1973. "Water stress effects in flooded tropical rice." In Water Management in Philippine Irrigation Systems: Research and Operations. Los Banos, Philippines: IRRI. De Datta, S. K., R. J. Buresh, and C. P. Mamaril. 1990. Increasing nutrient use efficiency in rice with changing needs. Fert. Res. (in press) De Datta, S. K., R. J. Buresh, M. I. Samson, and Kairong Wang. 1988a. Nitrogen use efficiency and nitrogen-15 balances in broadcast-seeded flooded and transplanted rice. Soil Sci. Soc. Amer. J. 52:849-55. De Datta, S. K., T. T. Chang, and P. G. Vicencio. 1976. "Prospects for overcoming yield-limiting factors of upland rice." In Proc. 2nd Sem., Variety Improv. West Africa Rice Develop. Assoc. (WARDA), 13-17 Sept., Monrovia, Liberia. De Datta, S. K., F. G. Faye, and R.N. Mallick. 1975. "Soil-water relations in upland rice." In Soil Management in Tropical America, Proc. Sem., 10-14 Feb. CIAT, Cali, Colombia. De Datta, S. K., K. A. Gomez, and J. P. Descalsota. 1988b. Changes in yield response to major nutrients and in soil fertility under intensive rice cropping. Soil Sci. 146:350-8.

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De Datta, S. K., J. A. Malabuyoc, and E. L. Aragon. 1988c. A field screening technique for evaluating rice germplasm for drought tolerance during the vegetative stage. Field Crops Res. 19:123-34. De Datta, S. K., and D. S. Mikkelsen. 1985. "Potassium nutrition of rice." In Potassium in Agriculture, 665-700. Madison, WI: Amer. Soc. Agron. De Datta, S. K., K. Moody, and S. Sankaran. 1986. "Integrated weed management practices for upland rice." In Progress in Upland Rice Research, 447-60. Philippines: IRRI. De Datta, S. K., W. N. Obcemea, R. Y. Chen, J. C. Calabio, andR. C. Evangelista. 1987b. Effect of water depth on nitrogen use efficiency and nitrogen-15 balance in lowland rice. Agron. 1. 79:210-6. De Datta, S. K., J. K. Park, and J. E. Hawes. 1968. Granular herbicides for controlling grasses and other weeds in transplanted rice. Int. Rice Comm. News 17(4):21-9. De Datta, S. K., F. A. Saladaga, W. N. Obcemea, and T. Yoshida. 1974. "Increasing efficiency offertilizer nitrogen in flooded tropical rice." In Proc. FAI-FAO Sem. Optimising Agricultural Production Under Limited Availability ofFertilizers, 265-88. De Datta, S. K., A. C. F. Trevitt, J. R. Freney, W. N. Obcemea, J. G. Real, and J. R. Simpson. 1989. Measuring nitrogen losses from lowland rice using bulk aerodynamic and nitrogen-15 balance methods. Soil Sci. Soc. Amer. 1. 53:1275-81. Engelstad, 0. P., A. Jugsujinda, and S. K. De Datta. 1974. Response of flooded rice to phosphate rocks varying in citrate solubility. Soil Sci. Soc. Amer. 38(3):524-9. Evans, L. T., and S. K. De Datta. 1979. The relation between irradiance and grain yield of irrigated rice in the tropics, as influenced by cultivar, nitrogen fertilizer application and month of planting. Field Crops Res. 2(1):1-17. Food and Agric. Organ. (FAO) Inventory Mission. 1970. "Development of rice cultivation in West Africa. Preliminary report of the Food and Agric. Organ. U.N. Inventory Mission, July." In Conf. Plenipotentiaries for the Establishment of a West Africa Rice Development Assoc., 1-4 Sept., Dakar, Senegal. Mimeo. FAO. 1973. Research on Rice. Bangkok, Thailand: Food and Agric. Organ., U.N. Proj. Working Paper l. FAO. 1989. Food Outlook, no. 3. Fillery, I. R. P., and S. K. De Datta. 1986. Ammonia volatilization from nitrogen sources applied to rice fields. II. Floodwater properties and submerged photosynthetic biomass. Soil Sci. Soc. Amer. 1. 50:86-91. Fillery, I. R. P., J. R. Simpson, and S. K. De Datta. 1984. Influence of field environment and fertilizer management on ammonia loss from flooded rice. Soil Sci. Soc. Amer. 1. 48:914-20. Garrity, D. P. 1990. Choice in onfarm experiments: Researcher-implemented, farmer-implemented, or farmer-participatory trials? Paper presented at the Workshop, On-Farm Research Design Including Farmers Participatory Experiments, 13-17 February, at NarendraDeva Univ. of Agriculture and Technology (NDUAT), Kumarganj (Faizabad), India.

RICE CULTURE

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Hasanuzzaman, S. M. 1974. "Cultivation of deep-water rice in Bangladesh." In Proc. Int. Sem. on Deep-Water Rice. Bangladesh Rice Res. Inst., Joydevpur, Dacca, Bangladesh. Hasegawa, S., M. Thangaraj, and J. C. O'Toole. 1985. "Root behavior: Field and laboratory studies for rice and nonrice crops." In Soil Physics and Rice, 383-95. Manila, Philippines: IRRI. Herdt, R. W., and R. Barker. 1977. "The status of potential of food production in Asia." In Proc. Int. Rice Res. Inst.-V.N. Univ. Workshop on Interfaces Between Agriculture, Nutrition and Food Sciences, Feb. 28-May 3. Los Banos, Philippines: IRRI. Int. lnst. Trop. Agric. (liTA). 1972. Farming Systems Program, Ann. Rep. for 1972. Ibadan, Nigeria. Int. Inst. Trop. Agric. (liT A). 1973. Farming Systems Program, Ann. Rep. for 1973. Ibadan, Nigeria. IRRI. 1974. Ann. Rep. for 1973. Los Banos, Philippines: IRRI. IRRI. 1988a. World Rice Statistics. Manila, Philippines: IRRI. IRRI. 1988b. Agricultural Economics Database. Manila, Philippines: IRRI IRRI. 1989. Implementing the Strategy Work Plan for 1990-1994. Manila, Philippines: IRRI. Jana, R. K., and S. K. De Datta. 1971. "Effects of solar energy and soil moisture tension on the nitrogen response of upland rice." In Proc. Int. Symp., Soil Fert. Eva/., edited by J. S. Kanwar, N. P. Datta, S. S. Bains, D. R. Bhumbla, T. D. Biswas. New Delhi: Indian Soil Sci. Soc., Ind. Agr. Res. Inst. J ayaweera, G. R., and D. S. Mikkelsen. 1990. Ammonia volatilization from flooded soil systems: A computer model. I. Theoretical aspects. Soil Sci. Soc. Amer. J. 54: 1447-55. II. Theory and model results. Soil Sci. Soc. Amer. J. 54: 1455-62. III. Validation of the model. Soil Sci. Soc. Amer. J. 54:1462-8. Kundu, D. K., and S. K. De Datta. 1988. Integrated nutrient management in irrigated rice. Paper presented at the Int. Rice Res. Conf. 7-11 November, Los Banos, Laguna, Philippines. La!, R. 1985. "Tillage in lowland rice-based cropping systems." In Soil Physics and Rice, 283-307. Manila, Philippines: IRRI. Levine, G., R. Barker, M. Rosegrant, and M. Svendsen. 1988. Irrigation in Asia and the Near East in the 1990s. Mahapatra, I. C., S. R. Bapat, and M. Singh. 1974. Economics of fertilizer use. Fert. Market News 5(12):1-17. Malabuyoc, J. A., E. L. Aragon, and S. K. De Datta. 1985. Recovery from drought-induced desiccation at the vegetative growth stage in direct-seeded rainfed rice. Field Crops Res. 10:105-12. Mambani, B., S. K. De Datta, and C. A. Redulla. 1989. Land preparation requirements for rainfed rice as affected by climatic water balance and tillage properties of lowland soils. Soil & Tillage Res. 14, 219-30. Mandai, L. N., and R. R. Mitra. 1982. Transformation of iron and manganese in rice soils under different moisture regimes and organic matter applications. Plant and Soil 69:45-56. Matsunaka, S. 1975. "Weed control and herbicides in rice culture." In Rice in Asia. Tokyo: Univ. of Tokyo Press.

184

RICE: PRODUCTION

Matsushima, S., et al. 1968. Analysis of yield determining process and its application to yield prediction and cultural improvement of lowland rice. LXXXI. Combined effects of air temperature, water temperature, shading and the amount of fertilizers in seedling period on the characteristics of seedlings of rice plants. Proc. Crop Sci. Soc. Japan, 37:169-74. Mikkelsen, D. S. 1987a. Rice production and constraints in Latin America. Rice Comm. Newslett. 36:38-43. Mikkelsen, D. S. 1987b. Nitrogen budgets in flooded soils used for rice production. Plant and Soil 100:71-97. Mikkelsen, D. S., and D. C. Finfrock. 1957. Availability of ammoniacal nitrogen to lowland rice as influenced by fertilizer placement. Agron. J. 49:296-300. Mikkelsen, D. S., and S. Kuo. 1976. "Zinc fertilization and behavior in flooded soils." In The Fertility of Paddy Soils and Fertilizer Applications for Rice. Taipei, Taiwan: Asian-Pacific Food and Fertilizer Tech. Cntr. Mikkelsen, D. S., and M.D. Miller. 1963. Nitrogen fertilizer of rice. Calif Agric. 17:9-11. Mikkelsen, D. S., and W. H. Patrick, Jr. 1968. "Fertilizer Use on Rice." In Changing Patterns in Fertilizer Use. Madison, WI: Soil Sci. Soc. Amer. Mikkelsen, D. S., S. K. De Datta, and W. 0. Obcemea. 1978. Ammonia volatilization losses from flooded rice soils. Soil Sci. Soc. Amer. J. 42:725-30. Moody, K. 1975. "Weed control systems for upland rice production." In Rep. Expert Consultation Meet. Mechanization ofRice Production, Int. Inst. Trap. Agric. 10-14 June. lbadan, Nigeria. Moomaw, J. C., P. G. Baldazo, and L. Lucas. 1967. Effects of ripening period environment on yields of tropical rice. Int. Rice Comm. Newslett., Special Issue, 18-25. Moorman, F. R., and R. Dudal. 1965. Characteristics of soils on which paddy is grown in relation to their capability classification. Soil Surv. Rep. 32. Land Devel. Dept. Bangkok. Moorman, F. R., H. P. F. Curls, and J. C. Ballaux. 1975. "Classification of conditions under which rice is grown in the tropics with special reference to mechanization in West Africa." In Rep. Expert Consultative Meet. Mechanization of Rice Production, 10-14 June. Int. Inst. Trop. Agric., lbadan, Nigeria. Mukherjee, D. K. 1974. "Problems of deep-water rice cultivation in West Bengal and possibilities for evolving better varieties." In Proc. Int. Sem., DeepWater Rice, Bangladesh Rice Res. lnst., Joydevpur, Dhaka, Bangladesh. Nguu, N. V., and S. K. De Datta. 1979. Increasing efficiency of fertilizer nitrogen in wetland rice by manipulation of plant density and plant geometry. Field Crops Res. 2(1):19-34. Nuttonson, M. Y. 1951. Ecological crop geography and field practices of Japan. Japan's natural vegetation and agro-climate analogues in North America. Washington, DC: Amer. Inst. of Crop Ecol. Obcemea, W. N., J. G. Real, and S. K. De Datta. 1990. Effect of soil texture and nitrogen management on ammonia volatilization and total nitrogen losses. Philipp. J. Crop Sci. (in press). Obermueller, A. J., and D. S. Mikkelsen. 1974. Effects of water management

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and soil aggregation on the growth and nutrient uptake of rice. Agron. J. 65:627-32. Okafor, L. 1., and S. K. De Datta, 1974. Competition between upland rice and purple nutsedge for nitrogen, moisture, and light. Weed Sci. 24(1):43-6. Okafor, L. 1., and S. K. De Datta. 1976. Chemical control of perennial nutsedge (Cyperus rotundus L.) in tropical upland rice. Weed Res. 16:1-5. Orticio, M. R., and F. N. Ponnamperuma. 1977. Zinc deficiency: a widespread nutritional disorder of rice in the Philippines. Paper presented at 8th Ann. Sci. Meeting of the Crop Sci. Soc. of the Philippines, La Trinidad, Benguet. Mimeo. Pathak, A. K., S. Sankaran, and S. K. De Datta. 1989. Effect of herbicide and moisture on Rottboellia cochinchinensis and Cyperus rotundus in upland rice. Trap. Pest Manage. 35(3):311-315. Patrick, W. H., and D. S. Mikkelsen. 1971. "Plant nutrient behavior in flooded soils." In Fertilizer Technology and Use. Madison, WI: Soil Sci. Soc. Amer. Inc. Pillai, K. G. 1978. Recent results of herbicide trials on rice in India. Paper presented at Int. Rice Res. Conf., April 1978. Los Banos, Philippines: IRRI Mimeo. Ponnamperuma. F. N. 1972. "The chemistry of submerged soils. Advan. Agron. 24:29-96. Ponnamperuma, F. N. 1975. "Growth limiting factors of aerobic soils." In Major Research in Upland Rice. Los Banos, Philippines: IRRI. Prechachart, C., and B. R. Jackson. 1974. "Floating and deepwater rice varieties in Thailand." In Proc. Int. Sem. Deep-Water Rice, Bangladesh Rice Res. In st., J oydevpur, Dacca, Bangladesh. Rodriguez, M.S., and R. Lal. 1985. Growth and yield of paddy rice as affected by tillage and nitrogen level. Soil Tillage Res. 6:163-78. Sakai, K. 1949. Cytohistological and thermmatological studies on sterility of rice in northern part of Japan, with special reference to abnormal hypertrophy of tapetal cells to low temperature. Rep. Hokkaido Agric. Exp. Sta. 42:1-46. Sanchez, P. A. 1972. Agricultural techniques to optimize the potential production of new varieties of rice in Latin America. Paper presented at Seminar on Rice Policies in Latin America. 10-14 October, 1971, Int. Cntr. Trop. Agric. (CIAT), Cali, Colombia. Sanchez, P. A. 1973a. Puddling tropical rice soils: 1. Growth and nutritional aspects. Soil Sci. 115(2): 149-58. Sanchez, P. A. 1973b. Puddling tropical soils: Effects of water losses. Soil Sci. 115(4):303-8. Sankaran, S. and S. K. De Datta. 1985. Weeds and weed management in upland rice. Adv. Agron. 38:283-337. Sasaki, T. 1927. On the relation of temperature to the longitudinal growth ofleaves of rice plant. Proc. Crop Sci. Soc. Japan. 1:23-42. Senewiratne, S. T., and D. S. Mikkelsen. 1961. Physiological factors limiting growth and yield of Oryza sativa under unflooded conditions. Plant Soil 14(2): 127-46. Sharma, P. K., and S. K. De Datta. 1985. "Effects of puddling on soil physical

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properties and processes." In Soil Physics and Rice, 217-34. Manila, Philippines: IRRI. Sharma, P. K., and S. K. De Datta. 1986. Physical properties and processes of puddled rice soils. Adv. Soil Sci. 5:140-78. Sharma, P. K., S. K. De Datta, and C. A. Redulla. 1989a. Effect of percolation rate on nutrient kinetics and rice yield in tropical rice soils. I. Role of soil organic matter. Plant and Soil119(1):111-20. Sharma, P. K., S. K. De Datta, and C. A. Redulla. 1989b. Effect of percolation rate on nutrient kinetics and rice yield in tropical rice soils. II. Role of straw amendments. Plant and Soil119(1):121-6. Shastry, S. V. S., W. H. Freeman, and K. G. Pillai. 1974. New rice varieties need rational management for optimum yields. Jojana 18(2):33-6. Smith, R. J., Jr. 1983. "Weeds of major economic importance in rice and yield losses due to weed competition." In Weed Control in Rice. Los Banos, Philippines: IRRI. Smith, R. J., W. T. Flinchum, and D. E. Seaman. 1977. Weed Control in U.S. Rice Production. Agric. Handbk. 497, Washington, DC. Stangel, P. J. 1985. Changes in the form and price of fertilizer-A global perspective. ASPAC Ext. Bull. 217. Food and Fertilizer Technology Center, Taiwan, Republic of China. Stansel, J. W. 1975. "Effective utilization of sunlight." In Six Decades of Rice Research in Texas. Res. Mono. 4. Texas Agric. Exp. Sta. Vergara, B. S. 1977. "Deep water rice. II. Problems of deep-water rice culture." In Genetic Evaluation and Utilization (GEU) Training Program. Los Banos, Philippines: IRRI. Watanabe, 1., B. C. Padre, Jr., and S. T. Santiago. 1981. Quantitative study on nitrification in flooded rice soil. Soil Sci. Plant Nutr. 27:373-82. Xuan, V., and D. G. Kanter. 1974. "Deep-water rice in Vietnam: Current practices and prospects for improvement." In Proc. Int. Sem., Deep-Water Rice. Joydevpur, Dhaka, Bangladesh: Bangladesh Rice Res. Inst. Yodkeaw, M., and S. K. De Datta. 1989. Effects of organic matter and water regime on the kinetics of iron and manganese in two high pH rice soils. Soil Sci. Plant Nutr. 35(3):323-35. Yoshida, S. 1973. Effects of C0 2 enrichment at different stages of panicle development on yield components and yield of rice (Oryza sativa L.). Soil Sci. Plant Nutr. 19:311-6. Yoshida, S., G. W. Mclean, M. Shafi, and K. E. Mueller. 1970. Effects of different methods of zinc application on growth and yields of rice in calcareous soil, West Pakistan. Soil Sci. Plant Nutr. 16(4): 147-9. Yoshida, T., and B. C. Padre, Jr. 1974. Nitrification and denitrification in submerged Maahas clay soil. Soil Sci. Plant Nutr. 20(3):241-7.

5 Rice Diseases T. W. Mew International Rice Research Institute

INTRODUCTION

In Asia, rice production has entered an era of change. The tall and low tillering traditional cultivars are giving way to improved semidwarf and nitrogen-responsive modern cultivars. In countries where rice cultivation and production are intensive and an average grain yield/ha is well over 3 t, the use of chemicals for pest management has also increased at an unprecedented rate (Mew 1988). In tropical Asia, these chemicals are primarily insecticides and herbicides, while in the temperate zone in eastern Asia, disease control represents the biggest share of chemical use. The use of modern semidwarf cultivars has been the key factor in the increase in rice yield; however, this was not achieved without a cost. As crop intensity increases, together with the demand for such inputs as fertilizer, diseases have become the destabilizing factor to rice production. The continuous and prolonged planting of cultivars with uniform genotypes over a large area exerts high selection pressures on those pathogen populations to which the cultivars are resistant, and enhances disease development and spread in favorable environmental conditions of less economic important diseases. 187

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Plant pathologists have focused their efforts on improving the understanding of major diseases and generating information gathered. They have worked closely with plant breeders to develop resistant cultivars, on the one hand, and to investigate and formulate disease management technology as part of the integrated pest management (IPM) strategy on the other. Remarkable progress has been made in both endeavors. The truth is that pathogens are shifty, and over the years, the disease spectrum in the rice fields has presented a changing scenario. The Bengal famine due to brown spot (Padmanabhan 1973) is unlikely to repeat itself, and other rice diseases, whether their epidemic potential is high or low, are also unlikely to create a similar effect. However, diseases remains a production constraint that is inevitably a reality. The blast epidemics in Korea (Crill 1981), Egypt (Balal personal communication) and elsewhere (Lee 1986), and the bacterial blight and virus diseases (grassy stunt and tungro) in southern and southeastern Asia in recent years (Mew 1987; Ou 1985; Ling 1983; Upadhyay 1985) never could match in scale the catastrophe of the Bengal famine but have nonetheless caused panic and hardship to farmers where the epidemic occurred. Since detailed information about rice diseases has appeared in Ou' s Rice Diseases (1985), the author intends simply to summarise and present a brief account of the common diseases. More important, the author has attempted to underline the importance of the diseases in specific rice ecologies. The diseases are discussed according to the various pathogen groups: bacterial, fungal, viral, and nematodal. BACTERIAL DISEASES

A dozen of rice diseases are caused by bacterial pathogens (Mew 1990). Among them, two are in the genus Xanthomonas, two in Erwinia, and the others are all in Pseudomonas. Rice diseases caused by mycoplasmalike organisms will not be treated in this section. Rice bacterial diseases can be classified into four major groups according to the tissues and organs of the rice plant generally infected: seedling diseases, foliar diseases, leaf sheath and grain diseases, and culm and root diseases. The classification is for convenience of management and for diagnosis. The fact that some of the pathogens attack more than one type of plant tissue or organ points out the difficulty in classifying diseases this way. Likewise, most of the bacterial pathogens attack the grain and are therefore likely to be seedborne and seed-transmitted; yet the role of seedborne inoculum and transmission varies according to the ecosystem in which the rice is cultivated. The two Erwinia species reported to cause rice diseases are E. chrysamthemi pv. oryzae (Goto 1979) and E. herbicola (Azegami et al.

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1983), causing foot rot and palea browning, respectively. Other Erwinia spp., especially those in the carotovora and amylovora groups, have also been isolated from seeds and are reported to attack rice (Ou 1985). It remains to be confirmed, however, if these bacteria do indeed affect the rice plant. Species of Pseudomonas attack rice grains, seedlings, leaf blades, and leaf sheaths. P. fuscovaginae (Tanii et al. 1976) and P. glumae (Kurita and Tabei 1969), which cause sheath brown rot and grain rot, respectively, are most economically important. P. plantarii (Azegami et al. 1987) and P. syringae pv. oryzae (Kuwata 1985), which cause seedling and halo blight, were reported recently. The economic importance of the last two is not fully understood. In the genus of Xanthomonas, X. oryzae pv. oryzae (Ishiyama 1922) and X. oryzae pv. oryzicola (Fang et al. 1957), which cause bacterial blight and bacterial leaf streak, respectively, are two of the most important bacterial pathogens of rice. Bacterial blight has been known for over a century in Asia, but other bacterial diseases of rice are relatively recent. Most, if not all, affect the grain and sheath, causing discoloration. The taxonomic status of most of the pseudomonads is uncertain. Little information is available about their economic importance, ecology, or epidemiology. Bacterial Blight (Xonthomonos oryzoe pv. oryzoe] The disease

Bacterial blight (BB) has been reported and studied for over a century (Tagami and Mizukami 1962; Ou 1985). However, its importance to rice production in tropical Asia was recognized only after the introduction of modern cultivars which are highly responsive to nitrogen fertilizer. Besides its occurrence in Asia, which has caused several epidemics in recent years, the disease has also been found in northern Australia on cultivated rice and on the wild species Oryza rujipogon and 0. australiensis. More recently, the disease has become widespread in Queensland. In Africa, the disease was reported in Mali, Nigeria, Cameroon, Senegal, and Burkina-Faso (Mew 1990). Bacterial blight has occurred in the Americas, first in Latin America and the Carribean region (Lozona 1977) and, more recently, in the United States (Jones et al. 1989). It therefore occurs globally; its distribution ranges from 20°S in Queensland, Australia, to 58°N in Hei-Long-Jiang, China, and from sea level to the Tibetan Plateau. Usually, it is more prevalent in the wet season than in the dry, and in lowland than in favorable upland environments. In subtropical regions where there are double crops, it occurs in both rice crops. In temperate countries such as Korea and Japan, where most rice is monocropped under irrigation, the disease is

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common during the rainy months from July to October, especially following heavy rainstorms. In countries like China and India, where several cropping patterns are practiced, the disease behaves according to the climatic conditions (Mew 1989). Damage due to BB has been extensively studied by many scientists. In Japan, about 300,000 to 500,000 ha of rice were affected by bacterial blight in the 1950s (Mizukami and Wakimoto 1969). Quantitative data on yield losses caused by BB are available, and its epidemic potential is well-documented (Mew 1987). In infected plants, the 1000-grain weight is reduced; in the panicles, the sterility percentage is increased as the number of immature grains increases (Fang et al. 1963). Grains from diseased plants are easily broken during milling. Moderate infection causes a 10 to 20% yield reduction, while in severely affected fields, the reduction may be as high as 50% (Ou 1982; Wakimoto 1968). In fields with kresek, the number of missing hills is increased, total crop failure is likely, and replanting is necessary (Mew 1990). Greenhouse experiment of potted rice plants inoculated with races of the bacterial pathogen resulted in yield losses of 47 and 75% for moderately resistant and susceptible cultivars, respectively (IRRI 1967). Reddy et al. (1979) found a high correlation between loss of rice yield and BB severity. Economically, bacterial blight is important mostly in Asia. If the cultivars have no adequate resistance, the disease can be very destructive. Several epidemics have occurred during the past two decades in Asia. In West Africa, bacterial blight has caused severe damage to rice cultivation in several districts. In the United States, it has caused concern to seed growers. Disease cycle

Although seed transmission may not play a major role in the tropics, the bacteria can infect the seeds and be seedborne. When the disease has already become established in a country, seed may not be an important source of inoculum. In countries where the disease has not yet been recorded, however, seed transmission may be very important (Mew et al. 1989). Infected straws, infected voluntary rice plants, and weed hosts are likely to play a major role in the disease cycle from one season to another. Once the disease starts in the field, its spread is closely related to rain splash. Wind-driven rain can carry the inoculum far and predispose the plants for infection. The causal bacterium

The causal bacterium was earlier named as Bacillus oryzae Hori et Bokura (1911) and was renamed Pseudomonas oryzae Uyeda and Ishiyama (1922) according to the Migula system, and later transferred to Bacterium oryzae

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Nakata following E. F. Smith's concept. Subsequently, it was named Xanthomonas oryzae. Later it was adopted to Xanthomonas campestris pv. oryzae (Uyeda and Ishiyama) dye (Dye et al. 1980) according to the Committee on Taxonomy of Phytopathogenic Bacteria of the International Society for Plant Pathology. More recently, it has been revised to X. oryzae pv. oryzae (Swings et al. 1990). Isolates of X. oryzae pv. oryzae constitute a homogenous group regardless of their geographic origin. The bacterial cell is a short rod with rounds, 0.55 to 0.75 x 1.35 to 2.17 ~-tm, with a single polar flagellum. The bacterium is gram-negative and nonspore-forming. The cells are single and surrounded by mucous capsules, and are joined to form an aggregated mass. On nutrient agar, the colonies are circular, convex, whitish-yellow to straw yellow, and opaque against transmitted light, with smooth surfaces and entire margins. They produce a water-soluble yellow pigment. Symptoms

Bacterial blight is a vascular disease and the infection is systemic. The bacterium normally enter the host through wounds or natural openings such as water pores and ends up in the xylem tissues, where it multiplies and moves throughout the plant (Mew 1987). Bacterial blight in rice has two symptoms: kresek and leaf blight. Kresek is the more destructive manifestation of the disease. At seedling and early tillering stages, leaves of the entire plants turn pale yellow and wilt. The kresek symptom may be observed from 1 to 6 weeks after transplanting; normally, new leaves become greyish-green and begin to fold up and roll along the midrib. The occurrence of kresek is usually associated with the age ofthe plants at the start of infection. In the tropics, transplanted rice is normally raised in nursery beds. At 21 days after seeding, the seedlings are pulled, and the operation often injures the roots. Prior to transplanting the tips of the leaves are often cut off. This provides entries for the bacteria, which multiply rapidly. Initially, the plants wilt, and finally the tiller or the whole plant may die. Kresek was first found in Indonesia and is now very common in the tropics. It has also been observed in Africa, China, and Korea. Leaf blight is the more common disease syndrome; the disease is often referred to as bacterial leaf blight. Lesions on the leaf blades may extend to the leaf sheath. The lesion enlarges in length and width and may have wavy margins. It turns a whitish-straw color from its initial water-soaked greyish or yellowish grey in 1 to 2 weeks. Bacterial ooze may be observed if the conditions are humid and warm. Leaf blight occurs at all growth stages, but it is common from maximum tillering until maturity. Yellow or pale yellow leaf is also considered a syndrome of bacterial blight. This is however, a secondary effect ofleafblight (Mew et al. 1986).

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Host range

Xanthomonas 0. pv. oryzae infects Oryza sativa and related wild species. Among the weed species, Leersia sayanuka is the most important weed in Japan. L. oryzoides, Zizania latifolia, Leprochloa chinensis, L. filiformis, L. panacea, and Cyperus rotundis are other hosts. Disease control

The disease has been effectively controlled by using resistant cultivars. Where resistant cultivars have been extensively planted in wide areas for a number of years, new races have emerged in the bacterial population with different virulence. Race identification is based on reaction to a set of differential cultivars. Fourteen resistance genes have been identified and utilized in national and international breeding programs, and resistant cultivars are developed and planted by farmers. Various chemicals such as dimethyl-nickel-carbamate, phenazine, kasumin, oryzemates, and copper compounds, as well as antibiotics have been evaluated for controlling the disease. In spite of all these efforts, no efficacious chemicals can be recommended or are used by farmers both in the tropics and temperate regions. Chemical seed treatment has been recommended with little measurable success. Bacterial Leaf Streak (Xanthomonas oryzae pv. oryzicola] The disease

Bacterial leaf streak (BLS) has been reported in most of tropical Asia and in Africa. It is common in lowland as well as upland rice during the rainy season. It has not been found in Japan, Korea, northern or central China, or other temperate countries. No realistic estimate exists as to how much damage the bacteria may cause. Some estimates of yield losses in susceptible cultivars in the wet season range from 7.0 to 8.3%, depending on disease intensity and, more important, on the stage of the crop (Ou 1962). Losses in the dry season are almost negligible at 1 to 3%. The infection can be observed at any growth stage of the crop depending on the weather. A recent report from China placed the disease in epidemic proportions. Apparently vast areas are affected by the disease, causing premature yellowing of all infected leaf tissues (Zhu zhe-da personal communication). This could be serious if the effect is at maximum tillering and flowering. Symptoms

Bacterial leaf streak was at first confused with bacterial blight (Ou 1985). It is characterized by small, water-soaked, interveinal, translucent streaks that advance lengthwise. The streaks begin as dark green and become

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translucent later. Eventually, the streaks may coalesce to cover the entire leaf, which turns brown, then greyish-white, and then dies. At this stage, the disease may be indistinguishable from bacterial blight. Old lesions turn light brown. In the tropics, numerous tiny bacterial exudates appear as yellow beads on the surface of the lesions, a distinct feature of the disease. Causal bacterium

In China, Fang et al. (1957) were the first to distinguish bacterial leaf streak from bacterial blight; they named the new bacterial pathogen Xanthomonas oryzicola. In accordance with the revision of Taxonomy of Phytopathogenic Bacteria (Dye 1978), the bacterium was renamed Xanthomonas campestris pv. oryzicola (Fang et al. 1957; Dye 1978), but more recently revised to X. oryzae pv. oryzicola (Swings et al.). Fang et al. (1975) provided details concerning the bacterium. The cells are rods, 1.2 x 0.3 to 0.5 11-m, usually single, and occasionally in pairs, but not in chains. They are nonspore-forming and motile by a single polar flagellum, with no capsules. The bacteria are gram-negative and aerobic, and they grow favorably at 28°C. Colonies on nutrient agar are pale yellow, circular, smooth with entire margins, convex, and viscid. All isolates grow luxuriantly on glucose yeast calcium carbonate agar medium with typical yellow-pigmented colonies. They produce a moderate amount of acetoin. X. o. pv. oryzicola displays a distinct protein pattern on polyacrylamide gels different from that of X. c. pv. oryzae. All X. o. pv. oryzicola isolates show strong gelatinase activity and effect strong peptonization of litmus milk, together with alkalinization starting at the top of the medium and reduction starting from the bottom. All isolates grown on 0.2% vitaminfree Casamino acids without a carbon source. Based on numerical analysis of phenotypic features and of protein electrophoregrams, all isolates of X. o. pv. oryzicola belong to one single phenon. The bacterial pathogen appears to have a fairly narrow host range, limited to species of Oryzae. No other gramineous weeds are reported to host the bacterium. There are severallysotypes, and isolates with different virulence exist. Disease cycle

Bacterial leaf streak is commonly observed in the rainy season. The disease normally spreads through rain splash, irrigation water (distance dissemination), and leaf contact (within the canopy in a single field). The bacteria enter the host tissues through stomata or wounds, and multiply in the parenchymatous tissues. Soon after a lesion develops, bacterial exudates form on the surface of the lesion under high temperature and humidity. The high temperatures that prevail in the tropics favor disease development and permit the growth of the organism throughout the year. In the dry season in the tropics, although the conditions are favorable for

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disease development, there is little natural infection or spread due to the lack of predisposing factors such as rain splash. The bacterial pathogen is believed to be seedborne and seed-transmitted (Fang et al. 1957); however, no experimental data are available to support the conclusion. The movement of seeds harvested from infected plants is believed to introduce the disease to new localities. Once the disease is established, seedborne inoculum seems to have little effect. Disease control

The disease can be adequately managed by host plant resistance. Many modern cultivars have various degree of resistance, but such cultivars have not been used solely for the purpose of controlling the disease. No other control measures are actually practiced to control the disease; however, many of the field sanitation operations, and use of clean seed should be helpful. Grain Rot (Pseudomonas g/umoe] The disease

The disease was first reported in 1958 in Japan (Hashioka 1969), but it probably had occurred long before it was noticed. In Japan, the affected area has increased every year (Uetmatsu et al. 1976). In 1975, 900,000 ha of rice were infected on northern Kyushu Island alone. The bacterium causes rot in seedlings raised indoors in seedboxes for mechanical transplanting. This has become one of the major problems since the advent of this technology. The pathogen also infects the grain. The disease is caused by P. glumae, which colonizes the surface of the basal part of the ligule and the inner surface of the lemma (U etmatsu et al. 1976). The bacterial cells invade the interspaces of host cells in the outer epidermis and the spongyparenchyma of the lemma. The disease is favored by high temperature and high humidity. Grain rot incidence is highest if infection occurs at heading and the plants are incubated at 32°C. When the plants are placed in a moisture chamber for 24 h, the infected plants may produce grain rot incidence as high as 100%. The effect of temperature on the growth of P. glumae and the development of grain rot is also positively correlated. The bacteria grow well at 28 to 32°C. High night temperature also favors grain rot development. The disease may reach 100% at 28/28°C. Symptoms

In a mature crop in the field, the disease is usually observed at the milky stage during the second crop in Taiwan (Chien et al. 1983) and during the wet season in tropical countries. Diseased grains are scattered throughout

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the panicles, but in severe cases more than half of the grains may be attacked. The sterile lemmas of infected grains are purplish-brown to dark brown, but the branches remain green. Infected grains are shrunken and pale green, then become dirty greyish, yellowish, and dark brown. Eventually, the grains dry up. When infection of the grains is light, only the palea becomes discolored. The discoloration is limited to the grain; both rachises and rachis branches are free from discoloration. The infected part of the hulled rice seed is grey, which is a distinct diagnostic feature. The causal bacterium

The disease is caused by P. glumae, a gram-negative aerobic rod with a single polar flagellum. The bacteria form white viscid colonies on nutrient agar. They are nonfluorescent on King's Medium B. The bacterium liquifies gelatin, reduces litmus milk and nitrate, produces ammonia and lecithinase, and hydrolyzes Tween 80. It is oxidase-positive and arginine dihydrolase-positive, and it grows at 40°C. The bacterial pathogen can be easily differentiated by a selective medium composed of the following: 1.3 g KH 2P04 , 1.2 g Na2HP0 4 , 5.0 g (NH 4)z S0 4 , 0.25 g MgS0 4 • 7H20, 24 mg Na2Mo0 4 , 2Hz0, 10 mg EDTAFe, 10 JLg L-cysteine, 10 g D-sorbitol, 50 mg pheneticillin potassium, 10 mg ampicillin sodium, 10 mg cetrimide, 1 mg methyl violet, 20 mg phenol red, and 15 g agar in 1 L of distilled water. Both P. glumae and other pseudomonads grow well in this selective medium, but confidence will be improved if it is used in combination with serological methods. Sheath Brown Rot [Pseudomonas fuscovaginae) The disease

Sheath brown rot was first observed in Hokkaido, Japan, and reported in 1975 by (Tanii et al. 1976) and co-workers. It occurred widely in the ricegrowing areas on that island. It may have occurred long before being identified as a bacterial disease, but the disease syndrome was often considered cold weather damaged. A similar disease caused by P. marginalis was reported in 1962; it was later confirmed to be sheath brown rot. Another similar disease was reported in Latin America (Zeigler and AI·· varez 1987). Scientists believed the disease was identical to sheath brown rot. It has caused substantial crop losses in a large rice-producing area in tropical and temperate South America. In addition to Asia and Latin America, this disease has also been reported in the Burundi highlands of Central Africa and Madagascar (Maraite et al. 1989; Rott et al. 1988). Symptoms

Initial symptoms appear on the flag leaf sheaths as water-soaked, dark green, irregular spots that enlarge to become dark to greenish brown

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blotches with no definite margins and bacterial ooze (Miyajima and Akita 1975 a,b). Brown necrosis on lower rachis also appear in nonemerged panicles when severe infection occurs on flag leaf sheaths. Young panicles in diseased sheaths are also affected by the pathogen. The florets exhibit water-soaked brown flecking surrounded by green tissues, resulting in dark or greyish-brown discoloration. Infection also occurs in the grains. The typical lesions on grains appear to show brown or water-soaked lesions on the glumes. Later, the lesions turn greyish-brown. Grains are partly or totally brownish and abortive or abnormal in shape. In 1986, it was confirmed that the disease was seedborne and seed-transmitted. The bacterium caused discoloration and rotting of the sheath surrounding the rice panicle and grains. Discolored seed from many tropical countries has been shown to be infected with this pathogen. Affected sheaths enclosing the panicle may show extensive water-soaking and necrosis, with poorly defined margins. Glumes become discolored before emerging from infected panicles. Grains on affected tillers may be symptomless, have only small brown spots, or be completely discolored and sterile. Seedlings are also affected by the disease, which occurs after transplanting (Miyajima and Akita 1975a,b). The diseased seedlings first show a yellowish-brown discoloration in the lower leaf sheaths, and then the leaf blades wilt. Eventually, the lower sheaths change to dark or greyishbrown and become soft, and rotting occurs in the lower leaf blades and young new leaves. At temperatures lower than 20°C, rotting is prevalent. Causal bacterium

Brown rot is caused by Pseudomonas fuscouaginae (Tanii et al. 1976; Miyajima 1983), a gram-negative, nonspore-forming rod with round ends and a size of 0.5 to 0.8 x 2.0 to 3.5 f.Lm. The bacterial cells occur singly or in pairs and are motile by one to four polar flagella. Colonies form on nutrient agar at 4 to 5 days at 28°C, are white to creamy, smooth, glistening, convex, gransluscent, circular, and butyrous, with a diameter of 3 to 5 mm. The bacteria produce a green fluorescent diffusable pigment on King's Medium B. No slime is produced on nutrient agar containing 5% sucrose. The bacteria are strictly aerobic and show no growth at 40°C The bacterial pathogen appears similar to other arginine dihydrolase and oxidase positive fluorescent pseudomonads. It differs from P. oryzicola in oxidase activity in that the latter is negative. It is most similar to the saprophytic pseudomonads P. marginalis, P. putida, and P. fluorescens biotypes G. P. fuscovaginae also seems to have a specific antigen as well as several antigens common to other Pseudomonas spp. Rott et al. (1988) believed that the bacterial pathogen can be properly identified by a pathogenicity test on 3-week-old rice plants, through posi-

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tive sero-reaction to anti-P. fuscovaginae serum (1/200), and biochemical profile identical to the one of P. fuscovaginae, including oxidase and arginine dihydrolase positive and acid production from trehalose. Host range

P. fuscovaginae has pathogenicity not only on Oryza sativa, but also on Hordeum vulgare, Triticum aestivum, Avenae sativa, Zea mays, Lolium perenne, Bromus marginatus, Phleum pratense, and Phalaris arundiacea (Tanii et al. 1976 and Miyajima 1983). The pathogens in northern Japan are divided into four lysotypes based on sensitivity to three bacteriophage strains. Disease cycle

Pseudomonasfuscovaginae survives in rice straw kept indoors in temperate regions but cannot be detected in straw scattered in an open field. In the tropics, other hosts as well as infected grains may be important sources of inoculum. The bacteria have also been detected on healthy leaves of Agrostis clavata var. nukabo and other gramineous weeds growing near rice fields. The bacteria are also able to survive and multiply on rice plants, and usually reach a high population level at booting. In field plants, the bacteria have been detected at high population levels on healthy leaf blades and sheaths 8 days before diseased plants were visible in the field, and then on all healthy plants 2 days after disease occurrence. Sheath brown rot occurs widely and frequently in rice. Severe infection is usually associated with rice plants suffering from cold temperature stress (Miyajima and Akita 1975a). The symptoms may appear early at tillering stage (in northern Japan, in early June to early July). Lesions characteristic of sheath brown rot occur on the sheaths of the flag leaves from booting to heading. Dark greenish water-soaked lesions appear on the sheath and later turn brown, with the central portion of the lesion becoming greyish-brown. At high temperature and low humidity the lesions produced are elongated and oblong, while at low temperature and high humidity, irregular lesions with unclear margins develop. In severe cases, the sheaths are totally dark brown or greyish brown. The panicles are withered and dried. Lesions may occur on sheath other than the flag leaves. Occasionally, streaks appear on the base of the flag leaves. Day rather than night temperature affects disease development. Low daytime temperature increases disease severity and delays heading. The bacteria multiply in the flag leaf sheath and panicle tissues and cause severe damage after inoculation when the plants are kept in a chamber with day/night temperatures of 17/11 or 23/17°C. Less bacterial multiplication and disease development occurs at 29/23°C.

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P. fuscovaginae survives in dry diseased straw, grains, and on wild gramineous plants. It is seedborne and seed-transmitted. Occurrence of the disease is associated with resident populations prior to infection (Miyajima 1989). Disease control

Streptomycin alone or with oxytetracycline (15 + 1.5%) has proved highly effective and can be used to control the disease. Dry heat therapy (65°C, 6 days) is also effective. Kasugamycin significantly reduces but does not eradicate the pathogen for seedborne inoculum (Zeigler and Alvarez 1987).

FUNGAL DISEASES

Among the 80 rice diseases, the fungal diseases form a major group. Ou (1985) has listed 40 fungal diseases of rice, i.e., approximately 50% of the recorded rice diseases are caused by fungal pathogens. These pathogens are distributed worldwide, covering almost every rice-growing country. As a group, they infect rice plant parts ranging from seed to leaves, leaf sheath, culm, nodes, panicles, and roots. Some have caused devastating epidemics, while others maintain endemicity year after year in certain localities. Many others affect the rice plant in ways that are not wellunderstood. Among all the fungal diseases, perhaps all rice diseases, blast has received the widest attention since ancient times (Ou 1985). On other diseases, little or no research work is being done. Bakanae (Fusarium moniliforme) The disease

This is a typical seedborne disease that occurs from seedbed to the mainfield. It is widely distributed in all rice-growing countries. The seed is infected at flowering. When severely infected, the kernel develops a reddish discoloration due to the presence of the conidia of the fungus. The fungus also infects the branches of the panicle. Yu and Sun (1977) believed that ascospores of G. fujikuroi are liberated and contaminate the grains in the field. Ascospores are generally discharged during harvest and on rice straw heaped in the paddy after rainfall, even during daytime. The fungus may survive in seed as long as 4 to 10 months at room temperature and up to 3 years in cold storage at 7°C. The fungus also produce conidia on diseased plant parts, and these are easily disseminated by wind and water to cause new infection. Studies in Taiwan indicate that grain contamination

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is due principally to airborne ascospores, but contamination may also occur from conidia during the harvest. Although most seedlots yield 100% F. moniliforme on agar plates, only 33% bakanae disease incidence occurred when infested seeds were planted in the soil. The pathogen is both seed- and soilborne. Chang (1973) found that both conidia and ascospores survived for about 4 months on stems under room conditions as well as in soil in the field. Panicle infection occurs in Taiwan but at a low frequency compared to that in Japan. Conidia and perithecia on diseased stems are often washed into the soil by rain, and diseased plants and stubble are often discarded in the field. Therefore, paddy soil is commonly contaminated by F. moniliforme. F. moniliforme survives in soil by means of thick-walled hyphae or macroconidia which function as chlamydospores; their longevity in soil is about 4 months in Taiwan. Panicle infection is due to airborne ascospores. No secondary cycle of the disease occurs in a single crop period.

Symptoms The most common symptom is the internode elongation. Diseased plants are slender, pale yellowish in color, and taller than the healthy ones. Diseased seedlings may die during or after transplanting, and healthy seedlings may be infected in the main field after transplanting. Besides elongation, bakanae symptoms include leaves bending over and the production of adventitious roots at nodes on the lower portion of the culms. Under high humid conditions, the infected culms may turn bluish-black, and blue-black perithecia form on the surface of the culm (Sun and Snyder 1981). Wilting is common in susceptible cultivars under high inoculum density, while node elongation is common among susceptible cultivars at low inoculum density (Lee et al. 1980).

Causal organism The. teleomorph of the pathogen is Gibberella fujikuroi (Sawada) Ito. Sun and Snyder (1981) indicated that the correct name should be G. moniliformis. Perithecia are dark blue, spherical to ovate, somewhat roughened outside, 250 to 330 x 220 to 280 fLm. The asci are cylindrical vistin-shaped, flattened above, 90 to 102 x 7 to 9 fLm, with four, six, or (seldom) eight ascospores. The ascospores are one septate, 14 to 18 x 4.4 to 7 fLm. The anamorph is Fusarium moniliforme. The microconidia are more or less agglutinated in chains and remain joined or are cut off in false heads. The surface of colonies is usually rose-colored with white colony mycelium. Macroconidia are delicate, slightly sickle-shaped or almost straight, narrow at both ends, occasionally somewhat bent into a hook at

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the apex, distinctly or slightly foot-celled at the base, three to five or, rarely, six to seven septate. The chlamydospores are absent but present with thickened walled hyphae. Physiologic Specialization

There are many rice cultivars resistant to bakanae. IR973-ll-2-2 and Nongbaek, Taipei 309, Minehikari, and Taichung 65 are highly resistant to all the races tested, even 4 weeks after seeding. The method of soaking seeds in Fusarium moniliforme spore suspension is used to determine the existence of pathogenic races of the fungus. The percentage of seedlings of each differential cultivar infected by each isolate was computed as criteria for evaluating varietal resistance and pathogenic races. Using this technique, Estrada et al. (1981) identified eight race groups from 56 isolates in the Philippines on eight differential cultivars. The diseases are common in both tropical and temperate environments under irrigated rice ecosystems. Control measures

Since the pathogen is seedborne and the infected seed occurs in high frequency, seed treatment is the important control measures of the disease. Many fungicides have been used for this purpose, beginning with formalin and mercuric compounds. More recently, benomyl, thiram-benomyl, and thiram-thiophanate methyl wettable powders have become common as seed disinfectants. Then, in 1980, benomyl-resistant strains were found (Ogawa 1988). Many of the fungus strains are less sensitive to benomyl. Currently in Japan, the wet powder dressing process is recommended to contain thiram-thiophanate-methyl or captan thiabendazole. This process has been registered for controlling the bakanae (Ogawa 1988). Blast (Pyricularia oryzae] The disease

Blast is one of the oldest rice diseases (Ou 1985). It is found wherever rice is cultivated: in irrigated and rain-fed lowlands as well as upland ecosystems, and from temperate to tropical zones. It is most important, however, in the irrigated ecosystem in the temperate regions, in tropical uplands, and in drought-prone rain-fed lowland ecosystems. It also occurs in deepwater and tidal wetland, but its importance in these ecosystems is negligible. The fungus infects leaves, nodes, panicles, and grains, though perhaps not the roots. The leaf sheath is either not or seldom infected, but the collar-the joint between leaf blade and leaf sheath-is infected; this is known as collar rot. Infection can begin in seedlings on mature plants.

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Infection of seedlings, often called seedling blast, occurs before the threeleaf stage. The infection is usually caused by seed borne inoculum. Seedling leaf blast occurs on leaves at three-leaf stage in seedbeds. Leaf blast normally refers to the blast on leaves after transplanting to the main fields, which occurs at any stage from tillering to maturity. Such classification is very distinct in irrigated rice in the temperate environment. In the tropics, however, whether in upland or rain-fed lowland, seedling blast and leaf blast may not be so distinguishable. When infected at the seedling or tillering stages, the plants are often completely killed under conditions favorable to the fungus. Leaf blast also causes stunting. Its effect is to reduce the active tiller numbers and seed weight. Panicle blast, which occurs at the flowering stage, is more destructive and causes great losses. Although blast occurrence in the tropics may be occasional, its epidemic potential is very high under favorable conditions. Symptoms The fungus causes elliptical spots with pointed ends on leaves. The center of the lesion is usually greyish or whitish, and the margins brown or reddish-brown. From seedborne inoculum, the lesion usually appears on the coleoptile and the first leaf (Kato et al. 1988). Initially, only a tiny water-soaked spot appears, which rapidly turns yellowish-brown, causing the bud to rot. When the seedling grows bigger, the dark green spot can be observed, but it turns brown shortly. Infected seedlings are often killed. The leaf blast lesions are of four different types (Chinese Academy of Agricultural Sciences 1986): the acute type, the chronic type, the brown necrotic spot type, and the white spot type. The acute-type lesions are round, dark green spots with pointed ends, the latter developing into a spindle shape. The center has a colony appearance caused by conidiophores and conidia. Such lesions usually develop in favorable conditions where the cultivar is also susceptible. Chronic lesions are very common. They are spindle-shaped with a greyish-white center and brown margin. Although sporulation occurs from these lesions, the quantity is considerably less than with the acute type. The brown necrotic spot type of lesions are pinhead size. They are common on resistant cultivars or on old leaves. The lesions usually will not sporulate. White-spot lesions appear as white or greyish-white, round or irregular in shape, and may gradually develop to ovoid shape. Such lesions usually develop when the conditions change to unfavorable for lesion development. When the conditions, such as weather, change to favorable, these lesions may become acute. Node blast occurs when the node is infected (Ou 1985). At first it is a

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tiny black spot, then becomes a ring around the node, and eventually enlarges to cover the whole internode and becomes dark brown. Under high humidity, the infected node is covered with a greenish-grey powdery substance which is the conidiophores and conidia. At a later stage, the node dries up and the plant is easily lodged. Panicle blast often occurs on the neck, rachis and panicle branches (Ou 1985). At first, the disease appears as a water-soaked brown spot which extends in both directions. The infected area appears brown or dark green. Usually panicle blast occurs after the panicle has exserted, but occasionally, the infection also takes place before the panicle exsertion. The fungus infecting the grains and glumes is known as grain blast, and the lesions vary (Kato et al. 1988). The distinct lesion only appears on the grains during the soft dough stage and is similar to the lesion on the leaf blades. As the panicles mature, the lesions on the grains become indistinct. When the glume is infected, it often turns to greyish-brown or dark brown. It has no effect on grain filling. The causal fungus

Rice blast is caused by Pyricularia oryzae Cavara. The conidiophores are grey, single or in fascicles that are usually simple and show sympodial growth, geniculate toward the apex and with a swollen base (Ou 1985). Conidia are pyriform to obclavate, about 17 to 23 x 8 to 11~-tm, have two septate with small basal hilum, and are aerogenous. Cultural morphology varies greatly with isolates and with the media used. The amount of aerial mycelium varies from very scant to a thick cottony mass. The colony color also varies from whitish or cream, through buff, grey, to dark olivaceous. The fungus is predominantly uninucleate; however, it has a consistent number of binucleate cells (10%) among the intercalary cells which may be important for heterokaryon formation (Leung and Williams 1986). The chromosome number observed during meiosis in fertile crosses is six, but the chromosome number in some isolates in the natural populations may vary. The teleomorph is Magnaporthe grisea (Hebert) Barr. It is an ascomycete that produces asci with eight unordered ascospores. Natural isolates of P. oryzae differ in host range, with regard to the ability both to attack various species of grasses and to infect different cultivars of rice. P. oryzae is a highly variable fungus that is capable of producing numerous races with virulence to rice cultivars possessing specific gene(s) for resistance (Ou 1985). The number of races and race compositions prevailing in an area is dependent on the cultivars grown in the area. Race identification has been very intensive in some of the major rice-growing countries such as China, Japan, Korea, the United States, and many others. It is done on the basis of differential cultivars, many

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differential cultivars being used in the different countries. In 1963, an international effort was made to test, establish, and eventually select a set of eight cultivars for this purpose. Different systems were also developed to name or designate the races (Atkins et al. 1967; Ling and Ou 1969). In 1976, Yamada et al. proposed a new set of nine differentials based on known resistance genes possessed by each of these cultivars, and following Gilmour's octal system in numbering the races. As more is learned about the population structure of P. oryzae in the different rice-growing regions, the pathogen can be readily described according to virulence frequency in various environments with respect to the resistance ofthe cultivars grown. However, races are continuously being identified and monitored in some countries. The fungal pathogen has a host range including rice, wheat, barley, and many gramineous weeds. It is not always certain if the isolates from other hosts are readily infective to rice, or vice versa. Disease cycle

The fungus pathogen, which hibernates in the rice seed or in the straw, may serve as the primary source of inoculum. However, seedborne inoculum is not important in conventional outdoor wetbed nurseries (Yamaguchi 1986). In the temperate zone, mycelium and conidia and mycelium overwinter in the straw piles near the farmstead readily infect a new crop in the following year. In the tropics, the airborne conidia are present all year round (Ou 1985). The fungus may live in diseased rice plants and alternative weed hosts at any time of the year. In the temperate zone, as well as in the tropics, airborne conidia during the rice-growing season are the most important means of dissemination or secondary infection. Conidia are produced on lesions on the rice plants about 4 to 6 days after inoculation. The rate of sporulation increases with the increase in relative humidity; below 93% relative humidity (RH), no conidia are produced (Suzuki 1970). A typical lesion is able to produce 2000 to 6000 conidia each day for about 14 days (Ou 1985). Most of the spores are produced and released during the night, particularly between 2 and 6 A.M. A diurnal periodicity is related to sporulation. In the tropics, a second peak of spore discharge occurs in the afternoon after a monsoon shower. Free moisture is required for spore release. The longer the dew period, the more spores are released. Most of the spores are vertically distributed in the canopy in the rice field. Disease control

Chemical control is commonly practiced in eastern Asia. Nine fungicides have been developed for blast control; each has a specific mode of action different from the other (Yoshino 1988). WhenP. oryzae becomes resistant

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to one of the fungicides in a specific district, another fungicide is immediately recommended and used. The method of application affects the efficiency as well as the economics of fungicide use. However, the methods and timing of application are site-specific, hence, the efficacy of the fungicides depends on climatic factors and the cultural practices adopted in a specific region or country. Fungicide may be applied in granular form to the seedbed, submerged in the field for leaf and neck blast control, and/ or foliar spraying and dusting by ground and aerial application. The effective use of fungicides requires basic information on the nature of the blast occurring in the area or its epidemiology. Silica increased the resistance of rice plants to blast. In irrigated rice, the ratio of total C/N, Si02/N, KzDIN in leaf blades increased with the application of silicate fertilizer. The negative correlation of these ratios with the incidence of rice blast was high (Paik 1975). A high dosage of nitrogen-fertilizer increased the total nitrogen and decreased the silicate and total sugar content in leaf blades, thus disposing the rice plants to blast. In tropical uplands, the rice hull is an important source of silica. Blast has been effectively controlled by the deployment of resistant cultivars. The feasibility of host plant resistance to blast is especially sound in tropical lowlands. Partial resistance in many newly developed cultivars such as IR36 appears adequate to protect the crop in irrigated rice ecosystem in the tropics. The same sort of resistance may not be adequate in irrigated upland or in temperate zones where the environments are highly conducive to blast (Lee et al. 1987; Yeh and Bonman 1986). Cultivar mixture was proposed for the control of blast in upland rice in Asia (Bonman et al. 1986). Chin and Ajmilah (1981) believed that cultivar mixture was a very important attribute in upland rice culture where rice is grown for subsistence, and blast is a major biological constraint. Brown Spot (Cochliobolus miyabeanusj The disease

First described by Breda de Haan in 1900 as a leaf spot on rice, the causal organism was named Helminthosporium oryzae. Since then, it has been reported in many countries and is now distributed worldwide. The disease is common in upland and rain-fed ecosystems and associated with adverse and poor soil. Its occurrence often indicates soil conditions adverse for rice production. In irrigated rice, the disease has not been considered a serious problem in the past decade in the temperate zone, while in the tropics, a serious brown spot epidemic has been observed in Southeast Asia. It appears to be prevalent in all rice-growing

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regions in India. The disease becomes prevalent in saline soil or soil in reduced condition in which toxic substances accumulate and is severe in soil with low pH and deficient in essential macro- and microelements. The addition of Mn at 5 and 10 parts per million (ppm) significantly reduced the disease, regardless of the cultivars planted. However, at low Mn levels even resistant cultivars showed susceptible reaction (Kaur et al. 1979). Kaur et al. (1982) investigated the relationship of phosphorus nutrition, and the expression of the disease in soil collected from regions where brown spot was known to be endemic showed a reduction in the disease intensity with the application of 50 ppm of phosphorus to most of the soils. Further increase in phosphorus-levels increased the disease intensity in all soils. A significant positive correlation was obtained between phosphoruscontent of the host and the disease intensity. The disease intensity was minimum at moderate levels of nitrogen (20-40 kg/ha) and was higher in both lower and higher dosages of nitrogen. It appears, therefore, that rice plants grown in both deficient and excess nitrogen levels were susceptible to the disease. Rice grown on nitrogen-deficient soil is more susceptible to the pathogen. However, the chemical formulation of nitrogen applied affects disease expression. Moharty and Chakrabarti (1981) and Vidhyasekaran et al. (1983) reported that slow release form of nitrogen fertilizers and coal tarcoated urea reduced the susceptibility of the plant. Other forms of chemical fertilizers may also influence the development of the disease, but quantitative information is lacking. In Latin America it was found that infection with the hajo blanca (HE) virus enhanced the spread of brown spot and the development of lesions. The lesions were sometimes as much as 40 times larger on HE-infected plants than on HE-free plants (Lamey and Everett 1967). Increased susceptibility of HE-infected rice leaves to Cochliobolus miyabeanus was reported. The causal organism

The teleomorph of the pathogen is Cochliobolus miyabeanus (Ou 1985). The perithecia are globose to depressed globose, with the outer wall a dark yellowish-brown and pseudoparenchymatous, 560 to 950 x 368 to 377 p,m. The asci are cylindrical to long fusiform with hyaline or pale olive green filamentous ascospores coiled together, 6 to 15 septate, and 150 to 469 x 6 to 9 p,m. The anamorph of C. miyabeanus is not typical of H elminthosporium and was transferred to Drechslera oryzae. The conidia are slightly curved, fusiform or obclavate, characteristic minute hilum, acropleurogenous, brown when mature, with 1-14 pseudoseptate, 14 to

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22 x 63 to 153 ~-tm. Conidiophores are single or in small fascicles, up to 600 ~-tm long and 4 to 8 ~-tm thick, sometimes geniculate, olivaceous at the base and lighter at the tip. Physiologic specialization of the pathogen has been reported. Nawaz and Kause (1962) identified five races of the fungus from pathogenicity tests on four rice cultivars. Eruotor (1986) tested 23 isolates against 11 rice cultivars and observed significant differences in virulence among test isolates and susceptibility of cultivars; these were insufficient to designate distinct races, however. Studies on the variation of the fungus in morphology, physiology, cultural characteristics, and sporulation ability were also reported. In addition to rice, the fungus is reported to infect wheat, oat, maize, millets, and weeds such as Digitaria sanguinalis, Eleusine coracana, Leersia hexandra, Panic urn colonum, Zisania aquatica, and others (Yamamoto et al. 1972). On the pathogenicity of Cochliobolus miyabeanus to several paddy weeds found to be susceptible, brown spot lesions were observed on Oryza sativa L., Leersia sayanuka Ohwi, Beckmannia syzigachne Fernald, Setari viridis Beaw. Many wild species of Oryza were susceptible to brown spot. 0. montana, 0. australiensis and 0. rujipogon, 0. punctata, 0. alta, 0. eichingeris, 0. granddiglumis, 0. latifolia, and 0. perennis (Subramanian and Ramakrishnan 1973).

Symptoms The symptoms are observed on leaves, glumes, coleoptiles, leaf sheaths, panicle branches, and on mature plants as well as seedlings. It is rarely observed on stems. At the initial stage of infection, the spots are small, circular, and may appear as a dark or purplish-brown dot. The spot may reach 1 em in length on susceptible cultivars. In severe case of infection, the leaves eventually wither. Symptoms on the glumes appear as black or dark brown spots which may cover the entire surface of the glume. When the glume is severely infected, blackish spots can be observed on the endosperm. The lesions on leaf blades are oval spots about the size and shape of sesame seeds. The spots are brown with grey or whitish centers when fully developed. A matured lesion is surrounded by a yellow halo. Black and dark brown spots appear on the glumes. The disease reduces the number of tillers, and inhibits root and shoot elongation. The disease cycle

The infected seed is likely the carrier of the pathogen and serves as the primary source of inoculum. Primary infection through infected seed is probably most common, although infected seeds do not necessarily result

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to infected seedlings. Airborne spores are responsible for secondary infection as well as the spread of the disease to adjacent fields. The dispersal of the airborne spores usually takes place in the middle of the day where large numbers of spores are discharged under dry condition from 10 A.M. until sunset, but the maximum discharge is between 5 and 6 P.M. The most dramatic occurrence of the disease so far recorded was during the Bengal famine of 1942, to which it was considered a major contributing factor. Losses amounted to 50 to 90%. Disease control

The disease can be controlled by chemical seed treatment, foliar applications of fungicide, planting of resistant cultivars, and by proper management of soil fertilizers, especially nitrogen fertilizer. Selection of cultivars for resistance to brown spot started many years ago, although not in any systematic breeding program. While many resistance sources have been identified and disease scoring developed for selection of resistance, breeding for resistance has not been a major endeavor in most of the rice improvement programs. Likewise, little is known about the inheritance of the resistance. This is partly due to the sporadic occurrence of the disease and to the improving agronomic practices which have minimized its importance in rice production. In the 1940s and 1950s, much of the research on varietal resistance and attempts to develop resistance cultivars were in India and Japan. The current effort at IRRI is to monitor advanced breeding lines to ensure that none is highly susceptible to brown spot, using the upland blast nursery. A significant positive correlation was obtained between phosphorus content of the host and disease intensity in all soils. Higher disease intensity was positive correlated with N, P, and Mn content and negatively correlated with Ca, Mg, K, KIN Fe, and Fe/Mn ratios of the plant under phosphorus treatments (Kaur et al. 1979). Mahsuri is known to be resistant to brown spot; other recently developed cultivars, such as IR42, are also resistant. Sowing healthy seeds or seeds treated with hot water or fungicides effectively keep the disease in check. Spraying fields with fungicides to prevent secondary infections is also practiced in many countries. The economical value of such practice is doubtful, however. The common fungicides are propiconazole, manzeb, and triphenyltinacetate. Balanced NPK fertilizers are important in lowering the incidence of the disease. While many antagonistic microorganisms have been reported to affect the growth and development of the fungus, biological control of brown spot is far from being practical. Recently, Mew and Rosales (1986) identified many antagonistic bacteria effective against the seedborne fungus pathogens that may make biological control of brown spot possible.

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False Smut (Usti/aginoidea viren} The disease

False smut has been reported in major rice-growing countries of the world. It is also known as green smut and is increasingly prevalent in high-input rice production systems. In China, scientists have found the disease to occur more frequently in hybrid rice fields than regular rice fields (Mew et al. 1986). Conventionally, it indicates a bumper harvest of the rice crop. False smut was recognized as a rice malady at an early date in Chinese literature, though without a proper given name (Ou 1985). Normally, little damage is caused by the disease but severe infection may affect the quality of the grain. Aside from the infected grain, which becomes a smut ball, the weight of the panicles and the 1000-seed weight are reduced with increased numbers of smutted grains. Increased chaffiness and sterility of grains adjacent to the infected ones is also reported (Hashioka 1971). False smut is caused by U stilaginoidea vir ens. In the temperate region, the pathogen overwinters by means of sclerotia and conidia. Primary infection is believed to be initiated mainly by ascospores produced from sclerotia, and conidia play an important role in secondary infection. Singh et al. (1985) indicated that the conidia remain viable for 3 months at room temperature and for 2 months under field conditions, the pseudosclerotia for 4 months in the field, and the sclerotia for 11 months in the field. They concluded that sclerotia is the major source of inoculum, and conidia is very important in the secondary spread of the disease in the tropics.

Symptoms Singh et al. (1985) observed the disease and described that, initially, the infection formed a small spore mass confined to the glumes. It gradually enlarges to 1 em or more in diameter, enclosing the floral parts. The young spore mass is yellow to orange, flattened, and covered with a membrane. When mature, the spore mass or ball changes to olive to dark green. The central portion of the spore mass is made up of hard mycelial tissues which are white or pale yellow and may contain intact floral parts, including style, stigma, and anther lobes. The glumes are closely attached to the lower part of the spore mass. The surface of the spore mass is covered with powdery spores of dark green to olive-black color. The number of smut balls varies from one to several, and two per panicle is common. The fungus transforms individual grains of the panicle into greenish balls of spore with a velvety appearance. It is generally believed that high moisture favors the development of false smut. Crops grown under high nitrogen fertilizer provide a luxurious plant growth at the vegetative phase that is predisposed to infection (Chi-

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nese Academy of Agricultural Sciences 1986). Therefore, avoiding excessive nitrogen application is advisable. Scheduling planting dates to avoid heading in the midst of the rainy period helps to prevent the disease. No chemical control is essential at the moment. The causal fungus

Ustilaginoidea virens (Cke.), Tak. is the name commonly accepted for the fungus (Ou 1985). Some of the greenish spore mass develops into one or four sclerotia in the center. In temperate environments, these sclerotia overwinter in the fields and produce stalked stromata the following summer. The stromata swell at the tip of the stalk and contain perithecia around the periphery. Each perithecium contains about 300 asci. Each ascus has eight ascospores that are hyaline filiform, unicellular, and 120 to 180 x 0.5 to 1 p,m. Chlamydospores are also formed on the spore mass. They are borne laterally on minute sterigmata on radial hyphae and are spherical to elliptical, warty, olivaceous, solitary, dry pleurogenous about 3 to 5 x 4 to 6 p,m. Younger spores are pale, smaller, and almost smooth. Chlamydospores germinate in water to produce fine germtubes bearing one to three conidia. The number of conidia produced and the growth of the germ tubes are influenced by the nutrition conditions. No pathogenic variation of the fungus has been reported.

Narrow Brown Leaf Spot (Cercospora oryzae) The disease

Narrow brown leaf spot (NBLS) is a rice foliar disease prevalent worldwide wherever rice is grown. It is considered a minor disease and usually comes late in the growing season. In recent years, it has occasionally been serious because of the planting of highly susceptible cultivars (Estrada et al. 1981). The disease was considered a major problem in Louisiana, in the United States in the 1940s (Ryker and Jodon 1940). NBLS is found on all growth stages of the plant and tends to be more severe at the flag leaf stage when the plants begin to mature. It can be observed in all ecosystems where rice is grown.

Symptoms The pathogen causes brown spots that are oval, elliptic, and linear, ranging from 3.5 x 1 to 1.5 mm (Ou 1985). Lesion size may be related to varietal resistance. The lesions, mostly seen in boot-leaf and/or in older leaves, were 1.5 to 2.5 mm in length and 0.5 to 1.0 mm in breadth, with the long axis parallel to the long axis of the leaf. Occasionally, lesions also develop

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on raches and glumes. Severely infected leaves have a scorched appearance similar to that caused by bacterial blight. Causal fungus

The conidial state is Cercospora oryzae Miyake. Conidia are hyaline or subhyaline, with 3 to 10 septa, 20 to 75 x 4 to 5 p,m, with conidiophores amphigenous solitary or in small fascicles, one to two geniculations, brown, and 30 to 130 x 4 to 6 p,m (Ou 1985). The teleomorph state is Sphaerulinia oryzina Hara. The perithecia are scattered or gregarious, black, globose to subglobose with a papilloform ostiole, immersed in epidermal host tissue, 60 to 100 p.m. Asci are cylindrical or clavate, stipitate 50 to 60 x 10 to 13 p.m. Ascospores are biseriate, spindle shaped, three-septate, hyaline, and 20 to 23 x 4 to 5 p.m. Host range

In addition to rice (Oryza sativa), Cercospora oryzae also infects some weed species. Adeoti and Adeniji (1982) reported Pennisetum purpureum and Panicum maximum served as collateral hosts to the pathogen. Sridhar (1970) reported that Panicum repens is a collateral host to the fungus. No information is available as how the weed host has contributed to the disease epidemics or to its survival. Disease development

Rice plants in all stages of growth are susceptible to C. oryzae. Symptoms are always delayed on upper leaves when compared to lower leaves. This indicates that older leaves are more susceptible to infection than younger ones. Symptoms always developed first on lower leaves, indicating the influence of leaf age on disease development. Disease control

Although the disease is generally considered minor, economic losses have been reported. Benlate 50 WP and Dithane M-45 50 WP are reported to control the disease and increase yield up to 30% in Indonesia. Resistant varieties provide a better means of managing the disease. Due to the pathogenic variation and the low epidemic potential, no specific effort has been made to develop varieties resistant to the disease. Generally, the advance lines or elite lines are assessed for NBLS resistance. The effort is to ascertain that no highly susceptible cultivar is released to the farmers. Several lines or cultivars were identified as rate-reducing resistant to C. oryzae. These cultivars always resulted in lower terminal disease severities with little or no lesion formation on flag leaves, as compared to susceptible

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cultivars. Rate-reducing resistance may be more durable than vertical resistance to C. oryzae. The cultivar Nato, grown in Louisiana since 1956, still has a comparatively high level of rate-reducing (partial) resistance compared to more recent cultivars released with monogenic resistance. Relative receptivity, the number of lesions per leaf, lesion length, conidial production per lesion, and incubation period, are all related to rate-reducing resistance. These resistance factors were operative whether plants were infected at the seedling or heading stages. Initial symptom appearance was delayed by 7 to 8 days on rate-limiting resistance cultivars at the heading stage (Sah and Rush 1988). Sheath Rot (Sarocladium oryzae) The disease

Sheath rot caused by Sarocladium oryzae (Sawada) Gams and Hawks was first recorded in 1922 by Sawada in Taiwan (Ou 1985). Since then, it has been reported worldwide in all rice-growing countries. The damage caused by the disease is variable, depending on the rice-growing conditions. The disease affects the development and production of rice. It causes sterility, abortion, and exsertion of the panicles, and infected rice normally yield chaffy grains. The yield reduction ranges anywhere from a few percentage to as high as 80%, according to the literatures. Most of the data on crop losses were based on rather small-scale assessment. The disease spread and epidemic conditions have been described generally, with few attempted at quantification. Formerly, sheath rot was considered a minor disease, but its occurrence has become widespread in recent years. The effect of nitrogen fertilizer on the incidence ofthe disease is not consistent. Tasugi and Ikeda (1956) showed that the incidence of sheath rot decreased with increases in nitrogen application. Chen and Chien (1964), on the other hand, indicated that it increased with increases in nitrogenous fertilizers but decreased with increases in the potassium level. High levels of nitrogen application favored the accumulation of reducing sugars in rice cultivars; sheath rot is reportedly a "high sugar" disease (Purkayastha and Cosgal 1982). The fungal pathogen is frequently isolated from sterile rice plants (Hsieh et al. 1977). There was a report (Chien and Huang 1979) that large numbers of conidia of S. oryzae were found associated with the body of mites. The disease is most prevalent in the rainy season in both irrigated and rain-fed cultures. It is also common in regions where rice plants frequently suffer from low-temperature stress.

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Symptoms

The infection normally occurs at the booting stage when the panicle is still embedded in the leaf sheath (Ou 1985). The margins of the lesions are dark brown with light brown centers, oblong or irregular in shape, and ranging from 5 to 10 mm. In severe cases, the panicle is aborted before exsertion. Under humid and high-temperature conditions, white powdery mycelium will be observed in or on the surface of the flag leaf sheath. Those panicles exserted later often show browning and sterility. An abundant whitish powdery growth may be observed inside the affected sheath and on the young panicles as they rot. Amin et al. (1974) describes the initial lesions as 0.5 to 1 x 0.2 to 0.5 em, oval, chocolate brown, and surrounded by a diffused light brown halo, while the healthy sheath around the lesion remained green. Lesions occur on the sheaths of all leaves but were most conspicuous and common on the flag leaves. Stressed plants with poorly emerged panicles are prone to infection with the disease. In severe cases, it is likely that the panicles are compressed in the sheath with dark brown lesions evident on the outside of the sheath. The panicles are covered with a white to light pink mat of mycelium and spores. It is often observed that plants suffer from insect injury or other diseases infected more than healthy plants. When the panicles emerge from infected sheath, the heads are commonly straight, with unfilled grains. The causal fungus

The fungus was named Acrocylindrium oryzae Sawada. Gams and Hawks worth indicated that it should belong to the genus Sarocladium, the species S. oryzae (Sawada) Gams and Hawks 1975. The mycelium is white, sparsely branched, septate, and 1.5 to 2 JLm in diameter. Conidiophores arise from the mycelium, are slightly thicker than the vegetative hyphae, and branch once or twice, each time with three to four branches in a whorl. Conidia are borne on the tip, produced consecutively, hyaline, smooth, single-celled, cylindrical, and 4 to 9 x 1 to 2.5 JLm. The size differs from host plants (2.1 to 8.5 x 0.5 to 1.6 J.tm) and from culture (1.8 to 13 x 1 to 1.6 ~.tm). The optimal temperature for fungus growth is 28 to 31 oc, and conidia germinate at 23 to 26°C (Tasugi and Ikeda 1956). Disease control

S. oryzae is seedborne and seed-transmitted. Many chemicals have been evaluated for the control of sheath rot; however, no field data support the use of fungicides for its management. Seed treatment with fungicides appears to improve the germination of infected seeds: 45% seeds died

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before emergence, and about 30% of the seedlings survived (Viswanathan and Mariappan 1980). RICE DISEASES CAUSED BY SCLEROTIAL FUNGAL PATHOGENS

Several sclerotia! fungi cause diseases in rice. In a survey of rice fields in Louisiana, Shahjahan and Rush (1979) found that, of the 86 fields examined, 93 and 60% were infected with stem rot and sheath blight, respectively. In recent years, as rice cultivation has intensified and most improved semidwarf cultivars are highly responsive to crop management, this group of diseases has increased. No true resistance has been identified, and little effort has been focused on cultural control or alterations in management that should be considered. The causal fungi can be differentiated and identified by the internal and external morphology of the sclerotia (Ou 1985). The sclerotia! surfaces of Sclerotium oryzae and S. oryzae var. irregulare sclerotia are covered with a thin layer of material secreted by the hyphae. This layer is much thinner on sclerotia of S. oryzae var. irregulare than S. oryzae, where the substance eventually covers the surfaces. This substance may serve to seal moisture in the sclerotia and as a barrier to microbial activity. A similar but much thicker layer of the exterior substance is present on the surface of S. rolfsii sclerotia, where it formed the bulk of the outer link. The surfaces of sclerotia of R. oryzae and R. solani consist ofloosely woven hyphae. The cells of R. oryzae are mostly 5 to 9 J.Lm wide, whereas the cells of R. solani are 8 to 12 J.Lm wide. The outer layer of S. hydrophilium sclerotia consists of a dense, uneven layer of cells that are free from any secreted, cementing substance. Among them, only sheath blight, sheath spot, aggregate sheath spot, and stem rot will be described in this chapter. Sheath Blight (Rhizoctonia so/ani] The disease

Caused by Rhizoctonia solani, sheath blight is one of the most widely distributed rice disease. In the last decade, it has gained major importance second only to blast among the fungus diseases. This is due primarily to the high-yielding modern cultivars which have short culms, are early to mature, and are highly responsive to nitrogen. Such cultural practices as close spacing and high seed rate for direct seedling to suppress weeds increase the epidemic potential of the disease. Total crop failure due to sheath blight has been observed for the first time since the disease was reported (Devadath personal communication). This offers a good illustration of the difficulties in controlling a disease caused by a pathogen that is

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nonhost-specific but is capable of inducing serious damage in conducive environments. Despite its high epidemic potential, it has not been properly recognized by farmers and extension specialists except in eastern Asia.

Symptoms The lesions usually start near the water line of the leaf sheath wherein a water-soaked, dark green spot with obscure margin develops. It enlarges, forming an ellipsoid with irregular shape having a greyish-brown center and light brown margin. In a highly infective, newly developed lesion, the hyphae extend upward along the leaf sheath. As the hyphae continue to extend to induce new lesions, the other lesions coalesce, forming a bandlike mosaic covering a large area of the leaf sheath or leaf blade. As the lesions grow older and under favorable conditions, they turn greyish-white with dark brown margin. The lesions then have limited hyphal growth, or do not produce new hyphae, and are not very infective. Lesion development on the leaf blade is similar to that on the leaf sheath. The spots are large, 1 to 3 em in length with irregular shape, giving a banded appearance; thus the disease is also known as banded blight. The appearance of alternative green and brown or greyish color is perhaps due to the diurnal effect on the infection process. When the lesions develop rapidly and aggressively, they appear dirty green and water-soaked. With slow lesion development, the edge of the lesions bleach to a yellow color. With favorable temperature and humidity, the lesions may extend throughout the entire plant, including the panicles, resulting in the death of infected tillers or the entire plant. With short-culmed cultivars, it is not uncommon to observe sheath blight on leaf blades with no extended lesion development from leaf sheath. If plants at the booting stage are severely infected, panicle exsertion may be aborted. Infected panicles develop dirty green lesions which later become dark brown. Under normal conditions, stems are seldom infected; when they are infected, they show lesions similar to those of the leaf sheath. The root systems of infected plants are often dark. The oxidating power of the root system is also weakened, and the redox potential is lowered, thus reducing the ability of the root to absorb potassium from the water. In the tropics, especially under favorable rain-fed environments when the soil remains saturated without standing water, a white, powdery, hymeniallayer is often observed on leaf blades or sheaths. This is believed to be the basidial stage of the fungus. It is not clear if it is the result of airborne infection of the basidiospores or the formation of the basidial stage of the fungus after infection.

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The causal fungus

Considerable confusion has existed about the name of the sheath blight fungus. Now, it is finally agreed that the teleomorph is Thanatephorus cucumeris and the anamorph is Rhizoctonia solani. The teleomorph has been observed in upland rice in the Philippines and may be produced by inoculating rice seedlings in an upland nursery with a mycelial culture. The teleomorph as described by Sawada and Matsumoto has these measurements: basidia 10 to 15 x 7 to 9 JLm; sterigmata 4.5 to 7 x 2 to 3 JLm, numbering from two to four; and basidiospores 8 to 11 x 5 to 6.5 JLm. The mycelium is colorless when young, becoming yellowish-brown when older, is 8 to 12 J.tm in diameter, with infrequent septations. Three types of mycelium are produced. A straight runner hypha which, at intervals, gives rise to a short, swollen, much-branched or lobate mycelium, from which penetration pegs arise. The lobate mycelium infects the tissue and produces lesions. On infected stem, the runner hyphae may cover most parts of the stem, but the lobate mycelium is found only on the lesions. The third type of mycelium consists of moniloid cells involved in the formation of sclerotia and may be found on petri dish covers or test tube walls. The sclerotia are superficial, more or less globose but flattened below, white when young, later becoming brown and dark brown. Individual sclerotia measure up to 5 mm but may unite to form a larger mass in culture. Although the fungus pathogen varies in physiologic characteristics such as colony morphology, rate of sclerotia production, and nutritional requirement for in vitro growth, it is not known to exhibit distinct physiological specialization in pathogenicity or virulence. The fungus has about nine anastomosis groups with subgroups based on hosts at large. R. solani that infects cereals is classified under anastomosis group 1, or AG-1, while those that are pathogenic to rice belong to the subgroup AG1-1a. Disease cycle

Sclerotia formed on the lesions drop to the ground at harvest or during crop management practices. These sclerotia later mature and become a dark brown color. When the fields are flooded, they become buoyant and serve as the major source of inoculum (Sugiyama 1988). The sclerotia floating on the surface of the water may be carried away or drift off and finally come in contact with the rice sheath at the water-line. About 40% of the total sclerotia formed float in water after puddling and weeding. Soon after the sclerotia come in contact with the rice plant, infection starts. Mycelium in plant debris also serves as an important source of inoculum. Horizontal spread of the disease occurs when the hyphae come in contact with adjacent leaf blades or sheaths (Hashiba 1982).

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Sclerotia are major surviving structures. Likewise, mycelium in infected crop debris such as straw, stubbles, etc., carries the fungus for the next cropping. The sclerotia can survive for more than 1 year in upland soil under a moisture tension varying from 0.25 to 0.80 bar (Kim et al. 1985, Part IV). Survival is reduced to 11% after 1 month, and 0% after 4 months in lowland soil with water tension not exceeding 0.05 bar. In flooded condition, the viability is reduced to 3.5% after 1 month and 0% after 2 months. The fungus may also survive in the tropics in a parasitic state through weeds in the rice fields (IRRI 1985; Ou 1985). The viability of sclerotia in soil is related to the microbial activity in the community. The survival is reduced to 2 weeks in the presence of Trichoderma spp (Mew and Rosales 1986). Its saprophytic survival ability is therefore affected by the community structure. Disease environments

The temperature range conducive for sheath blight infection and disease development is 22 to 3SOC, the optimum being 30°C with humidity greater than 95% (optimum at 100%). The temperature and humidity within the hills from panicle initiation to heading determine the severity of sheath infection and damage caused at maturity. Sheath blight severity is positively correlated to high nitrogen levels in the soil. A high nitrogen level predisposes rice plants to infection by producing more succulent tillers that are more susceptible. Tillers are also more numerous, and thus a microclimate favorable for sheath blight development is created within the canopy. Recently, it was shown that rice plants in upland environments under moisture stress have less sheath blight incidence (IRRI 1988). Cultural practices such as close spacing and high seeding rate for broadcast seeding also favor development of the disease. Rice cultivars with short culms tend to be more susceptible to sheath blight because of the rapid advancement of mycelium to upper leaf sheath and blades. Disease control Chemical control. Sheath blight is effectively controlled by fungicides in eastern Asia. Many fungicides are available for its control (Hori 1986; Sugiyama 1988). These chemicals include monzet, neoasozin polyoxin, validamycin, mepronil, pencycuron, ftutolanil, and diclomezine. The efficacy and application of these fungicides was recently reviewed and compiled by Mew (1990). Cultural control. There are many agronomic practices that can effec-

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tively control the disease to a certain degree. Removing, burning, or ploughing into the soil the infected plants removes part of the source of inoculum. Weeding prior to planting rice is effective if the practice is done a minimum of 2 weeks prior to planting. Proper decomposition of rice straw or turning over plant debris and weeds when the field is still wet and leaving it fallow from 2 weeks to 1 month will be helpful in managing the disease. Varietal resistance. The inherent level of resistance alone is too low to control the disease. A cultivar with a moderate level of resistance in combination with fungicide is effective in managing sheath blight (Chen et al. 1987) and reduces the number of fungicide applications. Biological control. Many antagonistic bacteria are found in the paddy field that effectively suppressed the development of the diseases. Field trial has indicated the potential of biological control of sheath blight. However, for use on a commercial scale, biological control of rice diseases, including sheath blight, remains impractical. Sheath Spot [Rhizoctonio oryzoe] The disease

Sheath spot, caused by Rhizoctonia oryzae, was first reported in Arkansas, in the United States, in 1932 and then in Japan in 1935 (Ou 1985). The disease was previously considered minor, but gained increasing importance with the changes in cultivars, cultural practices, and nitrogen fertilization. In the United States it was observed to be present in 10% of the rice fields surveyed in 1985 (Shahjahan and Rush 1979). Symptoms

Characteristically, the lesions appear as circular spots on leaf sheaths and range in size from 1 to 3 em. As with sheath blight, the lesions normally occur near the water lines on the sheath. They appear ovoid on lower leaf sheaths, bleached with brown margins. Two or more lesions may coalesce to form larger lesions. Occasionally, the fungus may infect the leaf blades. Host range

In addition to Oryza sativa, the fungus may also infect Echinocloa crusgalli, Fimbristylis littoralis, Phragmitis cummunis, and Zisania latifolia. The disease environments and control measures are similar to that of R. solani.

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Aggregate Sheath Spot (Rhizoctonio oryzoe-sotivoe] The disease

It is caused by R. oryzae-sativae which was first reported in Taiwan in 1922. It is now a common disease in most Asian countries and in the

United States. In India, it was reported to cause yield losses ranging from 20 to 60% in 1976 in four districts during the kharif season. Since then it is commonly observed in the rice crop (Ou 1985). Symptoms

The disease usually appears during and after heading in inundated fields. Lesions on leaf sheaths are brown, elliptical or oval, characteristically small (0.5 to 1.0 em in diameter), and aggregated, as compared to sheath blight and sheath spot. The lesion is encircled by a distinct brown border band which becomes lighter in color inside and outside of the band. The lesions on the lower sheath near the water line are water-soaked, discolored, and irregularly expanded. The lesions may coalesce to form larger lesions with indistinct margins. Severe infection leads to tissue rotting in both the sheath and stem of the affected plants and may cause lodging. Disease control

The survival of the fungus as well as the control measures of the disease is similar to that of the sheath blight. Stem Rot (Sclerotium oryzoe] The disease

Stem rot is one of the major diseases of rice in many rice-growing countries. The disease was first recorded in Italy, and subsequently, it was found in most of the rice-growing countries. Chen (1971), Huang (1978), and Ou (1985) have each reviewed the diseases caused by the sclerotiaproducing pathogens comprehensively. Little research on stem rot has been done in recent years. At the time of this writing, the author made use of the information available and drew his own conclusions. The disease appears during the tillering stage on the outer leaf sheath at the waterline and then enters the culm. It causes decay of the leaf sheath and culm and contributes to lodging. In early years, it was believed that the damage caused by stem rot was due primarily to the fact that it aggravates lodging: infected plants are weak and topple easily, leading to incomplete grain filling. However, because the symptoms in above ground parts are obscure, the effects of stem rot are often underestimated. Yield losses from 5 to 80% due to stem rot have been reported in different countries. The

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accuracy of these data has to be verified according to locality, disease intensity, cultivars, and cultural management. The losses due to stem rot are difficult to assess. Ou (1985) indicated that the stem rot pathogen is common and occurs in large quantity in the rice fields in southern and southeastern Asia. In the later stage of the plant growth, most of the stems are covered with numerous appressoria or other structures of the fungi. These stems are seldom infected before harvest, although the fungi are present in most of the stubble after the rice harvest. Despite a large volume of literatures, little adequate data are available to illustrate the significant and importance of stem rot. Stem rot is caused by two varieties of a fungus pathogen, Helminthosporium sigmoideum and H. sigmoideum var. irregulare. The two varieties have similar general morphology, cause similar diseases, and often occur together in the same field. Many scientists treat the diseases as one, but Ou (1985) believes that many differences exist between them. Rice plants infected with H. sigmoidea usually lodge while the others would not. The occurrence of H. sigmoidea and var. irregulare are also different. In Taiwan, var. irregulare usually occurs in the first crop while the var. sigmoidea occurs in the second crop. However, the damage on the second crop is 37% as compared to 25% in the first crop. Both fungi penetrate through the stomata. H. var. irregulare forms appressoria on the upper portion of the leaf sheath while var. sigmoidea is on the upper part of the node. The primary infection starts from sclerotia, and conidia only in secondary infection. In general, secondary infection does not occur often. In terms of penetration ability, it appears that var. sigmoidea is stronger than var. irregulare. However, once inside the tissue, var. irregulare grows as fast and destroys the host tissues as much as that of the former. The ratio of sclerotia formation also indicated that var. sigmoidea is greater than var. irregulare. No exogenous nutrients are needed for the sclerotia! germination of var. sigmoidea, but because of soil fungistasis the rate of germination is often different. Keirn and Webster (1975) indicated that its germination was strongly influenced by soil microorganisms. These authors identified many fungi capable of doing so. However, one would expect that many antagonistic bacteria would be involved in the paddy which the authors did not report. The optimal temperature for lesion development was 24°C. Above 36°C or below l2°C, both fungi would not cause any lesion (Hsieh 1966). In the rice field, sclerotia are mostly distributed in the the upper 2 to 3 em of soil. The sclerotia float on the water surface after land preparation and, when in contact with rice leaf sheath, germinate and initiates the infection. The ecology and epidemiology of both fungi have not been wellstudied in tropical conditions. Available information shows that the disease

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is common in irrigated and favorable rain-fed ecosystems, perhaps due partly to the viability of the sclerotia being reduced under alternate wetting and drying conditions. Sclerotia formation, germination, infection, and disease progression in the field is directly related to irrigation and drainage. The depth of water in the field also appears to influence the disease severity (Huang 1978). If the irrigation water is deep (around 20 em), infection rate is high, and if it is shallow (10 em), the infection is low. Ifthe irrigation water is deep during the infection period and shallow during incubation period, the disease becomes most severe, or vice versa. Applying high level of nitrogen fertilizer increases the disease severity. Drainage at flowering increases the severity of the disease, while late drainage decreases the disease severity. Symptoms

The disease starts with a small, black, irregular lesion on the outer leaf sheath near the water line. The lesion enlarges as the disease progresses. The fungus pathogen penetrates into the inner leaf sheath, the leaf sheath becomes partially or entirely rotted, and eventually infection reaches the culm. Finally, dark lesions form in one or two internodes, and the stem rots or collapses. The sclerotia are formed on infected leaf sheaths. The presence of numerous dark sclerotia is a distinct feature of diagnosis. Dark necrotic lesions appear on outer leaf sheaths near the water line, usually after the tillering stage of the plant growth. The inner sheaths and stem are sequentially infected and, in severe cases, the plants lodge. H. sigmoideum forms infection cushions on the culm. Numerous black sclerotia may be formed in the hollow internodes at maturity. Dark perithecia are occasionally embedded in sheath tissue but are not rough to the touch. H. sigmoideum var. irregulare also attacks the rachis, causing incomplete filling of the grains. The causal fungus

The teleomorph of Helminthosporium sigmoideum var. sigmoideum is called Magnaporthe salvinii, the sclerotial anamorph Sclerotium oryzae, and the conidial anamorph Nakataea sigmoidea. No teleomorph of H. sigmoideum var. irregulare is known. The hyphae of var. sigmoideum are white to olivaceous, septate, profusely branched, and 2 to 5 /Lm in diameter. Numerous irregular olivaceous appressoria form on the culm, 14 to 30 x 8 to 24/Lm. The hyphae of var. irregulare are also white to olivaceous, septate, profusely branched, and 2 to 5/Lm in diameter. Numerous appressoria are produced at times. Sclerotia of var. sigmoidea are spherical or nearly so, black at maturity, smooth surfaced, and formed on parenchyma tissues inside the central

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cavity of the culm. They measure 180 to 280 ~m. Sclerotia of var. sigmoidea are numerous, irregular in outline, black, rough surfaced, and are embedded in the parenchymatous tissues near the central cavity of the culm. They measure 90 to 119 x 268 to 342 ~m. Conidia var. sigmoidea are borne singly on sharp pointed sterigmata, fusiform and typically three-septate, simply curved or slightly sinuous, and 9.9 to 14.2 x 29 to 49 ~m. Conidia ofvar. irregulare, are borne singly or on sharp pointed sterigmata, fusiform, typically three-septate, 9-12 x 41 to 58 ~m. Very little is known about the pathogenic variability. One would assume that differences must exist among the isolates from different geographic regions; however, no information is available to support the notion. Both fungi infect several species of Gramineae and Cyperaceae, Agrostis matsumurae Hack. Eleusine indica, Leptochloa chinensis, Setaria pallide-fusca are infected by both fungi. There are many species of Oryza which have been reported to host the fungi. Zizania latifolia, Triticum and A venae are also reported to host the fungi. Field study has shown that rice plants are most susceptible at the maximum tillering stage. Varietal resistance

Many rice cultivars have been tested for resistance to stem rot. Likewise, many methods have been developed for the purpose. However, there is no active breeding program for resistance to the disease. Rice with strong culms is more tolerant than cultivars with weak culms. Shahjahan et al. ( 1986) tested 4614 accessions of rice for resistance to stem rot and identified very few resistant genotypes. However, several rice cultivars showed consistent reaction. Susceptible cultivars appear to have characteristics such as early maturity, weak culms, and absence of awn, while those with the contrasting traits were generally resistant. Chen (1971) indicated that the resistance seems to be associated with maturity: short-duration cultivars are less resistant than long-duration cultivars. Disease control

The pathogens survive as sclerotia in the soil or in the straw. If straws are not removed, burned, or decomposed, it becomes the source of inoculum. In the tropics, rice straw or stubble is common; burning is incomplete and difficult in the wet season. However, burning does have a positive effect in reducing stem rot (Bockus et al. 1979). Mulching eliminates the natural sclerotia population of Sclerotium oryzae in the soil (Usmani et al. 1985). Seven days of mulching with transparent polyethylene sheets killed the fungus. Loss of sclerotia viabil-

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ity corresponded well with an increase in soil temperatures from 36°C (nonmulched) to 48°C (mulched) at 28 em depth. Plastic mulching increased rice yield by 23% over the control. Mew (1990) believes that the effect of mulching and soil solarization definitely affects the number of sclerotia. The cost-effectiveness of such practice, however, should be assessed before it is recommended to farmers. VIRUS DISEASES

Virus diseases of rice have become a major constraint in rice production in tropical Asia since the introduction of modern cultivars. Prior to the 1960s, no rice virus diseases had been reported in tropical Asia except in the Philippines and in Japan (Ling 1975). During this time, only dwarf, stripe, and yellow dwarf were described and characterized. Since the beginning of modern rice production in the 1960s, several virus epidemics of rice occurred in Asia, and research on virus diseases has caught the attention of rice pathologists. Our knowledge on rice virus diseases has advanced greatly during the last two decades. Among the rice virus diseases with a high epidemic potential, tungro ranked number one, followed closely by grassy stunt and ragged stunt (Mew 1989). These three diseases will be discussed in some detail. The practical identification of virus diseases is often based on symptoms. However, distinguishing virus diseases from physiological disorders can be difficult in farmers' fields. Wherever and whenever possible, diagnosis should be based on the characteristics of the causal agents, serology, and virus transmission. The general information of rice virus diseases has been well-documented by Ling (1979) and Ou (1985), especially from a historical perspective. Many of the initiatives that have taken place in the past few years have not yet yielded concrete conclusion. It is evident, however, there are more virus diseases in the tropics than were previously known. Ou has listed about 20 virus and microplasm diseases. Among them, 18 have positive identity; two are caused by mycoplasm, while 16 are caused by viruses. In terms of geograpical distribution, four are found in the temperate environments and 12 in the tropical and subtropical zones. The four virus diseases found in the temperate environments are dwarf, black streak dwarf, stripe, and gaillume. The first three are found mainly in temperate Asian countries, while the last one occurs in Italy. Those that are found in the tropics and subtropics are transitory yellowing, tungro, waika, bunchy stunt, gall stunt, grassy stunt, ragged stunt, wilt stunt, yellow mottle, chlorotic streak, mosaic, necrosis mosaic, and hoja blanca. The two that are caused by mycoplasm are yellow dwarf and orange leaf.

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Tungro The disease

The disease was first reported by Rivera and Ou in 1965. The disease and/or similar diseases are generally believed to have been noted or reported elsewhere by different scientists a long time ago (Ling 1975). It is now one of the most destructive rice diseases and is widely distributed in tropical Asia. Its occurrence is most prevalent in irrigated and favorable rain-fed lowland rice ecosystems, although the viruses, especially rice tungro sperical virus (RTSV), have been detected in rice and gramineous weeds in upland rice ecosystems.

Symptoms Generally, tungro-infected rice plants are stunted and the tiller number is reduced. The distinct symptom, however, is the yellowing of the leaves, and this is visible from a distance. The infected leaves may be rolled inward and somewhat spirally twisted (Ling 1975). The degree of stunting and tiller decrease lessens with the increasing of plants at the time of infection. Yellowing usually starts from the tip of the lower leaves. The color varies among rice cultivars and with environmental conditions. The young leaves of infected plants are often mottled or have pale green to whitish strips of various length running parallel to the vein. Root development is poor. Infected plants may die, but they usually live until maturity. The maturity of infected plants is delayed, and the panicles are small, sterile, and not completely exserted. Rice tungro is one of the most important diseases in many southern and southeastern Asian countries including the Philippines. RTSV is known to be a latent virus that acts as a "helper" for the transmission of rice tungro bacilliform virus by leafhopper vectors. RTBV causes the tungro symptoms, and RTSV enhances the symptoms. RTBV and RTSV are transmitted by several species of leafhoppers in a semi persistent manner. Tungro is therefore a disease complex associated with RTBV and RTSV. Because of the complexity of the disease, tungro epidemiology is not well-understood. Recently, RTSV was found to spread as an independent virus. This information suggests a possible relationship to tungro epidemiology. Further studies have indicated that, in the fields, many rice plants without symptoms were infected with RTSV alone. RTSV is similar or identical to rice waika virus. Rice waika was epidemic in 1971-74 in Kyushu, Japan. Rice waika virus causes mild stunting and occasional leaf yellowing on some susceptiblejaponica cultivars. Indica rice infected with RTSV does not show clear symptoms. Rice waika virus in Japan is similar in properties and serologically

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homologous to RTSV and is naturally transmitted by N. cincticeps. Hibino (1983b) demonstrated that N. l'irescens efficiently transmitted RTBV, RSTV, and RWV from rice plants infected with both RTBV and RTSV or RWV and also from plants infected with RTSV or RWV alone. N. nigropictus also transmitted the three viruses but at a very low efficiency. Recilia dorsalis failed to transmit the three viruses, and they could not transmit RTBV from plants infected with RTBV alone. The causal viruses

The rice tungro agents consist of two virus particles: one which is spherical (RTSV) in shape and is responsible for transmission. The other is bacilliform (RTBV) and is for symptom development. The viruses can be transmitted by Nephotettix virescens, N. nigropictus, and Recilia dorsalis. The viruses do not persist in the vector. The acquisition feeding is 5 to 30 min. There is no incubation period in the vector. Infective insects usually transmit the virus immediately after acquisition feeding, and once it loses the infectivity, the insect vector remains noninfective for the rest of its life unless given access to another virus source. Host range

The virus appears to have a wide range of hosts. These include Leersia hexandra, Rottoellia compressa, Eleusine indica, Echinocloa crusgalli. Leaves of the weeds in or around rice fields, whether cultivated or idle, were tested by the ELISA technique with specific anti-RTSV or RTBV sera and showed positive reaction, indicating that they host either one of the tungro virus complexes (IRRI 1989). E. indica was positive to RSTV; Ec. crusgalli, E. colona, and Cyperus rotundus to antiserum of RSTV + RTBV; but L. hexandra was positive to RTBV and RSTV alone. These weeds were found both in lowland and upland rice fields. The transmission efficiency of N. nigropictus, and N. uirescens for RTSV and RTBV on weeds indicated that, on rice, N. virescens was the more efficient vector, and retained the viruses for 4 days. N. nigropictus was less efficient but retained the viruses for 5 days. N. malayanus and R. dorsalis retained the viruses for only 1 day. Young seedlings or rhyzomes of E. indica, Ec. crusgalli, Ec. colona, Leptochloa chinensis, L. hexandra, Panicum repens, and cyperus rotundus were infected with RTBV and/or RTSV when exposed to the four leafhoppers that had fed on RTBV and RTSV infected plants. These weeds were also infected with RTSV alone when exposed to the leafhoppers that had fed on RTSV-infected plants. Only N. nigropictus was able to acquire the viruses on doubly infected plants of Ec. crusgalli, P. repens, and C.

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rotundus and transmit them to rice seedlings. Apparently N. nigropictus could disperse RTBV + RTSV in weed hosts in the fields once the viruses are introduced from rice fields. Disease control

Tungro is a composite disease resulting from infection with both rice tungro bacilliform virus and rice tungro spherical virus. Both viruses are transmitted efficiently by the leafhopper N. virescens. Rice cultivars developed by IRRI with moderate resistance in the field had a low tungro infection rate under low virus inoculum and leafhopper population, but high infection rates regardless of inoculum and leafhopper levels. Resistance was due to both antibiosis and nonpreference to adult leafhoppers. In mass or test-tube inoculations with leafhoppers that had fed on plants infected with RTBV and RTSV, resistant cultivars showed increasing rate of infection with increasing numbers of leafhoppers. When the cultivars were indexed with latex serological test, resistant cultivars had increasing RTBV infection rates, whereas MR cultivars had increasing RTBV and RTSV infection rates. The RTBV and RTSV infection rates of some cultivars were high irrespective of leafhopper numbers. When resistant cultivars were inoculated with RTSV alone, fairly high infection rates occurred. The resistant cultivars in the field with low infection rates can be explained by the resistance to the leafhopper (Hibino et al. 1987). Many improved rice cultivars that had low RTBV and RTSV infection rates combined in the field had relatively high infection rates with RTBV alone. IR20, IR26, IR30, and IR40 had low infection rates ofRTSV. Their resistance to RTSV was not shown because of resistance to leafhopper. Since RTSV helps in the transmission of the tungro, these potentially provide the source of inoculum for tungro spread. The application of insecticides at the right time would control the virus diseases through the insect vectors. Spraying insecticides at the early stages of plant growth delays tungro development. Cypermethrim at 40 ai/ha, or Bubrofezin at 10 kg ai/ha with one application in the seedbed 10 days after sowing and three sprays at 1, 2, and 3 weeks after transplanting proved effective in controlling the disease. The cost-benefit relationship should be evaluated. Combining chemical control and resistant varieties is perhaps most desirable for management of tungro. Grassy Stunt The disease

The disease was first reported on rice in 1966 in the Philippines. By now it has been reported in most of the rice-growing countries in southern and southeastern Asia and also southern China, Taiwan, and Japan. Major

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epidemics were reported in the early 1970s in the Philippines and other Southeast Asian countries when the improved modern varieties possessed no resistance to either the virus or the insect vector, brown planthopper.

Symptoms When fully developed, the symptoms of the diseased plants are severe stunting, excessive tillering, and an erect growth habit. The leaves are short, narrow, pale green or pale yellow, and often have numerous small, dark-brown dots or spots of various shapes which may form blotches. The young leaves of some varieties may be mottled or striped. The growth of the rice plant following infection is greatly arrested, the diseased plant becoming markedly stunted, while numerous diminutive tillers develop that produce a rosette appearance. The infected plants usually live until maturity, but they produce no panicles or a few small panicles with dark brown, unfilled grains when infection occurs at early stage of plant growth. Rice plants infected at an older stage may not develop symptoms before harvest. The symptoms do occur, however, on ratoon tillers. The causal virus

The virus is circular filaments about 950 to 1350 nm in length and 6 to 8 nm in diameter. The filament is a nucleoprotein containing a single strain RNA. Two strains of the virus are reported in the Philippines. Strain 2 causes yellow to orange discoloration of leaves and premature death of infected plants, in addition to the symptom described for the ordinary strain. Strains 1 and 2 are serologically related, and are similar in morphology and vector relations. Strain 2 is pathogenic to rice cultivars with resistance deriving from 0. nivara. Isolates similar to strain 2 have been reported in Taiwan and Thailand (Hibino 1983). In Taiwan, a "wilted stunt" was reported. This wilted stunt strain appears similar to strain 2 in the Philippines. The grassy stunt virus is transmitted by the planthoppers Nilaparvata lug ens, N. baberi, and N. muiri in a persistent manner. The virus cannot be transmitted by mechanical means or through seeds (Ling 1975). No difference in ability and efficiency of transmissions exists between biotypes or genders. However, N. lugens nymphs, which also have a shorter incubation period, are more efficient than adults. InN. lug ens, the latent period averages eight days (a range of 3 to 28 days), and the minimum inoculation period is 9 min. The plant hoppers can transmit the virus after acquisition until its death (Ling 1975), but no transovarial transmission has been demonstrated. The life span (15.4 days) of transmitting planthoppers is shorter than that of nontransmitting hoppers (17.5 days).

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Host range

Many Oryza species are reported to be hosts of the grassy stunt virus. In addition to the Oryza spp., such as 0. australiensis, 0. barthii, O.latifolia, 0. longistaminata, other weed species, Cynodon dactylon, Cyperus rotundus, Ec. colona, L. hexandra, and Monochoria vaginalis are also infected with the grassy stunt virus. Disease control

Rice grassy stunt is effectively controlled by the resistant rice cultivars. All resistance is derived from the resistance of 0. nivara which is conditioned by a single dominant gene. This resistance gene is shown to be very effective for over 10 years until strain 2 of the virus evolves. A perennial rice plant, Guang-keng A/Oryza longistaminata (IRRI Ace. no. 104315) introduced from China, was identified to be resistant to both strains 1 and 2. None of the plants (tillers) inoculated with the two strains developed grassy stunt. The results indicate that the perennial rice plant was highly resistant to the two strains and became infected only under high insect pressure. The perennial plants segregated into dwarf and tall plant types, and only the dwarf plant types were resistant to both strains. NEMATODE DISEASES

There are several nematode diseases of rice. Rice white tip and stem nematodes are widely known. The others, however, are reported sporadically in the literatures and often do not cause distinct symptoms or, perhaps, measurable yield reduction. In recent years, because of seed treatment, white tip nematode has come under control. The stem nematode, also known as ufra nematode, is widespread in deepwater rice areas in Bangladesh, India, Myanmar, and Vietnam. More recently, the importance of root and lesion nematodes in irrigated and upland rice culture, respectively, appear to be increasing in importance. In this chapter, we will describe only the root and stem nematodes. Many genera of plant-parasitic nematodes are known to be associated with rice and its cultivation, but only a few have proven to be of actual or potential economic importance. These nematodes may feed on the leaves, stems, roots, and the panicles. Some have been reported to cause significant yield loss, while for others, no reliable information is available to indicate their importance. In general, among the 80 known rice diseases, nematode diseases are the least studied. Many rice nematodes are widely dispersed throughout the rice-growing countries. Among them, only one is definitely known to spread in seed:

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the white tip nematode (Aphelenchoides besseyi); another can be spread in dead foliage and possibly seed (the stem or ufra nematode, Ditylenchus angustus); and all others spread through soil or roots.

Stem Nematode (Ditylenchus angustus) The disease

Caused by D. angustus, which is a foliar nematode on rice, this disease can be transmitted in dried rice foliage. The nematode can survive in a dried state enclosed in the leaf sheath, particularly at the base of the panicle. In nature, D. angustus can survive for 4 to 5 months in dry foliage, but the number surviving decreases later on. D. angustus has been detected in filled and unfilled grains freshly harvested from an infested rice crop. The nematode may be killed after the grain is dried.

Symptoms

In the field, the symptoms are usually observed two months after planting but vary according to the activity of the nematodes. Discoloration and malformation of the leaves develop to normal size.

Control measure

In regions where ufra has become a problem, it is common to leave a large amount of infested material in the field after harvest. Under such conditions, the nematodes are dormant during the dry season and become active in the wet season when rice is planted. Since the nematode is an obligate parasite and active only in moist conditions, any measure to alter such condition would limit the infestivity of the nematode. There are varietal differences in response to the infestation of the nematode. Some cultivars are resistant to ufra nematode; however, resistance alone has not been reported as the only measure to manage the disease. Combining resistant cultivars with other measures, such as field sanitation, may effectively control the disease. Removal and destruction of the straw in infested fields to reduce the amount of inoculum would be helpful. Wherever possible, infested fields should be drained or flooded when fallow. Chemical control. Several chemicals are reported to be efficacious in controlling the disease. They include carbofuran, hexadrin, and benomyl. In practice, however, farmers use little or no chemical control for the disease.

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Rice Root Nematode (Hirschmaniella oryzaej

It is caused by Hirschmanniella oryzae and reported in 25 rice-growing countries. It is omnipresent in irrigated rice ecosystems all over in eastern, southeastern, and southern Asia. It is also reported to occur in deepwater

rice in Bangladesh and in Thailand. H. mucronata is present in irrigated fields in India and the Philippines. These nematodes cause physical damages to the roots, and they affect the physiology of the plant. They also reduce nitrogen-fixation in the rhizosphere. Under controlled experiments, the nematodes reduced the number of tillers, plant height, panicle length, number ofleaves, fresh root weight, and shoot dry weight. These effects result in grain yield reduction. However, no reliable information is available as to the actual yield loss caused by the nematodes. One has to assume that these are closely related to the nematode population, soil type, and cropping systems, etc. REFERENCES

Adeoti, A. A., and M. 0. Adeniji. 1982. Occurrence of narrow brown leaf spot disease of rice in Nigeria. Oryza 19:56-57. Amin, K. S., B. 0. Sharma, and C. R. Das. 1974. Occurrence in India of sheathrot of rice caused by Acrocylindrium. Plant Dis. Rept. 58:358-60. Anjaneyulu, A. 1975. Rice stubbles and self-sown rice seedlings, the reservoir host of tungro during off-seasons. Sci. and Culture 41:298-99. Atkins, J. G., A. L. Robert, C. R. Adair, K. Goto, T. Kozaka, R. Yanagida, M. Yamada, and S. Matsumoto. 1967. An international set of rice varieties for differentiating races of Pyricularia orzyae. Phytopathology 57:297-301. Azegami, K., K. Nishiyama, and H. Kato. 1987. Growth of Pseudomonas plantarii, production of tropolone, and protein under limited iron growth conditions. Ann. Phytopathol. Soc. Japan. Azegami, K., K. Ozaki, A. Matsuda, and K. Ohata. 1983. Bacterial palea browning, a new disease of rice caused by Erwinia herbicola. Bull. Nat. Inst. Agr. Sci. Series C, 37:1-12 (English abstract). Belmar, S. B., R. K. Jones, and J. L. Starr. 1987. Influence of crop rotation on inoculum density of Rhizoctonai solani and sheath blight incidence in rice. Phytopathology 77:1138-43. Bockus, W. W., R. K. Webster, C. M. Wick, and L. F. Jackson. 1979. Rice residue disposal influences overwintering inoculum level of Sclerotium oryzae and stem rot severity. Phytopathology 69:862-65. Bonman, J. M., and D. J. Mackill. 1988. Durable resistance to rice blast. Oryza 25:103-10. Bonman, J. M., B. A. Estrada, and R. I. Denton. 1986. Blast management with upland rice cultivar mixtures. In Proc. Symp., Progress in Upland Rice Research, 375-82. Los Banos, Philippines: IRRI. Chang, I. C. 1973. Studies on the perfect stage and ecology of the rice bakanae fungus. M.S. thesis, Nat. Chung-Hsing Univ., Taichung, Taiwan (in Chinese).

230

RICE: PRODUCTION

Chen, C. C. 1971. Stem rot of rice. InProc. Rice Diseases, ed. R. J. Chiu, 77-98. Taipei, Taiwan: JCRS (in Chinese). Chen, C. C., and C. C. Chien. 1964. Some observations on the outbreak of rice sheath rot disease. J. Agr. Res. 13:39-45 (in Chinese). Chen, Z. Y., Chong-jian Guo, Geng-yun Dai, Cheng-fang Ge. 1987. Field study of the effect of moderately resistant rice varieties on sheath blight. Jiang-su Nong-ye Ke-Xie 7:18-19 (in Chinese). Chien, C. C., Y. C. Chang, Y. M. Lao, and S. H. Ou. 1983. Bacterial grain rot of rice-A new disease in Taiwan. J. Agric. Res. China 32(4):360-366 (in Chinese). Chin, K. M., and B. N. H. Ajmilah. 1981. "Rice variety mixtures in disease control." In Proc., Int. Conf Plant Protection in the Tropics, 241-46. Chinese Academy of Agricultural Sciences (CAAS). 1986. The Science of Rice Cultivation in China. Beijing: Agric. Publ. (in Chinese). Dasgupta, M. K., and S. B. Chattopadhyay. 1975. Variation in susceptibility of rice leaves to the brown spot. Indian Phytopathol. 28(1): 17-21. De Datta, S. K. 1981. Principles and Practices of Rice Production. New York: Wiley. Duveiller, E., K. Miyajima, F. Snaken, A. Autrique, and H. Maraite. 1988. Characterization of Pseudomonas fuscovaginae and differentiation from other fluorescent pseudomonads occurring on rice in Burundi. J. Phytopathology 122:97-107.

Dye, D. W., J. F. Bradbury, M. Goto, A. C. Hayward, R. A. Lelliott, and M. N. Schrot. 1980. International standards for naming pathovars of phytopathogenic bacteria and a list of pathovar names and pathotype strains. Rev. Plant Pathol. 59: 153-68. Endo, Y. 1985. Infection time of bacterial grain rot of rice and chemical control of seedling rot resulted from infected seeds. Kongetsu-noNoyaku 29(2):77-81 (in Japanese). Eruotor, P. G. 1986. Varietal reaction of rice to isolates of Cochliobolus miyabeanus. Indian Phytopath. 31(1):62-64. Estrada, B. A., L. M. Sanchez, F. L. Nuque, and J.P. Crill. 1981. Physiologic races of Cercospora oryzae in the Philippines. Plant Dis. 65:793-95. Fang, C. T., C. F. Lin, and C. L. Chu. 1963. A preliminary study on the disease cycle of the bacterial leaf blight of rice. Acta Phytopathol. Sinica 2:17385.

Fang, C. T., H. C. Ren, T. Y. Chen, Y. K. Chu, H. C. Faan, and S.C. Wu. 1957. A comparison of the rice bacterial leaf blight organism with the bacterial leaf streak organism of rice and Leersia hexandra Swarts. Acta Phytopathol. Sinica 3:99-124. Goto, K., and K. Ohata. 1958. Bacterial grain rot of rice. Ann. Phytopathol. Soc. Japan 23:155. Goto, K., and K. Ohata. 1961. Bacterial stripe of rice. Spec. Pubis. Coli. Agric. Nat. Taiwan Univ. 10:49-59. Goto, M. 1965. A comparative study of the sheath rot bacteria of rice. Ann. Phytopathol. Soc. Japan 30:42-5. Goto, M. 1979. Bacterial foot rot of rice caused by a strain of Erwinia chrysantemi. Phytopathol. 69:213-16.

RICE DISEASES

231

Goto, M. 1979. Dissemination of Erwinia chrysanthemi, the causal organism of bacterial foot rot of rice. Plant Dis. Reptr. 63:100-3. Goto, M., R. S. Zeigler, and V. T. John. 1987. Progress on rice seedborne and seed contaminant bacteria, viruses, and nematodes. In Proc., Rice Seed Health. Los Banos, Philippines: IRRI (in press). Goto, M., R. S. Zeigler, and V. T. John. 1988. Progress in seed health research on seedborne and contaminant bacteria, viruses and nematodes, In Proc., Rice Seed Health, 131-150. Los Banos, Philippines: IRRI. Grams, W., and D. L. Hawksworth. 1975. The identity of Acrocylindrium oryzae Sawada and a similar fungus causing sheath rot of rice. Karaka 3:57-61. Guo, Y. X. 1982. The rice-based cropping system and its development in China. In Proc., Cropping Systems Research in Asia, 331-44. Los Banos, Philippines: IRRI. Hashiba, T., K.l{oike, I. Yuno, andY. Yamada. 1982. Model of vertical development of sheath blight lesions on rice plants caused by Rhizoctonia so/ani Kuhn. Ann. Phytopath. Soc. Japan 48:499-505. Hashioka, Y. 1969. Rice diseases in the world-III: Bacterial diseases. Riso 18:189-204. Hashioka, Y. 1971. Rice diseases in the world-VIII: Diseases due to hypocreales, ascomycetes (fungal diseases). Riso 20:235-58. Hibino, H. 1979. Rice ragged stunt, a new virus disease occurring in tropical Asia. Rev. Plant Protect. Res. 12:98-110. Hibino, H. 1983a. Relations of rice tungro bacilliform and rice tungro spherical viruses with their vector Nephotettix virescens. Ann. Phytopath. Soc. Japan 49:545-53. Hibino, H. 1983b. Transmission of two rice tungro-associated viruses and rice waika virus from doubly or singly infected source plants by leafhopper vectors. Plant Disease 67:774-77. Hibino, H., and I. Kimura. 1982. Detection of rice ragged stunt virus in insect vectors by enzyme-linked immunosorbent assay. Phytopathology 72:65659. Hibino, H., and R. C. Cabunagan. 1986. Rice tungro-associated viruses and their relations to host plants and vector leafhoppers. Trap. Agri. Res. Ser. 19. Hibino, H., E. R. Tiongco, R. C. Cabunagan, and Z. M. Flores. 1987. Resistance to rice tungro-associated viruses in rice under experimental and natural conditions. Phytopathology 77:871-75. Hibino, H., M. Roechan, and S. Sudarisman. 1978. Association of two types of virus particles with penyakit habang (tungro disease) of rice in Indonesia. Phytopathology 68:1412-16. Hibino, H., N. Saleh, and M. Choehan. 1979. Transmission of two kinds of rice tungro-associated viruses by insect vectors. Phytopathology 69:1266-68. Hori, M. 1984. Present status of occurrence and chemical control of sheath blight in Japan. Japan Pest Inf. No. 44:6-10. Hsieh, S. P. Y., W. J. Liang, and S. Y. Chan. 1977. Etiological studies on the sterility of rice plant. I. Association of sheath rot fungus, Acrocylindrium oryzae Sawada, with sterile rice plant. Plant Prot. Bull. Taiwan. 19:30-36 (in Chinese). Huang, Y. T. 1978. Ecology of stem-rot of rice. In Proc., Symp. Diseases and

232

RICE: PRODUCTION

Insect Pests of Rice: Ecology and Epidemiology, ed. R. J. Chiu, Taiwan: JCRR, China. Int. Rice Res. Inst. (IRRI). 1965. Rice blast. Baltimore, MD: Johns Hopkins Press. International Rice Research Institute IRRI. 1982. A plan for IRRI' s third decade. Los Banos, Philippines: IRRI. International Rice Research Institute IRRI. 1984. Terminology for rice growing environments. Los Banos, Philippines: IRRI. International Rice Research Institute IRRI. 1985. International Rice Research: 25 years of partnership. Los Banos, Philippines: IRRI. International Rice Research Institute IRRI. 1985-89 annual reports. Los Banos, Philippines: IRRI. Jones, R. K., L. W. Barnes, C. F. Gonzales, J. E. Leach, A. M. Alvarez, and A. A. Benedict. 1989. Identification oflow-virulence strains of Xanthomonas campestris pv. oryzae from rice in the United States. Phytopathology 79:984-90. Kato, H., K. Ohata, L. P. Kauraw, andY. H. Lee. 1988. Fungal diseases of rice seed. InProc., Int. Workshop ofSeed Health, 151-62. Los Banos, Philippines: IRRI. Kaur, P., S. Kaur, and S. Y. Padmanabhan. 1979. Effect of manganese and iron on incidence of brown spot disease of rice. Indian Phytopath. 32:287-8. Kaur, P., S. Kaur, and S. Y. Padmanabhan. 1982. Relationship of phosphorus concentration in the host and brown spot disease of rice. Indian Phytopath. 35:393-398. Keirn, R., and R. K. Webster. 1974. Effects of soil moisture and temperature on viability of sclerotia of Sclerotium oryzae. Phytopathology 64:1499-502. Keirn, R., and R. K. Webster. 1975. Fungistasis of sclerotia of Sclerotium oryzae. Phytopathology 63:518-23. Khush, G. S., and K. C. Ling. 1974. Inheritance of resistance to grassy stunt virus and its vector in rice. J. Heredity 65:134-36. Kim, C. K., D. S. Ra, H. S. Min, Y. H. Lee, and E. J. Lee. 1985. Ecological studies on rice sheath blight caused by Rhizoctonia solani. IV. Inoculation time of Sclerotium and disease development. Korean J. Plant Pathol. 1:169-72. Kim, C. K., C. S. Kang, S. J. Rim, E. J. Lee, andY. H. Lee. 1981. Ecological studies on rice sheath blight caused by Rhizoctonia solani. I. The difference of disease development between Jinheung and Yusin. Korean J. Plant Prot. 20:71-75. Kim, C. K., D. S. Ra, and H. S. Min. 1985. Ecological studies on rice sheath blight caused by Rhizoctonia so/ani. III. Cultural method and disease development. Korean J. Plant Prot. 24(1):7-10. Klement, Z. 1955. A new bacterial disease of rice caused by Pseudomonas oryzicola n. sp. Acta Microbial. Acad. Sci. Hung. 2:265-67. Kuwata, H. 1985. Pseudomonas syringae pv. oryzae pv. nov., causal agent of bacterial halo blight of rice. Ann. Phytopath. Soc. Japan 51:212-18. Lamey, H. A., and T. R. Everett. 1967. Increased susceptibility of Hoja Blanca virus infected rice leaves to Cochliobolus mija-beanus. Phytopathology 57:227. Lee, Y. H., F. L. Nuque, and J.P. Crill. 1980. Resistance to bakanae disease

RICE DISEASES

233

(Gibberella fujikuroi) Sawada and its symptom changes at seedling stage of rice plant. Philippine Phytopath. 17:9-10 (Abstract). Lee, E. J., Q. Zhang, and T. W. Mew. 1987. Durable resistance to rice diseases in irrigated environments. In Proc. 1987 Int. Rice Res. Conf. Los Bafios, Philippines: IRRI. Lee, L. N. 1980. Number, viability, and buoyancy of Rhizoctonia so/ani sclerotia in Arkansas rice fields. Plant Disease 64:298-300. Leung, H., and P. H. Williams. 1986. Enzyme polymorphism and genetic differentiation among geographic isolates of rice blast fungus. Phytopathology 76:778-83. Lim, G. 1967. Fusarium populations in rice field soils. Phytopathology 57:1152-53. Ling, K. C. 1966. Nonpersistence of the tungro virus of rice in its leafhopper vector Nephotettix impicticeps. Phyptopathology 56:1252-56. Ling, K. C., and S. H. Ou. 1969. Standardization of the international race numbers of Pyricularia orzyae. Phytopathology 59:339-42. Ling, K. C. 1979. Rice virus diseases. Los Bafios, Philippines: IRRI. Lo, T. C., and S. P. Y. Hsieh. 1964. Studies on stemrotofrice plant. I. Distribution and economic significance ofthe disease. Taiwan Plant Prot. Bull. 6:121-35. Lozano, J. C. 1977. Identification of bacterial leaf blight in rice, caused by Xanthomonas oryzae, in America. Plant Dis. Reptr. 61:644-48. Macatula, R. F., S. L. Valencia, and 0. Mochida. 1987. Evaluation of 12 insecticides against greenleaf hopper for preventing rice tungro virus disease. Los Bafios, Philippines: IRRI. Manwan, 1., S. Suma, and S. A. Rizvi. 1985. Use of varietal rotation in the management oftungro disease in Indonesia. Indon. Agric. Res. Dev. J. 7:43-8. Maraite, H., M. Nitbishimirwa, E. Duveiller, and J. E. Detry. 1989. Epidemiology of sheath brown rot of Graminae caused by Pseudomonas fuscovaginae in tropical highlands. In Proc. 7th Int. Conf. on Plant Pathogenic Bacteria, Budapest, Hungary. Mew, T. W. 1989. Disease management in rice. In CRC Handbook ofPest Management in Agriculture, Vol. 3, ed. D. Pimenteled, 279-99. Boston, Mass.:CRC Press. Mew, T. W., F. M. Wang, J. T. Wu, K. R. Lin, and G. S. Khush. 1988. Diseases and insect resistance in hybrid rice. In Proc. Hybrid Rice, 190-200. Los Bafios, Philippines: IRRI. Mew, T. W. 1987. Current status and future prospects of research on bacterial blight of rice. Ann. Rev. Phytopathol. 25:359-82. Mew, T. W. 1989. An overview of the world bacterial blight situation. In Proc. Bacterial Blight of Rice, 7-12. Los Bafios, Philippines: IRRI. Mew, T. W., and A. Ezuka. 1987. Rice bacterial disease management in Asia. In Proc. Rice Pest Management in the Tropics, lith ICPP, Manila, Philippines (in press). Mew, T. W., R. C. Reyes, and C. M. Vera Cruz. 1989. Screening rice for resistance to bacterial blight (Xanthomonas campestris pv. oryzae ), In Methods in phytobacteriology, 338-41, ed. Klement, Z., K. Rudolph, and D. C. Sands. Mew, T. W., and A. M. Rosales. 1986. Bacterization of rice plants for sheath blight control. Phytopathology 76:1260-64. Mew, T. W., F. M. Wang, J. T. Wu, K. R. Lin, and G. S. Khush. 1986. Disease

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and insect resistance in hybrid rice. In Proc. Int. Symp., Hybrid Rice. Hunan, China. Miyajima, K. 1983. Studies on bacterial sheath brown rot of rice plant caused by Pseudomonas fuscovaginae, Tanii. Miyajima, K., and T. Akita. Rep. Hokkaido Pref Exp. Stn. 43:1-74. (English Abstract). Miyajima, K. 1989. In Proc. 5th Int. Congr. of Plant Pathology, Hungary (in press). Miyajima, K., and T. Akita. 1975a. Effect of climatic factors on the bacterial sheath brown rot of rice. Bull. Hokkaido Prefect. Agric. Exp. Stn. 31:6776. Miyajima, K., and T. Akita. 1975b. Process of disease development of bacterial sheath brown rot of rice and multiplication of pathogenic bacteria. Bull. Hokkaido Prefect. Agric. Exp. Stn. 32:53-9. Mizukami, T., and S. Wakimoto. 1969. Epidemiology and control of bacterial leaf blight of rice. Ann. Rev. Phytopathol. 7:51-72. Mohanty, S. K., and N. K. Chakrabarti. 1981. Effect of slow-release form of nitrogen application on brown spot disease of rice. Oryza 18:241-3. Nawaz, M., and A. G. Kauser. 1962. Cultural and pathogenic variation in Helminthosporium oryzae. Biologia 8:25-48. Nuque, F. L., T. I. Verge! de Dios, and J. P. Crill. 1980. Pathogenic races of Fusarium moniliforme in the Philippines. Philippine Phytopath. 17:9 (Abstract). Nyvall, R. F., and T. Kommedahl. 1968. Individual thickened hyphae as survival structures of Fusarium moniliforme in corn. Phytopathology 58:1704-7. Ogawa, K. 1988. Damage by "bakanae" disease and its chemical control. Japan Pesticide Inform. 52: 13-5. Ou, S. H. 1972. Rice diseases. Kew, England: Commonwealth Mycol. Inst. Ou, S. H. 1985. Rice diseases. 2nd ed. Kew, England: Commonwealth Mycol. Inst. Padmanabhan, S. Y. 1973. The great Bengal famine. Ann. Rev. Phytopathology 11:11-26. Paik, S. B. 1975. The effect of silicate, nitrogen, phosphorus and potassium fertilizers on chemical components of rice plants and on the incidence of blast disease of rice caused by Pyricularia oryzae. Korean J. Pl. Prot. 14(3):97-109. Purkayastha, R. P., and A. Ghosal. 1982. Sheath rot of rice. Oryza 19:78-83. Reddy, A. P. K., J. C. Katyal, D. I. Rouse, and D. R. MacKenzie. 1979. Relationship between nitrogen fertilization, bacterial leaf blight severity, and yield of rice. Phytopathology 69:970-3. Rosales, A.M., F. L. Nuque, and T. W. Mew. 1986. Biological control ofbakanae disease of rice with antagonistic bacteria. Philippine Phytopath. 22:29-35. Rott, P., J. L. Notteghem, and P. Frossard. 1988. Identification and characterization of Pseudomonas fuscovaginae, the causal agent of bacterial sheath brown rot of rice from Madagascar and other countries. Plant Disease 73:133-37. Ryker, T. C., and N. E. Jodon. 1940. Inheritance of resistance to Cercospora oryzae in rice. Phytopathology 30:1041-7. Sah, D. N., and M. C. Rush. 1988. Physiological races of Cercospora oryzae in the Southern United States. Plant Disease 72:262-4.

RICE DISEASES

235

Saito, Y., M. Iwaki, and T. Usugi. 1976. Association of two types of particles with tungro-group disease of rice. Ann. Phytopath. Soc. Japan 42:375 (Abstract). Shahjahan, A. K. M., Z. Harahap, and M. C. Rush. 1977. Sheath rot of rice caused by Acrocylindrium oryzae in Louisiana. Plant Disease 61:307-10. Shahjahan, A. K. M., and M. C. Rush. 1979. Occurrence and distribution of diseases caused by sclerotia! fungi on rice in Louisiana. Plant Disease Reporter 63:220-23. Shahjahan, A. K. M., M.A. Hossain, S. I. Akanda, and S. A. Miah. 1986. Sources of resistance to stem rot of rice in Bangladesh. SABRAO J. 18:9-17. Singh, R. A., K. S. Bube, and R. K. Verma. 1985. Survival of Claviceps oryzae sativae-The incitant of false smut of rice. Indian Phytopath. 38:442-46. Sridhar, R. 1970. A new collateral host of Cercospora oryzae. Plant Disease 54:272-73. Subramanian, C. L., and G. Ramakrishnan. 1973. The occurrence of brown spot Helminthosporium oryzae Breda de Haan on some wild species of Oryza. Current Sci. 42:327. Sugiyama, M. 1988. Rice sheath blight and chemical control. Japan Pest. Inf. 52:9-12. Sun, S. K., and W. C. Snyder. 1981. The bakanae disease of the rice plant. In Fusarium diseases, biology, and taxonomy, ed. P. E. Nelson and R. J. Cook, 104-13. Univ. Park, PA: Penn. State Univ. Press. Suzuki, H. 1970. Interrelationship between the occurrence of rice blast disease and meteorological conditions. Rev. Plant Protection Res. 3:1-11. Swings, J. 1990. Classification of the bacterial blight pathogen. In Proc. Bacterial Blight of Rice. 13-17. Los Banos, Philippines: IRRI. Tanii, A., K. Miyajima, and T. Akita. 1976. The sheath brown rot disease of rice plant and its causal bacterium, Pseudomonas fuscovaginae, A. Tanii, K. Miyajima et T. Akita sp. Nov. Ann. Phytopathol. Soc. Japan 42:540-48. Tasugi, H., and Y. Ikeda. 1956. Studies on the sheath rot of rice plant caused by Acrocylindrium oryzae Sawada. Bull. NIAS 1C-6:151-66. Thomas, M. D., and S. A. Raymundo. 1983. Response of two rice varieties to Rhynchosporium oryzae infection. Int. Rice Res. Newslett. 8:11. Tsai, W. H., and C. M. Yu. 1978. Epidemiology of rice sheath blight and its effect on rice production. In Proc. Symp., Disease and Insect Pests ofRice: Ecology & Epidemiology, 247-62. Taiwan: JCRR. Uetmatsu, T., D. Yoshimura, K. Nishiyama, T. lbaraki, and H. Jujii.1976. Occurrence of bacterial seedling rot in nursery fiat caused by grain rot bacterium Pseudomonas glumae. Ann. Phytopathol. Soc. Japan 42:310-12 (Enging Abstract). Upadhyay, R. K. 1985. Rice diseases status in India. Int. Rice Res. Newslett. 10(5):17. Usmani, S. M. H., A. Ghaffer, S. Hussain, and W. Ahmad. 1985. Polyethylene mulching to control sheath rot. Int. Rice Res. Newslett. 10(1):10-11. Vera Cruz, C. M., F. Gossele, K. Kersters, P. Segers, M. Vanden Mooter, J. Swings, and J. Dely. 1984. Differentiation betweenXanthomonas campestris pv. oryzae, Xanthomonas campestris pv. oryzicola and the "brown blotch" pathogen on rice by numerical analysis of phenotypic features and protein gel electrophoregrams. J. Gen. Microbial. 130:2983-99.

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Vidhyasekaran, P., and N. Ramados. 1973. Quantitative and qualitative losses in paddy due to Helminthosporiose epidemic. Indian Phytopathol. 26:479-84. Vidhyasekaran, P., K. Ranganathan, S. P. Palaniappan, and S. Ramasamy. 1983. Effect of slow-release nitrogen fertilizers on rice brown spot disease. Int. Rice Res. Newslett. 4:11. Viswanathan, V., and V. Mariappan. 1980. Fungicidal control of sheath blight. Int. Rice Res. Newslett. 5(5):15. Yamada, M., S. Kiyosawa, T. Yamaguchi, T. Hirano, T. Kobayashi, K. Kushibychi, and S. Watanabe. 1976. Proposal of a new method for differentiating races of Pyricularia orzae cavara in Japan. Ann. Phytopath. Soc. Japan 42. Yamaguchi, T. 1986. Nursery-tray application of fungicides for the control of rice diseases. Japan Pesticide Inform. 49:10-4. Yamamoto, M., M. Nozu, and T. Murakami. 1972. On the pathogenicity ofCochliobolus miyabeanus (S. Ito et Kurib). Drech. to several paddy weeds. Bull. Fac. Agric. Shimane niv. 6:6-9. Yeh, W. H., and J. M. Bonman. 1986. Assessment of partial resistance to Pyricularia oryzae in six rice cultivars. Plant Pathol. 35:319-23. Yoshino, R. 1988. Present status of occurrence and control of blast disease in Japan. Japan Pesticide Inform. 52:3-8. Yu, K. S., and S. K. Sun. 1977. Studies on inoculum potential and incubation period of rice bakanae disease. Plant Prot. Bull. 19:245-50 (in Chinese with English summary). Zeigler, R. S., and E. Alvarez. 1987. Bacterial sheath brown rot of rice caused by Pseudomonas fuscovaginae in Latin America. Plant Disease 71:592-7. Ziegler, R. S., G. Aricapa, and E. Hoyos. 1987. Distribution of fluorescent Pseudomonas spp. causing grain and sheath discoloration of rice in Latin America. Plant Disease 71:896-900.

6 Insect Pests of Rice M. 0. Way and C. C. Bowling Texas A&M University Agricultural Research and Extension Center

INTRODUCTION

Rice is the most important food for mankind. Annual world rice production amounts to approximately 460 million tons grown on roughly 145 million ha (Norton and Way 1990). Over 90% of this area lies in Asia, while the remainder is divided among Latin America, Africa, Australia, Europe, and the United States (IRRI 1989). To keep pace with projected human population growth, rice production must increase from the 1987 levels to 20% more by 2000 and 65% more by 2020 (IRRI 1989). However, over 800 insect species attack standing and stored rice (Grist and Lever 1969). According to Pathak and Dhaliwal (1981) these pests account for rice losses of 24% while Cramer (1967) reports 35%. The importance of rice insect pests can be grasped by the fact that $910 million are spent annually in attempts to control their activities with insecticides (Woodburn 1990). Japanese rice farmers spend the most ($455 million), while farmers in developing countries spend much less per unit of production (Woodburn 1990). Furthermore, the value of insecticides applied to rice in 1988 was 15% of the total world usage of insecticides (Woodburn 1990). Thus, insect 237

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pests are serious enemies to rice production which must be protected and increased to foster human health and world peace and stability. Rice is grown in surprisingly varied habitats ranging from sea level to 3000 m, arid to wet environments, and temperate to tropical climates (Pathak 1968). Each geographical/climatic area harbors a distinct complex of insects associated with the rice cultivation and practices peculiar to that area. Production practices which impact insect populations and damage include varietal selection, method and date of planting, fertilizer and irrigation methods and schedules, pesticide usage,and multiple cropping. The following brief discussion illustrates the diversity of rice agroecosystems and associated cultural practices relative to the effect on broad groupings of insect pests and their activities. By 1985 the International Rice Research Institute (IRRI) had released 24 varieties (IR5-IR60) for commercial planting in the Philippines (Heinrichs et al. 1985; Khush 1984). Each variety possesses a unique set of characteristics which best take advantage of a targeted environment or demand. Many of these cultivars have genes conferring resistance or tolerance to certain planthoppers, leafhoppers, midges, defoliators, and stem borers. In Asia, 20- to 40-day-old rice seedlings are transplanted from nursery beds to paddies where plants are grouped to form hills. In the United States, rice seed is broadcast to flooded or dry paddies which are then irrigated, or else seed is drill-planted in dry soil which is subsequently flooded. The populations and behavior of seedling insect pests and root pruning weevils are profoundly affected by differences in planting methods. The Green Revolution, spawned by IRRI in 1962, came to fruition with the release of the high-yielding short-statured IRS in 1966 (Kisimoto 1984). This and subsequent dwarf cultivars responded without lodging to increased nitrogen. Production increases of21 and 22% were attributed to inherent high-yielding ability and increased nitrogen, respectively (Litsinger 1989). However, certain pest populations, such as planthoppers, leafhoppers, and stem borers, also responded positively to elevated nitrogen levels. Lowland rice is grown in paddies which are surrounded by levees to impound water received from a reliable or uncontrolled source. Upland rice relies on direct rainfall and is not grown within impounded paddies (Litsinger 1987). Approximately 75% of the world's rice is grown in lowlands, while 10% is in uplands (Wilson and Claridge 1985). The remaining 15% is deepwater rice grown in up to 6 m of standing water. Litsinger (1987) concluded that upland rice is attacked by a wider array of insects than lowland rice, although populations are generally smaller on upland rice. The major pests of upland rice attack seed and seedlings; however, no single insect has been observed as a key pest every year. As the Green Revolution varieties became more widely accepted and grown, more insec-

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ticides were applied to protect higher yielding crops requiring greater inputs. The increased use of insecticides decimated natural enemies and led to secondary pest outbreaks and the resurgence ofplanthoppers (Heinrichs 1979; Chelliah and Heinrichs 1980; Krishnaiah and Kalode 1987). Finally, the release of early-maturing varieties lacking sensitivity to photoperiod fostered asynchronous planting and the growth of more than one crop per year (Kenmore et al. 1984; Oka 1979). In the tropics, this provides a continuous supply of suitable host plants and an opportunity for pest populations to build to damaging levels. Clearly, a single chapter cannot describe all the world rice agroecosystems and associated insect pests. Grist and Lever (1969) consider 28 species in Asia, nine in Australia, 15 in Africa, and 13 in the Americas as major insect pests of rice. Space limitations require that only the most important pests, based on number of publications within the last five years and/or opinions of rice entomologists, be considered here. Consequently, the remainder of this chapter will describe pertinent aspects of the life history, damage, management, and current research efforts concerning only the most important insect pests of rice. BROWN PLANTHOPPER

The brown planthopper (BPH), Nilaparvata lugens (Stal) is the most serious insect pest of rice in the world. It occurs in tropical to temperate areas of southern and southeastern Asia including Pakistan, India, Nepal, Bhutan, Bangladesh, Sri Lanka, Thailand, Laos, Vietnam, Kampuchea, Malaysia, Indonesia, Papua New Guinea, Philippines, Japan, China, North Korea, and South Korea (Reissig et al. 1986). BPH also occurs in Australia and a related species, Nilaparvata maeander Fennah has been reported in Africa, where it may become a serious pest (Alam et al. 1985). Dyck and Thomas (1979) estimated at least $300 million in losses were attributable to BPH during the 1970s. Damage is by direct feeding ofBPH which removes excessive amounts of phloem sap, causing foliage to turn brown and die. Eventually, the entire plant also dies. This condition is called hopperburn and results in high yield losses. In physiological terms, hopperburn is probably caused by disruption of photosynthate flow to the root system which causes leaf senescence (Sogawa 1982). BPH also transmits viruses, the causative agents of grassy stunt and ragged stunt diseases. Symptoms of grassy stunt are severely stunted plants with many tillers which produce few panicles. Ragged stunt gives rise to ragged leaves during early growth stages, stunting, vein swelling, and more panicles but fewer filled grains than healthy plants (IRRI 1983). Both viruses are persistent but not transmitted transovarially.

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RICE: PRODUCTION

Brown planthoppers became a major pest after the release of highyielding, short-statured cultivars which drastically altered traditional cultural practices and insecticide use patterns. Increased nitrogen applications, construction and implementation of irrigation systems to allow multiple rice cropping, and greater reliance on insecticides which decimate natural enemies have largely been responsible for the change in pest status of BPH (Kenmore et al., 1984; Sogawa 1982). The eggs of the BPH are inserted in groups in leaf sheaths. Nymphs and adults feed at the base of plants where coverage by insecticidal sprays is often inadequate due to the foliage canopy. A complete generation requires about one month at 27°C; consequently, multiple generations develop during the rice growing season (Kisimoto 1981). Until recently, BPH was known only to reproduce on rice but Heinrichs and Medrano (1984) discovered populations ofBPH which could develop Leersia hexandra, a weed found in ditches and canals associated with rice cultivation. Thus, they speculate that BPH natural enemies may maintain their populations (during periods when rice is not growing) on BPH hosts developing on L. hexandra. BPH flight behavior, population dynamics, and damage patterns are different in tropical and temperate areas. The insect is endemic in the tropics where populations gradually increase; this increase is followed by long distance movement to temperate regions (Riley et al. 1987). The insect does not overwinter north of the Tropic of Cancer; therefore, infestations in northern China, northern India, Korea, and Japan develop every year from long distance migrants originating in the tropics and subtropics. In the tropics, movement from one area to another requires only short flights because of the continuity of rice cropping in both space and time (Perfect and Cook 1987). As densities of tropical BPH infestations increase and rice plants become hopperburned, older, or less preferred, a greater percentage of macropterous adults appear (Padgham 1983). Once these winged immigrants arrive in temperate rice-growing areas, BPH populations increase exponentially over three generations, eventually causing hopperburn damage (Kisimoto 1981). This damage may initially be restricted to small areas in paddies where the original migrants arrived, but gradually, these areas expand to cover entire paddies. On the other hand, population increases in the tropics are not as dramatic, possibly due to the action of natural enemies. This implies that BPH long distance movement separates the pest from its natural enemies. However, Okuma and Kisimoto (1981) collected Cyrtorhinus lividipennis Reuter, an important mirid predator of BPH, and spiders over the East China Sea. Presumably, these natural enemies were moving long distances from China to Japan as were the host BPHs.

INSECT PESTS OF RICE

241

Table 6-1. Rice Yield Loss and Time of Infestation of Brown Planthopper in Korea Time of lnfestationa (days after transplanting)

Percent of Yield Loss

46 56 66 76 81 86 91 Control

100 100 81 61 30 19 6 0

a Initial infestation of one pair of adults per hill. Source: Lee and Park (1976).

Since BPH is a serious pest over a wide range of environments, numerous economic threshold/injury levels have been proposed. In addition, the time of infestation relative to crop growth can influence damage and threshold values. For instance, in temperate areas hopperburn generally occurs during the reproductive phase of crop growth, while in the tropics it can occur at any time. Plants infested during the vegetative phase of development produce fewer panicles and grains per panicle, while later infestations reduce the percentage of fully developed grains (Sogawa and Cheng 1979). Furthermore, Kisimoto (1976) found that yield losses in Japan were greater when hopperburn occurred earlier relative to heading. In Korea, Lee and Park (1976) infested rice at various times with a single pair of adult BPH per hill. Data show that roughly a 50-day difference in the time of infestation can result in less than 10 to 100% yield loss (Table 6-1.). Kisimoto (1984) estimated the critical level of economic loss at 3%. This corresponds to 0.3 to 0.5 first generation brachypterous females per hill in temperate regions. In the tropics, a threshold of20 to 25 BPH per hill is widely accepted; however, Sogawa and Cheng (1979) believe that 10 per hill is more accurate. Their belief is supported by data from Taiwan showing that 10 BPH per hill can reduce yield 14% (Table 6-2.). Reissig et al. (1986) report the economic threshold for tropical Asia as one late instar nymph per tiller. Late instar nymphs were selected as the sample and treatment target because they are not sexually mature, have escaped egg and early instar parasitism and predation, and are capable of removing large amounts of sap. Since nymphs are not able to reproduce, treatments aimed at their

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RICE: PRODUCTION

Table 6-2. Brown Planthopper Density and Yield Loss in Taiwan Number of Insects Per

Percent of Yield Loss"

Hill

10 20 40 80 160

14.1 15.9 20.0 25.3 33.7

On susceptible variety Taichung Native 1. Source: Adapted from Cheng (1976). a

control can prevent population buildup. Shepard et al. (1986) developed a sequential sampling plan for BPH and white backed planthopper, Sogatella furcifera Horvath in the Philippines (Fig. 6-1.). The sampling unit is a hill, and the insect stages sampled are late instars and adults during tillering to flowering of the crop. Sampling is accomplished by beating plants in a hill over the water surface or a water pan trap and counting the dislodged

.300

280 260 1.... ~ 240 a. 0 220 1/)

..c

200

0 c

Q)

.~ -' 0 ::l

E

::l

0

180 160 140 120 100

80 50 4

5

6

7

8

9

10

11

12

1.3

No. hills sampled Figure 6-1. Sequential sampling plan for hopper pests in Philippines. Probability of making incorrect decision = 20%. Adapted from Shepard et al.

(1986).

INSECT PESTS OF RICE

243

hoppers on the water surface. The effectiveness of the sequential sampling plan was compared to an approved more extensive sampling method requiring 20 hills to be examined regardless of hopper population density. Results showed 100% agreement between the techniques with an 80% savings in time using the sequential sampling plan. Host plant resistance is the major control tactic for BPH. According to Heinrichs (1986) over 70,000 rice accessions have been evaluated for BPH resistance at IRRI. Roughly 1 to 2% were judged resistant. As of 1984, 20 BPH resistant varieties have been released by IRRI. These resistant varieties are well accepted in Asia and save farmers millions of dollars annually. For instance, IR36, which is resistant to BPH, is grown on 13 million hectares making this cultivar the most widely cultivated of any food crop variety (Heinrichs 1986). Breeding programs have employed a number of resistant donors, including TKM6, Mudgo, Ptb33, Neera, W1252, and W1256. Taichung Native 1 is often used as a susceptible check variety in these programs. Investigation into the mechanism of resistance revealed that BPH probes more but ingests less phloem sap when feeding on resistant cultivars (Khan and Saxena 1988; Kimmins 1989). In addition, on susceptible varieties, BPH produces more honey dew, lays more eggs, develops faster, and lives longer (Saxena and Khan 1988; Cook et al. 1987). This has important implications for BPH long distance movement, since insects reared on resistant varieties do not have as much lipid reserve as those reared on susceptible varieties. Padgham (1983) surmised that BPH reared on resistant IR36 would not have sufficient fuel reserves to cross the East China Sea successfully and establish in Japan. Also, Saxena and Okech (1985) extracted plant volatiles from resistant cultivars and applied them topically to a susceptible cultivar with the result that BPH feeding was reduced and mortality increased relative to the untreated susceptible cultivar. They concluded that these volatiles, which include terpenoids, have a repellent or toxic effect on BPH and play an important role in the establishment of the insect on rice. Although BPH-resistant varieties have provided farmers in developing Asian countries a relatively inexpensive method of control, the stability of resistance is being undermined by the development ofbiotypes with the ability to develop normally on previously resistant genotypes. Three BPH biotypes have been identified, and each has a distinct pattern of responses to a given set of cultivars (Pathak and Heinrichs 1982). Biotype 1 is affected by all BPH-resistant varieties; biotype 2 is unaffected by varieties with the Bph1 gene; and biotype 3 is unaffected by varieties with bph2 gene. Currently, IR56, IR58, IR60, and IR62 are resistant to all biotypes (Heinrichs 1986). To combat the development of new virulent biotypes, plant breeders and entomologists are selecting for genotypes with more than

244

RICE: PRODUCTION

one resistance gene to achieve a broader base of resistance-horizontal. Another tactic is to incorporate field resistance or tolerance into vertically resistant cultivars. Velusamy et al. (1987) reported that IR46, Utri Rajapan, and Triveni exhibited field resistance to BPH. In other words, although these varieties are susceptible during the seedling stage of development, they become increasingly resistant with age. Utri Rajapan is being used as a donor in attempts to develop more broadly based BPH-resistant cultivars. Other methods of control are (1) limit rice production to two crops per year, (2) synchronize planting on an areawide basis, (3) do not overfertilize, (4) plow down volunteer ratoon plants after harvest, and (5) apply the proper dosage of insecticide at the best time to conserve natural enemies and prevent BPH resurgence. Heinrichs et al. (1982a) found that certain insecticides, such as carbofuran and decamethrin, when applied as foliar sprays, stimulate egg production in BPH, resulting in much higher infestations on treated versus untreated rice. Since BPH feeds below the rice canopy, insects are often exposed to sublethal doses of foliar applied insecticides which fosters BPH resurgence due to physiological stimulation. Sprays should be directed toward the base of plants to help solve this problem. Heinrichs et al. (1982b) conclude that resurgence-promoting insecticides should be identified and not recommended for use by farmers. Furthermore, Reissig et al. (1982) evaluated 35 insecticides for toxicity to natural enemies of BPH. They found that most insecticides did not affect spiders or Microuelia atrolineata (Bergoth) (a veliid predator) populations but did reduce C. liuidipennis numbers. Selective insecticides that do not promote resurgence should be developed. Buprofezin is an insect growth regulator that shows excellent activity against N. lugens and does not upset the natural enemy balance or induce resurgence (Konno 1990). Recently, neem cake, which is made from the seed of Azadirachta indica, was evaluated by Saxena et al. (1984) for insecticidal action against BPH. Neem has systemic, antifeedant properties which significantly reduced food intake of female BPH. However, neem products degrade when exposed to sunlight; therefore, application to soil followed by incorporation is preferable to foliar treatments. Development of an effective neembased insecticide for BPH control would be highly beneficial to Asian farmers because of ready availability, low cost, and low toxicity to nontarget species. GREEN LEAFHOPPERS

Four species of green leafhopper (GLH) occur in Asia: Nephotettix cincticeps (Uhler), which is limited to temperate regions, and N. uirescens (Distant), N. nigropictus (Still), and N. malayanus Ishihara et Kawase,

INSECT PESTS OF RICE

245

which are distributed in the tropics. Nephotettix spp. are the most important insect pests of rice in tropical Asia (Saxena and Khan 1989). They damage rice by direct feeding which is secondary to their ability to vector viruses that cause rice dwarf, transitory yellowing, yellow dwarf, and tungro (IRRI 1983). Of these diseases, tungro is the most serious. Symptoms of tungro-infec1ed rice are stunting, decreased tillering, leaf color change from light yellow to orange-yellow to brown-yellow, and development of young leaves that are mottled or have pale green to white stripes parallel to the veins. Infected plants mature later with panicles that are often incompletely exserted and small. Yields are reduced, primarily due to fewer filled grains per panicle. Plants that are infected late may not exhibit symptoms which can occur on subsequent ratoon rice (IRRI 1983). Younger plants are more susceptible to virus infection and serve as a better source of inoculum than older plants (Sogawa 1976). Rapusas and Heinrichs (1987) exposed IR36 plants of varying age to viruliferous N. virescens. Roughly 85, 50, and 0% of 20-, 40-, and 60-day-old plants, respectively, became tungro-infected. Not surprisingly, yield is also reduced more by early than late infections relative to age of rice. For example, Ling (1969) and Ling and Palomar (1966) reported that IRS inoculated 15, 30, 45, 60, and 75 days after sowing gave yield reductions of 68, 57, 30, 16, and 7%, respectively. Various strains of rice tungro virus have been identified based on virulence to different rice varieties. The virus has a limited host range, with wild and cultivated rices being the most suitable. In addition, the major vector of tungro, N. virescens, also has a limited host range that includes only those species in the genus Oryza (Cook and Perfect 1989). Thus, volunteer, ratoon, and wild rice in and around paddies has a large influence on the epidemiology of tungro, particularly during the time of year when rice is not cultivated. Green leafhoppers move into seedling nurseries and paddies when rice emerges. Adults are capable of long distance movement, and all are macropterous though most movement is limited to several kilometers. Unlike BPH, GLH adults occur on the top portion of rice plants. Females insert egg batches in leaf sheaths or midribs of foliage near the base of plants. Nymphs are found on foliage during the morning but move down the plant during the heat of the day. In the tropics, a single generation requires about 30 days, while in temperate regions, more time is needed to complete a life cycle. Both nymphs and adults feed on leaf sheaths and blades and can transmit the tungro virus, but younger individuals are less efficient. Over 50% of N. virescens actively tranmit the tungro virus (Sogawa 1976). N. virescens can acquire the virus from virus-infected plants in only 30 min and transmit almost immediately since no incubation is required (Ling 1968). Infective insects quickly lose the ability to transmit but can reacquire the virus within a short time period. Infectivity is lost

246

RICE: PRODUCTION

upon molting, and transovariole transmission does not occur. Due to these characteristics, rice tungro virus is nonpersistent and probably stylet borne. Since direct damage by GLH is rare, economic threshold/injury levels are primarily concerned with disease damage. In the Philippines, the economic threshold is two GLH per sweep or five per hill sampled by plant tapping (Reissig et al. 1986). Monitoring rice should begin at emergence and terminate at panicle initiation. In Japan, the economic injury level for N. cincticeps is 6% for hills infected early or 17% for late-infected hills (Andow and Kiritani 1983). However, since this pest vectors rice dwarf virus, which has a 1- to 4-week incubation period before symptoms develop, control should be initiated before or soon after transplanting. In fact, control tactics can be employed even earlier, when paddies are fallow. Above-threshold densities of GLH are considered to arise from higher than normal vector populations surviving during the off-season on wild, ratoon, and volunteer rice. These populations move to young cultivated rice, increase rapidly, and cause extensive damage. Like the BPH, planting resistant varieties is a major control tactic for GLH. Resistance to N. virescens has been detected in about 1200 accessions from approximately 48,000 evaluated at IRRI (Heinrichs 1986). All cultivars, except one, released by IRRI since 1960 have high or moderate levels of resistance toN. virescens. However, none of these commercial cultivars possesses resistance to tungro virus (Heinrichs and Rapusas 1990). Six dominant and one recessive gene have been identified as conferring resistance to N. virescens (Saxena and Khan 1989). Japan also has embarked on an active breeding program to develop varieties resistant to N. virescens which transmits rice dwarf virus. Presently, no known GLH biotypes have the ability to develop normally on previously resistant varieties. However, Saxena and Khan (1989) reported that allopatric populations of N. virescens responded differently to the same set of cultivars. Heinrichs and Rapusas (1990) were able to select for increasingly virulent populations of N. virescens in the laboratory. They suggested that breeding efforts should include developing tungro-resistant varieties to combat biotype selection. The chances are that virulent biotypes will appear in the future; therefore, breeding programs should also emphasize incorporation of multiple genes for GLH resistance into agronomically desirable cultivars (Thresh 1989). Studies by Khan and Saxena (1985a,b) helped elucidate the mechanism of N. virescens resistance in selected varieties. Insects that fed on a resistant variety probed more often, ingested less phloem sap and more xylem fluid, and grew more slowly, with fewer nymphs becoming adults, than insects that fed on a susceptible variety. Application of steam distillate extracts of resistant plants to susceptible plants caused N. virescens to

INSECT PESTS OF RICE

247

probe more, ingest less phloem sap, and excrete more honeydew relative to untreated susceptible plants. They conclude that resistant varieties possess plant volatiles with antifeedant or repellent properties. Suggested cultural controls for GLH are similar to those for BPH. In addition, seed beds can be covered to protect young, highly susceptible plants from viruliferous insects. Also, the use of early-maturing varieties results in the production of fewer generations of GLH. A novel cultural tactic employing the early planting of a GLH-susceptible trap crop bordering a late-planted main crop was described by Saxena et al. (1988). GLH were effectively drawn to the early planted rice where they were killed with insecticide. Incidence of tungro was lower and yield higher in the rice protected by the trap crop than unprotected rice. Because low densities of viruliferous insects can cause extensive damage, chemical control is very important in quickly reducing GLH populations below economic injury levels. Systemic, granular insecticides applied to the seedbed can prevent early insect attack and tungro infection. Another insecticide treatment should be applied before or after transplanting to prolong protection. Insecticides that are effective in controlling GLH as a vector are liquid formulations of carbofuran, cypermethrin, acephate, bendiocarb, isoprocarb, and carbaryl (Satapathy and Anjaneyulu 1989a). Granular carbofuran was also shown to be very effective when applied to the root zone in mud balls (Satapathy and Anjaneyulu 1989b). The directed placement requires less pesticide, prevents photodegradation and volatilization, and is less harmful to beneficial insects. Krishnaiah and Kalode (1986) found that carbosulfan was effective as a seedling root dip treatment while granular thiocyclam hydrogen oxalate provided excellent initial and residual control ofGLH. The novel plant derivative insecticide, neem, was applied to rice seed, causing fewer N. virescens nymphs to develop to adults and greater seedling vigor (Kareem et al. 1989). Clearly, this demonstrates the systemic properties of neem. Also, Saxena et al. (1987) treated soil with neem and evaluated its effect on tungro incidence in seedlings growing in treated soil and exposed to viruliferous N. virescens. Protection of seedlings from tungro infection was similar to that afforded by carbofuran.

STEM BORERS

Before the release of the short-statured, high-yielding varieties, stem borers were the most serious pests of rice; however, their importance has decreased relative to planthoppers and leafhoppers which have taken advantage of the newer cultivars and associated cultural practices. The

248

RICE: PRODUCTION

Table 6-3. Major Stem Borer Pests of Rice Species and Family

Common Name

Pest Distribution

Chilo suppressa/is (Walker) Pyralidae Chilo zacconius Blesz Pryalidae Chilo po/ychrysus (Meyrick) Pyralidae Scirpophaga incertulas (Walker) Pyralidae Scirpophaga innotata (Walker) Pyralidae Sesamia inferens (Walker) Noctuidae Sesamia calamistis Hemps. Noctuidae Diatraea sacchara/is (F.) Pyralidae Ma/iarpha separatella Rag. Pyralidae Diopsis spp. Diopsidae

Striped stem borer Striped stem borer

Tropical and temperate Asia Africa

Dark-headed stem borer

Mostly tropical Asia

Yell ow stem borer

Tropical and temperate Asia Mostly tropical Asia and Australia Tropical and temperate Asia Africa

White stem borer Pink stem borer Pink stem borer

White stem borer

Southern United States and Latin America Africa

Stalk eyed fly

Africa

Sugarcane borer

reasons for the decline of stem borer pest status are (1) widespread use of synthetic insecticides, (2) cultivation of rice varieties with short, thin culms, (3) improved cultural practices including destruction of post-harvest stubble, and (4) planting of early-maturing varieties. Yet, stem borers remain chronic pests and in some regions, such as Africa, are considered the most serious insect constraint to rice production. Many species of stem borers attack rice, but some of the most common and damaging are listed in Table 6-3. Each species has a unique life history, but all of the Lepidoptera borers are sufficiently similar for generalities to be made. Adults do not fly long distances and are active at night, when they lay eggs in masses on rice leaves and sheaths. After the eggs hatch, larvae often balloon as a means of dispersal. They begin feeding between the sheath and the culm and eventually enter the culm where they consume the inner portions. Here they are protected from natural enemies and nonsystemic insecticides. Symptoms of early infestations relative to plant age are dead hearts, while symptoms of later infestations are whiteheads. Pupation occurs within the culm, often near the base. A single generation requires roughly 40 to 50 days, so multiple generations can develop on rice, depending on the length of the growing season, the number of rice crops grown per year, and varietal maturation time. Damage leads to lodging and yield reductions resulting from fewer

INSECT PESTS OF RICE

249

panicles and more unfilled grains. In Japan, data show that 2 to 3% of the stems infested with Chilo suppressalis (Walker) give a yield loss of 3.5% when infestations occur early relative to plant development (Kiritani 1979). Later infestations must approach 14% infested stems to give similar yield reductions. Kisimoto (1984) reportd that yield losses of 3% due to C. suppressalis economically justifies a control tactic. Thus, yield losses must be correlated to previous borer stages, densities, or early damage symptoms to allow implementation of control tactics to prevent economic damage. For instance, the economic threshold for stem borers in tropical Asia is two egg masses per 20 hills (Reissig et al. 1986). However, the egg masses must be held until parasites emerge, since an insecticide treatment is not required if at least 50% of the eggs are parasitized. Research has shown that egg densities of this magnitude will likely give rise to later damage equal to the cost of control. Population dynamics of and damage by stem borers are markedly influenced by cropping practices, phenology of the host, and environment. In China, Scirpophaga incertulas (Walker) prefers to oviposit on tillering and booting rice (Yu 1980). Newly hatched larvae can also more easily penetrate the culm during these stages. Therefore, staggered planting and multiple cropping provide a continuous supply of preferred stages of the host which leads to a buildup of populations to damaging levels over the course of three or four generations of the pest. This pest, as well as S. innotata (Walker), is monophagous so establishment of a rice-free period and destruction of stubble and volunteer rice during the off-season can greatly affect pest population dynamics. Rothschild (1971) reported densities of S. incertulas in stubble in Sarawak between 1200 and 1900 larvae per 200 plants which illustrates the significance of off-season hosts. Water management can also affect borer activity. For example, in a laboratory study, rice was exposed to flood depths of 0 to 20 em and to eggs and first instar larvae of C. suppressalis (Tsumuki et al. 1985). About three times as many stems were infested at 5 em vs. 20 em. Alam (1988) compared stem borer species abundance on upland and irrigated rice in Nigeria. In general, borers were more abundant on irrigated rice which was infested earlier by Diopsis spp. and later by three lepidopterous species: Maliarpha separatella Rag., C. zacconius Blesz, and Sesamia calamistis Hemps. M. separatella was the most abundant Lepidoptera borer in both environments, which could be due to a more limited host range than the other borers. Deepwater rice is also attacked by stem borers, primarily S. incertulas. However, feeding by the larvae often does not damage the vascular transport system; thus heavy infestations do not necessarily translate to high yield losses (Taylor 1988). Apparently, the large hollow stems of floating rice allow the larvae to feed on parenchyma tissue without interrupting nutrient transport.

250

RICE: PRODUCTION

Cultural controls include synchronous plantings of eariy-maturing varieties; destruction of ratoon, stubble, and wild rice; avoiding year-round rice cropping and excessive nitrogen fertilizer applications; and hand removal of borer egg masses. Also, some resistant varieties are available. Chandina, IR20, Ratria, IR1561-228-3-3, IR36, and IR42 possess resistance to C. suppressalis and have been released for commercial production (Khush 1984). These cultivars, of which IR36 is the most resistant, derive their resistance from TKM6. IR36 also is resistant to S. incertulas. Furthermore, host plant resistance research is being conducted in Africa against C. zacconius. Lac23, IR2035-120-3, IR4625-132-1-2, and Columbia 1 have been identified as resistant varieties. Larvae reared on these varieties weighed less and exhibited higher first ins tar mortality relative to susceptible varieties (Ukwungwu and Odebiyi 1987). Therefore, the mechanism of resistance is antibiosis. Beneficial insects are very important in maintaining most borer populations below economic threshold levels. Generally, egg parasitism is very high in Asian borers. Hikim (1988) recorded increasingly high rates of egg parasitization with each succeeding generation of S. incertulas. Lowest and highest parasitization rates were 47 and 94%, respectively. Telenomus spp. were the most common egg parasites. Insecticides with systemic and residual activity are preferred for borer control because most of their life history is passed within the plant where they are protected from contact insecticides. Reissig et al. (1986) suggest that sprays or granules be applied during tillering but only sprays after the vegetative phase. Often, multiple applications are required to effect longlasting control. Many insecticides have been evaluated for stem borer control. Among the most effective are carbofuran, chlorpyrifos, quinalphos, phosphamidon, fenitrothion, BPMC, fundal, carbaryl, phorate, and endosulfan. However, organophosphorus resistance was detected in C. suppressalis in Japan in 1978 (Tanaka et al. 1982). RICE GALL MIDGE

The rice gall midge CRGM), Orseolia oryzae (Wood-Mason) occurs in southern and southeastern Asia including Pakistan, India, Sri Lanka, Bangladesh, Myanmar, Thailand, Laos, Kampuchea, Vietnam, Indonesia, and China but not in Japan, Korea, or the Philippines (Reissig et al. 1986). A related species, Oryseolia oryzivora Harris and Gagne, is found in the African countries of Guinea Bissau, Senegal, Mali, Burkina Faso, Ivory Coast, Malawi, Cameroon, Sudan, Zambia, and Nigeria on irrigated and rainfed lowland rice (Alam et al. 1985). Like BPH, RGM has become a more serious pest since the release of photoperiod-insensitive, high-yield-

INSECT PESTS OF RICE

251

ing varieties that allow multiple cropping with an uninterrupted, abundant supply of host plants. Yield loss as high as 60% have been reported since severely damaged plants fail to produce panicles (Hidaka and Widiarta 1986). The RGM adult is a small fly in the family Cecidomyiidae. Before infesting rice, one or two generations are completed on alternate grass hosts. Once rice is planted, females lay eggs on leaves near the junction of blade and sheath. Eggs and larvae require high relative humidity; thus, upland rice is not damaged. However, lowland rice, grown in the monsoon season when rain is frequent, skies are cloudy and temperatures are high, suffers severe attack due to the rapid increase of RGM populations. After egg hatch, the small larva moves between the sheath and culm to the nodal meristem where feeding occurs. As the larva feeds, it secretes cecidogen which causes proliferation of plant cells and formation of a long, tubular gall called an onion leaf or silver shoot which fails to produce a panicle (Prakasa Rao 1989). Within the gall, the larva metamorphoses to the pupa which moves, with the help of abdominal spines, to the top of the gall where the insect emerges as an adult. Plants infested early in development produce compensatory tillers which suffer heavy damage and produce few panicles. According to Hidaka and Widiarta (1986), RGM larvae cannot develop in panicle primordia; therefore, rice is susceptible to attack only during the vegetative phase of growth (seeding through tillering). Prakasa Rao (1989) investigated the effect of RGM damage on 15 cultivars in India. Yield loss ranged from nil to 1.1% for each percentage increase in density of silver shoots. This large variation illustrates the importance of developing RGM economic injury levels for each variety grown in a distinct geographical area. Hidaka and Widiarta (1986) suggested that inspections for RGM damage be made two to four weeks after transplanting. An insecticide should be applied if 5% or more of silver shoots + tillers are silver shoots. Development of resistant varieties is the most promising method of control. Heinrichs and Pathak (1981) identified more than 170 varieties resistant to RGM. India embarked on an extensive breeding program after the release ofiR8. Several varieties such as Eswarakora, Leuang 152, and Siam 29 were used as donors to develop RGM-resistant varieties Shakti, Vikram, Kakatiya, Phalguna, and Surekha (Khush 1984). The mechanism of resistance in varieties with Siam 29 and Eswarakora as resistance donors appears to be larval antibiosis, possibly due to increasing phenol concentration in response to larval infestation (Kalode 1980). Nevertheless, RGM resistance is controlled by only one or a few genes which allows for relatively rapid selection of RGM biotypes with the ability to develop normally on previously resistant cultivars. At least four biotypes of RGM

252

RICE: PRODUCTION

Table 6-4. Response of Rice Gall Midge to Selected Varieties RESPONSE OF BIOTYPE

2

Variety

Eswarakora group Siam 29 group

Ra R

3 R

s

Resistant. Susceptible. Source: Kalode and Bentur (1989).

a b

have been identified (Kalode and Bentur 1989). Each biotype has a distinct response, as measured by certain criteria of developmental success, to a given set of varieties (Table 6-4.). Biotype 4 was identified in China and was able to develop on Eswarakora and Siam 29 groups (Lai et al. 1984). Obviously, the goal of plant breeders and entomologists is to develop RGM varieties possessing multiple genes for resistance to slow the development of virulent biotypes. Manipulation of cultural practices can reduce RGM problems. Dense stands of rice and applications of high amounts of nitrogen create a thick canopy and a moist, humid environment which is ideal for RGM development. Removal of alternate hosts during the off-season can cause an interruption in the pest's life cycle. Several grasses, including wild rice (Oryza nivara), are suitable hosts ofRGM. In fact, Srivastava (1986) found that RGM larval infestations in wild and cultivated rice were similar. An important control tactic recommended by Chinese entomologists is to weed the overwintering host Leersia hexandra (Chin 1980). Clearly, staggered planting dates and multiple cropping will also favor RGM; therefore, synchronous planting on an areawide basis will prevent continuous development of the pest. Finally, Reissig et al. (1986) suggest that photoperiodinsensitive varieties be planted early in the wet season to allow the crop to develop vegetatively before RGM moves from alternate hosts. In general, granular formulations of insecticides, such as carbofuran, phorate, diazinon, chlorpyrifos, and quinalfos, applied to flooded paddies during the vegative phase of growth provide control of RGM. Systemic insecticides kill larvae feeding within the gall. In areas where the RGM is a serious pest every year prophylactic application to seedling beds, root zone application of granular products, or soaking seedlings in an insecticidal bath may be justified. Natural biocontrol agents play a significant role in reducing RGM populations. At least 19 parasites and predators have been recorded for RGM (Kalode 1980). Probably the most important is an egg-larval para-

INSECT PESTS OF RICE

253

site, Platy gaster oryzae Cameron (Hidaka 1974). A field survey by Patnaik and Satpathy (1985) conducted in India revealed that P. oryzae comprised 80% of the parasite complex and accounted for an average of 21% parasitization of RGM over a 3-year period. However, Hidaka et al. (1988) evaluated the effect of selected insecticides commonly applied for RGM control onP. oryzae and found that all chemicals were toxic to the parasite. Granular formulations appear to be less disruptive to beneficial insects than emulsifiable concentrates. RICE WATER WEEVIL Lissorhoptrus oryzophilus Kuschel infests rice in all the rice-producing states of the United States, where estimated annual losses in the absence of carbofuran (the only insecticide approved for weevil control by the U.S. Environmental Protection Agency (EPA) and state agricultural departments) approach $50 million (Grigarick 1984; USDA 1989). The pest also occurs in Japan, where it was introduced via California in 1976 and spread to all prefectures within ten years (Ohto 1989). Japanese farmers spend roughly $160 million annually to control the rice water weevil (RWW) which is 50% more than any other country spends on rice insect control (Woodburn 1990). The RWW invades rice fields from overwintering sites located in the crowns of perennial grasses and woodland leaflitter. Muda et al. (1981) reported that indirect flight muscles of overwintered weevils degenerate upon adult arrival and feeding on the foliage of rice in newly flooded paddies. Presumably, muscles are resorbed to provide for the development of eggs which are laid under water in the coleoptiles, leaf sheaths, and culms of young plants. Thus, once the RWW invades a paddy, movement is restricted since flight is curtailed. Morgan et al. (1984) monitored RWW emergence from overwintering sites and found a consistent pattern based on heat unit accumulation. Using a threshold temperature of 18°C, 50% and 90% of adults emerged by about 100 and 175 cumulative degree days, respectively. Currently, an extension program based on these data alerts Arkansas rice producers to begin scouting paddies for RWW activity. Eggs hatch within 7 days, and the larvae move to the rice roots where feeding occurs for the entire larval life which consists of four instars. Larvae obtain oxygen by tapping roots with dorsal abdominal tracheal hooks. Depending on temperature, the larval stage lasts from approximately 2 to 4 weeks, while the pupal stage, which occurs within a mud cell attached to roots, lasts 1 to 2 weeks. Thus, in the most southern states, two generations can develop in a year; in California, Arkansas, and Japan, however, only one generation is normally completed. In addition, bisexual

254

RICE: PRODUCTION

populations occur in all states except California and Japan where only parthenogenetic females exist (Grigarick and Beards 1965). Damage from root pruning results in stunted plants, delayed maturity, and reduced yield, ranging from an average estimated 33% in California to 10% in Arkansas (USDA 1989). Losses are greater in California, in large part due to irrigation and planting methods. Paddies are flooded and seeded, with the flood maintained to near maturity of the crop, whereas in the southern states the majority of paddies are seeded and periodically flooded and drained until the rice is actively tillering, at which time a permanent flood is applied. Thus, in California, weevil infestations, which initiate development when paddies are permanently flooded, occur earlier in relation to plant phenology than in the other states. These earlier infestations are more damaging because rice is more vulnerable in the seedling vs. the tillering stage. An overall average yield reduction for weevil infested rice in the United States is between 10 and 20%. Control of this damage is primarily chemical; however, the EPA is considering banning the use of granular carbofuran due to avian toxicity problems (USDA 1989). In Japan, damaging infestations develop on newly transplanted seedlings which can be protected by applying granular insecticides to the seedling box or flooded paddy. Carbosulfan, benfuracarb, buprofezin, diazinon, disulfoton, BPMC, and cartap are commonly used insecticides (Woodburn 1990). Economic threshold/injury levels have been developed for the RWW. In Arkansas, Tugwell and Stephen (1981) used cages with varying infestations of the RWW and reported that ten larvae per core (9.2 em diameter and 10 em deep plug of soil and roots) was associated with a loss in yield of 360 kg/ha. Sooksai (1976) regressed larval densities on adult feeding scars on the youngest leaves of rice plants under permanent flood for less than a week. From these data, an economic threshold of 60% of plants with scarred leaves was established. Seldom does adult feeding affect rice growth; however, feeding scars are an indicator of the magnitude of subsequent larval infestations and damage. Tugwell and Stephen (1981) also developed a sequential sampling plan utilizing feeding scars and a sampling unit of 40 plants. Other states have also developed economic threshold/injury levels for the RWW. Smith et al. (1986) reported that average paddy populations in Louisiana of one larva per core reduce yield 45 kg/ha. This relationship is linear, so that five larvae per core reduce yield 225 kg/ha, which was established as the economic injury level. Texas has adopted this level, but Mississippi uses one larva per plant (MCES 1983). In California, most insecticide treatments are applied prophylactically; however, soon after emergence through the water, rice can be inspected for RWW activity. At this time the economic threshold is 10 to 20% of rice plants with feeding scars on

INSECT PESTS OF RICE

255

the youngest leaves (University of California 1983). Iffeeding scar density equals or exceeds the economic threshold, paddies are drained, treated with carbofuran, and reflooded. In Japan, Tsuzuki et al. (1983a) found that one adult per hill caused a yield loss of over 10% and early plantings sustained less damage because plants were older when attacked. Tsuzuki et al. (1983b) conducted cage studies on newly transplanted rice infested with adult RWW. They reported that adult feeding did not affect yield; however, larval infestations caused significant yield losses. Adult infestations of 0.25 per hill or less resulted in no yield loss. The economic thresholds for seedling box and paddy insecticidal treatments were set at less and greater than 0.5 adult per hill, respectively (Ohto 1989). Other research efforts have emphasized host plant resistance. Robinson et al. (1981) screened 2500 plant introductions for larval resistance and found seven lines exhibiting antibiosis (22-34% fewer larvae than susceptible Saturn). Using paired protected and unprotected plots, over 5000 lines were evaluated for antixenosis, which was detected most consistently at highest levels in WC1403, WC1711, and Cl11048 (Grigarick and Way 1982; Robinson et al. 1988). These lines and others are being used as genetic donors or sources in conventional breeding programs to develop a RWW-resistant variety for the United States. In addition, clones derived by tissue culture of selected lines, including Cl11048, are currently being evaluated for resistance (Croughan et al. 1989). In spite of these efforts, the probability of developing a cultivar with a level of resistance that precludes the need for insecticide is slight. Nevertheless, a moderately resistant cultivar could reduce insecticide usage by increasing the economic threshold of the RWW and/ or restricting insecticide applications to the margin of paddies where weevil activity is greatest. Since the RWW is semi-aquatic, water management as a control tactic has received recent attention. In the southern rice-producing states, delay of the permanent flood results in RWW infestations developing later relative to plant growth stage; consequently, less damage is sustained. However, water depth does not appear to affect RWW-plant interaction. Morgan et al. (1989) investigated the effect of draining paddies soon after invasion and oviposition by RWW. If paddies were drained and dried until soil cracked, control was similar to that achieved by carbofuran. Apparently, draining paddies 10 days after flooding exposes and kills young larvae; however, the cost of this tactic was estimated to be between $5.44 and $10.95/ha more than the cost of a carbofuran application (Smith 1981). Chemical control remains the first line of defense against the RWW. However, U.S. governmental approval of the continued and future use of insecticides is becoming more difficult. Because of the fragile and diverse aquatic ecosystem associated with rice production, broad spectrum activ-

256

RICE: PRODUCTION

ity insecticides which persist in the environment and result in adverse effects on the native flora and fauna will not be approved for use on rice. Recently, RWW insecticide research has concentrated on insect growth regulators and better timing of carbofuran applications. Smith et al. (1985) found that diflubenzuron and alsystin only affected the egg while developing within the adult or soon after oviposition. Thus, adult ingestion of treated foliage or egg contact with treated water resulted in the highest mortality. Under field conditions, the timing of application of insect growth regulators must coincide with peak adult activity. Later applications are less effective. RICE LEAFFOLDER

The rice leaffolder (RLF), Cnaphalocrocis medina lis (Guenee), is a pyralid Lepidoptera whose recent elevation to major pest status is a result of the Green Revolution. As with BPH, GLH, and RGM, multiple cropping of modern varieties that require high amounts of nitrogen fertilizer, and asynchronous planting have encouraged RLF epidemics. RLF is found in temperate and tropical Asia, Oceania, Australia, and Africa where it feeds on rice, sorghum, millet, oat, sugarcane, wheat, and a variety of wild grasses and sedges (Khan et al. 1988). However, Yadava et al. (1972) reported that rice varieties IRS and Taichung Native 1 were preferred relative to wild grasses based on larval development and survival. Adults lay single eggs in batches on the upper and lower surfaces of leaf blades. After egg hatch, first instar larvae move to the base of the youngest, unfurled leaves and begin feeding. The larvae fold the leaves longitudinally by means of silk stitches. Generally, young larvae are gregarious but become solitary during the second ins tar, so that only a single larva is found per leaf roll. Feeding behavior, as described by Fraenkel et al. (1981), consists of scraping and consumption of green mesophyll tissue. The resulting damage appears as white longitudinal stripes. Larvae move from leaf to leaf so more than one leaf can be damaged by a larva. Heavily infested paddies appear scorched. Pupation occurs on leaf blades and stubble. Completion of a generation requires approximately 5 weeks in the tropics. This pest has the ability to move long distances. In fact, specimens, presumably from China, have been collected over the East China Sea (Kisimoto 1984). No hibernating RLF have been found in Japan, but during the rainy season many immigrants appear in western Japan. Thus RLF is now thought to move every year during early summer from China to Japan (Miyahara et al. 1981). In addition, Wada et al. (1988) gave evidence for a second annual movement from China to Japan during autumn when host

INSECT PESTS OF RICE

257

.------------------------------------------ --------

-

~8

Economic loss

I I)

iGl

5

.J::

4

i!

3

E

2

j

3:

0 ..0

s

(I)

1 -

2

3

4

5

8

7

8

9

10

l.eaffoJder damaged leaves (%) Figure 6-2. Multiple pests thresholds for stem borer and leaffolder in the ripening stage. From Polis et al. (1989).

plants are scarce and the environment unsuitable. This migration appears nonadaptive. Insect/damage relationships have been developed for tropical and temperate areas. Bautista et al. (1984) infested caged rice with varying densities of RLF moths and measured subsequent leaf damage and yield. They found that 17.5 and 26.6% damaged leaves gave yield losses of 16.5 and 21.3%, respectively. From these data, they estimated the economic injury level at greater than 5% damaged leaves. This corresponds to an action control threshold of 0.5 to 1 larva per hill (Bandong and Litsinger 1988). Miyashita (1985) observed that infestations during grain filling did not affect yield; however, infestations at heading reduced the percentage of filled grains. Yield was reduced in proportion to the percentage of damaged area of the upper two leaves. Palis et al. (1989) developed multiple pest thresholds for stem borers and leaffolders. They found that leaffolder and stem borer damage was additive in terms of effects on yield. In addition, yield loss resulting from the damage of one insect could be expressed in terms of the other. For example, the economic value of yield loss due to a combination of 5% whiteheads and 2.8% damaged leaves or 3% whiteheads and 5.4% damaged leaves is equal to the cost of control and lies on the iso-loss line (Fig. 6-2.). Therefore, any combination of damage that results in the economic value of yield loss being above the iso-loss line will lead to economic loss, which is that amount greater than the cost of control.

co

1\) ()1

12.85

28.42

20.63

12.85

Spray Cost ($/ha) 4 4 4 6 5 5 7 7 7 9 9 9 14

Loan

5 4 4 7 6 6 9 8 8

12 12 11 15+

Plant Date (mol day)

4/1 5/1 6/1 4/1 5/1 6/1 4/1 5/1 6/1

4/1 5/1 6/1 4/1

5040 kglha Rice Price $0.20/kg

9 9 9 13

4 4 4 5 5 5 7 7 7

Loan

6720 kg/ha Rice Price $0.20/kg

10 8 8 14

THRESHOLDS AT MILK

4 3 3 6 5 5 7 6 6 7 7 7 11

3 3 3 4 4 4 6 6 6

THRESHOLDS AT HEADING

$0.24/kg

Yield

7 7 7 11

3 3 3 4 4 4 6 6 6

$0.24/kg

8 6 7 12

3 3 3 5 4 4 6 5 5

Loan

6 6 6 9

3 3 3 4 4 4 5 5 5

8400 kg/ha Rice Price $0.20/kg

Table 6-5. Economic Thresholds for Oeba/us pugnax for 1989. Values Indicate Average Number of Adults per 10-Sweep Sample

6 6 6 9

3 3 3 4 4 4 5 5 5

$0.24/kg

"-l

~

IO IO IO I4 I4 14 15+ 15+ 15+

9-13 11-I5 + 9-I5+ 11-I5 13-I5+ 15+ 15+ 15+ 15+

4/1 5/1 6/1 4/1 5/1 6/1 4/1 5/1 6(1

4/1

5/I 6/I

13

15+ I5+ I5+

13

15+ 14+ 15+ I5+ I5+

5/1 6/1

Source: Adapted from Harper (1988).

28.42

20.63

I2.85

28.42

20.63

14 12 15+ I5+ I5+ 14 I4 I4

11 11

10 10 IO I4 14 14 15+ 15+ 15+

8-I2 10-12 8-12 IO-I4 12-I5 + 10-15+ ll-I5+ I3-15 + 15+ II 14 14 14

11

8 8 8 11

THRESHOLDS AT SOFT DOUGH

13 13 15+ I5 + I5+

11

11 14 14 14

11 11

8 8 8

11 I4 14 I4 8-ll 7-II 7-11 9-I3 11-I5 9-I5 10-14 12-I5 + 11-15+

12 10 I5 I5+ 13 7 7 7 IO 10 10 I2 12 I2

9 9 I2 I2 II 7 7 7 IO 10 9 12 I2 12

9 9 I2 I2 I2

260

RICE: PRODUCTION

Breeding programs are actively developing resistant vanetles, although no resistant commercial cultivars have yet been released. Heinrichs et al. (1985) evaluated nearly 20,000 genotypes for RLF resistance. Fewer than 50 were judged resistant. Of these, TKM6, GEB24, W1263, Muthumanikam, and Ptb33 are being used as donors. Khan et al. (1989) compared RLF larval growth on TKM6 and wild rices, some of which exhibited higher levels of resistance than TKM6. In the future, novel breeding techniques may allow the transfer of resistant genes from wild to domestic rice.

SEED-FEEDING INSECTS

A number of Hemiptera attack rice from heading to maturity. Probably the most damaging are Leptocorisa spp., which occur in temperate and tropical Asia, and Oebalus pugnax (F.), which occurs in the southern United States. These pests damage rice by ingesting the contents of developing grains. Microorganisms are associated with this feeding activity, which can result in a discolored, weakened area surrounding the feeding puncture (Marchetti 1984). Damaged kernels are described as pecky and are more apt to break during milling. The blemished rice and lower milling yields can reduce grade and price substantially in the United States. Brorsen et al. (1984) determined that a unit percentage reduction in peck increased Texas farm revenue by as much as $160/ha. Life histories of seed-feeding bugs are similar in that they develop on alternate grass hosts before moving to rice when it begins to head. Adults are highly mobile and lay eggs in rows on foliage and panicles. Nymphs and adults feed on grain, but adults are more damaging. Leptocorisa spp. insert their stylets in the small opening between the lemma and palea, but 0. pugnax can penetrate the hull. Stylet sheaths are produced where insects probe. Because the time from heading to harvest is relatively short (about 30 days in the United States), only one generation can develop on a single crop, but adult immigration can occur at any time during the ripening period. The economic threshold for Leptocorisa spp. is four bugs/m2 (Dyck 1978). In the United States, dynamic thresholds have been developed for 0. pugnax (Harper 1988). Data for the thresholds were taken from large field plot experiments in which natural infestations of 0. pugnax were manipulated by insecticides applied at various times from heading to maturity. Dynamic programming was the methodology selected to develop flexible thresholds which take into account planting date, cost of insecticidal control, projected yield and price of rough rice, and stage of grain

INSECT PESTS OF RICE

261

maturation (Table 6-5.). Thresholds vary from three to greater than 15 adult bugs per 10 sweeps, depending on the above variables. Since the vulnerable stage of the crop is short, chemical control of seed feeders is the most effective tactic. In the case of 0. pugnax, farmers can choose from several insecticides with differing residual activity and cost. However, since immigrant 0. pugnax infestations can occur, the selection of an insecticide with low residual activity requires frequent sampling of paddies to guard against postapplication infestations. Recommended insecticides with residual activity for 0. pugnax are a liquid formulation of carbaryl and an encapsulated formulation of methyl parathion (Way and Wallace 1990).

REFERENCES Alam, M. S. 1988. Seasonal abundance of rice stem borer species in upland and irrigated rice in Nigeria. Insect Sci. Applic. 9(2):191-95. Alam, M. S., V. T. John, and K. Zan. 1985. Insect pests and diseases of rice in Africa. In Rice improvement in eastern, central and southern Africa, 67-82. Los Banos, Philippines: Int. Rice Res. Inst. (IRRI). Andow, D. A., and K. Kiritani. 1983. The economic injury and control threshold. Japan Pestic. Info. 43:3-9. Bandong, J. P., and J. A. Litsinger. 1988. Development of action control thresholds for major rice pests. In Pesticide management and integrated pest management in Southeast Asia, ed. P. S. Teng and K. L. Heong, 95-102. Maryland: Consortium for Int. Crop Protection. Bautista, R. C., E. A. Heinrichs, and R. S. Rejesus. 1984. Economic injury levels for the rice leaffolder Cnaphalocrocis medina/is (Lepidoptera:Pyralidae): Insect infestation and artificial leaf removal. Environ. Entomol. 13:439-43. Brorsen, B. W., W. R. Grant, and M. E. Rister. 1984. A hedonic price model for rough rice bid/acceptance markets. Amer. J. Agric. Econ. 66:156-63. Chelliah, S., and E. A. Heinrichs. 1980. Factors affecting insecticide induced resurgence of brown planthopper, Nilaparvata lugens on rice. Environ. Entomol. 9:773-77. Cheng, C. H. 1976. A preliminary report on application of insecticide for controlling brown planthopper based on thresholds of economic damage. Paper presented at Int. Rice Res. Conf., Los Banos, Philippines: IRRI. Chiu, S. F. 1980. Integrated control of rice insect pests in China. In Rice improvement in China and other Asian countries, 239-50. Los Banos, Philippines: IRRI, and Beijing:Chinese Acad. of Agricultural Sci. Cook, A. G., and T. J. Perfect. 1989. Population dynamics of three leafhopper vectors of rice tungro viruses, Nephotettix virescens (Distant), N. nigropictus (Stat) and Recilia dorsalis (Motschulsky) (Hemiptera:Cicadellidae), in farmers' fields in the Philippines. Bull. Ent. Res. 79:437-51. Cook, A. G., S. Woodhead, V. F. Magalit, and E. A. Heinrichs. 1987. Variation

262

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in feeding behavior of Nilaparvata lugens on resistant and susceptible rice varieties. Entomol. Exp. Appl. 43:227-35. Cramer, H. H. 1967. Plant protection and world crop production. PjlanzenschutzNachr 20:1-524. Croughan, T. P., Q. R. Chu, M. M. Meche, R. P. Regan, D. B. Trumps, S. D. Linscombe, S. A. Harrison, D. E. Groth, J. M. Jaynes, and S. S. Quisenberry. 1989. Rice and wheat improvement through biotechnology. In 8Jst Ann. Res. Rep., 66-7. Crowley, LA: Rice Experiment Station. Dyck, V. A. 1978. Economic thresholds in rice. Paper presented at Short Course on Integrated Pest Control for Irrigated Rice in South and Southeast Asia, October 16-November 18, at Los Banos, Philippines. Dyck, V. A., and B. Thomas. 1979. The brown planthopper problem. In Brown planthopper:Threat to rice production in Asia, 3-17. Los Banos, Philippines: IRRI. Fraenkel, G., F. Fallil, and K. S. Kumarasinghe. 1981. The feeding behavior of the rice leaf folder, Cnaphalocrocis medina/is. Entomol. Exp. Appl. 29:14761. Grigarick, A. A., and G. W. Beards. 1965. Ovipositional habits of rice water weevil in California as related to a greenhouse evaluation of seed treatments. J. Econ. Entomol. 58: 1053-56. Grigarick, A. A., and M. 0. Way. 1982. Evaluating tolerance of water-sown rice to the rice water weevil. In Proc. Rice Technical Working Group. 19:44. Grigarick, A. A. 1984. General problems with rice invertebrate pests and their control in the United States. Protection Ecol. 7:105-14. Grist, D. H., and R. J. Lever. 1969. Pests of rice. London:Longmans, Green. Harper, J. K. 1988. Developing economic thresholds for rice stink bug management in Texas using dynamic programming. Ph.D. thesis. Texas A&M Univ., College Station. Heinrichs, E. A. 1979. Chemical control of the brown planthopper. In Brown planthopper:Threat to rice production in Asia, 145-67. Los Banos, Philippines: IRRI. Heinrichs, E. A. 1986. Perspectives and directions for the continued development of insect-resistant rice varieties. Agric., Ecosyst. Environ. 18:9-36. Heinrichs, E. A., G. B. Aquino, S. Chelliah, S. L. Valencia, and W. H. Reissig. 1982a. Resurgence of Nilaparvata lugens (Sta1) populations as influenced by method and timing of insecticide applications in lowland rice. Environ. Entomol. 11:78-84. Heinrichs, E. A., W. H. Reissig, S. Valencia, and S. Chelliah. 1982b. Rates and effects of resurgence-inducing insecticides on populations of Nilaparvata lugens (Homoptera:Delphacidae), and its predators. Environ. Entomol. 11:1269-73. Heinrichs, E. A., E. Camanag, and A. Romena. 1985. Evaluation of rice cultivars for resistance to Cnaphalocrocis medina/is Guenee (Lepidoptera:Pyralidae). J. Econ. Entomol. 78:274-78. Heinrichs, E. A., and H. R. Rapusas. 1990. Response to selection for virulence of Nephotettix virescens (Homoptera:Cicadellidae) on resistant rice cultivars. Environ. Entomol. 19:(1):167-75.

INSECT PESTS OF RICE

263

Heinrichs, E. A., and F. G. Medrano. 1984. Leersia hexandra, a weed host of the rice brown planthopper, Nilaparvata lugens (Stal). Crop Prot. 3:77-85. Heinrichs, E. A., and P. K. Pathak. 1981. Resistance to the rice gall midge, Orseolia oryzae in rice. Insect Sci. Appl. 1:123-32. Hidaka, T. 1974. Recent studies on the rice gall midge, Orseolia oryzae (WoodMason) (Cecidomyiidae, Diptera). Rev. Plant Prot. Res. 7:99-143. Hidaka, T., E. Budiyanto, V. Ya-Klai, and R. C. Joshi. 1988. Recent studies on natural enemies of the rice gall midge, Orseolia oryzae (Wood-Mason). JARQ 22(3): 175-80. Hidaka, T., and N. Widiarta. 1986. Strategy of rice gall midge control. JARQ 20(1):21-24. Hikim, I. S. 1988. Seasonal parasitism by egg parasites of the yellow riceborer, Scirpophaga incertulas (Lepidoptera:Pyralidae). Entomophaga. 33(1): 11524. IRRI. 1983.Field problems of tropical rice. Los Banos, Philippines: IRRI. IRRI. 1989. IRRI toward 2000 and beyond. Los Banos, Philippines: IRRI. Kahn, Z. R., and R. C. Saxena. 1985a. Effect of steam distillate extract of a resistant rice variety on feeding behavior of Nephotettix virescens (Homoptera:Cicadellidae). J. Econ. Entomol. 78:562-66. Kahn, Z. R. and R. C. Saxena. 1985b. Mode offeeding and growth of Nephotettix virescens (Homoptera:Cicadellidae) on selected resistant and susceptible rice varieties. J. Econ. Entomol. 78:583-87. Kalode, M. B. 1980. The rice gall midge-varietal resistance and chemical control. In Rice improvement in China and other Asian countries, 173-93. Los Banos, Philippines: IRRI. Kalode, M. B., and J. S. Bentur. 1989. Characterization oflndian biotypes of the rice gall midge, Orseolia oryzae (Wood-Mason) (Diptera:Cecidomyiidae). Insect Sci. Applic. 10(2):219-24. Kareem, A. A., R. C. Saxena, M. E. M. Boncodin, V. Krishnasamy, and D. V. Seshu. 1989. Neem as seed treatment for rice before sowing: effects on two homopterous insects and seedling vigor. J. Econ. Entomol. 82(4):121923. Kenmore, P. E., F. 0. Carino, C. A. Perez, V. A. Dyck, and A. P. Gutierrez. 1984. Population regulation of the rice brown planthopper (Nilaparvata lug ens Stal) within rice fields in the Philippines. J. Pl. Prot. Tropics 1(1):19-37. Khan, Z. R., A. T. Barrion, J. A. Litsinger, N. P. Castilla, and R. C. Joshi. 1988. A bibliography of rice leaffolders. Insect Sci. Applic. 9(2):129-74. Khan, Z. R., B. P. Rueda, and P. Cab~llero. 1989. Behavioral and physiological responses of rice leaffolder Cnaphalocrocis medina/is to selected wild rices. Entomol. Exp. Appl. 52:7-13. Khan, Z. R., and R. C. Saxena. 1988. Probing behavior of three biotypes of Nilaparvata lugens (Homoptera:Delphacidae) on different resistant and susceptible rice varieties. J. Econ. Entomol. 81(5):1338-45. Khush, G. S. 1984. Breeding rice for resistance to insects. Protection Ecol. 7:147-65. Kimmins, F. M. 1989. Electrical penetration graphs from Nilaparvata lugens on resistant and susceptible rice varieties. Entomol. Exp. Appl. 50:69-79.

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Kisimoto, R. 1976. Bionomics, forecasting of outbreaks and injury caused by the rice brown planthopper. Paper presented at the Int. Seminar, Rice Brown Planthopper, Asian and Pacific Council, Food and Fertilizer Technology Center, Tokyo, Japan. Kisimoto, R. 1981. Development, behavior, population dynamics, and control of the brown planthopper, Nilaparvata lugens Still. Rev. Plant Protec. Res. 14:26-58.

Kisimoto, R. 1984. Insect pests of the rice plant in Asia. Protection Ecol. 7:83104. Konno, T. 1990. Buprofezin; a reliable IGR for the control of rice pests. In Pest management in rice, ed. B. T. Grayson, M. B. Green, and L. G. Copping, 210-22. New York: Elsevier Appl. Sci. Krishnaiah, N. V., and M. B. Kalode. 1986. Toxicological investigations against rice green leafhopper, Nephotettix virescens (Distant). Tropical Pest Management 32(1):44-8. Krishnaiah, N. V., and M. B. Kalode. 1987. Studies on resurgence in rice brown planthopper Nilaparvata lugens (Still). Indian J. Ent. 49(2):220-9. Lai, K., X. Tan, andY. Pan. 1984. Rice gall midge biotypes in Guangdong Province. Int. Rice Res. Newslett. 9:17-18. Lee, J. 0., and J. S. Park. 1976. Biology and control of brown planthopper (Nilaparvata lugens S.) in Korea. Paper presented at the Int. Seminar, Rice Brown Planthopper, Asian and Pacific Council, Food and Fertilizer Technology Center, Tokyo, Japan. Ling, K. C. 1968. Mechanism of tungro-resistance in rice variety Pankhari 203. Philip. Phytopath. 4:21-38. Ling, K. C. 1969. Virus disease of rice in the Philippines and their effect on yield. Sci. Rev. 10(9):23-30. Ling, K. C., and M. K. Palomar. 1966. Studies of rice plants infected with the tungro virus at different ages. Philip. Agr. 50:165-77. Litsinger, J. A. 1987. Upland rice insect pests: Their ecology, importance, and control. IRRI Res. Paper Series 123. Los Banos, Philippines: IRRI. Litsinger, J. A. 1989. Second generation insect pest problems on high yielding rices. Tropical Pest Management 35(3):235-42. Marchetti, M. A. 1984. The role of Bipolaris oryzae in floral abortion and kernel discoloration in rice. Plant Dis. 68(4):288-91. MCES. 1983. Rice Insect Control. Cooperative Extension Service, Mississippi State Univ. Publication 888. Miyahara, Y., T. Wada, and M. Kobayashi. 1981. Appearance of Cnaphalocrocis medina/is Guenee in early planted rice fields in Chikugo. Japan J. Appl. Ent. Zoo!. 25:26-32. Miyashita, T. 1985. Estimation of the economic injury level in the rice leaf roller, Cnaphalocrocis medina/is Guenee (Lepidoptera:Pyralidae) 1. Relation between yield loss and injury of rice leaves at heading or in the grain filling period. Japan J. Appl. Ent. Zoo!. 29:73-76. Morgan, D. R., N. P. Tugwell, and J. L. Bernhardt. 1989. Early rice field drainage for control of rice water weevil (Coleoptera: Curculionidae) and evaluation of an action threshold based upon leaf-feeding scars of adults. J. Econ. Entomol. 82(6):1757-59.

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Morgan, D. R., P. H. Slaymaker, J. F. Robinson, and N. P. Tugwell. 1984. Rice water weevil (Coleoptera:Curculionidae) indirect flight muscle development and spring emergence in response to temperature. Environ. Entomol. 13:26-28. Muda, A. R. B., N. P. Tugwell, and M. B. Haizlip. 1981. Seasonal history and indirect flight muscle degeneration and regeneration. Environ Entomol. 10:685-90. Norton, G. A., and M. J. Way. 1990. Rice pest management systems-Past and future. In Pest management in rice, ed. B. T. Grayson, M. B. Green, and L. G. Copping, 1-14. New York: Elsevier Appl. Sci. Ohto, K. 1989. The spread and distribution of the rice water weevil, Lissorhoptrus oryzophilus Kushel and its control in Japan. Japan Pesticide Inform. 54: 7-10. Oka, I. N. 1979. Cultural control of the brown planthopper. In Brown plant hopper: Threat to rice production in Asia, 357-69. Los Banos, Philippines: IRRI. Okuma, C., and R. Kisimoto. 1981. Air borne spiders collected over the East China Sea. Japan J. Appl. Entomol. Zoo/. 25:296-8. Padgham, D. E. 1983. The influence of the host-plant on the development of the adult brown planthopper, Nilaparvata lugens (Still) (Hemiptera:Delphacidae), and its significance in migration. Bull. Ent. Res. 73:117-28. Palis, F., P. Pingali, and J. Litsinger. 1989. Multiple pest threshold for rice production: the case of the Philippines. Paper presented at Int. DLG-Symp., Integrated Pest Management in Tropical and Sub-tropical Cropping Systems, 8-15 February, Bad Durkheim, Germany. Pathak, M. D. 1968. Ecology of common insect pests of rice. Ann. Rev. Entomol. 13:257-94. Pathak, P. K., and G. S. Dhaliwal. 1981. Trends and strategies for rice pest problems in tropical Asia. IRRI Res. Paper Series 64. Los Banos, Philippines: IRRI. Pathak, P. K., and E. A. Heinrichs. 1982. Selection of biotype populations 2 and 3 of Nilaparvata lugens by exposure to resistant rice varieties. Environ. Entomol. 11:85-90. Patnaik, N. C., and J. M. Satpathy. 1985. Influence of biotic and abiotic factors on the distribution and abundance of rice gall midge, Orseolia oryzae (WoodMason) (Diptera:Cecidomyiidae). J. Ent. Res. 9(2): 122-28. Perfect, T. J., and A. G. Cook. 1987. Dispersal patterns of the rice brown planthopper, Nilaparvata lugens (Stal), in a tropical rice-growing system and their implications for crop protection. J. Pl. Prot. Tropics 4(2): 121-27. Prakaso Rao, P. S. 1989. Yield losses due to gall midge Orseolia oryzae (WoodMason) in some rice varieties and characterization of tolerance. Tropical Pest Management 35(2):205-13. Rapusas, H. R., and E. A. Heinrichs. 1987. Plant age effect on the level of resistance of rice 'IR36' to the green leafhopper, Nephotettix virescens (Distant) and rice tungro virus. Environ. Entomol. 16:106-10. Reissig, W. H., E. A. Heinrichs, J. A. Litsinger, K. Moody, L. Fiedler, T. W. Mew, and A. T. Barrion. 1986. Illustrated guide to integrated pest management in rice in tropical Asia. Los Banos, Philippines: IRRI. Reissig, W. H., E. A. Heinrichs, and S. L. Valencia. 1982. Effects of insecticides

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on Nilaparvata lugens and its predators: Spiders, Microvelia atrolineata, and Cyrtorhinus lividipennis. Environ. Entomol. 11: 193-99. Riley, J. R., D. R. Reynolds, and R. A. Farrow. 1987. The migration of Nilaparvata lugens (Stal) (Delphacidae) and other Hemiptera associated with rice during the dry season in the Philippines: A study using radar, visual observations, aerial netting and ground trapping. Bull. Ent. Res. 77:145-69. Robinson, J. F., C. M. Smith, and G. B. Trahan. 1981. Evaluation of rice lines for rice water weevil resistance. In 73rd Annu. Progress Rep., 260-65. Crowley, LA: Rice Experiment Station. Robinson, J. F., S.D. Linscombe, F. Jodari, G. B. Trahan, and S. S. Quisenberry. 1988. Rice water weevil resistance: evaluation of breeding lines. In 80th Annu. Res. Rep., 245. Crowley, LA: Rice Experiment Station. Rothschild, G. H. L. 1971. The biology and ecology of rice stem borers in Sarawak. J. Appl. Ecol. 8:287-322. Satapathy, M. K., and A. Anjaneyulu. 1989a. Management oftungro virus disease by application of wettable powder and flowable insecticides. Tropical Pest Management 35(1):41-47. Satapathy, M. K., and A. Anjaneyulu. 1989b. Effect of root zone placement of granular insecticides for tungro prevention and its control. Tropical Pest Management 35(1):51-56. Saxena, R. C., H. D. Justo, Jr., and P. B. Epino. 1984. Evaluation and utilization ofneem cake against the rice brown planthopper, Nilaparvata lugens (Homoptera: Delphacidae). J. Econ. Entomol. 77:502-7. Saxena, R. C., H. D. Justo, Jr., and E. L. Palanginan. 1988. Trap crop for Nephotettix virescens (Homoptera:Cicadellidae) and tungro management in rice. J. Econ. Entomol. 81(5):1485-88. Saxena, R. C., Z. R. Khan, and N. B. Bajet. 1987. Reduction of tungro virus transmission by Nephotettix virescens (Homoptera:Cicadellidae) in neem cake-treated rice seedlings. J. Econ. Entomol. 80(5):1079-82. Saxena, R. C., and Z. R. Khan. 1989. Factors affecting resistance of rice varieties to planthopper and leafhopper pests. Agricultural Zoology Reviews 3:97132.

Saxena, R. C., and S. H. Okech. 1985. Role of plant volatiles in resistance of selected rice varieties to brown planthopper, Nilaparvata lugens (Stal) (Homoptera:Delphacidae). J. Chern. Ecol. 11(12):1601-16. Shepard, M., E. R. Ferrer, P. E. Kenmore, and J.P. Sumangil. 1986. Sequential sampling: planthoppers in rice. Crop Protection 5(5):319-22. Shrivastava, S. K. 1986. Role of wild rice as an alternate host to rice gall midge. Entomon 11(4):243-44. Smith, D. 1981. An economic analysis of two rice water weevil control demonstrations-Northeast Arkansas. Ark. Coop. Ext. Serv. Rpt. Al26. Smith, C. M., J. L. Bagent, S.D. Linscombe, and J.F. Robinson. 1986. Insect pests of rice in Louisiana. Louisiana Agric. Exp. Sta. Bull. 774. Smith, K. A., A. A. Grigarick, J. H. Lynch, and M. J. Oraze. 1985. Effect of alsystin and diflubenzuron on the rice water weevil (Coleoptera:Curculionidae). J. Econ. Entomol. 78:185-89. Sogawa, K. 1976. Rice tungro virus and its vectors in tropical Asia. Rev. Plant Protec. Res. 9:21-46.

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Sogawa, K. 1982. The rice brown planthopper: feeding physiology and host plant interaction. Ann. Rev. Entomol. 27:49-73. Sogawa, K., and C. H. Cheng. 1979. Economic thresholds, nature of damage, and losses caused by the brown planthopper. In Brown planthopper: Threat to rice production in Asia, 125-42. Los Banos, Philippines: IRRI. Sooksai, S. 1976. Rice water weevil (Lissorhoptrus oryzophilus Kuschel) feeding scars-larval density relationship. M. S. thesis. Univ. of Arkansas, Fayetteville. Tanaka, F., S. Yabuki, and A. Tsuboi. 1982. On the outbreaks of the rice stem borer, Chilo suppressalis, in Okayama Prefecture 2. Susceptibility to insecticides on the out breaking districts. Kinki Chugoku Agr. Res. 64:60-65. Taylor, B. 1988. The impact of yellow stem-borer, Scirpophaga incertulas (Walker) (Lepidoptera:Pyralidae), on deepwater rice, with special reference to Bangladesh. Bull. Ent. Res.78:209-25. Thresh, J. M. 1989. Insect-borne viruses of rice and the Green Revolution. Tropical Pest Management 35(3):264-72. Tsumuki, H., K. Kanehisa, and T. Shiraga. 1985. Effects of deep water culture of rice plants on the injury of the rice stem borer, Chilo suppressalis Walker in its second generation. Japan. J. Appl. Ent. Zoo/. 29:131-36. Tsuzuki, H., T. Asayama, K. Oishi, andY. Uebayashi. 1983a. Assessment of yield loss due to the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera:Curculionidae). I. Effect of initial adult density on the growth of rice plants and yield. Japan. J. Appl. Ent. Zoo/. 27:211-18. Tsuzuki, H., T. Asayama, M. Takimoto, T. Shimohata, J. Kayumi, and S. Kobayashi. 1983b. Assessment of yield loss due to the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera:Curculionidae). II. Damage caused by adult and larval infestation and estimation of the tolerable injury level. Japan. I. Appl. Ent. Zoo/. 17:252-60. Tugwell, N. P., and F. M. Stephen. 1981. Rice water weevil seasonal abundance, economic levels, and sequential sampling plans. Ark. Agric. Exp. Stn. Bull. 849.

Ukwungwu, M., and J. A. Odebiyi. 1987. Larval survival and development of the rice stem borer Chilo zacconius Bleszynski. Trap. Agric. 64(1):65-67. University of California. 1983. Integrated pest management for rice. Univ. of California Statewide Integrated Pest Management Project. Publication 3280. USDA. 1989. The biologic and economic assessment of carbofuran. Tech. Bull. 40. Velusamy, R., E. A. Heinrichs, and G. S. Khush. 1987. Genetics of field resistance of rice to brown planthopper. Crop Sci. 27:199-200. Wada, T., Y. Ogawa, and T. Nakasuga. 1988. Geographical difference in mated status and autumn migration in the rice leaf roller moth, Cnaphalocrocis medina/is. Entomol. Exp. Appl. 46:141-8. Way, M. 0., and R. G. Wallace. 1990. Residual activity of selected insecticides for control of rice stink bug (Hemiptera:Pentatomidae). J. Econ. Entomol. 83(2):591-95. Wilson, M. R., and M. F. Claridge. 1985. The leafhopper and planthopper faunas of rice fields. In The leafhoppers and planthoppers, ed. L. R. Nault and J. G. Rodriguez, 381-404. New York: Wiley.

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Woodburn, A. T. 1990. The current rice agrochemical market. In Pest management in rice, ed. B. T. Grayson, M. B. Green, and L. G. Copping, 15-30. New York: Elsevier Appl. Sci. Yadava, C. P., G. Santaram, P. Israel, and M. B. Kalode. 1972. Life history of rice leaf-roller, Cnaphalocrocis medina/is Guenee (Lepidoptera:Pyralidae) and its reaction to some rice varieties and grasses. Indian J. Agric. Sci. 42:520-3. Yu, L. 1980. Studies on control of the yellow rice stem borer. In Rice improvement in China and other Asian countries, 157-71. Los Bafios, Philippines: IRRI, and Beijing:Chinese Academy of Agricultural Sciences.

7 Insect Pests of Stored Rice* Robert R. Cogburn USDA Rice Research Center

Stored-product insects damage agricultural commodities during storage, processing, and distribution. Postharvest losses are particularly costly. The production costs already invested in the crop place the value at its highest point, and the loss of relatively small percentages is financially significant. Many insect species are associated with stored grain and grain products, but only about 50 are injurious, either occasionally or frequently (Cotton 1956). The more common species are listed in Table 7-1. Photographs and drawings of these and other stored-product insects are contained in Agricultural Handbook 500 (USDA/ARS 1986). The relative abundance of particular species may vary from country to country, but most stored-product insects are distributed throughout the world, and the same species do the same types of damage everywhere. Many species damage several types of commodities. For example, the flour beetles, Tribolium spp., are found in all grains and grain products; the cigarette beetle, Lasioderma serricorne (F.), breeds in tobacco, red pepper, cinnamon, other spices, flour, cornmeal, grains such as rice, *Cooperative research by the U.S. Department of Agriculture, Texas Agricultural Experiment Station, Texas Rice Improvement Association, and Texas Rice Research Foundation. Mention of a proprietary product does not imply endorsement by any of the cooperating agencies.

269

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Table 7-1. Stored-Product Insects Associated with Harvested Rice Preferredh Foods

Common Namea MAJOR INSECT PESTS OF RICE IN THE UNITED STATES

Angoumois grain moth Lesser grain borer Rice weevil Red flour beetle Almond moth Sawtoothed grain beetle Merchant grain beetle Cigarette beetle "Flat grain beetle" Indian meal moth

*

Sitotroga cerealella (Olivier)

P.B

* * * *

*

Rhyzopertha dominica (F.) Sitophilus oryzae (L.) Tribolium castaneum (Herbst) Ephestia cautella (Walker)c Oryzaephilus surinamensis (L.)

P,B P,B,M P,B,M,O P,B,M,O P,B,M,O

(S,W,T)

Oryzaephilus mercator (Fauvel)

P,B,M,O

*

Lasioderma serricorne (F.) Cryptolestes spp.

B,M,O P,B,M,O

*

Plodia interpunctella (Hubner)

P,B,M,O

OTHER INSECT PESTS OF RICE IN THE UNITED STATES

Confused flour beetle American black flour beetle Maize weevil Larger black flour beetle Foreign grain beetle Squarenecked grain beetle Cadelle Smalleyed flour beetle Longheaded flour beetle Siamese grain beetle Spider beetles Grain mite (Acarina)

(P)

Tribolium confusum du Val

B,M,O

(T)

Tribolium audax Halstead

B,M,O

(P) (T)

Sitophilus zeamais Motschulsky Cynaeus angustus (Le Conte)

P,B,M B,M,O

(S,P,T)

Ahasverus advena (Walt!)

P,B,M,O

(S)

Cathartus quadricollis (Guerin-Meneville)

P,B,M,O

(T) (S)

Tenebroides mauritanicus (L.) Palorus ratzeburgi (Wissman)

M,O P,B

(S)

Latheticus oryzae Waterhouse

P,B,M,O

(S,W)

Lophocateres pusillus (Klug)

B,M

(P) (S,P,W)

Ptinidae Acarus siro L.

B,M p

FUNGUS-FEEDING INSECTSd

Hairy fungus beetle

*

Typhaea stercorea (L.)

p

INSECT PESTS OF STORED RICE

271

Table 7-1. Continued Cereal psocid "Sap beetle" Dried fruit beetle Pink scavenger caterpillar

(W) (W)

Liposcelis diuanatorius (Mueller) Carpophilus pilosellus (Motschulsky) Carpophilus hemipterus (L.) Pyroderces rileyi (Walsingham)

P.B.M,O M M

M

a The author has observed the species infesting the type of storage indicated: S-silos (farms and commercial); P-processing plants, rice mills; W-warehouses/ports; T -transportation carriers (rail cars, ships); *-all. h Commodities that each species commonly infests: P-paddy (rough rice); B-brown rice; M-milled (polished) rice; 0-other (bran, rice flour, processed cereal, etc.). c Several other species of Ephestia may infest rice. d These species do not damage rice, but their presence could indicate other problems (leakage, spoilage).

wheat, and sorghum, and processed commodities such as breakfast cereals or animal feeds; and the saw-toothed grain beetle, Oryzaephilus surinamensis (L.), attacks all grains, processed farinaceous commodities (flour, cornmeal, etc.), dried fruits (e.g., raisins), and various nutmeats. Storage insects are most abundant in areas with warm, humid climates, but they can and do cause severe problems anywhere grain is stored. Because most rice is produced and stored in tropical or subtropical areas, conditions usually favor infestation. Rough rice is somewhat less susceptible to infestation than other grains because the hull partially protects the edible portions of the seed. Even so, the rice hull will not totally prevent infestation in rough rice. All commercially harvested rice has a proportion of grains with hull defects which admit pest insects. Methods of harvesting, drying, and handling, as well as environmental conditions during the growing season and the variety of rice, can all affect hull condition. Also, some pests can find ways to enter grains in spite of intact hulls. Rice weevils, Sitophilus oryzae (L.), do not attack grains with intact hulls (Breese 1960; Cogburn 1974), but both lesser grain borers, Rhyzopertha dominica (F.), and Angoumois grain moths, Sitotroga cerealella (Olivier), can infest rice grains selected for perfect hulls. Larvae of these two species may penetrate through the hull or, more likely, force entry through gaps between the palea and lemma that are too small to be detected even under high magnification. Both are known to enter through the abscission scar at the base of the grains (Cogburn et al. 1983). Brown rice is an excellent medium for the growth of storage insects. Rice is not often stored as brown rice, but the United States exports a significant amount of rice to countries that have milling facilities. Brown

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RICE: PRODUCTION

rice and rice bran products are being promoted as health foods, and the growth of this industry may require storage of brown rice and bran for extended periods. Both products are especially susceptible to infestation. Milled rice (white or polished rice) is a relatively poor growth medium for storage insects because essential nutrients are removed with the bran coat and germ (Le Cato 1975). However, the major problems associated with insects in milled rice derive from contamination rather than from destruction of the commodity. The significance of contaminants such as live and dead insects, insect fragments, excreta, webbing, cast larval skins, eggs, etc.' varies wnh local laws and traditions, but in most countries, allowable foreign matter, especially insect contamination, in processed foods is strictly limited. In the United States, infestation of milled rice is a greater problem in rice that is exported than in rice consumed locally. Rice for local consumption is usually ''well milled,'' i.e., removal of the bran coat is total and the rice is milled, packaged, and distributed in a continuous operation. Even if a few eggs or young larvae survive the milling process, they usually do not have time to develop to the adult stage and increase to detectable levels before the rice is consumed. The infestability of milled rice relates directly to the degree of milling. Lightly milled rice is much more infestable than highly polished rice (McGaughey 1970, 1974) and rice for export is often more lightly milled to accommodate the specifications of the recipient country. Since some of the bran coat remains on the kernels, lightly milled rice retains more nutrients and will support insect development. If the rice is exposed to sources of infestation before or during shipment and contains a few insects when it leaves the port (Cogburn 1973a,b), transit time and rice temperature determine whether these few insects increase to detectable populations that can damage the product. If the destination is an area with a mild climate and transit time is short, detectable infestations are rare. If the transit time is protracted and crosses tropical waters, extremely large, multispecies infestations can develop. These result in severe financial losses, international incidents, ill will between all parties involved in the shipment and suspicion of the quality of U. S. rice in general. Financial losses are real and measurable, but losses in terms of international relations and good will are no less important, even though they defy quantification (Howe 1965; Cogburn 1977). Infestation in exported rice is not peculiar to the United States (Freeman 1965). Elimination of insect contamination in exported foodstuffs, whether rice or other commodities, is a major concern of any country that exports agricultural produce (Freeman 1974).

INSECT PESTS OF STORED RICE

273

STORED RICE INSECTS

The insect species discussed in this chapter include the major pests of stored rice, all of which occur throughout the world. References to these species from various countries include Trinidad (Breese 1960), Ceylon (Easter 1954), Taiwan (Li 1953), Sierra Leone (Prevett 1971), Egypt (Bishara et al. 1973), all of western Europe (Freeman 1973), and many points in Asia (Freeman 1974). To many people, any insect that is found in grain or grain products is a "weevil." Several species of weevil do indeed damage stored grain, but the term is correctly applied only to members of the Sitophilus complex. In addition, vague terms like "bran bugs" are applied to almost anything that crawls and "millers" to any moth. Such terms often lead to misidentification of insects and/or misapplication of control measures. All people involved in the storage, handling, or processing of grain should become adept in the proper identification of storage insects and learn something of the life history and habits of each important species. This knowledge would facilitate better insect control at reduced cost. All insect pests of stored grain are either beetles (Coleoptera) or moths (Lepidoptera); thus, all undergo complete metamorphosis-i.e., they have four distinct life stages: egg, larva, pupa, and adult. The type and extent of damage that a species inflicts on rice depends on whether immature stages develop inside or outside of the kernels. Insects that develop from larva to adult inside kernels of rice consume the endosperm. Thus, each one that develops in a bin of rice is equivalent to the loss of one grain. Not only do these "primary" insects consume rice, heavy infestations produce heat which induces moisture gradients and spoilage. Most species develop outside of the kernels and feed on the bran coat, germ, dust, or other debris. These do relatively little damage to the endosperm but are noxious because of contamination. Heavy infestations of these "secondary" species can also cause grain to heat and spoil. Some moth larvae form clumps of kernels by webbing individual grains together. These clumps are removed from the rice and discarded with straw and trash when the grain is cleaned before processing. Infestations in milled rice necessitates fumigation and then remilling to remove insect carcasses. Insects That Develop Inside Kernels of Rice Weevils

The weevils that infest rice belong to the family Curculionidae and are characterized by the elongation of the front part of the head into a snout or proboscis, the tip of which bears the mouthparts. This structure is

274

RICE: PRODUCTION

utilized for both feeding and to facilitate oviposition (egg laying). All weevils have similar habits and inflict the same type of damage on grain. The female chews a hole into a kernel of rice, inserts her ovipositor, and deposits an egg at the bottom of the hole. As the ovipositor is withdrawn, she secretes a mucouslike substance that fills the hole to the surface of the grain and dries into a hard plug which protects the egg and, later, the young larva from desiccation. The larva feeds on the endosperm, hollowing out most of the kernel as it grows. The pupal and early adult stages are also spent inside the kernel. After the exoskeleton hardens, the adult weevil chews its way out of the kernel, seeks a mate, and the cycle begins anew. Three species of weevil can attack stored rice: the rice weevil, the maize or corn weevil, S. zeamais, and the granary weevil, S. granarius (L). The rice weevil (Fig 7-lA) is the most common. Maize weevils are less common. Granary weevils are rarely if ever found in rice in the southern United States but are widely distributed and are significant pests in other grains. Rice and maize weevils are strong fliers, but granary weevils have no functional flight wings. All are dark brown to black and about 3 mm long, although the size can vary with the type of grain on which the insects developed and possibly among different strains of the same species. Rice weevils and maize weevils have four lighter colored spots on the back, two on each wing cover. The granary weevil is a uniform color. The species can be separated by the shape and arrangement of the pits on the pronotum, the shape of the genitalia, and other characteristics (Boudreaux 1969). Lesser grain borer

The lesser grain borer, Rhyzopertha dominica (F.) (Fig. 7-lB), is potentially the most destructive insect pest that infests stored rice. A member of the family Bostrichidae (powder post beetles), it has the characteristic shape of this family-elongated and cylindrical, with the head deflexed beneath the hoodlike prothorax. Lesser grain borers are about 3 mm long, 1 mm wide and are dark brown. They can live deep within a grain mass, develop large populations and destroy many kilograms of rice before their presence is noticed. The relatively long-lived adults feed and reproduce for several months. Each female deposits 300 to 500 eggs that are deposited loose in the grain mass (Cotton 1956). When the larvae hatch, they bore into individual kernels and then develop much as weevils do. The adults are strong fliers and can migrate over large areas (Cogburn 1988), easily spreading infestations from isolated populations to newly harvested grain.

INSECT PESTS OF STORED RICE

275

Figure 7-1. A: Adult rice weevil, Sitophilus oryzae, with kernels of long-grain rice showing iypical damage. B: Adult lesser grain borers, Phyzopertha dominica, with kernels of long-grain brown rice showing iypical damage. C: Adult angoumois grain moth, Sitotroga cerealella, with kernels of medium, grain rough rice showing iypical damage. D: Adult red flour beetles, Tribolium castaneum, on kernels of long-groin brown rice. E: Adult cigarette beetles, Casioderma serricorne, on grains of long-grain rice. F: Adults of Crypto/estes Spp. with long-groin rice. G: Adult almond moth, Ephestia cautella, on kernels of long-grain brown rice. H: Adult Indian meal moth, P/odia interpunte/la, on kernels on long-grain brown rice. 1: Larvae of almond moth, Ephestia caute/la, on kernels of long-grain brown rice.

276

RICE: PRODUCTION

Angoumois grain moth

The Angoumois grain moth (Fig. 7-lC) is abundant in stored rough rice in the southern United States. Its capacity for damage is limited by an inability to penetrate deep into a grain mass, infestations being confined to the top 30 or 40 em of the grain surface and to other accessible surfaces around doors or perforated bin floors. The moth is small (5-6 mm), tan or buff in color, and the posterior edges of the wings are fringed with fine hairs. Females deposit eggs, usually in clusters, in protected places in the grain or storage structure (in the interstices between grains, beneath the husk of grains with broken hulls, small crevices in bin walls, etc.). When the eggs hatch, each larva bores into a rice kernel and consumes the endosperm as it grows. Just before pupation, the larva cuts a circular "window" to the outside of the grain and webs it over lightly. The adult moth pushes the window aside and emerges from the grain, leaving a neat, round hole in the hull, damage unique to the Angoumois grain moth. Insects That Develop Outside Kernels of Rice Other insect pests of rice do not penetrate the kernels but are common in stored paddy, brown rice, milled rice, rice bran, consumer packages, and processed products such as breakfast cereals. Over half the rice produced in the United States is exported as milled or brown rice, and the following species are particularly troublesome to the export industry. Flour beetles

The flour beetles, Tribolium spp., are among the most common of the stored-product insects. The red flour beetle, T. castaneum (Herbst) (Fig. 7-lD), is by far the most abundant in the southern United States. The confused flour beetle, T. confusum Jacquelin duVal, is generally more abundant in cooler regions. Each species is about 3 to 4 mm long, 1 mm wide, dark reddish brown, and somewhat flattened. Magnification is required to distinguish between the species, the distinguishing characters being the shape of the antennal segments and the structure of the compound eye. The red flour beetle is a strong flier, but the confused flour beetle, though its wings appear functional, is flightless. Neither species consumes the endosperm of rice. Adults and larvae of both feed on the bran coat, germ, loose flakes of bran, or on grain dust.

The red flour beetle is abundant in rough rice stored on farms or in

commercial silos, in mills and milling machinery, and in rail cars, ships, and warehouses. Two other species of Tribolium infest grain in the United States (Cotton 1956) but are rare in rice. These are the black flour beetle, T. Audax

INSECT PESTS OF STORED RICE

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(Halstead), and T. destructor Uyttenboogaart. Presumably, either species will infest rice if it is available. Cigarette beetle

As the name implies, the cigarette beetle (Fig. 7-lE) is a major pest of tobacco but is an omnivorous feeder and extremely abundant in rice mills and port warehouses on the U.S. Gulf Coast (Cogburn 1973a). Strangely, it was relatively uncommon in boxcars that delivered rice and wheat flour to Gulf Coast ports (Cogburn 1973b). Between 1953 and 1963, it was the third most common insect found infesting cargoes of rice and rice bran shipped from the United States to Great Britain (Freeman 1965). The insect is about 2.5 mm long, more or less rounded, and reddish brown. It is a strong flier, and in badly infested tobacco warehouses, large numbers can be caught in light traps (Childs 1958). In rice mills and warehouses, it breeds in farinaceous debris of all kinds and migrates to clean rice that is being processed, stored, or transported. Sawtoothed grain beetle

The sawtoothed grain beetle is occasionally found in rice mills and warehouses (Cogburn 1973a) and was reported by Freeman (1965) to occur frequently in milled rice imported into England. The adults are about 2.5 mm long and flattened, and the lateral edges of the thorax bear six toothlike spines on each side, which explains the insect's name. A closely related species, the merchant grain beetle, 0. mercator, is superficially identical to the sawtoothed grain beetle and inflicts identical damage in identical habitats. The species cannot be separated without a microscope. Both feed and breed similarly to the flour beetles. Cryptolestes complex

The smallest of the grain-infesting beetles are several members of the genus Cryptolestes (Fig. 7-1F). Three species have been identified from stored rough rice in Texas: the flat grain beetle, C. pusillus; the rusty grain beetle, C.ferrugineus; and the "flour mill beetle," C. turcicus. The adult insects are 1.5 to 2 mm long and less than 1 mm wide. For specific identification the reader is referred to Biege and Partida (1976). All three species do similar damage, and although small, they can increase to huge populations that cause heating, spoilage and contamination of stored grain. Cryptolestes larvae normally crawl about among the interstices between kernels of grain and feed on flakes of bran, grain dust, etc. Occasionally, however, a larva will tunnel into the germ of a rice kernel and thus be hidden from inspectors or others examining the grain for infestation. They do not normally pupate inside the germ or damage the endosperm.

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These insects infest rough or milled rice, rice bran, rice flour, or other processed rice products. Moths

Except for the Angoumois grain moth, which was discussed previously, Lepidoptera (family-Pyralidae) that infest stored rice do not penetrate the kernels and usually do little damage to the endosperm. Rather, they feed on the bran, germ, grain dust, or other debris. However, heavy infestations can and do cause severe financial losses for those who store, process, or transport rice. In bulk storage of rough rice, infestations are restricted to the grain surface. In bagged milled rice, the surface of the bags may be webbed over, but sometimes the larvae will penetrate throughout the bag, webbing together kernels and leaving frass and cast skins in the rice. In the southern United States, the almond moth, Ephestia cautella (Fig. 7-lG), accounts for most infestations, but the Indian meal moth, Plodia interpunctella (Fig. 7-lH), is also significant. The "rice moth," Corcyra cephalonica, is often thought to be a pest of rice in the southern United States, but in 20 years of experience, this author has never encountered the species. It apparently is a major pest of rice in other areas ofthe world because it is listed by Freeman (1974) in his tabulation of insects found in foods imported into Britain. In addition to those species named, other members of the Ephestia genus, such as E. kuhniella (Zeller), E. elutella (Hubner), and E.figuliella (Gregson), probably can infest rice but rarely do so in the United States. Regardless of the species, the habits and the damage caused by the Pyralid moths are similar. An adult female produces about 200 eggs (rarely, as many as 400) that are laid singularly, scattered at random over the surface of the commodity. These usually hatch in about 4 or 5 days. The larval stage of Ephestia cautella (Fig. 7-11) lasts about 4 weeks. Spinnerets are located near the mouthparts of the larvae, and as they feed, they weave together particles of dust, bran, or kernels of rice with fine, silken threads. This habit accounts for most of the damage other than contamination. Heavy infestations can completely mat over the surface of grain in a bin (Cotton 1956), which restricts air movement in the grain mass, increases moisture content and promotes heating and spoilage. Even in less severe infestations, clumps of webbed grain are removed during cleaning and discarded along with straw and other trash. Thus, moth infestations cause the loss of far more grain than is consumed by the insects. The pupa transforms into the adult sta1w in ahout 7

d~vs.

Insects That Feed on Fungi

The hairy fungus beetle, Typhaea stercorea, and a sap beetle, Carpophilus pilosellus, are extremely abundant in rail cars, warehouses, and sometimes

INSECT PESTS OF STORED RICE

279

farm storage units. Both species feed on fungi or other microorganisms and do not damage rice. Rather, their presence indicates that the grain is going out of condition or that unsanitary conditions exist somewhere in the storage facility. The species occasionally cause financial losses, not from any damage that they do, but because they are misidentified as damaging pests and expensive control measures are applied unnecessarily. For example, when rice lodges in the field, molds grow on some of the fallen panicles moistened by rain or irrigation water, thus providing a source of food for fungus-feeding insects which proliferate in the field. When the grain is harvested, fungus beetles are collected by the combine along with the rice. When drying is begun, heat and desiccation drives the insects to the surface of grain where they are often mistaken for damaging species and unnecessarily fumigated. Both species are common in rail cars (Cogburn 1973b), and the adults are active insects. Movement of the car stimulates them to migrate throughout the car and over the load where they are seen by inspectors and often mistaken for damaging species. As a result, the rice is fumigated unnecessarily. ORIGINS OF INFESTATIONS

Residual Insect Populations

Most infestations of storage insects initiate when a clean commodity is stored or processed near residual infestations in trash grain or grain products that were not removed from storage areas when they should have been. For example, rough rice in the United States is frequently stored on farms in cylindrical metal bins with perforated metal floors that are elevated about 0.5 m above a concrete slab. The bins, which double as grain driers, are equipped with heaters and fans that force heated air into the void beneath the perforated floor and through the grain mass. Dust, flakes of bran, particles of grain, etc., fall through the perforations into the void area and remain until the bins are cleaned. If the bins are not cleaned, the trash becomes infested and the insects invade new grain as soon as it is stored. Residual infestations will remain in any type of storage area or transportation carrier unless the unit is cleaned between uses. For example, 77% of the boxcars delivering commodities to Gulf Coast ports were found to contain farinaceous debris (Cogburn 1973b). Grain dust that collects in elevators or rice mills is sufficiently nutritious to support infestation. Spillage and trash of any kind is potential harborage for insects. Migration

"Cross-contamination" occurs when clean commodities are stored adjacent to infested ones, and many storage insects that are strong fliers

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migrate across open areas to infest new grain. Rice weevils, lesser grain borers, red flour beetles, and all moths are capable of sustained flight, but relatively little is known of the migratory ability of storage insects, how they locate new food sources, or the conditions that stimulate migration. Field Infestation

Before the advent of combine harvesting, rice was cut, tied into bundles, and left in the field to dry where it frequently became infested before threshing. Today, rice with a moisture content of about 20% is harvested by combine and then dried with heated air to about 12.5% moisture. Highmoisture rice in the field seemed to be unsuitable for insect development until Chau and Kunze (1978) showed that grain maturity and moisture content varies widely between panicles in the same field and even between grains on the same panicle. Also, Angoumois grain moths and lesser grain borers frequently are captured in pheromone-baited traps in fields of standing rice (Cogburn 1988). Undoubtedly, some eggs, larvae, and/or adults are harvested with the grain and some survive harvesting and drying. In countries where mechanized harvesting equipment is uncommon, field infestation may be of even greater significance. Studies with pheromones show that some species are distributed over wide geographical areas and apparently survive and breed in woodlands and other places remote from rice production and storage. Captured individuals from these "wild" populations reproduce in rice and undoubtedly can migrate to freshly binned grain.

CONTROL OF STORAGE INSECTS Cultural Control

Sanitation is a cheap and effective way of minimizing the impact of storage insects. The rationale is quite simple: insects deprived of food and harborage cannot survive, breed, and disseminate. Remove all trash grain, grain dust, or other farinaceous debris from the storage premises, and clean all bins, floors, windows sills, milling machinery, harvesting machinery, conveying equipment, etc., on a regular schedule. Destroy trash by burying or burning it at a place remote from the storage facility. The importance of sanitation cannot be overemphasized. Not only does it enhance food quality and safety, it is the most economical and widely applicable method of pest control. Also, sanitation deprives other pests such as rodents and birds of food and harborage, thereby reducing problems with them as well as insects.

INSECT PESTS OF STORED RICE

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Chemical Control

Sanitation programs include the judicious use of chemical pesticides as supplemental measures, but chemicals cannot overcome dirty conditions. Space does not permit a comprehensive discussion of insecticides and fumigants or of methods of application. For more information on useful chemicals, see Monro (1961) and Harein and de las Casas (1974). Insecticides

Insecticidal sprays, usually formulated as water emulsifiable liquids or powders, are applied as residual treatments to the exposed surfaces of empty grain bins, warehouses, mills, or other areas after the facilities have been cleaned and before new commodities are stored or processed. Carefully treat all cracks and crevices where farinaceous debris lodges and is difficult to remove. Malathion, methoxychlor, synergized pyrethrins, synthetic pyrethroids, lindane, fenitrothion, pirimiphos methyl, chlorpyrifos methyl, and dichlorvos all have been used as residual sprays for grain storage facilities at one time or another somewhere in the world. Specific materials cannot be recommended here because labeled chemicals, methods of use, dose rates, and residue tolerances are strictly governed by local laws and change frequently. Any user of an insecticide must identify those approved for use in his country or area. Materials called "protectants" are applied directly to bulk rough rice as it goes into final storage. Only rough rice (paddy), not brown or milled rice, may be so treated. Protectants are meant to prevent infestation, not to eliminate established infestations. Malathion, the preferred protectant for many years, was remarkably successful (Freeman 1974), but many species of storage insects around the world have developed resistance to malathion (Bengston et al. 1975; Zettler 1975). Thus, the utility of this chemical is threatened, and alternative materials such as pirimiphos methyl and chlorpyrifos methyl are being developed and used in some areas (Cogburn 1976; Cogburn et al. 1983b). Insecticides applied as aerosol space treatments for control of flying insects, particularly moths, in mills and warehouses supplement sprays and protectants. Aerosols are mists, fogs, or vapors blown into a building with specialized equipment using special formulations of the insecticide. Aerosol particles impinge on the setae of insects and puddle on the membranes at the base, where the insecticide enters the insect through the integument (Anon. 1971). Dichlorvos was an especially effective aerosol (Cogburn 1975), but concerns about human safety have restricted its use in the United States. Commodities stored in areas treated with aerosols must be protected from contamination, and no personnel other than the

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applicator can be present. Automatic systems dispense aerosols at predetermined times in the absence of all personnel. Fumigants

Aerosols consist of very small droplets of solutions suspended in air and are sometimes confused with fumigants. Fumigants are gases that act as individual molecules (Monro 1961) and enter the insect almost entirely through the respiratory system. Fumigation is the preferred method of eliminating an established infestation from stored rice or rice products. Mills and warehouses, if properly sealed, can be fumigated to clean up indigenous populations of insects that were not eliminated by sanitation procedures. A successful fumigation, regardless of the fumigant, always depends on holding a lethal concentration of the fumigant in air long enough to kill all metamorphic stages of all insects. Eggs and pupae are the stages most difficult to kill by fumigation because respiration and metabolism proceed more slowly than in larvae or adults. Although some fumigants may penetrate the chorion of the egg or the integument of the pupa, it is best to continue fumigation until eggs become larvae or pupae become adults-stages that are highly susceptible to the lethal action of fumigants. Fumigants forrimlated as liquids or solids must become gases to be effective. Liquid fumigants, mixtures of highly volatile substances like carbon tetrachloride, carbon bisulfide and ethylene dichloride, volatilize into gases that are heavier than air and, when applied to the grain surface, penetrate downward through the grain mass by gravity. They were particularly useful in farm bins and very tall concrete silos, but all liquid fumigants have been banned from use in the United States. They still may be used in some other countries. Methyl bromide is widely used for space fumigation of mills, warehouses, etc.; fumigation of grain in large, flat storages equipped with recirculation systems; fumigation of bagged rice under plastic tarpaulins; and fumigation of various carriers such as rail cars, ships, trucks, and barges. Pressurized canisters containing 454 g to 170 kg or more retain methyl bromide as a liquid. The low boiling point (3.6°C) causes volatilization to the gaseous state immediately when the cylinder is opened and the pressure released. Methyl bromide is colorless and odorless; therefore, it is usually formulated with about 2% chloropicrin (tear gas) as a warning agent for the applicator or others that accidentally enter an area under fumigation. Methyl bromide is extremely dangerous. Not only is it acutely toxic to man and other mammals, but sublethal exposure can result in permanent, chronic damage to the liver and other organs. In addition, the liquid or

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high concentrations of the gas may cause severe skin blisters (Monro 1961). Phosphine gas, introduced in the mid-1950s, now is used worldwide. Aluminum phosphide (or magnesium phosphide) chemically reacts with atmospheric moisture and releases hydrogen phosphide, also called phosphine gas (PH3). Phosphine is flammable and, under certain conditions, can ignite spontaneously; thus, the precautions on the label must be followed explicitly. The gas has a distinctive odor that can warn people of its presence, but the odor is not imparted to the product being fumigated. Phosphine is used to fumigate rice in bags and in bulk (Cogburn and Tilton 1963; Tilton and Cogburn 1965). Successful fumigation with phosphine is sensitive to temperature. Thus, applicators must monitor ambient conditions and take appropriate steps to insure the lethal concentrations of gas are maintained long enough to kill all stages of the target insects.

REFERENCES

Anon. 1971. Nat. Pest Control Operators Newslett. 31(10):3-7. Bengston, M., L. M. Cooper, and F. J. Grant-Taylor. 1975. A comparison of bioresmethrin, chlorpyrifos methyl and pirmiphos- methyl as grain protectants against malathion-resistant insects in wheat. Queensland J. Agric. Animal Sci. 32(1):51-78. Biege, C. R., and G. H. Partida. 1976. Taxonomic characters to identify three species of Cryptolestes (Coleoptera: Circujidae). J. Kan. Entomol. Soc. 49:161-64. Bishara, E. 1., A. Koura, and M.A. El-Halfawy. 1973. Oviposition preference of the granary and rice weevils on Egyptian rice varieties and recommendations for grain protection. Bull. Soc. Entomol. Egypte 56:145-50. Boudreaux, H. B. 1969. The identity of Sitophilus oryzae. Ann. Entomol. Soc. Amer. 62:169-72. Breese, M. H. 1960. The infestibility of stored paddy by Sitophilus sasakii (Tak.) and Rhyzopertha dominica (F.). Bull. Entomol. Res. 51:599-630. Chau, N. N., and 0. R. Kunze. 1982. Moisture content variation among harvested rice grains. Trans. ASAE 25:1037-40. Childs, D. P. 1958. Warehouse fumigation of flue-cured tobacco with HCN to control the cigarette beetle. J. Econ. Entomol. 51:417-421. Cogburn, R. R. 1973a. Stored-product insect infestations in port warehouse of the gulf coast. Environ. Entomol. 2:401-7. Cogburn, R. R. 1973b. Stored-product insect infestations in boxcars delivering flour and rice to Gulf Coast ports. Environ. Entomol. 2:427-31. Cogburn, R. R. 1974. Domestic rice varieties: Apparent resistance to rice weevils, lesser grain borers and Angoumois grain moths. Environ. Entomol. 3:681-685.

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Cogburn, R. R. 1975. Dichlorvos for control of stored-product insects in port warehouses: Low-volume aerosols and commodity residues. J. Econ. Entomol. 69:361-65. Cogburn, R. R. 1976. Pirimiphos-methyl as a protectant for stored rough rice: Small bin tests. J. Econ. Entomol. 69:369-73. Cogburn, R. R. 1977. Susceptibility of varieties of stored rough rice to losses caused by storage insects. J. Stored Prod. Res. 13:29-34. Cogburn, R. R. 1988. Detection, distribution and seasonal abundance of Sitotroga cerealella and Rhyzopertha dominica as indicated by pheromone-baited sticky traps. In Proc. XVIII Int. Congr. Entomol., Vancouver, BC, Canada. 451. Cogburn, R. R., and E. W. Tilton. 1963. Studies of phosphine as a fumigant for sacked rice under gas-tight tarpaulins. J. Econ. Entomol. 56:706-8. Cogburn, R. R., C. N. Bollich, and S. Meola. 1983a. Factors that influence the relative resistance of rough rice to Angoumois grain moths and lesser grain borers. Environ. Entomol. 12:936-42. Cogburn, R. R., D. L., Calderwood, B. D. Webb, and M.A. Marchetti. 1983b. Protecting rough rice stored in metal farm bins from insect attack. J. Econ. Entomol. 76:1377-83. Cotton, R. T. 1956. Pests of Stored Grain and Grain Products. rev. ed. Minneapolis, MN: Burgess Publishing Co. Easter, S. S. 1954. Infestation control in stored rice. Trop. Agric. Peradeniya 110:217-19. Freeman, J. A. 1965. On the infestation of rice and rice products imported into Britain. In Proc. 12th Int. Congr. Entomol., 1964, London. Freeman, J. A. 1973. Problems of infestation by insects and mites of cereals stored in Western Europe. Ann. Techno/. Agric. 22(3):509-30. Freeman, J. A. 1974. A review of changes in the pattern of infestation in international trade. Eur. Mediterr. Plant Prot. Organ. Bull. 4(3):251-73. Harein, P. K., and E. De Las Casas. 1974. Chemical control of stored grain insects and associated micro- and macro-organisms. In Storage of cereal grains and their products. V, rev. St, Paul, MN: Amer. Assn. Cereal Chern. Howe, R. W. 1965. Losses caused by insects and mites in stored foods and feeding stuffs. Nutr. Abst. Ev. 35:285-93. Le Cato, G. L. 1975. Red flour beetle: Population growth on diets of corn, wheat, rice or shelled peanuts supplemented with eggs or adults of the Indian meal moth. J. Econ. Entomol. 68:763-65. Li, C. S. 1953. A preliminary study with stored rice insect pests and their control in Taiwan. Memoirs Nat. Taiwan Univ., College of Agric. 2(5):99-103. McGaughey, W. H. 1970. Effect of variety and degree of milling on insect development in milled rice. J. Econ. Entomol. 63:1375-76. McGaughey, W. H. 1974. Insect development in milled rice: Effects of variety, degree of milling, parboiling and broken kernels. J. Stored Prod. Res. 10:81-86. Monro, H. A. U. 1961. Manual of Fumigation for Insect Control. New York: UN F.A.O. Prevett, P. F. 1971. Storage of paddy and rice (with particular reference to pest infestation). Trop. Stored Prod. Inf. 22:35-49.

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Tilton, E. W., and R. R. Cogburn. 1965. Phosphine fumigation of rough rice in upright bins. Rice J. 69(11):8-9. USDA/ARS. 1986. Stored-Grain Insects, Agric. Handbook 500. Washington, DC: U.S Gov. Printing Office. Zettler, J. L. 1975. Malathion resistance in strains of Tribolium castaneum collected from rice in the U.S.A. J. Stored Prod. Res. 11:115-17.

8 Weed Management D. E. Bayer University of California, Davis

GENERAL PRINCIPLES OF WEED MANAGEMENT

Cultural methods for controlling weeds have been used since the beginning of systematic rice production and remain an integral part of successful weed management programs. Cultural methods aid not only in suppressing weed growth but may be equally beneficial in enhancing rice seedling establishment and growth. Intensively farmed rice fields are areas of medium to high disturbance and low stress to achieve maximum yields. Disturbance may be viewed as partial or total elimination of the weed biomass, while stress functions to reduce photosynthesis or productivity of the crop. Weeds are plants that can adapt to areas of high disturbance and/or high stress and plague the grower, regardless of the weed management program employed. The selection of the methods used to control rice weed problems depends on the type of rice culture, the technology available, and the resources of the grower. The selection of weed management inputs should emphasize maximum returns to the grower with the lowest cost. Landforming and land preparation are important components of rice weed control programs. Land preparation provides favorable conditions 287

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for the growth and development of rice, as well as a weed-free condition at planting. Proper field preparation discourages the subsequent growth of weedy plants by allowing rice to establish itself and use the available resources before weeds germinate and emerge. This forms the basis for competition, because later emerging plants must garner sufficient resources to allow them to support some type of interference. Given this concept, then, competition between crops and weeds may be referred to as the capture and utilization of resources and depends on time of germination, rate of growth of the plants and the spatial arrangement of their foliage and roots. The competition between rice and weeds is most severe during early growth of the rice when yield components (tillers, panicles, kernels, etc.) are being formed. Limiting crop growth at this time will have a negative effect on the rice yield. Limiting resources during the reproductive phase may also negatively impact yield but, more typically reduces grain quality and harvestability. The competitive ability of a weed may be viewed as the overall integration of root and shoot growth or surface area, the metabolic activity, and the distribution in time (when the weed is growing in relation to the rice plant) and space (location of roots and foliage in relation to the rice plant) of the organs that acquire the resources. The onset of competition is determined by the time when a resource becomes limiting to either the weed or rice plant. Seedbed Preparation

The seedbed should be prepared in a manner that will enhance the establishment and growth of rice while suppressing, delaying, or eliminating the growth and development of weeds. The major weeds in drier upland rice are primarily C4 plants, while C3 weedy plants tend to dominate in submerged rice culture. Competition between rice, a C3 plant, and C4 weeds may be very severe in dry land rice or in rain-fed wetland rice where rainfall is limited. C3 weeds tend to be more prevalent in submerged conditions. Land preparation on dry soils is of little value in reducing annual weed problems because most seed will not germinate under low moisture conditions, especially the aquatic weed species. However, dry tillage at this time may aid in killing vegetative organs of perennial weeds, provided that the storage organs can be exposed to the sun and dried. In the more temperate climates where soils dry between crops, tilling the soil will increase aeration, temperature, and the rate of drying. Deep plowing where the soil is completely inverted will bury weed seeds lying on the surface deep enough to inhibit germination and/or emergence. Weed seed burial, however, should be done with the knowledge that deep burial may reduce

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Figure 8-1. Grass weeds growing on large clod exposed above water surface.

oxygen and/or buildup carbon dioxide or other gases around the seed that will induce a secondary dormancy. Seeds with a secondary dormancy could be returned by subsequent tillage to a zone where germination could occur. Deep plowing is an effective method of reducing the soil weed seed bank, provided that the seeds are left buried in the soil until they lose their viability. The rice seedbed should be tilled to eliminate as many weeds and germinating weed seedlings as possible before the rice is planted. Smooth, compacted seedbeds create an environment that favors weed seed germination and seedling establishment , thus reducing the soil weed seed bank, while rough, loose, cloddy seedbeds tend to discourage weed seed germination and seedling establishment and thus is favorable for increasing the soil weed seed bank. Large clods should be broken up by tillage operations. Clods so large that they are exposed above the water surface provide an excellent site for growth and development of grassy weeds (Fig. 8-1). If rice is grown under flooded conditions, decomposition of crop residue should be encouraged prior to flooding to decrease the incidence of algae and other weed problems. Cover crops and other green plant material used for green manure should be incorporated and allowed to decompose before the field is flooded.

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Fertilizer Management

Nitrogen and phosphorous fertilizers and manure should be incorporated into the soil 5 to 10 em deep to reduce their availability to weed seedlings that germinate at or near the soil surface. In upland or unflooded rice culture, decomposition of animal and green manure crops incorporated into the soil prior to planting rice is not as critical as for rice grown under flooded conditions. Most weeds including submersed weeds, such as southern naiad (Najas guadalupensis) and algae, grow very vigorously when nitrogen is applied in the flood water or left on the soil surface. Barnyardgrass or watergrass (Echinochloa Sp.) and algae are also stimulated to grow and develop when phosphate fertilizers are left on the soil surface. Applications of fertilizers after the rice crop has become established and the weeds have germinated encourages rapid growth of the weeds. Fertilizers applied in excess will stimulate weed growth to outcompete rice. The yield of rice is enhanced as nitrogen is increased in the presence oflow infestations of weeds provided sufficient nitrogen is added for both the rice and the weed. However, as the level of the weed infestation increases, it becomes impossible to add sufficient fertilizer for both the weeds and the rice. With the added fertilizer most rice weeds will become so aggressive they will outcompete the rice plants for other resources such as space and light. Weed-Free Rice Seed

The use of good quality rice seed free of weed seeds helps prevent the spread of weed infestations. Weeds have been reported to move from one continent to another in rice purchased for seed. Late watergrass (Echinochloa phyllopogon) has reportedly been introduced from Italy and/ or France into Morocco around 1986 when Morocco expanded its rice acreage. Both early watergrass (Echinochloa oryzoides) and late watergrass were introduced into California through importation of rice seed from Asia. More localized spread of weeds occurs from grower to grower and field to field through the use of seed rice infested with weed seed, dirty equipment carrying weed seed, and weed seed floating from field to field in irrigation water. Weeds often mimic the crop in maturity, seed size, and seed shape which enhances their opportunity to contaminate rice seed and spread. Weeds that mature and shatter before the crop tend to spread more slowly and are more localized than weeds that mature at the same time as the rice crop. Early-shattering weeds are spread mostly by the movement of equipment and in water and air. Weeds that mature with the crop tend to spread as a contaminant in the harvested rice crop and in subsequently planted seed.

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Crop Rotation

Carefully planned crop rotation is among the most effective cultural techniques for controlling rice weeds and should be used whenever feasible. Weeds are often associated with specific crops because of similar growth requirements and/or similar plant characteristics. Because weeds vary in their growth habits and life cycles, it is essential to select rotation crops with dissimilar life cycles and cultural requirements to interrupt the dominant weed complex. Both crops and weed control measures should be changed in longterm crop rotation programs. If the same crops and weed control practices are used in the rotation year after year, weeds associated with the entire rotation complex will be as severe as in a monoculture cropping system. Water Management

The use of water in the production of rice can have a profound influence on the weed spectrum that will be present as well as the program employed to manage or eliminate their growth. Plants that possess the C3 photosynthesis apparatus tend to be found more frequently in rice grown under continuous flooded conditions, and plants possessing the C4 photosynthetic apparatus tend to be more common in rice grown under dryland conditions for at least a portion of the cropping season. Rice is a C3 plant and has the same basic photosynthetic restrictions as C3 weeds, while C4 plants have higher photosynthetic activity, higher light and temperature optimum and lower moisture requirement (see Table 8-1). Weed problems may be expected to be more varied in species and intensity in dry-seeded rice than in wet-seeded or transplanted rice because

Table 8-1. Characteristics of C 3 and C4 Plants Leaf anatomy Photosynthesis (ttmol C0 2 mg- 1 chlorophyll h-I) PEP carboxylase (ttmol C0 2 mg- 1 chlorophyll h- 1) Optimum temperature (0 C) Light saturation (ttmol photon m- 2 s- 1) C0 2 compensation point (ppm) Water use efficiency (g water/g dry wt) Growth rate (g m- 2 day- 1) Percent inhibition of photosynthesis by normal (21%) atmospheric 0 2 concentrations Source: Modified from Matsunaka and Saka (1977).

C3 Plants

C4 Plants

chloroplasts in mesophyll cells

chloroplasts in bundle sheath

15-50 25-50 15-25 400-1200 30-70 400-1000 5-20 40

50-100 800-1200 30-45 1500-2500 0-10

250-400 40-60 0

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of differences in seedbed preparation, the presence or absence of moisture during germination, and early growth stages of the rice. Competition

The most critical period for competition between rice and weeds is when the rice is in the vegetative phase and the yield components of the rice plant are being differentiated. Worldwide yield losses attributed to weeds average approximately 10%, while on individual fields losses may range from 40 to 100%. Competition varies widely from situation to situation and from culture to culture. Short weeds and those that germinate late in the cropping season tend to compete less than tall weeds or those that germinate at the beginning of the cropping season. The replacement of the older tall-statured rice cultivars with the modern short-statured cultivars has created a situation more favorable for tall-growing weeds. Shorter growing broadleaf and sedge weeds traditionally infesting the older cultivars are being replaced by grassy annual weeds in many areas. A good stand of rice can withstand competition from weeds better than a thin stand of rice. Use of Herbicides

Although herbicides are considered by some to be an essential component of rice weed control programs, they should be considered as another viable component to use in an overall weed management program and should be used in combination with good agronomic practices. No one weed control practice will effectively and economically provide consistent control of all weeds in all situations. Continued use of a single herbicide will result in a shift of weed species to those that are tolerant or resistant to the herbicide or to individuals within the same species that are resistant to the herbicide. The type of use and the method of application are listed on the label but generally involve an application of the herbicide prior to seeding (preplant) or following seeding (postplant). Preplant applications are sprayed on the foliage of existing vegetation prior to planting or they are made to the soil and may be incorporated (mixed into the soil profile) in areas where rainfall is unpredictable or if the herbicide is volatile or is subject to rapid photodecomposition. Postplant applications may be made to (1) the soil surface following planting and prior to emergence of either crop or weeds (preemergence) or (2) to the weed and crop seedling whether in contact with the plant foliage or into the water (postemergence). The movement of the herbicide during and following an application is an environmental concern that should always be addressed. Proper application procedures are essential to prevent symptoms or injury to adjacent crops as a result of herbicides drifting either in the gaseous

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293

(volatile) phase or as discrete particles. Drift can be significantly reduced when proper attention is given to the method of application, the formulation, and the environmental conditions. The size and density of the herbicide particle released by the application equipment is a major factor affecting movement. The smaller and/or less dense the droplet or particle, the farther it will drift. When foliar sprays are used, a compromise must be reached between the potential for herbicide movement off target (drift) and the good coverage or distribution on the weed foliage necessary for sufficient uptake and control. Large droplets tend to provide poorer coverage of weed foliage than fine droplets from a given volume. Weather plays a major role in herbicide drift. Herbicides should never be applied in winds greater than approximately 30 km/h. Whenever possible, avoid applying materials during air temperature inversions because even a slight wind can move an inverted air mass, transporting the suspended herbicide off target. It is always advisable to spray with at least a slight positive wind speed to avoid significant movement onto susceptible crops. Contamination of rice floodwater resulting from herbicide application is unavoidable with certain rice production systems. Treated floodwater in these systems should be maintained on the field or paddy until the herbicide has dissipated to avoid contaminating nontarget water supplies and to maximize the effect of the herbicide for controlling the weeds in the treated field. In some rice-producing systems, tail or drainwater leaving a rice field may be reused to irrigate other crops. This practice may cause injury to that crop or result in illegal residues if the herbicide has not dissipated from the water prior to its use on the crop being irrigated. Even discharging water containing herbicide into drainage systems should be controlled, as these systems often provide habitat for aquatic organisms that may be affected by the herbicide or are food for other organisms and the herbicide may thus enter the food chain. The potential for herbicides used in rice floodwater to leach through the soil profile and enter the groundwater is always present. Whenever possible, select herbicides that have low water solubility, high adsorption to soil colloids, and relatively short soil residual time (no longer than is required to provide the desired amount of weed control). Be aware of water movement patterns through the soil profile, and avoid treating areas with high percolation rates if it is possible for the herbicide to be leached through these soil profiles to the groundwater table. TRANSPLANTED RICE

Transplanting is the most widely used cultural system for producing rice (Fig. 8-2). Competition from weeds is generally less in this than in other rice culture methods because the rice plants are established in a transplant bed and grown to the three- to four-leaf stage before being transplanted

294

RICE: PRODUCTION

Seedbed Preparation -> Irrigation-> Transplanting-> Pesticide Application-> Harvesting (Plowing) (Puddling) (Herbicide) (Harrowing) (Insecticide) (Fertilizer) (Fungicide)

Figure 8-2. Generalized production scheme for growing transplanted rice showing major input areas.

into a weed-free paddy or field. Under these conditions the rice plant has a major head start on any germinating weed seeds. When rice plants free of weeds are planted, weed control becomes easier whether it is accomplished by mechanical or chemical methods. Good seedbed preparation should always be the first consideration of any rice weed management program. The seedbed should be weed-free at the time of planting and prepared in a manner that will enhance the growth and development of the rice plant and suppress the development of weeds as much as possible. Crop residues and weeds should be plowed under to a depth of 15 to 20 em. Plowing at shallower depths encourages the growth of both annual and perennial weeds. After plowing, the field should be flooded. One week later, two or three puddling operations are recommended at weekly intervals to reduce weed seedling establishment and to level the field. Puddling the field results in shifting the weed spectrum more toward broadleaf weeds than grassy weeds which predominate if the seedbed is prepared dry. The degree of weed infestation is directly related to the quality of seedbed preparation. The poorer the preparation, the more weeds will be present; the better the seedbed preparation, the fewer weeds will be present. Fertilizers should be applied in a manner and at a time when they will be most beneficial to the rice plant and least beneficial to the weeds. Fertilizer placed several centimeters below the soil surface will be less available to germinating weed seedlings. Growers frequently will fertilize their rice following the first cultivation or weeding operation to allow the rice to become established and to minimize weed growth and competition. Weeds are extravagant users of fertilizers and, unless controlled, will increase proportionately with increasing fertilizer rates. Rice is more competitive as plant density is increased. However, spacing may be limited by the method of weed control used. Wider spacings are necessary when mechanical implements are used. When herbicides are used, closer spacings are advantageous because the rice canopy will close in more quickly, enhancing competition for light which will allow the grower to use shorter soil residual herbicides or reduced herbicide

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Table 8-2. Major Herbicides Used in Transplanted Rice and Principle Weeds Controlled Herbicide

Primary Species Controlled

Oxadiazon Butachlor Piributycarb Pretilachlor Thiobencarb Chlomitrofen Dymron Bensulfuron-methyl Pyrazolate Pyrazoxyfen Bromobutide

Grass, broadleaf, sedge Grass Grass Grass Grass Grass, broadleaf, sedge Broadleaf, sedge Broadleaf, sedge Broadleaf, sedge Broadleaf, sedge Broadleaf, sedge

rates. Modern cultivars require more input into weed management than was necessary with the older, traditional cultivars. Water management is a major aspect of any weed control strategy. One major reason for flooding rice fields is to decrease weed problems. Many weed seeds are unable to germinate under flooded conditions, and exposing the soil after transplanting will increase weed seed germination. Once the field is flooded, the water should not be removed. Alternate wetting and drying of the soil encourages weed seed germination and seedling establishment. Good water management is essential in minimizing the influence of weed competition. Emerged weed populations decrease as water depth is increased. Weed control is enhanced under flooded conditions. Mechanical weeders work better in soft saturated soils when the weeds are 4 to 5 em or less in height. Hand pulling continues to be a major method of removing weeds in areas where the pulled weeds are used for fodder for animals. However, there tends to be a conflict where this occurs between early removal of the weeds to reduce competition with the rice plant and letting the weeds grow larger to provide more forage for the animals. Although water management is especially critical with the use of herbicides, maintenance of 4 to 5 em of floodwater is equally important for enhancing and maintaining weed control when using mechanical methods. Herbicides (Table 8-2) should not be used as the exclusive method of controlling weeds. A well-planned program integrating several control methods will provide the most economical and effective control and will retard the buildup of resistant weeds. Some herbicides ar~ registered for use prior to transplanting; however, the majority of herbicides are registered for post-transplanting use (see Fig. 8-3).

296

RICE: PRODUCTION

Chlornitrofen + Thiobencarb Dymron Oxadiazon

t

Seedbed Preparation __,. Puddling__,.

t

Transplanting---~

i

Harvesting

I Butachlor Bensulfuron-methyl Bromobutide I Piributycarb + Pyrazolate + Dymron Pyrazoxyfen Pretilachlor Thiobencarb Figure 8-3. Herbicide application timing in transplanted rice culture.

The list of major weed problems in transplanted rice (Table 8-3) is not complete and will vary from region to region as a result of crop rotations, environment, weed management, etc. Weeds are opportunistic and invade any niche where resources are available. However, if the crop is wellestablished, competition that would reduce rice yield will come too late, and the major impact will occur in grain quality and harvesting. Application of any herbicide presents an environmental concern, especially if it is applied to water. Caution should be used when applying herbicides in paddy floodwater to avoid movement of the herbicide into groundwater or to keep treated water from contaminating other water as it drains from the treated paddy.

Table 8-3. Ten Common Weeds Infesting Transplanted Rice Fields Scientific Name

Common Name

L!fe Cycle

Echinochloa oryzoides Echinochloa crus-galli Scirpus juncoides Cyperu.1· rotundus Cyperu.1· d!fformis

Early watergrass Barnyardgrass Rush Purple nutsedge Smallftower umbrella sedge Arrowhead Monochoria False pimpernel Indian toothcup Ammannia

Annual Annual Perennial Perennial Annual

Sa[?itaria py[?mae Monoclwria vaf?inalis Lindernia pyxidaria Rota/a indica Ammannia sp.

Perennial Annual Annual Annual Annual

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297

UPlAND RICE

Although rice yields are lower in upland rice culture (Fig. 8-4) than in other cultures where the rice is flooded during the growing period, approximately 10 to 15% of the total rice area is devoted to growing upland rice. Weed management programs vary largely from country to country, ranging from highly mechanized systems to individually operated systems utilizing human and animal labor. Besides unpredictable rainfall, inadequate weed control is the major cultural characteristic limiting upland rice yields. The problem weeds are more diverse in upland rice than in flooded rice cultures. Most of the major weeds are C4 plants which are extremely competitive (Table 8-1), and because floodwater levels are not maintained, grass weeds tend to predominate. Because of variation in edaphic and climatic conditions and the varied agriculture in the upland rice-growing regions, weed problems vary widely. Table 8-4 lists 10 of the common weed problems in upland rice. The time of emergence and number of weeds depends on soil moisture. Because the weeds start growing with the rice, the intensity of the weed problem may be extreme, resulting in 80 to 100% rice yield loss. The cost

Land Preparation---> Fertilizer---> Seed---> Fertilizer---> Weed Control-> Harvesting (Plow and Harrow) (Dibbled) (Slash-and-Burn) (Broadcast) (Drilled)

Figure 8-4. Generalized production scheme for growing upland rice showing major input areas.

Table 8-4. Ten Common Weeds Infesting Upland Rice Fields Scientific Name

Common Name

Life Cycle

Echinochloa colona Cyperus rotundus Eleusine indica Cyperus iria Cynodon dactylon Rottboellia exaltata Echinochloa crus-galli Ageratum conyzoides Digitaria sanguinalis Portulaca oleracea

Junglerice Purple nutsedge Goosegrass Rice flatsedge Bermudagrass Itchgrass Bamyardgrass Tropic ageratum Large crabgrass Common purslane

Annual Perennial Annual Annual Perennial Annual Annual Annual Annual Annual

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Table 8-5. Major Herbicides Used in Upland Rice Culture and Principle Weeds Controlled Herbicide

Primary Species Controlled

Butachlor 2,4-D, MCPA Propanil Oxyfluorfen Oxadiazon Thiobencarb Pendimethalin Piperophos-dimethametryn Bifenox

Grass Broadleaf, sedges Grass Grass, broadleaf Grass, broadleaf Grass Grass, broadleaf Grass, broadleaf Grass, broadleaf

of the weed control program, whether it be handweeding, mechanical cultivation, or the use of herbicides, must be carefully evaluated in terms of the resulting yield increase. The rain-fed environment where upland rice is grown is so varied that land preparation differs from area to area. In rain-fed rice-growing regions, the land is generally left fallow during the dry season and plowing and harrowing begins at the beginning of the rainy season. Weed growth should be kept under control during the dry season by harrowing or by the use of herbicides to prevent the weeds from completing their life cycle and producing large numbers of seed. The land should be deeply plowed (approximately 30 em) and harrowed to prepare the seedbed. Minimum tillage or no tillage practices have produced inconsistent results because of the rapid invasion of perennial weeds. The use of fertilizer has a major bearing on the weed management program. Weeds are extravagant users of both nitrogen and phosphorous. Both placement and timing of the fertilizer application are important in preventing the enhancement of weed growth and development and in maximizing the benefit in terms of rice yield. With no or low weeding levels, rice yields will be unaffected by increasing fertilizer levels, and weed biomass will be significantly enhanced. However, with an effective weed management program, it is possible to enhance rice yields by increasing the rate of fertilizer. Herbicide usage (Table 8-5) in upland rice has been limited in many areas due to the cost of herbicides, their application, and lack of predictable control. Figure 8-5 illustrates application timings for some of the major herbicides. Weed seedling emergence is strongly influenced by the frequency and amount of rainfall, and competition can be critical during the early growth

WEED MANAGEMENT

Land

Preparation--~

i

Preplant Incorporated Herbicide

299

Seeding - - - - - - - - . . . ; . Harvesting

i

Preemergence Herbicide

i

Postemergence Herbicide

Figure 8-5. Herbicide application timing in upland rice culture.

and development of the rice plant. Since more weeds emerge under high moisture levels than low moisture levels and moisture levels may fluctuate widely during the cropping season, a combination of control methods will be the most effective and economical. Herbicides applied on dry soil or followed by an extended dry period will be less effective than those applied to moist soil or followed by rainfall. However, excessive rainfall can leach the herbicide into the rooting zone of the developing rice plant and may injure the rice plant. Where upland rice is grown on a large scale or where economics permit, the use of herbicides has been increasing. Preemergence applications that control weeds during the period of rice seedling establishment eliminates weed competition during the most critical period of rice plant development and may conserve moisture and nutrients for the rice plant. Postemergence applications allows the grower to assess the weed problem before investing in the herbicide; however, often the weed problem is too advanced, and the benefit of using a herbicide is much reduced. Because of the expense of the herbicide, the availability of cheap labor, and the unpredictability of the weather, hand and mechanical weeding are still the most widely used weed control methods in upland rice culture. Although the timing for physical weed control varies, the first weeding generally occurs early in the seedling stage, approximately 3 weeks after seeding. Integration of more than one proven method of weed control is the best weed management system for upland rice. Rotating crops and varying weed control methods will prevent the buildup of species resistant or tolerant to a specific practice and will tend to reduce perennial weed problems. Applications that allow the herbicide to escape into the environment should always be avoided. Caution should be used to prevent drift from contaminating nearby crops or allowing the herbicides to reach surface or groundwater. Sound integrated weed management programs tend to minimize these problems.

300

RICE: PRODUCTION

WATER-SEEDED RICE Water-seeded rice culture (Fig. 8-6) was developed as a method for reducing weed problems where dry-seeding rice had encouraged the development of a major grassy weed problem. This culture requires high energy input while minimizing labor input and is increasing in popularity throughout much of the world. Cultural methods for weed control are essential parts of a successful integrated weed management program in water-seeded rice. Every management practice affects the competitive ability of both the rice and weeds. In this system, a good integrated pest management program is essential for satisfactory weed control as neither herbicides nor cultural practices alone can provide satisfactory weed control. The rice seedbed should be tilled 15 to 20 em deep as early as possible to allow sufficient time for crop residue decomposition and to allow the seedbed to dry. The seedbed should be left in a cloddy condition with clod sizes ranging from 4 to 7 em in diameter. Large clods or high spots in the field that are exposed above the water surface (Fig. 8-l) are excellent sites for grassy weeds to become established. Smooth, compacted fine textured seedbeds favor germination and establishment of small seeded weeds. A dry seedbed is desirable because weed seeds cannot germinate and become established until the soil is flooded, which is just prior to seeding. Nitrogen and phosphorous fertilizers should be incorporated into the soil 5 to I0 em deep to reduce the availability of the nutrients to weed seedlings that germinate near the surface and to algae that forms on the soil surface. Proper water management is a major component of a successful weed control program in water-seeded rice and laser leveling has improved the precision for water manipulation. A continuous water depth of 10 to 20 em is essential for reducing the severity of competition from weeds. Lowering the floodwater or growing rice under upland conditions favors competition from grass, sedge, and many broadleaf weeds. Exposure of soil

Land preparation ~ (Plowing) (Leveling) (Fertilizer)

Irrigation ~ Fertilize~ Seed~ (Flood) (Soaked or Weighted Seed)

Harvest

Figure 8-6. Generalized production scheme for growing water -seeded rice showing major input areas.

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Table 8-6. Herbicides Commonly Used for Weed Control in Water-Seeded Rice Herbicide

Primary Species Controlled

Molinate Thiobencarb

Grass Grass, some broadleaf and sedges Grass, broadleaf, sedge Broadleaf, sedge Broadleaf, sedge Broadleaf, sedge

Propanil Bensulfuron-methyl Bentazon MCPA, 2,4-D

to air as a result of draining a rice field greatly increases the diffusion of oxygen into the soil. This increase in oxygen concentration in the soil initiates the germination of many weed seeds that otherwise would not have germinated. A continuous flood restricts oxygen diffusion into the soil and contributes to a reduced-oxygen or anaerobic environment. Floodwater alone, maintained 8 to 10 em deep, will provide partial control of many weeds, especially grassy weeds, if water temperature is in the range of 20 to 30°C. Herbicides have become an integral part of weed management programs in water-seeded rice. To be effective, they must be used in combination with good cultural and water management practices. The list of herbicides (Table 8-6) available for use in water-seeded rice is limited because of the restrictions associated with this system of growing rice. If the herbicide is applied preflood, it may be leached into the soil profile; however, if the herbicide is applied after flooding, its movement into the soil profile will be limited because of limited percolation of water through the heavy impervious clay soils commonly associated with rice culture. When the rice seed is dropped into the water, it comes into direct contact with the herbicide, eliminating several of the bases for selectivity (i.e., placement). Herbicides for a continuous-flood system are restricted to (1) the preplant type applied to dry soil before flooding and possibly incorporated into the soil or applied following flooding but before seeding; (2) the postplant type applied before the weeds and/or rice plants emerge above the water; and (3) the postplant type applied after the weeds and rice plants have emerged above the water surface. Herbicides should be applied during the early growth stages of the rice plant, approximately the first 30 days following seeding or when the rice plant is still in the vegetative phase and the major yield components either have not been initiated yet or are just being developed. Competition from weeds (Table 8-7) is most limiting during this period. Each herbicide controls a slightly different spectrum of weeds and should be selected on

302

RICE: PRODUCTION

Table 8-7. Ten Common Weeds Infesting Water-Seeded Rice Fields Scientific Name

Common Name

Life Cycle

Echinochloa oryzoides Cyperus difformis

Annual Annual

Scirpus species

Early watergrass Smallflower umbrella sedge Bulrush

Ammannia species Heteranthera limosa Sagittaria species

Ammannia Ducksalad Arrowhead

Leptochloa fascicularis Bacopa species Alisma species Potamogeton species

Bearded sprangletop Waterhyssop Waterplantain Pond weed

Annual, Perennial Annual Annual Annual, Perennial Annual Annual Annual Perennial

the basis of this activity. This is why it is important to keep records on weed infestations from previous years. All herbicides can be phytotoxic to rice plants when used improperly or under certain environmental conditions. Hot weather may enhance uptake and/or cause contact burn, resulting in injury to the rice plant and frequently reduced weed control. Cool temperatures reduce the effectiveness of all rice herbicides. One of the most important considerations when using herbicides is the timing of the application. To be effective and not injure the rice plant, herbicides must be applied at the proper growth stage of both crop and weed. If applied at other stages of growth, the herbicide may injure the rice plant or provide poor control of the weed. Figure 8-7 provides examples of proper growth stages of rice when certain herbicides may be applied without injuring rice. Figures 8-8 and 8-9 show when these herbicides should be used to be most effective for controlling two of the major weed problems. If the correct stage of growth of the rice and proper stage of weed development do not occur simultaneously for a specific herbicide, be prepared to select an alternative; otherwise, the use of the herbicide may injure the rice and/or provide less than optimal results. Poorer control or higher herbicide rates are frequently associated with foliar applied herbicides in continuous-flood rice because the weedy plants are physiologically more advanced by the time sufficient foliage has emerged above the water surface and sufficient herbicide is not absorbed and translocated to kill the plants. To spray less developed plants, the floodwater level must be manipulated in such a manner as to expose the weed foliage of these younger plants so sufficient herbicide can contact the foliage for uptake and translocation.

WEED MANAGEMENT

303

Rice

i germ1nat•on

j prellood

~rrT

td

t1ler ll'lltlahon

n~

pan•ete 1M1aoon

flowenng

MOUNATE BENSULFURON

ii:Oel :l4~11f·i;!:

MCPA

Figure 8-7. Rice development in relation to when herbicides should be applied.

If these herbicides are not applied at these times, they may injure rice or provide less than optimal control. Propanil may be used as early as third leaf stage if weather is cool. In hot weather, leaf burn may occur. Adapted from Bayer et al. (1983).

BARNY ARDGRASS (Watergrass)

q

germonabon

1 leal

2 leal

3teat

41eal

51eat

elongation

THIOBENCARB MOLINATE PROPANIL

Figure 8-8. Stages of barnyardgrass or watergrass development and herbicide

timing for most effective control. If propanil is applied earlier than this, floodwater must be lowered to expose foliage . From Bayer et al. (1983).

304

RICE: PRODUCTION

Smallflower Umbrella Sedge

1s1 10 3rd leal

4Ulleal

THIOBENCARB BENSULFURON BENTAZON MCPA

conuol • kJU

c:=:::J

bum back only

[PROPANIL

Figure 8-9. Herbicide application timing for smallflower umbrella sedge at various growth stages. Adapted from Bayer et al. (1983).

Proper application procedures are essential if herbicides are to be used successfully. Prevent unwanted release into the environment. Hold treated water on field or in paddy until the herbicide dissipates to enhance weed control and to eliminate contamination of other water. DRY SEEDING AND FLOODED RICE

The most effective weed control system must integrate preventive, cultural, mechanical, chemical, and biological methods of weed control. Omission of one or more of these components frequently results in less than optimal control. Conditions favorable for growing rice in this system are also favorable for the growth and development of many terrestrial weeds, especially grasses that will tolerate flooding after germination, as well as aquatic and semiaquatic weeds (Table 8-8). Broadcast seeding and drill seeding rice into narrow row spacings eliminates most opportunities for cultivation after the rice emerges. Both the density of weeds in a rice field and the duration of time weeds are allowed to compete with the rice plant are important in weed-rice

WEED MANAGEMENT

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Table 8-8. Ten Common Weeds Infesting Dry-Seeded and Flooded Rice Fields Scientific Name

Common Name

Life Cycle

Echinochloa crus-galli Commelina di.ffusa Ipomoea sp. Oryza sativa L. Aeschynomene sp. Heteranthera sp. Ammannia sp. Leptochloa sp. Brachiaria platyphylla Sesbania exaltata

Barnyardgrass Spreading dayfiower Morning glory Red rice Join tv etch Ducksalad Ammannia Sprangletop Broadleaf signalgrass Hemp sesbania

Annual Annual Annual Annual Annual Annual Annual Annual Annual Annual

competition. Most terrestrial weeds germinate in moist soil prior to flooding while aquatic weeds germinate and grow after the soil is flooded. The complexity of these weed mixtures vary from country to country and from field to field. Thorough seedbed preparation is as important in dry seeding and flooding systems as it is for all rice-producing systems, and the goal is the same: to eliminate and suppress the growth and development of weeds and to enhance the establishment and development of the rice crop (Fig. 8-1 0). Repeated cultivations during seedbed preparation reduce such terrestrial weeds as barnyardgrass. The last cultivation should be shallow, approximately 5 em deep, to avoid bringing buried weed seeds to the soil surface where they may germinate. Drying of the soil prior to seeding is an effective method for preventing germination and establishment of seedling weeds and discourages development of many perennials. However, in many areas or years, rainfall prevents sufficient drying of the

Land Preparation ......, Seeding ......, Irrigation ......, Fertilizer......, Flooding......, Harvest (Plowing) (Disking) (Harrowing) (Rotary Tilling)

Figure 8-10. Generalized production scheme showing major input areas for growing rice using dry-seeded and flooded methods.

306

RICE: PRODUCTION

Table 8-9. Common Herbicides Used in DrySeeded and Flooded Rice Systems Herbicide

Primary Species Controlled

Propanil Molinate Benthiocarb MCPA, 2,4-D Bentazon Pendimethalin Butachlor

Grasses, broadleaf, sedges Grasses Grasses, some broadleaf and sedges Broadleaf, sedges Broadleaf, sedges Grasses, broadleaf Grasses, broadleaf, sedges

soil and germination and growth of weeds are continuous, reducing the effectiveness of this technique. Rice may be drilled or broadcast and disked or harrowed to cover the seed with soil. This method of rice culture has become more popular with the advent of safe and effective herbicides that will selectively control the weedy grasses. When short-statured varieties are planted, weed control becomes more critical because these short-statured cultivars do not compete with weeds as effectively as the tall and leafy varieties. Since most weed seeds germinate at or near the surface of the soil, placing phosphate fertilizer below the drilled rice seed is an effective method for making it readily available to the rice seedling and less available to the weeds. In fields with light weed infestations, fertilizer applications may be delayed until just prior to flooding to take advantage of the inhibition of weed growth resulting from flooding. Although some herbicides (Table 8-9) may be used before the rice has been planted, most herbicides are applied preemergence or postemergence to the rice plants (Fig. 8-11). Combinations of pre- and postemergence herbicides have been particularly effective where the postemergence herbicide controls the weeds that are present, and the preemergence herbicide, in combination with the floodwater, will control the subsequent

Postemergence Preplant Preemergence Postemergence + Preemergence ~

Land Preparation ~

~ Seed~

~ Irrigate~

~ Flood~

Harvest

Figure 8-11. Generalized production scheme showing primary application timings for herbicide usage.

WEED MANAGEMENT

307

germinating weed seedlings. As with any application of herbicide, caution should be exercised to prevent movement of the herbicide off the treated field, whether in the atmosphere as drift or in the floodwater.

OTHER RICE-PRODUCING SYSTEMS

There are many other systems for growing rice, and well-planned and executed weed control programs are critical for maintaining adequate yields of rice grain. Since most other methods for producing rice are reasonably close variations of the systems described, the principles discussed can be extrapolated to the new system. Before a herbicide can be used for weed control in rice, it must be registered for that use. The label will provide precise instructions for its application. Always read the herbicide label and follow the label instructions. Additional instructions can be obtained from local authorities and should be relied on when available.

REFERENCES Ahmed, N. 1981. Plant height as a varietal characteristic in reducing weed competition in rice. Int. Rice Res. Newslett. 6:3. Barker, R., and Y. Hayami. 1983. Weed control practices as a component of rice production systems, 37-46. Los Banos, Philippines: Int. Rice Res. Inst. (IRRI). Barrett, S. 1984. Rice mimicry in barnyardgrass. Weeds Today 15:6. Barrett, S., and F. Wilson. 1981. Colonizing ability in the Echinochloa crus-galli complex (barnyardgrass) I. Variation in life history. Can. J. Bot. 59:1844-60. Barrett, S., and F. Wilson. 1983. Colonizing ability in the Echinochloa crus-galli complex (barnyardgrass) II. Seed biology. Can. J. Bot. 61:556-62. Bayer, D., J. Hill, D. Seaman, and B. Fischer. 1983. Weeds. In Integrated pest management for rice, ed. M. Flint, 27-48. Div. of Agric. Sci., Univ. of Calif. Publ. 3280. Bhan, V. 1983. Effects of hydrology, soil moisture regime, and fertility management on weed populations and their control in rice, 47-56. Los Banos, Philippines: IRRI. Bouhache, M. 1989. Barnyardgrass complex (Echinochloa sp.) in rice: Taxonomy and comparative photosynthesis, growth, and competitive ability. Ph.D. diss., Inst. Agronomique et Veterinaire, Hassan II, Morocco. Castin, E., and K. Moody. 1989. Effect of different seeding rates, moisture regimes, and weed control treatments on weed growth and yield of wet-seeded rice. Proc. Asian-Pacific Weed Sci. Soc. 12:337-44. Chadoeuf-Hannel, R., and R. Taylorson. 1985. Enhanced phytochrome sensitivity and its reversal in Amaranthus a/bus seeds. Plant Physiol. 78:228-31.

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RICE: PRODUCTION

De Datta, S., and R. Herdt. 1983. Weed control technology in irrigated rice, 89-108. Los Bafios, Philippines: IRRI. De Datta, S., and M. Llagas. 1982. Weed problems and weed control in upland rice in tropical Asia. In Proc. 1982 Bouake, Ivory Coast, Upland Rice Workshop., 321-41. Los Bafios, Philippines: IRRI. De Datta, S., and V. Ross. 1975. Cultural practices for upland rice. In Major research in upland rice, 159-83, Los Banos, Philippines: IRRI. Edwards, G., and D. Walker. 1983. C3 and C4 : Mechanisms, and cellular and environmental regulation ofphotosynthesis. Boston: Blackwell Scientific Publications. Gupta, P., and J. O'Toole. 1986. Upland rice-A global perspective. Los Banos, Philippines: IRRI. Harper, J. 1977. Population biology of plants. New York: Academic Press. Hill, J., and D. Bayer. 1990. Integrated systems for rice weed control. Proc. California Weed Conf. 42:85-89. Ibrahim, T. 1989. Integrated weed control in rice. In Rice farming systems-New directions, 161-66. Manila, Philippines: IRRI. Int. Rice Res. Inst. (IRRI). 1983. Weed control in rice. Los Banos, Philippines: IRRI. Kim, S., and K. Moody. 1989. Growth dynamics of rice and several weed species under density and fertilizer stresses. Proc. Asian-Pacific Weed Sci. Soc. 12:47-56.

Kovach, D. 1986. Germination responsiveness of barnyardgrass (Echinochloa crus-galli var. oryzicola) to light, temperature, and anaerobiosis. M.S. thesis, Univ. of California, Davis. Le Strangle, M. 1986. Competition between rice (Oryza sativa) and barnyardgrass (Echinochloa sp.): The influence of rice stature, barnyardgrass density, and nitrogen fertility. M.S. thesis, Univ. of California, Davis. Matsunaka, S. 1983. Evolution of rice weed control practices and research: World Perspective. In Weed control in rice, 5-18. Los Banos, Philippines: IRRI. Matsunaka, S., and H. Saka. 1977. C3 and C4 plants-classification and weed control (in Japanese). Weed Res., Japan. 22:131-39, 177-83. Michael P. 1983. Taxonomy and distribution of Echinochloa species with special reference to their occurrence as weeds of rice, 291-306. Los Banos, Philippines: IRRI. Migo, T., and S. De Datta. 1984. Chemical control of Rottboellia exaltata in upland rice (Oryza sativa). Philippine J. Weed Sci. 11:83-93. Moody, K., and D. Drost. 1983. The role of cropping systems on weeds in rice, 73-88. Los Banos, Philippines: IRRI. Moody, K., S. De Datta, V. Bhan, and G. Manna. 1986. Weed control in rainfed lowland rice. In Progress in rainfed lowland rice, 359-70. Los Banos, Philippines: IRRI. Mukhopadhyay, S. 1983. Weed control technology in rainfed, wetland rice, 109-18. Los Banos, Philippines: IRRI. Nantasomsaran, P., and S. De Datta. 1988. Effect of cultivar, rotovation interval and nitrogen fertilizer management on weed control in upland rice. In Proc. 2nd Tropical Weed Science Conf. 2:128-46.

WEED MANAGEMENT

309

Pathak, A., S. Sankaran, and S. De Datta. 1989. Effect of herbicide and moisture level on Rottboellia cochinchinensis and Cyperus rotundus in upland rice. Tropical Pest Management 35:311-5. Radosevich, S., and J. Holt. 1984. Weed ecology-Implications for vegetation management. New York: Wiley. Sankaran, S., and S. K. De Datta. 1985. Weeds and weed management in upland rice. Advances in Agron. 38:281-336. Sarkar, P., and K. Moody. 1983. Effects of stand establishment techniques on weed population in rice, 57-72. Los Banos, Philippines: IRRI. Smith, R. J., Jr. 1983. Weeds of major economic importance in rice and yield losses due to weed competition. In Weed control in rice, 19-36. Los Banos, Philippines: IRRI. Smith, R. J., Jr., W. T. Flinchum, and D. E. Seaman. 1977. Weed control in U.S. rice production. Washington, DC: U.S. Dept. Agric., Agric. Handbook 497. Swarbrick, J. 1989. Major weeds of the tropical South Pacific. Proc. Asian-Pacific Weed Sci. Soc. 12:21-30. Willson, J. 1979. Rice in California. Richvale, CA: Butte County Rice Growers Assoc. Yakuno, T. 1983. Weed control technology in rainfed wetland rice, 109-18. Los Banos, Philippines: IRRI. Yamasue, Y., A. Nakamura, K. Ueki, and T. Kusanagi. 1989. Drought resistance for the habitat segregation in Echinochloa weeds. Japan J. Breed. 39:159-68. Yamasue, Y., T. Tanisaka, and T. Kusanagi. 1990. Alcohol dehydrogenase zymogram, its inheritance and anaerobic germinability of seeds of Echinochloa weeds. Japan J. Breed. 40:53-61. Yamasue, T., Y. Asai, K. Ueki, and T. Kusanagi. 1989. Anaerobic seed germination for the habitat segregation in Echinochloa weeds. Japan J. Breed. 39:159-68. Zimdahl, R. 1980. Weed-crop competition-A review. Corvallis, OR: Int. Plant Protection Center.

9 Harvest Drying/ and Storage of Rough Rice C. Y. Wang Nabisco Brands, Inc.

Bor S. Luh University of California, Davis

The importance of postharvest management of food grains is underscored by the fact that large food losses occur in the world due to poor grainhandling techniques. Therefore, the harvesting, drying, and storage of rice should receive serious attention. This chapter provides some guidelines for achieving this goal. The harvesting of rice is carried out by manual labor in most ricegrowing countries. On the other hand, combines are used to harvest and thresh rice in developed countries with mechanized agriculture. The section on harvesting in this chapter addresses the mechaniZed rice harvesting conditions prevalent in California. Pillaiyar (1988) has discussed postharvest operations in underdeveloped countries. Rice processing consists of several unit operations such as drying, husking, milling, and polishing. During these operations, various parts of the kernel are removed. Over the years, a terminology has developed to describe the grain at different stages in the process. The grain, after it comes from the field, is called rough rice or paddy. Amounts of rough rice may be expressed as bags (100 lb), bushels (45 lb), or barrels (162 lb). After the hull or husk is removed, the product is called brown rice. Milled or white rice is what remains after the bran and part of the germ have been removed during milling. White rice is composed of whole and broken kernels. Whole kernels are referred to as head rice, and head yield is the 311

312

RICE: PRODUCTION 100 kgs ROUGH RICE

~

80 BROWN RICE

20 HULLS

10 BY-PRODUCTS

70 WHITE RICE

~

~

48 HEAD RICE

3

22 BROKEN RICE

POLISH

7 BRAN

~

8

10 SECOND SCREENINGS

4 BREWERS

Figure 9-1. Product fractions from standard milling of rice. From Henderson (1976).

quantity of unbroken kernels milled from a specified amount of rough rice. The various parts of rice during processing are shown in Fig. 9-1. An important quantitative factor in drying rice is moisture content. The measure of moisture content can be expressed as a wet-basis or a drybasis number. The wet -basis measure specifies the quantity of water in a solid as a percentage of the total wet weight. Thus, the percentage of wetbasis moisture content (%MCwb) is

%MCwb

=

total wet weight-~ry weight x 100 total wet weight

(l)

and the percentage of dry-basis moisture content (%MCdb) is

%MCdb

=

total wet weight~dry weight x 100 dry weight

(2)

The relationship between wet- and dry-basis moisture content is shown in Fig. 9-2. Moisture content expressed on a wet basis has traditionally been used by rice growers, drier operators, and processors. Dry-basis moisture content is generally used in research on drying rice because the denominator in the working equation is independent of the quantity of water in the grain.

HARVEST, DRYING, AND STORAGE OF ROUGH RICE

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RICE HARVESTING

Many factors must be considered to obtain an optimum rice harvest. The grain must be mature, high in quality, and have the proper moisture content. The soil should also be sufficiently dry to support the harvesting and field transport equipment. Careful planning can help to insure that these conditions prevail simultaneously. However, in spite of all precautions and the best planning, unusual or unexpected weather conditions may upset good harvesting. The cultivation of early maturing rice varieties may be desirable because they help to extend harvest periods and allow grain to be gathered under favorable weather and field conditions. In California, the rice head yields of early-maturing varieties may be reduced by high daytime temperatures and dry north winds that can dry the rice field rapidly and make it difficult to harvest the crop at an optimum moisture content. Late-maturing varieties are not exposed to the extreme variations in the day-night temperatures and humidities that cause rapid field drying. Preharvest Quality

The preharvest quality of paddy rice helps its postharvest quality, which in turn determines the income rice growers receive in the United States. Maximum head yields are next to crop yields in economic importance. The physical quality of rough rice is dependent on variety, stage of maturity at harvest, moisture content, and physical damages (impact, abrasion, and

314

RICE: PRODUCTION

stress) caused during the harvest, handling, transport, processing, and storage of the grain. All varieties of rice tested in California reach a maximum head rice yield at a moisture content slightly higher than when maximum crop yield occurs. Variety, day and night grain temperatures during the maturing period, planting rates, germination rates, water management, plant population, and weed competition all affect the uniformity of maturation and consequent grain quality. Rice is harvested at 20 to 27% MCwb in most countries. Rice does not mature simultaneously in an entire field, an individual plant, or even on individual panicles. Chau and Kunze (1982) measured the moisture contents of grains from a rice plot during a harvesting period. They found that differences of 1S to 20% MCwb existed between panicles in the same plot. If the harvest were delayed until all kernels were mature, the earlymaturing kernels would become overripe and the overall quality would decrease. Overripe kernels, generally identified by moisture contents below 22% MCwb for early-maturing varieties in California, are subject to field cracking if not harvested promptly when they are mature. Most early-maturing rice grown in California should be harvested at an average moisture content of 24 to 26% MCwb when the highest daytime temperatures are over 23.9°C (7S°F). Later in the season (after October 10 in California), when maximum daily air temperature drops below 23.9°C (7S°F), the late-maturing rice varieties can be harvested at low cylinder speed (609.6 m/min) even wheh the grain moisture content is as low as 13 to 14% MCwb and still maintain high head rice yields. Research on rice grown in the southern United States, India, Surinam, and the Philippines shows that most varieties have reduced head yields after reaching a certain maturity. Kunze (1979) demonstrated that the exposure to varying temperatures and humidities results in lower head yield as lower moisture contents are reached. It appears that harvesting procedures should be determined for each variety grown in each climatic region. Appropriate harvest timing, harvester cylinder speed, and clearance adjustments should be prescribed to minimize impact damage in the harvester at various stages of maturity. Harvest Preparation

Various harvest-relatedfactors such as variety, planting time, local weather patterns, soil type, field water temperature and management, and date of heading affect maturity. After the planting date is fixed, the next critical observation regarding harvest is the date of the "first heading" when approximately 10% of rice heads have emerged. In California, crops of average yield should bereadyfor harvest4S toSS days after the first heading. Tropical

HARVEST, DRYING, AND STORAGE OF ROUGH RICE

315

rice is usually harvested 30days after flowering (50% flowering is considered as the first day), but in cooler climates maximum head yield is attainable by harvesting up to 60 days after flowering (Juliano I972). After the date of maturity is estimated, field draining is given primary consideration. This draining must be related to the maturation characteristics of the variety, the expected weather, the soil type, the field characteristics for draining surface water, and the effects of plant evapotranspiration on drying the soil surface. The proper selection of a draining date is important because the soil must be sufficiently dry to support the harvesting and transport machinery when the grain is ready to be harvested. The final decision for draining is made with the knowledge and experience of individual growers and farm advisors. If the field is drained too early, the rice plants will run short of moisture before maturing. After the field has been drained, the moisture content of rice is monitored as it reaches maturity. When draining, the moisture content may be 40 to 50% wb. The grain moisture content will drop approximately I% wb/ day when the grain has a high moisture content and the weather is hot and dry. When the weather is cool and overcast or the rice moisture content is 20 to 25% wb, the moisture loss may be as low as 0.5% wb/day. Rain or dew may cause an increase in grain moisture content. Harvesting should commence at 24 to 26% MCwb, particularly with early-maturing varieties harvested during hot dry periods in California. Minimum cylinder speed should be used except in an emergency, especially when moisture contents drop below 22% wb and daytime temperatures exceed 23.9°C (75°F). This precaution is not so important when the moisture content is 24 to 26% wb. Research carried out at the International Rice Research Institute (IRRI) on cylinder types and speeds indicates that about 25% of the kernels will be ruptured if the rice is at 22% MCwb and the cylinder speed is I280.2 m/min, compared to 5% at 609.6 m/min. Related work being conducted at the Agricultural Engineering Department at the University of California, Davis, indicates similar trends. A relationship appears to exist between the rate of drying resulting in internal kernel stresses and the potential for damage from impact in the cylinder of the rice harvester. Harvesting begins each day when the dew is off the plants. In California, this is usually at about IO to II A.M. Pacific Standard Time (PST). Harvesting is usually stopped when dew begins to form at 8 to 9 P.M. If the sky is overcast or a dry north wind has been blowing all night, these schedules may change. Operators will adjust the height of cut, forward speed, and reel speed to reflect changes in the height of the plants. Other factors affecting the harvesting operation include stem thickness, lodging, yield, and rice variety.

316

RICE: PRODUCTION

Figure 9-3. Combine in grain field with 4.87-m header.

Rice Harvesters

Rice harvesters have been developed over the years from the binders and stationary-type threshers used in the early days of grain threshing to selfpropelled combines that directly cut and thresh rice. Most of the major farm machinery manufacturers make grain harvesters for small-grain harvesting. With certain modifications and special traction units, headers, conveyors, straw walkers, and shoe design, these machines are used for rice harvesting. In use in California are combines designed and built specifically for harvesting rice. They are large, high-capacity, self-propelled combines with full track support that can generally operate under wet field conditions (Figs. 9-3 and 9-4). Two types of cylinders are available for rice harvesting in the United States. These are the rasp bar and the spike-toothed cylinder. Practically all rice in California is harvested with spike-toothed cylinders. This is partially due to the large volumes of straw produced in the high-yielding California rice fields and the easier cleaning a spike-toothed cylinder allows. In addition, the harvesting process may be a little more efficient with the spike-toothed cylinder in removing the grain from the straw.

HARVEST, DRYING, AND STORAGE OF ROUGH RICE

317

Figure 9-4. Rice combine with 5.48-m header.

Small Japanese harvesters often have wire loop cylinders which, for slowspeed cylinder operation with hold-on systems (the straw does not pass through the cylinder), result in an efficient harvest with a high-quality product. IRRI has been conducting research on axial-flow-type harvesters and stripper harvesters for a number of years. Axial-flow harvesters feed the grain and straw through inclined cylinder(s) mounted longitudinally in the harvester as compared to conventional cylinders that are mounted crosswise to the movement of the harvester. This method eliminates the conventional straw walker. Research on stripper harvesters, conducted at the University of California, Davis, indicates that they have the advantage of removing the grain from the plant without cutting the stem. This allows the grain to be removed at lower cylinder speeds with less grain damage. The total machinery and overall weight are considerably less than the conventional harvesters. These harvesters appear to operate well but have problems with lifting lodged rice and feeding it into the stripper cylinder. New shortstatured varieties that have more standing rice at harvest may improve the

318

RICE: PRODUCTION

prospects for this type of machine, although the shorter stem may create feeding problems. For the present, it appears that the conventional spike-toothed cylinder harvester, with suitable modifications made by manufacturers and growers, will be used for harvesting most of the rice in the highly mechanized agricultural areas of the world. Manual methods and small handfeed machine harvesters continue to be best suited for areas where rice is grown on small individual plots of ground and where labor is available. For more information on rice harvesting methods in developing countries, the reader may refer to Araullo et al. (1976) and Pillaiyar (1988). Postharvest Management

When widely varying maturity occurs in a rice field at harvest, the harvested grain should be quickly transported to the drier and given priority in the drying schedule. The importance of this has been demonstrated by Kunze and Parsad (1976). In their tests, grain ruptured in storage when high moisture kernels were stored in contact with low moisture kernels. The high humidity produced in the vicinity of the high moisture grain was sufficient to rupture low moisture kernels. This may occur within a few hours, depending on the moisture differentials. Field transport equipment has been developed for the bulk handling of rice. These units allow high-speed transport from the harvester to waiting trucks while keeping the harvester in continuous operation. Road transport trucks move the crop to the driers, since the rice moisture must be reduced from approximately 24 to 26% MCwb down to 13 to 14% MCwb for safe storage. The risk of heat damage (i.e., discoloration of milled rice grains, altered texture, rapid growth of microorganisms, and low milling yield) is always present in high-moisture rice and early transport to the drying facility is therefore important. RICE DRYING

Equilibrium Moisture Content

The equilibrium moisture content of rice, commonly abbreviated as EMC, refers to the quantity of moisture in the product when it is at equilibrium with the surrounding air. The EMC of rice will depend on the air temperature and humidity, grain variety, maturity, and previous history. In addition, EMC will depend on whether or not the rice had to adsorb or desorb moisture to achieve equilibrium. The EMC achieved by desorption will be higher than that achieved by adsorption. This phenomenon is referred to as a hysteresis effect.

HARVEST, DRYING, AND STORAGE OF ROUGH RICE

319

25

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Figure 9-5. Equilibrium moisture content of rough rice. From Pfost et al. (1976).

Zuritz and Singh (1978) reviewed various methods described in the literature for evaluating EMC. They experimentally determined constants in the following EMC equation for medium grain rough rice. Figure 9-5 shows EMC curves generated by Pfost et al. (1976). (3)

where RH TA T,

f

g k

relative humidity, decimal temperature (K) = 647.1K, critical temperature of water = -26.1911 = 4.49488 x Io-s = 2.2244 X 106

320

m Mep

RICE: PRODUCTION

= -2.4160 equilibrium moisture dry basis (percent)

Rough rice consists of an outer husk layer made of Si02 , a middle layer of fibrous bran, and an inner core of white rice (mostly starch and some protein). The EMC of rice obtained in laboratory is an overall average moisture content of these three different materials and is called the static EMC. During multipass drying operations, only the husks on the surface are at equilibrium with the local air temperature and relative humidity. To account for the differences, Wang (1978) used a dynamic EMC in the simulation of a thin-layer rice-drying process.

Rice-Drying Methods In this section different types of rice driers are discussed, and some recommendations for operating them are presented. Note that no single set of operating instructions applies to any particular type of drier. Establishing a drying procedure is a situational proposition; many factors such as ambient air conditions, the quantity of grain which has to be dried, and the expected use of the grain must all be considered. Drier operating methods established for a certain location, rice variety, and time of year may be inappropriate for another situation. Two types of mechanical driers are in use in various parts of the world: fixed-bed driers and continuousflow driers. Fixed-bed driers

Fixed-bed driers are used for complete on-farm drying, or for finish drying after the major step of moisture removal has been completed in a continuous-flow drier. After drying, these driers may also be used for grain storage. Two common types of fixed-bed driers used in California, having either circular or rectangular bins, are shown in Figs. 9-6 and 9-7. The depth of grain in fixed-bed driers may vary, but 4.3 to 6 m is the maximum practical depth (Henderson and Parsons 1974). Grain in a fixed-bed system is dried with forced air, which may or may not be heated. Grain quality and drying time are affected by the temperature and relative humidity of the drying air. Figure 9-8 indicates that the number of whole kernels in milled rice increases with the humidity of the drying air and decreases with the drying air temperature. Figure 9-9 shows the effect of air temperature and humidity on drying time. Circular bins (Fig. 9-6) are constructed with perforated floors, and a high-pressure area is created under the grain by a fan attached to the structure. Stirring devices may be added to the bin to aid drying by grain mixing. Drying air is pulled in from outside and forced up through the rice;

HARVEST, DRYING, AND STORAGE OF ROUGH RICE

321

. _. . . . . . . . . . ___ NL

Figure 9-6. Circular bin with stirring device.

the moistened air exits through the top of the bin. Supplemental heaters are usually added to systems of the type shown in Fig. 9-6. These heaters are used when the relative humidity of ambient air is too high to make it suitable for drying. When high-moisture air is used in a fixed-bed drier, it can rewet the rice and cause serious quality deterioration. Large rectangular bins (sometimes called flats) of the type shown in Fig. 9-7 are usually not designed with supplemental heating equipment. These systems are used for finish drying (removal of moisture after column drying) and storage of rice. The walls and floor of these structures are normally made of concrete. Large fans are located outside the bin and air distribution tunnels are placed from wall to wall on the floor of the bin. Maintaining the proper air flow when drying rice is vital. If the air flow is insufficient, the rice may spoil before the storage moisture content is reached. Rice provides a resistance to air flow that must be overcome by applying positive pressure at the air inlet to the grain or negative pressure at the air outlet. Resistance to air flow is evidenced as a drop in pressure as the air travels through the bed.

322

RICE: PRODUCTION

Figure 9-7. Rectangular bin for drying rice.

Continuous-flow driers

Most of the rice produced in the United States is dried commercially in continuous-flow driers. These driers use forced heated air as drying medium . Two common continuous-flow driers are the mixing and nonmixing types. A nonmixing columnar-type drier is shown in Fig. 9-10. The rice flows by gravity in a straight path between two screens. The grain flow rate is controlled by a variable-speed discharge roll. The grain is taken away from the drier with a screw conveyor. This drier is sometimes called a "cross-flow" drier because air is forced to flow across a moving bed of rice . The screens are generally 15.2 to 22.9 em apart, and the drier may be 12.2 m high and 3 to 3.7 m wide. The nonmixing column-type drier is probably the most common commercial rice drier in use today. A mixing-type columnar drier that uses baffles is presented in Fig. 9-11 . Another mixing-type drier designed at Louisiana State University is shown in Fig. 9-12 . In this drier , rice flows downward over inverted Vshaped air channels . Air flows in and out alternate rows of channels, and

HARVEST, DRYING, AND STORAGE OF ROUGH RICE

323

100

I" ~

thick

rice

bed

80

0

I I 0° F

Ui __J

74°C. BEPT is a varietal characteristic but can be affected directly by ambient temperature during grain development

PROPERTIES OF THE RICE CARYOPSIS

399

(Resurreccion et al. 1977). BEPT is estimated by the alkali test in which the chemical gelatinization of head milled rice in 1. 7% potassium hydroxide is read after a 23-h soaking. The degree of disintegration correlates negatively with BEPT (Juliano 1980). BEPT correlates with cooking time during boiling of rice. The extent of 2.2 N-hydrochloric acid corrosion correlates negatively with BEPT regardless of starch composition (Evers and Juliano 1976). Although maximum varietal spread of acid corrosion in 2.2 N acid at 35°C occurs after 4 days, corrosion rate levels off at about 15 days when residual starch ranges from 6 to 22%. Residual starch is directly affected by BEPT and amylose content (Juliano 1980). Amylopectin and Amylose

Rice starch is composed of a branched fraction (amylopectin) and a linear fraction (amylose). The major linkage is a-1,4-D-glucopyranosidic, but amylopectin contains, in addition, the a-1 ,6-D-glucopyranosidic linkage at branched points. The degree of branching of amylopectin is 4 to 5%; a mean chain length of 20 to 28 anhydroglucose units has been determined by periodate oxidation. Amylopectin is the major fraction of rice starch. In waxy rice, the amylose content ranges between 1 and 2% only. The amylose content of nonwaxy milled rice is classified as follows: low (10 to 20%), intermediate (20-25%), or high (25-33%). The amylose content varies directly with ambient temperature during grain development, particularly in low amylose rices (Resurreccion et al. 1977). It is usually determined by iodine colorimetry, and amylopectin can be calculated indirectly. The amylose:amylopectin ratio is the most important factor determining the eating quality or texture of cooked milled rice and rice cakes (Perdon and Juliano 1975b). Amylopectin interferes with amylose-iodine colorimetry at the pH 4.5 used in the simplified assay. By the use of a carbonate-bicarbonate buffer at pH 10.2, a deep blue color is obtained, as in the original Williams method, instead of the greenish blue at pH 4.5. In addition, similar absorbtance of starch-iodine color can be obtained at 590 and 630 nm. Residual fat or lipid in the endosperm, however, can reduce the iodine blue color probably by forming a helical complex with amylose; the decrease is more pronounced at pH 10.2 than at pH 4.5. "Absolute" amylose values are obtainable by defatting rice flour with a 95% ethanol reflux, or by ambient temperature defatting with water-saturated butanol (Bolling and El Baya 1975). Starch is normally prepared from milled rice by using 0.1 N sodium hydroxide or 1.2% sodium dodecylbenzene sulfonate-0.12% sodium sulfite to remove protein (Juliano 1984). Bound lipids (fat-by-hydrolysis) occur in rice starch at about 0.6 to

400

RICE: PRODUCTION

1.0% after ether extraction of0.6% lipids and are only extracted with 85% methanol or 95% ethanol, or with water-saturated butanol. Bolling and El Baya (1975) found lysocephalin in addition to lysolecithin in the butanolwater extract of milled rice, together with a variable amount of lecithin. Hirayama and Matsuda (1973) reported 61% of phospholipids of rice starch to be lysolecithin. Fractionation of Starch

Starch fractionation can be achieved by gelatinizing and dispersing starch, in water or dimethylsulfoxide-water, and the precipitation of amylose occurs with slow cooling after addition of 1-butanol, isoamyl alcohols or thymol (Juliano and Perdon 1975). Amylose can be further purified by recrystallization from 1-butanol saturated water. Preferably, the first crystallization is done with isoamyl alcohol or thymol to obtain pure amylopectin. Amylopectin is precipitated as amorphous powder from the mother liquor, with three to four volumes of ethanol. Waxy Rice Starch

Among waxy starches, molecular weight based on intrinsic viscosity and sedimentation constant correlates positively with BEPT (Perdon and Juliano 1975a). Gel consistency, which measures the relative rate of retrogradation of waxy rice gels, also correlates with BEPT. In waxy rice, gel consistency is best determined by dispersing 200 mg milled rice flour in 2 mL 0.15 N potassium acetate and measuring the length of the cooled gel after 30 min in a horizontal position. For rice cake, the rices with a BEPT of 64 to 66°C had better cake quality than those with a BEPT of 57 to 60°C. High-BEPT rices produce processed (gelatinized) products that harden faster during storage, particularly under refrigeration. Nonwaxy Rice Starch

Among nonwaxy starches, gel consistency correlates with molecular weight of amylopectin but is not simply correlated with BEPT (Juliano and Perdon 1975). Amylopectin contributes to a greater extent to gel consistency and viscosity than amylose. Gel consistency is determined in nonwaxy rices by dispersing 100-120 mg of flour in 2 mL 0.2 N potassium hydroxide and measuring the dispersion of the cooled gel. After 1 h in a horizontal position, the gel is scored as hard (27-40 mm); medium (41-60 mm); and soft (61-100 mm) (Cagampang et al. 1973). Hard gel consistency is observed exclusively in high amylose rices with high Brabender amylograph consistency (>400 Brabender units or BU) and setback (> 300 BU) and low BEPT. In the alkaliviscogram, those rices with hard gel consis-

PROPERTIES OF THE RICE CARYOPSIS

401

tency have exceptionally high peak viscosity (Suzuki and Juliano 1975). These rices also have a lower content of both amylopectin and the amylose soluble in boiling water (Maningat and Juliano 1978). They are generally less preferred than those of the same amylose content with a softer gel consistency (Juliano et al. 1974). Cellulose and Hemicellulose

The distribution of cellulose in brown rice is 62% in bran, 4% in the embryo, 7% in polish, and 27% in milled rice. High cellulose content in the bran is consistent with the thick cell walls of the pericarp, the seed coat, and the aleurone layer. The mean carbohydrate content for five milled rice samples was 89% starch, 0.4% pentosans, 0.3% sugars, and 0.4% dietary fiber. Brown rice contains 84% starch, 1.2% pentosans, 0.9% dietary fiber, and 0.7% sugars. The hemicellulose constituents of dietary fiber are highest in the rice bran. Leonzio (1967) reported 1.4 to 2.1% pentosans in brown rice, 0.6 to 1.1% in milled rice, 8.6 to 10.9% in bran, and 3.2 to 6% in polish. The embryo has 4.8 to 7.4% pentosans. The corresponding distribution of pentosans is 43% in bran, 8% in embryo, 7% in polish, and 42% in milled rice. Milled rice contains 0.02% water-soluble and 0.1% 0.5N-sodium-hydroxide-soluble hemicelluloses. Enzymic studies indicate that rice hemicelluloses are of the arabinoxylan type containing galactose in the bran polish fraction and galactose and glucose in the milled rice fraction. The water-soluble hemicelluloses are probably more branched arabinoxylans, as is evident from their higher arabinose:xylose ratio. Proteoglycans

Proteoglycans have been isolated and characterized from rice bran by Yamagishi et al. (1975, 1976). They are rich in hydroxyproline and arabinose. Pronase and hemicellulase hydrolysis of proteoglycans yielded a sugar-amino acid compound, 0-a-L-arabinofuranosyl hydroxyproline. Free Sugars

While the rice embryo and endosperm contain sucrose, glucose, and fructose, with small amounts of raffinose, free sugars are concentrated in the aleurone layer with higher levels in waxy (0.52%) than in nonwaxy (0.25%) rice (Singh and Juliano 1977; Pascual et al. 1978). The principal reducing sugars are glucose and fructose, together with melibiose and maltooligosaccharides.

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Phytin

Phytin or myo-inositol hexaphosphate salt is an important constituent of the aleurone layer and embryo. Reported phytate phosphorus contents are as follows: brown rice 0.21 to 0.28%; milled rice 0.04 to 0.06%; bran polish 2.0 to 2.6%, and embryo 0.8 to 1.9% (Juliano 1972b; Hayakawa 1977). At least 80% of the phosphorus content of brown rice, 90% of bran phosphorus, and 40% of the phosphorus in milled rice is phytate phosphorus. Phytate phosphorus in a nonwaxy Japanese rice accounted for 78% of the total phosphorus of brown rice, 38% of milled rice phosphorus, 94% of bran phosphorus, and 88% of embryo phosphorous. Nitrogenous Compounds Protein

The protein content of brown rice is about 8%, and that of milled rice is 6 to 7%. As the second major constituent of milled rice, it is the major protein source in the diets of tropical Asians. The factor 5.95 converts Kjeldahl nitrogen to rice protein based on the 16.8% nitrogen content of the major rice protein, glutelin. Milled rice protein consists of 5% albumin, 10% globulin, >80% glutelin (alkali soluble protein), and 38,000 had higher lysine content than the major subunits. The glutelin of the aleurone layer is similar in subunit composition to milled rice glutelin (Villareal and Juliano 1978). Those from the pericarp and embryo showed subunit compositions differing from milled rice glutelin. Of the four solubility fractions of endosperm glutelin, the major (74%) fraction extracted by 0.5 M sodium chloride-0.6% ,8-mercaptoetha-

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nol-0.5% SDS in 0.1 M sodium borate buffer pH 10 was closest in properties to glutelin. Prolamin- and globulinlike fractions are first extracted with the usual solvents in the presence of 0.6% ,8-mercaptoethanol. Free amino acids and nucleic acids

The major free amino acids in a developing rice grain include alanine, aspartic acid-asparagine, valine, glutamic acid, histidine, and ornithine, whereas the principal amino acids of rice protein are alanine, arginine, aspartic acid, glutamic acid, leucine, and valine. Free amino acids constitute 0.7% of brown rice protein, 0.2% of milled rice protein, 1.35% of bran polish protein, and 4.6% in embryo protein, equivalent to a distribution of 53% in embryo, 30% in bran polish, and 17% in milled rice. The nucleic acid of brown rice is mainly ribonucleic acid: 0.1 to 0.3% in brown rice, 0.9% in embryo, and 0.01% in milled rice (Juliano 1972b). The deoxyribonucleic acid content is about 0.01% in brown rice. Lipids

The lipids on the surface of the rice caryopsis had a composition of fatty acids and unsaponifiable matter closer to that of the rice hull than to bran and brown rice lipids (Hartmen and Lago 1976). It is present in spherosomes (lipid droplets) about 0.1 to 1 ~-tm in size in the embryo and the aleurone layer (Bechtel and Pomeranz 1977, 1978a). In the endosperm, the lipids are associated with protein bodies and starch granules probably in the membrane fraction as lipoprotein (Hirayama and Matsuda 1973). In addition to membrane lipids, the starch granules contain bound lipids (fatby-hydrolysis), mainly phospholipids, particularly lysolecithin. Tocopherols and Tocotrienols

The tocopherols are very important natural antioxidants present in rice. Ito et al. (1981) reported the presence of 10.3 ppm tocopherols in brown rice, 48.0 ppm in rice bran, and 7.0 to 9.4 ppm in milled rice. They used TLC, GLC, and HPLC chromatographic methods to separate and determine the levels of tocopherols on a fresh weight basis. Crude rice bran oil contains 19 to 46 mg a-tocopherol, 1 to 3 mg ,atocopherol, 1 to 10 mg y-tocopherol, and 0.4 to 0.9 mg a-tocopherol per 100 g oil (Kanematsu et al. 1983; Tanabe et al. 1982), plus 14 to 33 mg of a-tocotrienol and 9 to 69 mg y-tocotrienol per 100 g of oil (Tanabe et al. 1981, 1982). Refined rice bran oil contains fewer tocopherols, having 13 to 37 mg a-tocopherol, 1 to 2 mg ,8-tocopherol, 3 to 6 mg y-tocopherol, and 0.1 to 0.5 mg 8-tocopherol per 100 g oil (Kato et al. 1981; Tanabe et

PROPERTIES OF THE RICE CARYOPSIS

407

al. 1981, 1982; Kanematsu et al. 1983), plus 10 to 24 mg a-tocotrienol and 8 to 20 mg y-tocotrienol per 100 g of oil. The mean tocopherol content was 93 mg/100 g crude oil, and 50 mg/100 g refined oil. About 7% of the tocopherols are in the esterified form, and the remainder in the free form (Kato et al. 1981). Aromatic Compounds in Cooked Rice

Yajima et al. (1978) used glass capillary gas chromatography and mass spectrometry to identify the aromatic compounds in cooked rice. They analyzed the aromatic compounds in the steam distillate of cooked koshihikari rice by the GCMS method, and found 100 volatile compounds, including 13 hydrocarbons, 13 alcohols, 16 aldehydes, 14 ketones, 14 acids, eight esters, five phenols, three pyridines, and six pyrazines. Of these, 92 volatile flavor compounds were newly identified. Later study on kaorimai scented rice revealed the presence of an unknown compound (peak 41) and more indole than in koshihikari rice. a-Pyrrolidone was found in kaorimai but not in koshihikari (Yajima et al. 1979). Koshihikari rice contained more 4-vinylphenol, and 1-hexanal than kaorimai. Although the characteristic flavor compounds were not found, differences in the balance of volatiles were shown. In the rice bran, the major acid component in the steam concentrate is 4-vinylphenol, which has a characteristic unpleasant odor (Fujimaki et al. 1977). Of 146 compounds in the neutral and basic fractions, 2acetylthiazole and benzothiazole were considered the key compounds of the rice bran odor (Tsugita et al. 1978; 1979) These compounds decreased with an increase in the degree of milling of brown rice (Tsugita et al. 1980). Data from the odor evaluation tests and chromatographic analysis suggested that the volatiles of the surface layer of rice grain play an important role in the formation of the odor of cooked rice. The volatile sulfur compounds evolved from cooked rice are hydrogen sulfide, methyl mercaptan, dimethyl sulfide, n-butyl mercaptan (butane-1thiol), and dimethyl disulfide (Tsuzuki et al. 1978). The compound 2-acetyl-1-pyrroline has been identified as an important aroma component of cooked rice (Buttery et al. 1982). It is present at 0.04 to 0.09 J.tglg (dry weight) of aromatic milled rices and at 0.1 to 0.2 J.tglg of aromatic brown rices. Nonaromatic U.S. rices have less than 0.01 J.tg of 2-acetyl-1-pyrroline per gram. A consumer panel describes the odor of 2-acetyl-1-pyrroline as "popcorn like" (Buttery et al. 1983). Odor evaluation of the amount of popcorn like odor in the different rice samples ranked them closely in order of the concentration of this compound. The compound is relatively unstable but is more stable in aqueous solution.

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Pandan leaves (Pandanus amaryllifolius Roxb., fragrant screw pine), which have been added during cooking to impart aroma to nonaromatic rices contain 2-acetyl-1-pyrroline in freeze-dried leaves at 1 p.g/g. Vitamins and Minerals Vitamins

Vitamins are generally present at higher levels in brown rice than in milled rice (Table 11-5). The contributing factor is the concentration of vitamins in the embryo and aleurone layer. Thus, milling results in the loss of more than 50% of the vitamin B complexes of brown rice. Parboiled milled rice tends to have higher vitamin content than milled rice despite the partial thermal decomposition of vitamin during parboiling. Parboiling results in inward diffusion of water-soluble vitamins to the endosperm. Minerals

The mineral composition of rice grain depends considerably on nutrient availability of the soil in which the crop is grown. The ash distribution in brown rice is calculated to be 51% in bran, 10% in embryo, 11% in polish, and 28% irt milled rice. Iron, phosphorus and potassium show a similar distribution as total ash. However, some minerals, such as sodium and calcium show a relatively more even distribution in the grain (Table 11-6). Phosphorus and potassium are the major mineral elements of brown rice followed by silicon and magnesium. Distribution of mineral elements in the bran layers parallels closely the phytin distribution in the aleurone layer and scutellum, as shown by electron microprobe X-ray analysis (Tanaka et al. 1976). Changes During Grain Development

In nonwaxy rice there is an increase in amylose content during grain development, but in waxy rice a slight decrease in amylose content is noted (Singh and Juliano 1977). The X-ray diffraction pattern and BEPT of starch granules remain unchanged during development. Amylopectin shows a slight increase in intrinsic viscosity during grain development but no change in gel consistency. Intrinsic viscosity of amylose also increases progressively during grain ripening. Protein accumulation has been studied in detail in developing rice grain (Cagampang et al. 1976). Albumin and globulin are the major proteins accumulated at early stages, together with free amino acids. The appearance of protein bodies 7 days after flowering coincides with the increase in glutelin and prolamin of the rice endosperm. Although the percentage

~

-o

Trace Trace-1.8 0.1 - 0.4 -26 8 0.4 - 6.2 3.4 - 7.7 0.005 - O.Q7 0.06 - 0.16 0.0016 Trace

0.1 2.1 - 4.5 0.4 - 0.9 -62 44 1.6 -11.2 6.6 -18.6 0.06 - 0.13 0.20;0.60 0.0005 13

Vitamin A Thiamin Riboflavin Niacin (nicotinic acid) Pyridoxine Pantothenic acid Biotin Folic acid Vitamin B 12 Vitamin E (tocopherols)

Source: Hayakawa (1977); Juliano (1980).

Milled Rice

Brown Rice

Vitamin

Table 11-5. Vitamin Content of Brown Rice and Its Fractions (J.tg/g)

Rice Embryo 1.3 -76 45 2.7 - 5.0 15 -99 -16 15 3 -13 0.26 - 0.58 0.9 - 4.3 0.0105 87

Rice Bran 4.2 10 - 28 1.7 - 3.4 241 -590 10 - 32 28 - 71 0.16 - 0.47 0.50- 1.46 0.005 149

0.95 16 - 30 1.4 - 3.4 -385 228 10 - 31 26 - 92 0.14 - 0.66 0.4 - 1.9 0.003 63

Rice Polish

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Table 11-6. Inorganic Constituents of Brown Rice and Its Fraction

Aluminum Calcium Chlorine Iron Magnesium Manganese Phosphorus Potassium Silicon Sodium Zinc

Brown Rice

Milled Rice

Rice Bran

Rice Embryo

65- 400 203- 275 7- 54 380-1400 13- 42 2500-4400 1200-3400 190-1900 31- 176 15- 22

0.737.23 46 - 385 163 -372 2 - 27 170 - 700 10 - 33 860 -1920 140 -1200 50 - 370 22 - 85 3 - 21

54- 369 250- 1310 510- 970 130- 530 8,600-12,300 110- 880 14,800-28,700 13,200-22,700 1700- 7600 180- 290 50- 160

510- 2750 1520 110- 490 6000-15,300 120;140 17,100-27,300 3800-21 ,500 460- 1900 160- 240 100;300

(~-tg/g) Rice

Polish 90-

910

100- 280 5700- 7600 50;80 15,300-25,100 9300-18,000 560- 2400 65- 210 40;60

Source: Fossati eta!. (1976); Kennedy and Schelststraete (1975); Juliano (1980).

of glutelin in brown rice increased (Villareal and Juliano 1978), the percentage of prolamin in the rice dropped during grain development (Mandac and Juliano 1978). High protein rice differs from low protein rice by a more efficient nitrogen translocation from leaves to developing grain, not in nitrogen absorption. Protein content of rice grain is influenced by environmental factors such as the time and rate of nitrogen fertilizer application, solar radiation during grain development, and spacing and application of herbicides at subherbicidallevels (Esmama and Juliano 1976). Such variability in protein content in a rice variety makes breeding efforts to improve protein content of the rice grain quite difficult (Juliano and Beachell 1975). Changes due to Storage and Parboiling

Rice grain stored for 3 to 4 months ages and loses dormancy. The changes include increases in volume expansion and water absorption during cooking, a decrease in extractable solids during cooking, flakier cooked rice, and increased resistance to breakage during milling (Villareal et al. 1976). Protein and starch changes contributed to the aging of rice to a marked extent. Waxy rice and petroleum ether surface-defatted nonwaxy milled rice do not increase in hardness index during storage (Villareal et al. 1976). The increase in water absorption and decrease in extractable solids during cooking were similar regardless of the form in which the rice was stored (rough, milled, and defatted milled) or of the amylose content of rice (1-26%). The stickiness of nonwaxy rice decreased during storage but that of waxy rice did not. The amylograph peak viscosity of all samples including rice starch increased. Corresponding increases in gel viscosity were noted for the milled rice but not for starch. The salt-soluble protein of all samples decreased during storage at

PROPERTIES OF THE RICE CARYOPSIS

411

both 2 and 29°C. The highest levels of free fatty acids and carbonyl compounds were found in the stored milled rice and the lowest occurred in the defatted milled rice. Protein and starch changes contributed to the aging of rice to a marked extent. Lysine availability remains high during storage. Parboiling is a modified form of aging because starch granules are gelatinized without much volume expansion. Changes are mainly physical, resulting from the retrogradation of gelatinized starch (Watson and Dikeman 1977). Parboiling hardens the endosperm which improves grain translucence and hardness. Milled parboiled rice is slower to cook and more resistant to disintegration than raw milled rice. Cooked parboiled rice is relatively shorter but thicker girthwise than cooked raw rice. Only high amylose rices show considerable decrease in amylograph peak viscosity on parboiling, in contrast to waxy and low amylose rices. The characteristic A-type X-ray diffraction pattern of rice starch is destroyed during parboiling, but the weak V-pattern of the amylose-helix complex remains (Priestley 1976). The amylose helix complex is the major factor that makes parboiled rice more water-insoluble than raw rice, and the V-pattern is determined by both the amylose content and oil content of the rice. The degree of parboiling and percentage of parboiled grains are measured by a modified alkali test in 1% potassium hydroxide for 1 h, in which only parboiled grains disintegrate. Parboiling and cooking reduce the digestibility of milled rice protein for rats, but results in increase in the quality of digested protein (Eggum et al. 1977). Hence, net protein utilization remains high, because the proteins rendered indigestible are the poorer quality ones.

BIOCHEMICAL PROPERTIES OF RICE

Compared to other cereals, rice grain development has a fast rate of dry matter accumulation, which is complete within 14 days after anthesis (Yoshida 1981). However, enzyme production during germination and the subsequent breakdown of endosperm reserves in rice are not as dramatic as in barley (Juliano 1985). Developing and Mature Grain

The enzymes involved in starch metabolism in rice grain were reviewed by Akazawa (1972). Phosphorylase, starch-branching enzyme (Q-enzyme), and debranching enzyme (R-enzyme) have peak activities 10 days after flowering in the IR8 rice caryopsis (Baun et al. 1970). The a- and {3-

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amylases have maximum activity 14 days after flowering, whereas starch synthetase (ADP glucose-a-glucosyl transferase) bound to starch granules increase in activity up to 21 days after flowering. The activities of the enzymes related to conversion of sucrose to ADP-glucose are high throughout starch deposition in developing rice grain and are highest 8 to 18 days after flowering. The content of 3-phosphoglycerate, an effector of ADP-glucose pyro-phosphorylase, and chlorophyll was highest in the grain 7 to 8 days after flowering when starch synthesis was at a maximum (Villareal and Juliano 1977). In the immature rice grains, a-amylase is associated with the pericarp (MacGregor 1983). Myo-inositol 1-phosphate synthetase has also been characterized in mature and developing rice grain (Hayakawa 1977) and is located with the protein bodies of aleurone layer (Tanaka et al. 1976). The ability of the developing grain to incorporate 14 C-u-leucine into protein was at maximum about 8 days after flowering and was higher in the high protein rice. Protease and ribonuclease showed a similar trend, as did ribonucleic acid and soluble amino nitrogen. Higher protein grain had more rough endoplasmic reticulum in endosperm cells than lowerprotein grains (Harris and Juliano 1977). Enzyme activity is relatively low in mature rice grain, as compared to the developing and germinating grain. Shinke et al. (1973) demonstrated that the mature rice grain has no a-amylase, but free and zymogen {3amylases. A limit dextranase, which hydrolyzes a-1,6-D-glucosidic linkage, has been characterized from ungerminated rice (Dunn and Manners 1975). a-Glucosidases, which convert starch to glucose, have also been characterized. Native lipase activity is also low, and the lipase activity in rice bran is probably microbial in origin (Juliano 1977a). The lipolytic acylhydrolases in bran and milled rice have been purified and characterized (Hirayama and Matsuda 1975). Lipase, phospholipase, and galactolipase were detected in both fractions. Lipase activity predominates in bran and phospholipase in milled rice. Dormancy and Germination Changes

Dormancy in rice is not embryo dormancy, as the embryo can germinate, even in the developing grain, within 7 days after flowering (Navasero et al. 1975). Peroxidase activity is higher in dormant than in nondormant grains. Oxygen uptake is also higher in dormant grains, indicating that nongermination of dormant grain is due to depletion of oxygen supply to the embryo due to high peroxidase activity of aleurone layer. Slight disruption of the aleurone layer over the embryo results in complete breaking of dormancy. Various treatments such as dry heat, acid, and hydrogen peroxide can break dormancy. Rice grains lose dormancy on

PROPERTIES OF THE RICE CARYOPSIS

413

storage for a few weeks (Navasero et al. 1975). Maintenance of viability of the germ requires storage below 14% moisture or 75% relative humidity. Starch and protein reserves of the endosperm and protein and lipid of the aleurone are broken down and utilized by the growing embryo. Gibberellic acid from the embryo is translocated into the aleurone layer, which activates the synthesis of hydrolyzing enzymes. Yoshida et al. (1975) showed that phytase activity was associated with the phytin-containing inclusions of aleurone protein bodies. Most of the other enzymes-phosphatases, protease, esterase, lipase, peroxidase and catalase, ,13-glucosidase, and a- and ,13-galactosidase follow the increase in soluble protein by the fourth day of germination. REFERENCES

Ajayi, 0. A., and A. B. Agun. 1989. Effect of degree of parboiling on some quality parameters of rice. 1. Food Sci. Techno/. 26 (5):245-47. Akazawa, T. 1972. Enzymes of rice. In Rice chemistry and technology, ed D. F. Houston. St Paul, MN: Amer. Assoc. Cereal Chern. Alvarez R., and H. L. Rook. 1978. NBS Standard reference materials 1567, Wheat flour, and 1568, rice flour, certified for concentrations of selected trace element nutrients and to environmentally important constituents. In Proc nat. conf, wheat utilization research, 156-62. Albany, CA: Western Regional Res. Lab. Baldi, G., G. Fossati, and G. C. Fantone. 1976. By-products of rice. II. Protein fractions and amino acid composition. Riso 25:347-56 (in Italian). Banks, W., and C. T. Greenwood. 1975. Starch and Its Fractions. Edinburgh, Scotland: Edinburgh Univ. Press. Barber, S., L. Navarro, and E. Tortosa. 1976. Histochemistry of rice embryo. II. Lipids, proteins, amino acids and minerals. Rev. Agroquim. Tecnol. Aliment. 16:516-29 (in Spanish). Baun, L. C., E. P. Palmiano, C. M. Perez, and B. 0. Juliano. 1970. Enzymes of starch metabolism in the developing rice grain. Plant Physiol. 46:429-34. Bean, M. M., C. A. Essen, and K. D. Nishita. 1984. Some physicochemical and food application characteristics of California waxy rice varieties. Cereal Chern. 61:475-80. Bechtel, D. B., and B. 0. Juliano. 1980. Protein body formation in the starchy endosperm of rice (Oryza sativa L): A reinvestigation. Ann Bot. London 45:503-9. Bechtel, D. B., andY. Pomeranz. 1977. Ultrastructure of the mature ungerminated rice (Oryza sativa) caryopsis: The caryopsis coat and aleurone cells. Amer. J. Bot. 64:966-73. Bechtel, D. B., andY. Pomeranz. 1978a. Utrastructure of the mature ungerminated rice (Oryza sativa) caryopsis. The germ. Amer. J. Bot. 65:75-85. Bechtel, D. B., andY. Pomeranz. 1978b. Ultrastructure of the mature ungerminated rice (Oryza sativa) caryopsis: The starchy endosperm. Amer. J. Bot. 65:684-91.

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Bechtel, D. B. and Y. Pomeranz. 1980. The rice kernel. In Advances in cereal science and technology, vol. 3, ed. Y. Pomeranz, 73-113. St. Paul, MN: Amer. Assoc. Cereal Chemists. Bhattacharya, K. R., C. M. Sowbhagya, and Y. M. Indudhara Swany. 1978. Importance of insoluble amylose as a determinant of rice quality. J. Sci. Food Agric. 29:359-64. Bhattacharya, K. R., C. M. Sowbhagya, and Y. M. Indudhara Swamy. 1982. Quality profile of rice: A tentative scheme for classification. J. Food Sci. 47:564-69. Biswas, S. K., and B. Juliano. 1988. Laboratory parboiling procedures and properties of parboiled rice from varieties differing in starch properties. Cereal Chern. 65(5):417-23. Bolling, H., and A. W. El Baya. 1975. Effects of lipids on the determination of amylose content in rice and wheat. Chern. Mikrobiol. Techno[. Lebensrn. 3:161-63 (in German). Buttery, R. G., L. C. Ling, and B. 0. Juliano. 1982. 2-Acetyl-1-pyrroline: An important aroma component of cooked rice. Chern. Ind. London 958-59. Buttery, R. G., L. C. Ling, B. 0. Juliano, and J. G. Taurnbaugh. 1983. Cooked rice aroma and 2-acetyl-pyrroline. J. Agric. Food Chern. 31:823-26. Cagampang, G. B., A. A. Perdon, and B. 0. Juliano. 1976. Changes in salt soluble proteins of rice during grain development. Phytochern. 15:1425-30. Cagampang, G. B., C. M. Perez, and B. 0. Juliano. 1973. A gel consistency test for eating quality of rice. J. Sci. Food Agric. 24:1589-94. Chang, S.M., and C. Y. Lii. 1985. The pasting behaviors and eating qualities of some rice in Taiwan. Bull Inst. Chern. Acad. Sinica 32:57-61. Damardjati, D. S. 1983. Physical and chemical properties and protein characteristics of some Indonesian varieties. Dr. Agric. Sci. thesis, Bogor Agricultural Univ., Bogor, Indonesia. Damardjati, D. S., and B. S. Luh. 1989. Physicochemical properties of extrusioncooked rice breakfast cereals. In Proc. 7th world congress on food sci. and techno!., vol. 2, p. 1. 12. De Datta, S. K. 1981. Principles and Practices of Rice Production, New York: Wiley. Dunn, G., and D. J. Manners. 1975. The limit dextrinases from ungerminated oats (Avena sativa L.) and ungerminated rice (Oryza sativa L.). Carb. Res. 39:283-93. Eggum, B. 0., and B. 0. Juliano. 1975. Higher protein content from nitrogen fertiliser application and nutritive value of milled-rice protein. J. Sci. Food Agric. 26:425-27. Eggum, B. 0., A. P. Resurreccion, and B. 0. Juliano. 1977. Effect of cooking on nutritional value of milled rice in rats. Nutr. Rep. Int. 16:649-55. Enevoldsen, B.S., and B. 0. Juliano. 1988. Ratio of A chains to B chains in rice amylopectins. Cereal Chern. 65:425-27. Esmama, B. V. and B. 0. Juliano. 1976. The effect of subherbicidal application of simetryne and Benzomarc on the nitrogen metabolism of rice seedlings. Kalikasan Philip. J. Bioi. 5:315-24. Evers, A. D., and B. 0. Juliano. 1976. Varietal differences in surface ultrastructure of endosperm cells and starch granules of rice. Starke 28:160-66.

PROPERTIES OF THE RICE CARVOPSIS

415

Food and Agriculture Organization (F AO). 1973. Energy and protein requirements. FAO Nutr. Meet. Rep. Ser. 52:63. Fossati, G., G. Baldi, and F. Ranghino. 1976. By-products of rice. I. Chemical composition and inorganic constituents. Riso 25:339-45. Fujimaki, M., T. Tsugita, and T. Kurata. 1977. Fractionation and identification of volatile acids and phenols in the steam distillate of rice bran. Agric. Bioi. Chern. 41:1721-25. Hagakama, T., S. W. Seo, and lgaue. 1980. Electron microscopic observation of rice grain. 1: Morphology of rice starch. J. Japan Soc. Starch Sci. 27: 173-79. Harris, N., and B. 0. Juliano. 1977. Ultrastructure of endosperm protein bodies in developing rice grains differing in protein content. Ann. Bot. 45:1-5. Hartman, L., and R. C. A. Lago. 1976. The composition of lipids from rice hulls and from the surface of rice caryopsis. J. Sci. Food Agric. 27:939-42. Hayakawa, T. 1977. Variation of myo-inositol and myo-inositol phosphate contents and some starch properties in rice seed (Biochemical studies of myoinositol on rice seed. VI.). Bull. Fac. Agric. Niigata Univ. 29:35-42. (Japanese) Hirayama, 0., and H. Matsuda. 1973. Lipid components and distribution in brown rice. J. Agric. Chern. Soc. Japan, 47:371-77. Hirayama, 0., and H. Matsuda. 1975. Purification and characterization oflipolytic acyl-hydrolases from rice bran. J. Agric. Chern. Soc. Japan 49:569-76. Horikoshi, M., andY. Morita. 1975. Localization of y-globulin in rice seed and changes in y-globulin content during seed development and germination. Agric. Biol. Chern. 39:2309-14. Houston, D. F. 1972. Rice bran and polish. In Rice chemistry and technology, lst ed., ed. D. F. Houston, 272-309. St. Paul, MN: Amer. Assoc. Cereal Chern. Inc. Houston, D. F., and G. 0. Kohler. 1970. Nutritional properties ofrice. Washington, DC: Nat. Acad. Sci. Ilag, L. L. and B. 0. Juliano. 1982. Colonisation and aflatoxin formation by Aspergillus spp. on brown rices differing in endosperm properties. J. Sci. Food Agric. 33:97-102. Ito, S., Y. Tsukidate, andY. Fujino. 1981. Separation and determination oftocopherol homologues in cereal grains and bean seeds. Obihiro Chikusan Daigaku gakujutsu kerkyu Hokoku Dai-1-Bu 12:143-48. Juliano, B. 0. 1972a. Physicochemical properties of starch and protein and their relation to grain quality and nutritional value of rice. In Rice breeding. Los Banos, Philippines: Int. Rice Res. Inst. Juliano, B. 0. 1972b. The rice caryopsis and its composition. In Rice chemistry and technology. ed. D. F. Houston. St. Paul, MN: Amer. Assoc. Cereal Chern. Juliano, B. 0. 1977a. Rice lipids. Riso 26:3-21. Juliano, B. 0. 1977b. Recent developments in rice research. Cereal Foods World 22:284-87. Juliano, B. 0. 1980. Properties of the rice caryopsis. In Rice: Production and utilization. ed. B. S. Luh, 403-38. Westport, CT: Avi. Juliano, B. 0. 1984. Rice starch: Production, properties, and uses. In Starch:

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Chemistry and technology, 2nd ed. ed. R. L. Whistler, J. N. Bemiller, and E. F. Pschall. Orlando, FL: Academic Press. Juliano, B. 0. 1985. Rice chemistry and technology. St. Paul, MN: Amer. Assoc. Cereal Chemist. Juliano, B. 0., and H. M. Beachell. 1975. Status of rice protein improvement. In High-quality protein maize. Stroudsburg, PA: Int. Maize and Wheat Improvement Cntr./Purdue Univ. Dowden, Hutchinson and Ross. Juliano, B. 0., and D. Boulter. 1976. Extraction and composition of rice endosperm glutelin. Phytochem. 15:1601-6. Juliano, B. 0., and A. A. Perdon. 1975. Gel and molecular properties ofnonwaxy rice starch. Starke 27:115-20. Juliano, B. 0., A. A. Perdon, C. M. Perez, and G. B. Cagampang. 1974. Molecular and gel properties of starch and texture of rice products. In Proc. 4th Int. Congr. Food Sci. Techno!. Madrid, vol. 1, ed. E. Portela. Valencia, Spain: Inst. Agroquim. Tecnol. Aliment. Kanematsu, H., T. Ushigusa, T. Maruyama, I. Niiya, D. Fumoto, T. Toyoda, Y. Kawaguchi, and T. Matsumoto. 1983. Comparison of tocopherol contents in crude and refined vegetable oils and fats by high performance liquid chromatography. Yukagaku 32:122-26. Kato, A., K. Tanabe, and M. Yamaoka. 1981. Esterified tocopherols and tocotrienols in rice bran oil, soybean oil and sesame oil. Yukagaku 30:515-16. Kennedy, B. M., and M. Schelstraete. 1975. Chemical, physical and nutritional properties of high-protein flours and the residual kernel from the over milling of uncoated milled rice. III. Iron, calcium, magnesium, phosphorus, sodium, potassium, and phytic acid. Cereal Chern. 52:173-82. Kennedy, B. M., M. Schelstraete, and K. Tarnai. 1975. Chemical, physical and nutritional properties of high-protein flours and residual kernel from the overmilling of uncoated milled rice. IV. Thiamin, riboflavin, niacin and pyridoxine. Cereal Chern. 52:182-88. Kongseree, N., and B. 0. Juliano. 1972. Physicochemical properties of rice grain and starch from lines differing in amylose content and gelatinization temperature. J. Agric. Food Chern. 20:714-18. Leonzio, M. 1967. Contents of pentosans in rice caryopses and in principal by products. Riso 16:313-20 (in Italian). Lii, C. Y., S.M. Chang, and H. L. Yang. 1984. Some physico-chemical properties of nonwaxy rices in Taiwan. Bull. Inst. Chern. Academia Sinica 31:63-

8.

Lii, C. Y., S.M. Chang, and H. L. Yang. 1986. Correlation between the physicochemical properties and the eating quality of milled rice in Taiwan. Bull. Inst. Chern. Academia Sinica 33:55-62. Lu, S., and C. Y. Lii. 1989. The influence of various milling processes on the physico-chemical properties of rice flours and rice flakes. Food Sci. (Taiwan) 16:22-35. Lu, S., S. J. Wu, and C. Y. Lii. 1988. Studies on the structure and physicochemical property of rice at different harvest times. J. Chinese Agric. Chern. Soc. 26:552-62. Luh, B. S. 1980. Rice: Production and Utilization. Westport. CT: Avi.

PROPERTIES OF THE RICE CARYOPSIS

417

MacGregor, A. W. 1983. Synthesis and action pattern. In Seed proteins. ed. J. Laussant, J. Mosse, and J. Vaughan, 1-34. London: Academic Press. Mandac, B. E., and B. 0. Juliano. 1978. Properties of prolamin of mature and developing rice grain. Phytochem. 17:611-14. Maningat, C. C. 1981. Isolation and characterization of cell walls of rice bran and germ. M.S. thesis, Univ. of Philippines at Los Banos, Los Banos, Laguna, Philippines. Maningat, C. C., and B. 0. Juliano. 1978. Alkali digestibility pattern, apparent solubility and gel consistency of milled rice. Starke 30:125-27. Maningat, C. C., and B. 0. Juliano. 1982. Composition of cell wall preparations of rice bran and germ. Phytochem. 21:2509-16. Mod, R. R., E. J. Konkerton, R. L. Ory, and F. L. Normand. 1978. Hemicellulose composition of dietary fiber and milled rice and rice bran. J. Agric. Food Chern. 26:1031-35. Morrison, W. R., and M. Nasirazudin. 1987. Variation in the amylose and lipid contents and some physical properties of rice starches. J. Cereal Sci. 5:35-44. Mosse, J., J. C. Huet, and J. Baudet. 1988. The amino acid composition of rice grain as a function of nitrogen contents as compared with other cereals: A reappraisal of rice chemical scores. J. Cereal Sci. 5:35-44. Murata, K., T. Kitagawa, and B. 0. Juliano. 1978. Protein quality of a high protein rice in rats. Agric. Biol. Chern. 42:565-70. Navasero, E. P., L. C. Baun, and B. 0. Juliano. 1975. Grain dormancy peroxidase activity and oxygen uptake in Oryza sativa. Phytochemistry 14:1899-1902. Ogawa, M., K. Tanaka, and Z. Kasai. 1975. Isolation of high phytin containing particles from rice grains using an aqueous polymer two phase system. Agric. Bioi. Chern. 39:695-700. Padhye, V. W., and D. K. Salunkhe. 1979. Extraction and characterization of rice proteins. Cereal Chern. 56:389-93. Pascual, C. G., R. Singh, and B. 0. Juliano. 1978. Free sugars of rice grain. Carb. Res. 62:381-85. Perdon, A. A., and B. 0. Juliano. 1975a. Gel and molecular properties of waxy rice starch. Starke 27:69-71. Perdon, A. A. and B. 0. Juliano. 1975b. Amylose content of rice and quality of fermented cake. Starke 27:196-98. Perdon, A. A., and B. 0. Juliano. 1978. Properties of a major y-globulin of rice endosperm. Phytochem. 17:351-53. Priestley, R. J. 1976. Studies on parboiled rice. 1. Comparison of the characteristics of raw and parboiled rice. Food Chern. 1:5-14. Proctor, A., and D. E. Goodman. 1985. Physicochemical differences between milled whole kernel rice and milled broken rice. J. Food Sci. 50:922-25. Rasper, V. F. 1979. Chemical and physical properties of dietary cereal fiber. Food Techno!. 33(1):40-44. Resurreccion, A. P., T. Hara, B. 0. Juliano, and S. Yoshida. 1977. Effect of temperature during ripening on grain quality of rice. Soil Sci. Plant Nutr. 23:109-12. Schalier, D. 1978. Fiber content and structure in foods. Amer. J. Clin. Nutr. 31(supplement): s99-s 102.

418

RICE: PRODUCTION

Shinke, R., H. Nishira, and N. Mugibayashi. 1973. Types of amylases in rice grains. Agric. Bioi. Chern. 37:2437-38. Singh, R., and B. 0. Juliano. 1977. Free sugars in relation to starch accumulation in developing rice grain. Plant Physiol. 59:417-21. Suzuki, H., and B. 0. Juliano. 1975. Alkaliviscogram and other properties of starch of tropical rice. Agric. Bioi. Chern. 39:811-17. Tabata, S., K. Nagata, and S. Hizukure. 1975. Studies on starch phosphate in some cereal starches. Starke 27:333-35. Tabekhia, M. M., R. B. Toma, and B.S. Luh. 1981. Crude protein and amino acid compositions of three California varieties. Nutri. Rep. Inst. 23:805-11. Tanabe, K., M. Yamaoka, and A. Kato. 1981. High performance liquid chromatography and mass spectra of tocotrienols in rice bran oils. J. Japan Oil Chern. Soc. 30:116-18. Tanabe, K., M. Yamaoka, A. Tanaka, A. Kato, andJ. Amemiya. 1982. Determination of tocopherols in rice bran oils by high performance liquid chromatography. Yukagaku 31:205-8. Tanaka, K., M. Ogawa, and Z. Kasai. 1976. The rice scutellum: studies by scanning electron microscopy and electron microprobe X-ray analysis. Cereal Chern. 53:643-49. Tanaka, K., T. Yoshida, K. Asada, and Z. Kasai. 1973. Subcellular particles isolated from aleurone layer of rice seeds. Arch. Biochern. Biophys. 155:136-43. Tanaka, K., T. Yoshida, and Z. Kasai. 1976. Phosphorylation of myoinositol by isolated aleurone particles of rice. Agric. Bioi. Chern. 40:1319-25. Tanaka, K., T. Sugimoto, M. Orgawd, and Z. Kasai. 1980. Isolation and characterization of two types of protein bodies in the rice endosperm. Agric. Bioi. Chern. 44:1633-39. Tanaka, K., S. Hayashida, and M. Hongo. 1975. The relationship of the feces protein particles to rice protein bodies. Agric. Bioi. Chern. 39:51518. Tsen, H. H. 1987. Physicochemical properties of rice protein fractions and their effects on the pasting of rice flour. Ph. D. diss., Nat. Taiwan Univ., Taipei, Taiwan. Tsugita, T., T. Kurata, and M. Fujimaki. 1978. Volatile components in the steam distillate of rice bran; Identification of neutral and basic compounds. Agric. Bioi. Chern. 42:643-51. Tsugita, T., T. Imai, Y. Doi, T. Kurata, and H. Kato. 1979. GC and GC-MS analysis of head space nolatiles by tenax G C trapping techniques Agric. Bioi. Chern. 43:1351-54. Tsugita, T., T. Kurata, and H. Kato. 1980. Volatiles components after cooking rice milled to different degrees. Agric. Bioi. Chern. 44:835-40. Tsuzuki, E., C. Matsuki, K. Morinaga, and S. Shida. 1978. Studies on the characteristics of scented rice IV. Volatile sulfur compounds evolved from cooked . rice. Nippon Sakurnotsu Gakkai kiji 47:375-80. Utsunomiya, H., M. Yamagata, andY. Doi. 1975a. Scanning electron microscopy of the endosperm of cereal crops. 3. Starch cell layer of white-core rice. Bull. Fac. Agric. Yarnaguti Univ. 26:1-18 (in Japanese). Utsunomiya, H., M. Yamagata, andY. Doi. 1975b. Scanning electron microscopy

PROPERTIES OF THE RICE CARYOPSIS

419

of the endosperm of cereal crops. 4. Starch cell layer of imperfect grain of rice (non-glutinous) and glutinous rice. Bull. Fac. Agric. Yamaguti Univ. 26:19-44 (in Japanese). Villareal, R. M., and B. 0. Juliano. 1977. Some properties of 3-phosphoglycerate phosphatase from developing rice grain. Plant Physiol. 59:134-38. Villareal, R. M., and B. 0. Juliano. 1978. Properties of glutelin of mature and developing rice grain. Phytochem. 17:177-82. Villareal, R. M., A. P. Resurreccion, L. B. Suzuki, and B. 0. Juliano. 1976. Changes in physicochemical properties of rice during storage. Starke 28:88-94. Watson, C. A., and E. Dikeman, 1977. Structure of the rice grain shown by scanning electron microscopy. Cereal Chern. 54:120-30. Wieser, H., W. Seilmeier, and H. D. Belitz. 1981. Vergles chende untesserchungen Uber partielle Aminosauresequenzen Von Prolaminen Und glutelinen Verschiedener Getreidearten. III. Amidgehalt der Proteinfraktionen E.Lebensm Untessuch. Forsch. 173:90-94. Willis, R. B. H., L. B. Palipane, and H. Greenfield. 1982. Composition of Australian foods. 13: Rice. Food Techno!. Aust. 34:66-68. Wu, H. K., and H. T. Chen. 1978. Protein bodies in developing rice grain. InProc. Nat. Sci. Council (Taiwan) 2:281-92. Yajima, 1., T. Yanai, M. Nakamura, H. Sakakibra, and T. Habu. 1978. Volatile flavor components of cooked rice. Agric. Bioi. Chern. 42:1229-33. Yajima, 1., T. Yanai, M. Nakamura, H. Sakakibara, andK. Hayashi. 1979. Volatile flavor components of cooked kaorimai scented rice 0. sativa J aponica. Agric. Bioi. Chern. 43:2425-29. Yamagishi, T., K. Matsuda, and T. Watanabe. 1975. Studies on the proteoglycan from rice bran. 1. Isolation and partial characterization of proteoglycans from rice bran. Carb. Res. 43:321-33. Yamagishi, T., K. Matsuda, and T. Watanabe. 1976. Characterization of the fragments obtained by enzymic and alkaline degradation of rice-bran proteoglycans. Carb. Res. 50:63-74. Yoshida, S. 1981. Fundamentals of rice crop science. Los Banos, Philippines: Int. Rice Res. Inst. Yoshida, T., K. Tanaka, and Z. Kasai. 1975. Phytase activity associated with isolated aleurone particles of rice grain. Agric. Bioi. Chern. 39:289-290.

1 Introduction Bor S. Luh University of California, Davis

RICE IN RETROSPECT

Rice is considered a semiaquatic annual plant, although it could survive as a perennial in the tropics or subtropics. Cultivars of the two cultivated species, Oryza sativa L. and 0. glaberrima Steud., can grow in a wide range of water-soil regimes, from a prolonged period of flooding in deep water to dry land on hilly slopes. The crop has remarkable diversity because of its long history of cultivation and selection under diverse climatic and biotic environments, frequently in geographically separated areas. Today rice is grown in more than 100 countries, extending from 53°N latitude to 40°S and from sea level to an altitude over 3000 m. 0. glaberrima is grown only in Africa on a limited scale. The production practices for rice in various countries vary from extremely primitive to highly mechanized operations. Books on rice production have been published by De Datta (1981), Luh (1980), and Yoshida (1981). Pillaiyar (1988) published the "Rice Postproduction Manual," which deals largely with postharvest operations. Juliano (1990) reviewed the literature on rice grain quality, with emphasis on problems and challenges.

2

RICE: UTILIZATION

. . \

••

............ D ..·· ..-..

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• • - n lfl25%) rices are used for extruded rice noodles. Among high-amylose rices, soft-gel consistency is preferred to hard-gel consistency. Various processed rice products are presented in the subsequent chapters of this book. They include "Rice Flours in Baking" (Chap. 2); "Rice Enrichment" (Chap. 3); "Parboiled Rice" (Chap. 4); "Quick-Cooking Rice" (Chap. 6); "Canning, Freezing, and Freeze-drying" (Chap. 7); Rice Breakfast Cereals and Baby Foods" (Chap. 8); "Fermented Rice Products" (Chap. 9); "Rice Snack Foods" (Chap. 10); "Rice Vinegar" (Chap. 11); "Rice Hulls" (Chap. 12); "Rice Oil" (Chap. 13); and "Rice Bran" (Chap. 14). In addition, there are chapters entitled "Rice Quality and Grades" (Chap. 5), and "Nutritional Quality of Rice Endosperm" (Chap. 15).

REFERENCES

Chang, T. T. 1976a. Rice, In Evolution of Crop Plants, edited N. W. Simmonds. New York: Longman, pp 98-104. Chang, T. T. 1976b. The rice cultures. Phil. Trans. Roy. Soc. London, Ser. B 275:143-157. Chang, T. T. 1976c. The origin, evolution, cultivation, dissemination, and diversification of Asian and African rice. Euphytica 25:425-441. Chang, T. T. 1989. Rice-the starchy staple, In Plants and Society, edited by M. S. Swaminathan and S. L. Kochhar. London: Macmillan, pp. 127-150. De Datta, S. K. 1981. Principles and Practices of Rice Production. New York:

Wiley.

FAO. 1982. 1981 FAO Production Yearbook. F AO Statistics Ser. 40, Rome: Food and Agricultural Organization of the United Nations.

INTRODUCTION

7

FAO. 1987. World Crop and Livestock Statistics. 1948-1985. Rome: Food and Agriculture Organization of the United Nations. FAO. 1988. Quart. Bull. Stat. 1(3) FAO. 1989. Quart. Bull. Stat. 2(1). Herdt, R. W., and Palacpac, A. C. 1983. World Rice Facts and Trends. Los Banos, Philippines: International Rice Research Institute (IRRI). Hsieh, S.C., Flinn, J. C., and Amerasinghe, N. 1982. The role of rice in meeting future needs. In Rice Research Strategies for the Future. Los Banos, Philippines: IRRI, pp. 29-49. IRRI. 1985. International Rice Research: 25 Years of Partnership. Los Banos, Philippines: IRRI. IRRI. 1988. World Rice Statistics 1987. Los Banos, Philippines: IRRI. Juliano, B. 0. 1979. The chemical basis of rice grain quality. In Proceedings of the Workshop on Chemical Aspects of Grain Quality. Los Banos, Philippines IRRI, pp 69-90. Juliano, B. 0. 1985. Rice Chemistry and Technology. St. Paul, MN: AACC. Juliano, B. 0. 1990. Rice grain quality: Problems and challenges. Cereal Foods World 35(2):245-253. Lu, J. J., and Chang, T. T. 1980. Rice in its temporal and spatial perspectives. In Rice: Production and Utilization, edited by B. S. Luh. Westport, CT:AVI, pp. 1-74. Luh, B. S. 1980. Rice: Production and Utilization. Westport, CT:A VI. Mercier, C., Linko, P., and Harper, J. M. 1989. Extrusion Cooking. St. Paul, MN: AACC. Pillaiyar, P. 1988. Rice Postproduction Manual. New Delhi: Wiley Eastern. Yoshida, S. 1981. Fundamentals of Rice Crop Science. Los Banos, Philippines: . IRRI.

2 Rice Flours in Baking Bor S. Luh University of California, Davis

Yuan-Kuang Liu Del Monte Corporation Research Center

There are two types of commercial rice flour available in the United States (Hogan 1977). The first is produced from waxy or glutinous rice, which is grown in limited quantities in California. The waxy rice flour has superior qualities for use as a thickening agent for white sauces, gravies, and puddings and in oriental snack foods. It can prevent liquid separation (syneresis) when these products are frozen, stored, and subsequently thawed. A characteristic of waxy flour is that it has little or no amylose. Since the waxy rice starch is essentially amylopectin, flour prepared from it has this unique food use property. The other type of rice flour is prepared from broken grains of ordinary raw or parboiled rice. The flour prepared from parboiled rice is essentially a precooked flour. It differs from wheat flour in baking properties because it does not contain gluten, and its doughs do not readily retain gases generated during baking. There is, however, a steady basic demand for rice flours for use in baby foods, breakfast cereals, and snack foods; for separating powders for refrigerated, preformed, unbaked biscuits, dusting powders, and breading mixes; and for formulations for pancakes and waffles (Luh and Liu 1980; Bean and Nishita 1985). These uses are sufficient to sustain a market for rice-flour production. Rice is consumed largely as a whole grain. Some breakage, however, is unavoidable. Some of the rice kernels are cracked while still in the husk, and some breakage occurs during harvesting, handling, drying, and 9

10

RICE: UTILIZATION

milling. The amount of broken rice produced annually in the United States ranges from 263,000 to 408,000 tons, about 15% of the rice milled. The larger pieces of broken rice sell for a little more than half the price of whole rice, whereas the smaller fragments sell for less than half of comparable whole grains. Therefore, these smaller pieces are used for grinding into rice flour or for brewing. Second heads are also used for riceflour production in the United States. About a third of the broken rice produced in the United States is used by brewers and a small portion by cereal manufacturers and baby-food formulators. The amount of rice used in the brewing industry is generally a function of the price of broken rice. The brewing industry would use more broken rice if the price were competitive with that of other grains, such as corn grits. Lewis (1988) reported that rice appears to be as good as corn grit as an adjunct for brewing. Some of the broken rice is ground into flour. The amount used is determined by the price paid for the flour, which must be high enough to cover the cost of grinding and related changes, since there is a ready market for this fraction at a lower price in the brewing industry. PROPERTIES OF RICE FLOURS

Rice flours made from long-, medium-, and short-grain and waxy rice are available commercially. Since rice flours are made from broken milled rice, their chemical composition is the same as that of whole rice. There are, however, varietal differences in protein, lipid, starch contents, and the amylose and amylopectin ratios in the starch. The proximate analyses of some rice are presented in Table 2-1 (Ejlali et al. 1978). Composition differences contribute to the diversity of chemical and physical properties of various rice flours, such as viscometric properties, starch gelatinization temperatures, bifringence end-point temperatures, water absorption, and other characteristics. The rheological properties of starch slurries and gels have been reviewed by Kruger and Murray (1976) and Juliano et al. (1985). Table 2-1. Proximate Analyses of Four Rice Varieties Grown In California Variety

Grain Type

S-6 M-5 74-y-52 72 3764

Short Medium Medium Long

Source: Ejlali et al. (1978).

Amylose, %

Amylopectin, %

Protein, %

Fat, %

Ash, %

19.0 22.5 24.0 27.8

56.5 54.7 56.2 54.2

6.50 6.60 6.75 7.07

2.05 1.50 1.82 1.88

1.22 1.07 1.55 1.65

RICE FLOURS IN BAKING

11

Developers of new rice foods should recognize the wide diversity in composition and properties of various rice flours. Occasionally, discovery of a unique property of a variety has led to new uses for rice flours made from it. For example, the freeze resistance of waxy rice-flour pastes led to their use in frozen gravies (Hanson et al. 1953). The viscosity behavior of rice-flour pastes provides information for the application of rice flour to food formulation. The varieties used in pancake mixes and expanded breakfast cereals are examples. Rice flours from each variety, with the exception of the waxy type, have characteristic viscosity patterns during the heating and cooling cycles of their pastes. The changes in viscosity depend largely on the composition of the starch and, to a lesser extent, on the protein and oil components. Usually, long-grain rice containing starch with an amylose content of over 22% has a relatively low peak viscosity and forms a rigid gel on cooling (high setback viscosity). Those with starches low in amylose have high peak and low setback viscosities. Determination of Rice-Flour Properties

Bifringence end-point temperature (BEPT) of rice flour can be determined on a 1% slurry using a polarizing microscope equipped with a Kofler hot stage and set at a heating rate of 5°C/min. BEPT is usually recorded at 95-98% loss of bifringence. Amylograph pasting curves of 10% flour slurries (50 g of rice flour to 450 ml of water) give useful information on rice starch characteristics important in baking applications. Test on 20% flour slurries (100 g of rice flour to 400 ml of water) can give estimates of initial gelatinization temperature of rice starch within± 0.5°C when gelatinization temperature is taken as the point of initial increase in viscosity. These values correlate significantly (r = 0.94), with BEPT determined microscopically. Nishita and Bean (1979) used these techniques to characterize rice varieties that gave contrasting texture results in yeast-leavened rice breads. Figure 2-1 shows representative results with four flours. The short curves (20% slurries) indicate distinctly different temperatures for initial viscosity increase (i.e., estimate of gelatinization temperature) among the rices. The full curves (10% slurries) show initial viscosity increases occurring much later in the heating cycle; this is because the amylograph lacks the sensitivity to detect small increments in viscosity in less concentrated slurries. However, the 10% slurries do provide a complete pasting history that can be correlated with the textural properties of the baked products. For example, sample B (IRS variety) had a low initial gelatinization temperature, which is favorable for baking, but a high final viscosity and high positive setback (viscosity at 50°C minus peak viscosity), which adversely affect bread texture. Sample B had a high amylose content,

RICE: UTILIZATION

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known that undissociated compounds permeate the hydrophobic membrane at a higher rate. Numerous organic acids, amino acids, and short peptides found in rice vinegar are a reason for its demonstrable superior antimicrobial activity. The possibility that a short hydrophobic peptide, combined with the acetic acid in rice vinegar, does exist, resembling the way a hydrophobic signal sequence facilitates the excretion of extracellular enzymes, cannot be excluded. A readily tested but rather imprecise method is to determine the permeation rate of rice vinegar through a section of raw fish approximately 2 em thick (similar to the raw fish found in a sushi bar). Using a cross section, the depth of denaturation due to the permeation of rice vinegar can be determined. Pure rice vinegar should permeate the entire 2-cm section, whereas vinegars of the same strength (4.2% acetic acid) produced from fruit or ethanol usually show a permeation only in the range of 1 mm in the same allotted time (Sugi 1983). In addition to the Japanese authors, L. J. Diggs (1989) has recently compiled documents on the use of vinegar as a medicine, listing cures for many human ailments, ranging from alcoholism to weight loss. Although it is difficult to quantitate its medicinal effectiveness, rice vinegar, with high-amino acid content and characteristic aminopeptidase profiles, has been found to be far superior to any other vinegars for such medical benefits. A better approach to the medicinal benefits of rice vinegar would be to link the function of acetic acid, which is present in a much more

RICE VINEGAR

265

permeable form in rice vinegar, to the central pathways of anabolism and catabolism (i.e., the citric acid cycle). This cycle, as the central hub of metabolism of almost all aerobic cells, provides a focus for the discussion of the acetic acid in rice vinegar. This cycle set of reactions functions to catalyze the complete combustion of acetyl CoA to C02 and H 20. It is important to note, however, that the reactions in the cycle by themselves can bring about dehydrogenation (e.g., when linked to the electron transport system in the mitochondria) of any of the di- or tricarboxylic acids within the cycle to malate or oxaloacetate but not beyond. The cycle, therefore, stops operation unless acetyl CoA is constantly replenished. In the absence of an external supply of acetyl CoA, the following additional reactions are essential to regenerate acetyl CoA from malate or oxaloacetate: malate (or oxaloacetate)--? acetyl CoA + 2C02 acetyl CoA + oxaloacetate --? citrate --? 2C02 + 2H20 + oxaloacetate Although acetic acid and pyruvic acid are made in the cytoplasm, both molecules must move from the cytoplasm and enter the mitochondrion through its relatively smooth outer membrane and the highly structured inner membrane (cristae), which penetrates deeply into the intramitochondrial matrix. There, both pyruvate and acetate are converted to acetyl CoA and subsequently oxidized to C0 2, provided a sufficient supply of one of the cycle acids is present to allow initiation of the first condensation step of the citric acid cycle. It is therefore reasonable to assume that acetic acid, present in a much more permeable form in rice vinegar, can readily traverse (1) the cytoplasmic membrane, (2) the outer mitochondrial membrane, and (3) the inner mitochondrial membrane. This increased permeation explains the superior beneficial effects of rice vinegar compared to all vinegars of other origins. The large number of organic acids found in rice vinegar are either members of the citric acid cycle or readily converted to those components of the cycle. Many of these organic acids and reactions play a critical role in the anabolism of important metabolites such as amino acids, purines, pyrimidines, long-chain fatty acids, and porphyrins. Members of the cycle that are thus drained can be more readily replenished by the organic acids present in the more readily permeable form in rice vinegar. REFERENCES

Adams, M. R. 1985. Vinegar. Microbiology of Fermented Foods, edited by B. J. B. Wood. London: Elsevier Applied Science. Ameyama, M., and Adachi, 0. 1982a. Alcohol dehydrogenase from acetic acid bacteria, Membrane Bound. Meth. Enzyme 89:450-457.

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Ameyama M., and Adachi, 0. 1982b. Aldehyde dehydrogenase from acetic acid bacteria, Membrane Bound. Meth. Enzyme 89:491-497. An-shin Editorial Board, Div. of. 1986. A Book on Treatment of Diseases with Rice Vinegar. Tokyo: Makino Publishing (in Japanese). Asai, T. 1968. Acetic Acid Bacteria. Tokyo: Univ. of Tokyo Press. Diggs, L. J. 1989. Vinegar. San Francisco: Quiet Storm Trading Co. Ebner, H., Pohl, K., and Enenkel, A. 1967. Self-priming aerator and mechanical defoamer for microbiological processes. Biotechnol. Bioeng. 9:357-364. Ebner, H. 1982. Vinegar. Prescott and Dunn's Microbiology, 4th ed., edited by G. Reed. Westport, CT: AVI. Greenshields, R.N. 1978. Acetic Acid: Vinegar. Primary Products ofMetabolism, edited by A. H. Rose. New York: Academic Press. Higashi, K., Mizumoto, H., Minami, H., Mori, T., and Maeda, F. 1974. Studies on fukuyama vinegar fermentation and improvement of brewing technique. Kagoshima-Ken Tech. Res. Lab. Rept. 21:61-66 (in Japanese). Higashi, K., Mizumoto, H., Mori, T., and Maeda, F. 1973. Studies on fukuyama vinegar fermentation and improvement of brewing technique. KagoshimaKen Tech. Res. Lab. Rept. 20:58-77 (in Japanese). Hsu, E. J. 1989. Automated method for a semi-solid fermentation used in the production of ancient quality rice vinegar and/or rice wine. U.S. Pat. No. 4,808,419, Feb. 28. Hsu, Z.-B. 1987. Fermentation technology of Shau-Xing rice wine. Special Topics on Science and Technology of Alcoholic Beverages. Research Institute for Wine, Taiwan Tobacco and Wine Monopoly Bureau (in Chinese). Hsu, E. J., Godsey, J. H., Chang, E. K., and Landuyt, S. L. 1981. Differentiation ofpseudomonads by amplification of metabolic profiles. Int. J. Syst. Bacterial. 31:43-55. Kunimatsu, Y., Okumura, H., Masai, H., Yamada, K., and Yamada, M. 1981. Production of vinegar with high acetic acid concentration. U.S. Pat. No. 4,282,257, March 4. Kuroiwa, T. 1975. Rice Vinegar: An Oriental Home Remedy. Tokyo: Kenko Igakusha (in Japanese). Lai, M.-N., Chang, W. T. H., and Luh, B.S. 1980. Rice vinegar fermentation. In Rice: Production and Utilization, edited by B. S. Luh. Westport, CT: AVI. Masai, H. 1980. Recent technical developments in vinegar manufacture in Japan. Proceedings of the Oriental Fermented Foods. Taiwan: Food Industry Research and Development Institute. Nakayama, T. 1961a. Studies on acetic acid bacteria. III: Purification and properties of coenzyme independent aldehyde dehydrogenase. J. Biochem. 49(2): 158-63. Nakayama, T. 1961b. Studies on acetic acid bacteria. IV: Purification and properties of a new type of alcohol dehydrogenase, alcohol-cytochrome-553 reductase. J. Biochem. 49(3):240-251. Nishida, T. 1981. Increasing Life Expectancy to 100 with Rice Vinegar. Tokyo: Lyon Books (in Japanese). Ohmori, S., Uozumi, T., and Beppu, T. 1982. Loss of acetic acid resistance and ethanol oxidizing ability in an Acetobacter strain. Agric. Bioi. Chern. 46(2):381-389.

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Ohta, K., and Shinsaku, H. 1983. Role of Tween 80 and monoolein in a lipidsterol-protein complex which enhances ethanol tolerance of sake yeasts. Appl. Environ. Microbial. 46(4):821-825. Osada, S. 1982. Treatment of Diseases with Rice Vinegar. Tokyo: Ken-Yu-Kan (in Japanese). Peterson, E. H., and Hsu, E. J. 1978. Rapid detection of selected gramnegative bacteria by aminopeptidase profiles. J. Food Sci. 43:1853-1856. Sugi, Y. 1983. Recommended by Doctors: Improve Your Health with Pure Brown Rice Vinegar. Tokyo: Kodama Books (in Japanese). Vaughn, R. H. 1942. The acetic acid bacteria. Wallerstein Labs. Commun. 5:5-26. Yu, J. P. 1985. Problems encountered in the solid-state fermentation of vinegar. China Condiment. 2:27-29 (in Chinese).

12 Rice Hulls Bor S. Luh University of California, Davis

According to the statistics supplied by the IRRI (1988), the world's paddy rice (Oryza sativa) production in 1987 was 470 million MT. Most of this tonnage is produced in Southeast Asia. A major derivative of the rice crop is the hull, a fibrous, nondigestible commodity representing some 20% of the dried paddy on-stalk (Yoshida 1981). Dried paddy on-stalk yields 52 wt% of white rice, 20% hull, 15% stalk, and 10% bran. The remaining 3% is lost in the conversion process. If all the paddy rice available were commercially milled, 98 million MT of hulls would have been produced in 1987. Because of their abrasive character, poor nutritive value, low bulk density, and high ash content, only a small percentage of the hulls can be disposed of for certain low-value applications such as chicken litter, juice-pressing aids, and animal roughage. If not properly utilized, rice hulls will create a growing problem of space and pollution in the environment. In some countries, rice hulls and straw are used as fuel in parboiling paddy rice. It is likely that hull utilization will increase in light of the high cost of fuel and the energy crisis confronting the world population. The chemistry and technology of rice hulls have been reviewed (Houston 1972; Beagle 1978; Govindarao 1980; Hsu and Luh 1980; Juliano 1985). 269

270

RICE: UTILIZATION

MORPHOLOGY

The literature on the structure of rice hulls has been reviewed by Houston (1972), Yoshida (1981), and Juliano (1985). Long, rectangular to elliptical cells with thickened, slightly waxy walls were noted in rice hulls. Scanning electron microscopy (SEM) of the rice hull shows a unique cell pattern of the outer surface. The irregular undulating walls of the outer epidermal cells are arranged in axial rows, with unicellular, simple, thick-walled hairs irregularly distributed in both lemma and palea. The cells are somewhat rectangular, with their lateral walls highly wavy or toothed and thickened so that the adjacent cells fit snugly together at these undulations. Watson and Dikeman (1977) described the outer surface of rice hull as composed of dentate rectangular elements. The inner surface of the hull is relatively smooth and free of hair. Thomas and Jones (1970) and Thomas et al. (1972) stated that silica is highly concentrated in the outer layer which is coated with a thick cuticle and surface hairs. The midregion contains little silica. The structural layers of the rice hulls are (1) the outer epidermis, coated with a thick cuticle of highly silicified sinuous cells, among which the surface hairs are found; (2) sclerenchyma of hypoderm fibers, also with a thick and somewhat lignified and silicified wall; (3) spongy parenchyma cells, both elongated with a rather wavy outline and short or quadrilateral, and (4) inner epidermis, generally of isodiametric cells (Houston 1972).

PHYSICAL PROPERTIES

Most rice hulls are straw-colored. Some rice hulls may be white, russet, or reddish brown. The length of rice hulls is about 5-10 mm, and the width varies from 2.5 to 5 mm. The bulk density of rice hulls ranges from 0.10 to 0.16 g/ml, and a true density ranges from about 0.67 to 0.74 g/cm3 (Chopra 1981). The hulls can be compressed to 0.4 gm/cm3 • Hulls are an excellent insulating material. Grinding can raise the bulk density two to four times. The high concentration of opaline silica present in the outer layer of rice hulls results in an effective hardness of approximately 51/z-61/z (Mohs' scale) reported for opal. Therefore, rice hulls can be used as an abrasive. The abrasive characteristics of rice hulls when crushed into angular fragments are intensified. Regular whole-rice hulls have an angle of repose of 35 deg. When ground to 80- and 160-mesh, their angle is 43-45 deg; for material passing 80-mesh, it lowers again to 40 deg.

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271

Table 12-1. Comparative Composition of Rice and Oat Hulls Moisture,% Crude protein, % Crude fat,% Crude fiber, % Available carbohydrate, % Ash,% Silica,% Calcium, mg/g Phosphorous, mg/g Neutral detergent fiber, % Acid detergent fiber, % Lignin,% Cellulose, % Pentosans,% Hemicelluloses, % Total digestible nutrients, %

Rice Hull

Oat Hull

7.6-10.2 1.9- 3.7 0.3- 0.8 35.0-46.0 26.5-29.8 13.2-21.0 18.8-22.3 0.6- 1.3 0.3- 0.7 66 -74 58 -62 9 -20 28 -36 21 -22 12 9.4

8.0-10.5 2.7- 4.3 1.3 25.4-30.1 47.5-51.5 4.9- 6.1 1.9 0.9 66 31 2;14 23;51 39 27 29

Sources: Juliano (1985); Miller and Eisenhauer (1982); National Academy of Science (1971).

CHEMICAL PROPERTIES

The composition of hulls from rice and oats are presented in Table 12-1. It is apparent that rice hull is lower in crude protein, crude fat, and available carbohydrates but higher in crude fiber, ash, and silica compared to oat hull. The total digestible nutrient content of rice hull is less than 10%.

Carbohydrates The major carbohydrates of rice hulls are cellulose, crude fiber, and hemicellulose (Table 12-1). Hemicellulose, chiefly pentosan, is a glucoxylan that can be hydrolyzed to xylose. Starch is usually absent although small amounts are noted in some commercial products.

Delignification of Lignocellulose Solvent refining of lignocellulose residues involves extraction with a solvent containing some water with acid or base, such as butanol, ethanol, phenol, or formic acid (Bungay 1985). Hemicellulose is hydrolyzed during delignification by solvent refining. Delignification of rice hull with a twostage alkali treatment and solvent treatment improves the accessibility of the substrate to cellulose hydrolysis (Ghose 1981). A two-stage catalytic solvent process with 0.5% aromatic acid involving presoaking at sooc

272

RICE: UTILIZATION

followed by delignification at l20°C in 1:1 (v/v) aqueous butanol resulted in 69% removal of lignin from rice hull (Ghose et al. 1983). Conversion of polysaccharides into mixed sugars was 62% for rice hull. Presoaking in an alkaline solution and grinding improved cellulolytic susceptibility of hull. Cryomilling in a hammer mill in liquid nitrogen at -100°C results in a 250mesh rice-hull flour that no longer has the X-ray crystallinity of cellulose and has about one-fourth the volume of the original hull (Sasaki et al. 1977a,b). For pure cotton cellulose, X-ray crystallinity correlates negatively with susceptibility to microbial cellulase (Sasaki et al. 1979c). Cryomilling increases the enzymatic hydrolysis of cellulose with Trichoderma viride from 3 to 35% of glucose, suggesting the incomplete disruption of the physical structure of noncellulose components such as lignin. However, extraction of cryomilled cellulose with cellulose solvent (60% sulfuric acid) increases saccharification of the soluble cellulose by endo-{3-( 1-4)-Dglucanase of A. niger to 86.6%, compared to the 85.3% saccharification achieved using the C 1 enzyme of T. viride. Combined action of the two cellulases gives 93.2% saccharification. Crude Protein

The crude protein content of rice hulls ranges from 1.9-3.0%. A higher protein value undoubtedly reflects some bran contamination. The amino acid composition of protein in hulls is presented in Table 12-2. Lipid

The lipid content of rice hulls ranges from 0.39 to 1.0%. Higher values reported in the literature are probably due to the presence of bran in the sample. According to Hartman and Lago (1976), the lipids from rice hulls contained unsaponifiable matter and free fatty acids four times higher than those from rice bran and rice caryopsis. There were also differences in the fatty-acid composition, as evidenced by the presence of 2-3% of saturated C22 and C24 acids and a lower proportion of unsaturated acids in the lipids of rice hulls. Chromatographic analysis of the unsaponifiable matter of lipids from rice hulls showed that the sterols consist of about 51.95% {3sitosterol, 22.32% campesterol, 20.13% stigmasterol, and 2.92% cholesterol. During grain development, hull lipids decreased in total amount 12-16 days after flowering, mainly from decreases in glycolipids and phospholipids per grain (Choudhury and Juliano 1980).

Lignin and Cutin A large part of the lignin is chemically combined with the hemicellulose. The middle lamella of the cell walls may contain 70% of the lignin associated with pentosans and some cellulose (Neish 1965). Therefore, lignin

RICE HULLS

273

Table 12-2. Amino Acid Content of Rice Hulls Amino Acid Alanine Arginine Aspartic acid Cystine Glutamic acid Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine

Amount, g/16.0 g of N 6.1- 7.0 4.0- 4.7 8.6-10.4 1.8- 2.0 10.4-13.1 5.4- 6.0 1.6; 2.0 3.2- 4.0 8.0; 8.2 3.8- 5.4 1.5; 1.8 4.4- 5.1 6.5-10.3 4.6- 5.4 4.2- 5.0 0.6 2.2 5.5- 7.5

Source: Houston et al. (1969).

values depend greatly on the extraction process used. Leonzio (1966) reported the presence of 19.20-24.47% purified lignin in rice hulls. Cutin is a water-repellent material covering the outer layers of rice hulls. It appears to be a polymer of long-chain hydroxymonocarboxylic acids. The cutin content of rice hull is about 2.2-6.0%.

Vitamins and Organic Acids According to the National Academy of Science report (1971) and Hsu and Luh (1980), the levels of thiamin, riboflavin, and niacin in rice hulls are 0.84-2.40 y/g, 0.62-0.93 y/g, and 14.0-39.5 y/g, respectively. Total acid extracted from rice hulls is 57.8 ± 1.4 meq/kg, of which 30.3 meq is organic acid. Oxalic and citric acids are the major organic acids in rice hulls. The other acids are acetic, fumaric, malic, succinic, and an aromatic acid. The aromatic acids are ferulic, vanillic, p-coumaric, sinapic, p-hydroxybenzoic, salicylic, and indolacetic acids (Mikkelsen and Sinah (1961). Some of these phenolic acids and related substances act as germination inhibitors.

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RICE: UTILIZATION

Table 12-3. Inorganic Components of Rice Hull COMPONENTS AS PERCENT OF HULL

Location

u.s. u.s.

Spain

Ash

K

Na

Ca

Mg

21.5 19.9 20.3

0.73 0.34 0.18

O.Q2

0.08 0.09 0.15

0.04 0.03 0.04

0.01

Fe

p

Cu

Mn

Zn

0.006

0.001

0.001

0.04 0.08 0.01

Source: Hsu and Luh (1980).

Inorganic Component

The major inorganic component of rice hull is ash. It varies from 13.2-29.0% of the weight of rice hull. The silica content of the ash is around 94-96%. A value near or below 90% may indicate a mixture of bran or other low-silica material in the hull sample (Table 12-3). X-ray diffraction studies have shown that pink ash consists essentially of tridymite and cristobalite (Jones 1954). The other components of the ash are K20, CaO, Fe20 3 , P20 5 , S03 ,Na20, MgO, and Cl. The rather wide range of values shown for the elements determined indicates variation in purity of the samples and the accuracy of the analytical procedures used (Table 12-4).

HULL UTILIZATION Agricultural Uses Animal and poultry feeding

Numerous efforts have been made to use rice hulls as cattle feed (Hsu et al. 1976; Hamad et al. 1976; Choung and McManus 1976). Rice hulls are low in digestibility and nutritive value and have sometimes caused harmful effects. This characteristic may be related to the mineral nature of the rice hulls rather than the massive encrusting silica sheath and the lignin that exist in the rice hulls (McManus and Choung 1976; Guggolz et al. 1971). If the integrity of the silica shield and the lignin existing in the hulls were the barrier to microbial attack on the sequestered organic matrix, it would be reasonable to expect that prior grinding of rice hulls to expose the organic matrix would enhance the efficiency of the microbial attack. The nutritive value of rice hulls is: digestion coefficiency (for poultry), 0.17; nitrogen-free extract, 0.17; other extract, 0.41; protein, 0. The National Academy of Science report (1971) showed that the energy of hulls is 0.48

1\.)

Ol

0-0.78

-

0.40 0.0 0.21 Trace-0.21

-

0.53 0.36 0.30

Trace 0.94b Trace _c

0.23 0.28 0.25 0.76 0.24 0.76 0.99 0.23-0.99

0.25 0.86 0.25 0.32 0.24 0.88 0.65 0.25-0.88

-

0.3-2.85

0.46 2.85

-

P205

Fe203

MgO

CaO

0.10 0.10-1.13

-

Trace-0.42

-

Trace 0.42

1.00 0.40

-

-

Trace

Cl

-

1.13

so3

a

Source: Hsu and Luh (1980). Total of potassium plus sodium as oxides. b Total of iron plus aluminum as oxides. c Trace elements present include aluminum, copper, iron, and manganese, as well as detectable amounts of barium, boron, and zinc.

4.75b 0.79-1.59

-

0.78

1.10 1.88Q 1.00 1.59 0.79

94.5 95.5 96.5 96.6c 96.2 94.0 91.2 91.2-96.6

-

Na 20

K 20

Si02

Table 12-4. Analysis of Rice-Hull Ash (% Dry Basis) 1928 1933 1952 1953 1966 1968 1970 Range

Year

276

RICE: UTILIZATION

DE (digestible energy) Meal/kg or 0.39 ME (metabolizable energy) Meal/ kg for cattle; 0.68 DE Meal/kg or 0.5 ME Meal/kg for sheep. The TDN (total digestible nutrients) of hulls for cattle and sheep are 10.8 or 15 .4%, respectively. Hsu et al (1976) found 8.75% total solubles in rice hulls after enzyme treatment. Animals will not voluntarily consume a diet of raw rice hulls alone. Substitutions of 5-50% have been reported, with little economic or nutritional benefit (Choung and McManus 1976). Feed for ruminants

Because of its low total digestible nutrient level, rice hull is used mainly as roughage for ruminants. Houston (1972) stated that rice hull may have a useful role in cattle feed rations in proportions of 20% or less. Rice hull forms the major part (80%) of the concentrate fed to the cattle in India although it should not be more than 15% (Govindarao 1980). About 25% ground rice hull can be fed to finishing lambs, and 80% ground rice hull can be incorporated into the rations of muzzafarnagri sheep in India without any detrimental effect (Ranjhan and Beagle 1978). Houston (1972) reported a rice mill by-product composed of about 61% rice hull, 35% bran, and 4% polish. It is similar to the bran produced in village mills. The legally accepted analysis of rice-mill by-products is 5% protein, 6% fat, 30% crude fiber, and 16% ash. Reported total digestible nutrients in rice hull of 14 moisture content is 9.4% (NAS 1971), 15% in cattle, and 25% in sheep (Kearl 1982). Total digestible nutrients for rice straw was 40% in cattle, 43% in sheep, and 39% in goats. Chemical treatment

The benefit of the sodium hydroxide treatment came from removal of the silica, or modification of the silica and other components of rice hulls. Treatment with increasing amounts of sodium hydroxide results in removal of more silica and lignin (McManus and Choung 1976). Acid treatment following the alkali treatment removed silica to a lesser extent than when the materials were not neutralized. The greatest removal oflignin occurred in alkali and alkali-plus-acid treatment. Huntanuwatr et al. (1974) found that treatment of rice hulls with 8% NaOH, 12% NaOH, and 16% NaOH for 24 hr, followed by centrifugation, increased the rice hull solubility in water and reduced silica content from 21.9% to 10.79%, 4.58%, and 3.02%, respectively, with little change in lignin, hemicellulose, or cellulose content. The digestibility of lignin and cellulose of the rice hulls was not significantly increased by alkali treatment. The function of the alkali treat-

RICE HULLS

277

ment was to free the hemicellulose of the cell wall of rice hulls for digestive attack. Rice hulls treate::i with NaOH increase the digestibility coefficient of dry matter from 5 to 20, of fiber from 12 to 28, and of extract matter from 5 to 38. Guggolz et al. (1971), using an enzymatic digestion test, showed that when rice hulls are treated with 28 kg/cm 2 of steam, there is an increase in DMD (dry-matter digestibles) to 22% and that 28 kg/cm 2 of steam combined with alkali raises the DMD to 38%. Hsu et al. (1976) used the enzymatic digestion test to determine the in vitro digestibility of alkalitreated rice hulls. They found that when the rice hulls were soaked at ambient temperature in NaOH solutions of various concentrations at a ratio of 1:8 (w/v), the enzymatic digestibility was raised from 8.81 to 40.79% as the concentrations of NaOH increased from 0 to 30% (w/v). The limitation in the alkali-soaking process involves its use in large volumes of treatment solution and washing water and the resulting loss of solubilized materials. Hsu et al. (1976) described a "dry process" in which a much reduced volume of concentrated NaOH solution was used, resulting in an in vitro dry-matter digestibility of 35.32% for treated rice hulls. Considering the in vitro nutritive value, cost of treatment, and pollution abatement, the optimal process may be achieved by spraying the rice hulls with 30% NaOH solution until a total of 5% NaOH (w/w) is obtained. Choung and McManus (1976) tested and treated rice hulls in feeding trials with sheep against lucerne (alfalfa). Slow growth was shown by animals receiving 5.0 and 10.0% alkali-treated diets. Animals tolerated the salt content of diets containing rice hulls treated with high levels of alkali. The sheep were able to clear the excess salt from their bodies without significant alteration of their blood hematocrit ratios, and they drank significantly more water. All the sheep fed diets containing rice hulls had appreciable amounts of soluble silica in their blood plasma (> 100 J,tg/1) and urine. Interest in the use of ammonia is related to its potential to increase both digestibility and the nitrogen content of the rice hulls. Hiroshi et al. (1975) found that when rice hulls were treated with ammonia (10 wt%) and water (30 wt%) for 12 months at ambient temperature, the crude protein content of rice hulls was tripled through this treatment. Most of the increased nitrogen was occupied with nonprotein nitrogen. After ammonia treatment, the cell wall constituent of rice hulls was decreased by 6%, and all the noncell wall material was increased. This treatment significantly raised the nutritive value of rice hulls. Another process used to produce ammoniated rice hulls was developed by Ulrey (1966). In this method, the rice hulls were treated in the presence of catalysts with heat and pressure in an atmosphere of ammonia.

278

RICE: UTILIZATION

After ammoniation, the fiber was softened, and it provided a feed acceptable to sheep or cattle. This feed, when fed to steers, produced average daily gains of 1.25 kg on the 10% ration, and 1.16 kg on the 20% ration. When fed at a level of 20% of the total feed mixture, ammoniated rice hulls have been shown to cause toxicosis; 20% ammoniated rice hulls in the feed is considered the maximum level that can be tolerated by cattle without depressing weight gain or feed intake. The U.S. Food and Drug Administration (1966) established the limit for ammoniated rice hulls as a feed supplement not to exceed 20%. Physical Treatment

Physical means of enhancing the nutritional value of low-quality forage include grinding (Minson 1963) and use of gamma irradiations (McManus and Choung 1976). Neither means is very satisfactory. Ground rice hulls are not injurious to cattle when the level in the ration does not exceed 30% (Rusoff et al. 1956). However, according to McManus and Choung (1976), grinding treatment could not increase the dry-matter digestibility of rice hulls. Gamma irradiation slightly increased the solubility in water of ground rice hulls (McManus and Choung 1976). Application of 5-g NaOH/100-g dry matter prior to grinding markedly increased their solubility in water at all levels of gamma irradiation, with no evidence of major interaction between alkali and the irradiation effects. Bedding and litter

Bedding or littering is probably the oldest and most widespread utilization of rice hulls. It is especially good for poultry operations. The litter might also be used as a fertilizer, but information must be developed as to beneficial effects obtainable with various combinations oflitters available. Soil treatment and fertilizers

Incorporating hull into the soil normally occurs as an adjunct to disposal operations. Past efforts have been largely confined to demonstrating that the hull is not harmful to the soil but is slightly beneficial as a fertilizer. Some farmers apply rice hulls or ash to soils to increase the uptake of silica by the plants. Decomposing hulls make soil phosphorus more available. Such benefits appear confined to tight clay or sandy soil, in which decomposing hulls offset silica deficiencies. In some instances, the benefit stems from the effect of hulls as a mulch instead of a fertilizer. Heavy soil, such as claypan, that is incorporated with rice hulls, which have open texture and slow decomposition charac-

RICE HULLS

279

teristics, may result in a good yield of crops. One must be sure that anaerobic decomposition effects are not promoted by excessive compaction or wetness of the treated areas. Rice hulls have been used successfully as a support medium for growing vegetables hydroponically. The hulls have beert found to be satisfactory only after heating, grinding, and treating with a synthetic detergent. The determination to use them should be based on the effect of rice hull ash and silica on the product grown. If the hull particles interfere with root movement and if objectionable materials are leached out from the hull particles, the use of rice hulls as a supporting medium will be limited (Beagle 1974). Building Materials Lightweight concrete blocks

Rice hull can be used as an aggregate in the preparation of lightweight concrete building blocks. A mixture of cement: presoaked hull: water (1.00: 0.25: 0.35 by weight) is pressed in a mold to get the product. The price of lightweight concrete building blocks prepared with rice hull as the aggregate compared unfavorably with the price of other types. Hollow blocks comparable in strength and durability to commercial concrete hollow blocks can be fabricated from rice hull mixed with soil and cement. In Egypt, red bricks were made with rice hull as an ingredient at 1% of the mud. Rice hull has also been used as kiln fuel in combination with furnace oil in a 1: 2 ratio (Ranjhan and Beagle 1978). Fiberboards

There are several thermomechanical processes that have been used for making high-density fiberboards from rice hull. 1. Binderless Boards. The powdered hull (0.25-0.39 mm) was mixed thoroughly with 2 vol% concentrated sulfuric acid or 5-8 wt% rice hull and was sundried. The board was formed by pressing at 60-70 kg/cm 2 for 20-25 min at 165°C or for 12-15 min at 175-200°C. 2. Boards Made with Resin as Binder. The Lignex Products Group of Canada (1980) used phenolformaldehyde resin as a binder for making rice-hull fiberboards. In the production process: a. Hull is mechanically treated, which increases its bulk density from 0.13 to 0.26 g/cm3 • b. The product is blended with 7-8 wt% liquid phenolformaldehyde resin and passed through a tack-removal system, which initially heats the hull and then cools it to make the material free-flowing.

280

RICE: UTILIZATION

c. The hull is deposited on a steel caul plate and hot pressed at 210°C. d. The pressed boards are piled to form a "hot stock" for 8 hr to aid in curing the resin before the boards are trimmed to final size and sanded. At a density of 0.800 g/cm3 with 7-8% resin, the board has a modulus of rupture of 141-176 kg/cm2 , a modulus of elasticity of 28,000-42,000 kg/cm 2, and an internal bond of 4.2-8.4 kg/cm2 • The rice hull board has properties similar to the wood-based fiberboards and is resistant to termites, fire, and rot fungi. Similar results were reported by Shukla et al. (1983). 3. Boards with Sodium Silicate as Binder. Another process uses a mixture of rice hull (100 parts), diatomaceous earth (20 parts), sodium silicate solution, zinc oxide (10 parts), and jute (5 parts) to produce boards of suitable strength. Since the waxy surface of hull or straw rejects the glue, prescratching the surface creates attachment points for the binding material (Rexen 1981). Industrial Uses Absorbent

Rice hull ash has been utilized to absorb oil and provide an antiskid surface. Another area of application of rice hull or its derivative is as a medium for physically dispersing surrounding materials. Its behavior should be determined when it is mixed with a viscous, cohesive, semisolid material. This would allow for additional handling or processing of the mass. Calcium silicide

Current practice for manufacturing calcium silicide is to heat lime, sand, and carbon in an electric furnace. The product is a powerful reducing agent used in explosives and a deoxidizing agent in steel manufacturing. Raw rice hulls contain approximately 20% silica in a very finely dispersed form. Pyrolyzed hull can be chlorinated at 1000°C to give a nearly quantitative yield of silicon tetrachloride, free of most other inorganic chlorides. Solid, organic chlorine-contaminating species have been found to be reaction-intermediates. Commercial application of such silicon derivatives appears economically attractive. Activated carbon

Considerable confusion stems from the use of the term ''activated carbon'' to describe both rice hull carbon containing silica and carbon with silica removed. There is an obvious significant difference in characteristics be-

RICE HULLS

281

tween the two. Similarly, much diverse activity, with confusing results, has been undertaken in connection with the production of activated carbon from rice hulls. Many apparent market opportunities for rice-hull carbon have been deferred because most existing processes for char production result in a very fine material whereas the demand is for larger and more uniform particles (Beagle 1974). Carrier

Rice hull has been used as a carrier in many products. Both the rice mill byproduct and the ground hull have found markets as carriers for vitamins, pharmaceuticals, biologicals, toxicants, and seeds. Most rice-hull utilizations today are based on an empirical reaction to a need. There is a need to study the effect of particle size, shape, and distribution on adsorption of various agents and carrier-concentrate ratios as they affect shelf life and appearance. Cement

A hydraulic cement can be made by grinding together 20-30% lime with rice hull ash (Mehta and Pitt 1974, 1976). The setting and hardening characteristics of rice-hull ash cement are similar to normal portland cement. Typical compressive strengths of rice-hull ash cement mortars, when tested in accordance with the ASTM C109, were 175 kg/cm 2 (2500 psi) at 3 days, 320 kg/cm 2 (4500 psi) at 7 days, and 450 kg/cm 2 (6400 psi) at 28 days. The tensile strength and elastic modules of concretes made with rice-hull ash cement are satisfactory. The water demand of the cement is generally higher than portland cements; hence, mortars made from such cements tended to exhibit higher shrinkage. The hydraulic cements made from rice-hull ash can be treated as a premium product. The unique characteristic, a permanent black color in portland cement, is usually produced by blending with black pigments. Portland cement with up to 10 wt% carbon black or black iron oxide is used for this purpose. The black color produced by these pigmenting agents does not have good long-time stability because of the discoloring effect of Ca(OH)2 produced by portland cement hydration. The setting and strength characteristics of cements containing 10% carbon black or iron oxide are adversely affected. The rice-hull ash cement or a portland cement containing 10-20% rice-hull ash as the black pigment produced mortars and concretes of permanent black color. Moreover, when the rice-hull ash was used as a pigmenting agent, the strength of the portland cement showed improvement (Mehta and Pitt 1976). The mortars and concrete specimens made with a rice-hull-ash cement containing 20% CaO were far superior in resistance to acidic attack

282

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to companion specimens made with an ordinary portland cement. It may be noted that portland cement contains 60-65% CaO and that, upon cement hydration, a considerable proportion of it is invariably present as free Ca(OH) 2 • This accounts for the relatively poor performance of portland cement concretes under acidic environments. The acid-resisting nature of the rice-hull-ash cement is of great interest to the food industry. Many food products contain organic acids such as acetic acid and lactic acid. The former is present in vinegar and pickles and the latter in milk, curds, cheese, green fodder, etc. Fruit juices and soft drinks are also acidic in nature. Since the Ca(OH)2 constituent of hydrated portland cement is readily attacked by acidic materials, the floors and other structural parts made with portland cement concretes do not last when exposed to such environments. Colloidal usage

Rice hull produces an ash with a high silica content made up of extremely fine particles with a high surface area. For utilization as a catalyst carrier, it must have a high surface area as well as the capability for conversion into pellets. For use as a thickening agent, it must have good swelling properties. Where it acts as a dehydrating agent, it must offer efficient water adsorption and provide a high waterholding capacity. Fuel

Utilization of rice hull as fuel can be achieved by combustion in an excess of air and in a controlled atmosphere, by destructive (dry) distillation, by pyrolysis, by gasification (producer gas), and by chemical and biochemical processes (Beagle 1978). Rice hull has been used as boiler fuel for parboiling plants and rice mills in Brasil, India, Italy, and other countries. Rice hull has 60% of the boiler efficiency of coal but produces more ash than coal (Beagle 1978). Approximately 30% of the rice hull in India is used in hull-fired boilers both for parboiling and for steam production (Chopra 1981). The char obtained from traditional rice-hull furnaces contains 36-40% organic matter, mainly carbon, reflecting incomplete combustion of hull as a result of its high ash content (Hamad 1981). The temperature of combustion and sufficient oxygen supply are the major factors influencing the degree of combustion of rice hull. Differential thermal analysis (DTA) of rice hull showed an endothermic peak at 100-l10°C for evaporation of water; an endothermic peak at 200°C due to chemical decomposition of organic compounds; a slow exothermic reaction above 400°C due to gradual change in the structure

RICE HULLS

283

of silica; and a broad peak at about 850°C due to sintering of silica particles (Singh et al. 1977, 1981). Corresponding thermogravimetric analysis showed that loss of hull weight occurred mainly at 100-110 and 230-250°C. Loss of weight continued slowly up to 500°C, which indicated that fine carbon was burned inside the silica pores. At 450°C, more than 90% of the total volatile matter was removed in the absence of air (Hamad 1981). Loss of weight was higher in the presence of air because of oxidation reactions. The carbon content of the residue increased with pyrolysis temperatures between 200 and 500°C, whereas oxygen and hydrogen content decreased sharply. Pyrolysis of hull at 800-850°C for 7 min resulted in 37-40% residue containing 50% organic matter and 50% ash, but the char of combustion at 800°C in the presence of oxygen was 32%, consisting of 38% organic matter and 62% ash (Hamad 1981). Increasing air rates during combustion of rice hull in a fixed-bed furnace favored crystallization of silica, probably because of the higher combustion temperature (Hamad and Khattab 1981). Differential thermal analysis of rice hull fired at 700°C or lower did not show the exothermic peak at 420°C, but that of hull fired at 750°C or higher did (Singh et al. 1981). A DTA rerun of the rice hull fired at 750°C or higher did not exhibit the 420°C peak shown by ash fired at 1100°C. Since the weight loss at 420°C was negligible in ash fired at 900°C and almost the same as ash fired at 750 and 600°C, Singh et al. (1981) considered that this peak was the result of rearrangement of silica. Amorphous silica (disordered cristobalite) was obtained on ashing rice hull up to 700°C (Bartha and Huppertz 1977; Hanafi et al. 1980). Crystallization of silica occurs at 725°C in 24 hr as 20% cristobalite or even at 700°C between 30 min and 1 hr of firing. Firing at 700°C for 15 min was optimum for converting a thin layer of rice hull into white ash with amorphous silica. The silica in white rice-hull ash in hull-fired boilers and in the burning of hull at temperatures exceeding 700°C is a mixture of amorphous and crystalline silica (Chopra 1981). Pyrolysis of rice hull at 500-900°C produced pyrolysis oil, fuel gas, and char, all of which are combustible (Beagle 1978; Allen and Mosley 1981). Calculated heat of combustion was 13.9 MJ/kg for rice hull, dry basis (Hamad et al. 1982). Pyrolysis of rice hull at 420°C produced 45% char, with an energy value of 15.9 MJ/kg; 18.6% oil, with an energy value of 22.6 MJ/kg and 11% gases, with a heat of combustion value of 6.5 MJ/kg. Char may be converted to charcoal briquettes with cooked cassava starch as a binder (20: 1:20 for char, starch, and water). The inflammable gases in producer gas that result from burning of rice hull in a limited supply of air are carbon monoxide and hydrogen (Beagle 1978). The proportion of hydrogen in the mixture is increased if water vapor is introduced into the generator. Producer gas from rice hull may

284

RICE: UTILIZATION

displace 60-90% of the diesel fuel in diesel engines; the comparative thermal efficiency of common systems is over 26% for diesel, 16% for corn cobs or wood waste, 14% for pelletized rice hull, and 8% for loose rice hull (Cruz 1983). The high ash (>20%) content of rice hull caused poorer efficiency and required a rotating grate and an oversized cyclone in the gasifier. Rice-hull briquettes may be prepared in an extruder using hull with 12% moisture at an extrusion temperature of 260-280°C without binder (Pitakarnnop 1983). The briquette had a density of 1.321.34 g/ml. Charcoal yield from the briquette was 40-50%. In addition, because of their high density, the briquettes burned too slowly for producer-gas production. Specific fuel consumption was estimated to be 3.5 kg/ kW-hr. According to Grist (1975), the fuel value of rice hull is approximately 3200 kcal/kg. One can produce 2.5 kg of steam from 1 kg of hull (Schule 1971). Steam consumption is around 7 kg/hp/hr. A mill with a capacity of 1 MT /hr or more can yield sufficient rice hulls to produce necessary steam for milling with a 20% surplus for drying and parboiling. Because of their high ash content, hulls are not easy to burn. It is essential that a special stepped grate furnace, preferably with an automatic feeding device, be supplied. A well-designed combustion chamber can prevent the excessive formation of furnace ash. Automatic ash collectors are used to draw off the incinerated residue. The ash should be cooled, bagged up, and packed for usage as a fertilizer base, thus eliminating hull residue. The main outlet is to use rice hulls and straw as a fuel. The siliceous ash obtained can be incorporated into cement and used as a potential source of silicon for solar batteries. Maheswari and Ojha (1977) presented a detailed report on the fuel characteristics of rice hulls. Furfural

Adequate furfural technology exists to permit its utilization on a plantsized basis. Cooking rice hulls in the presence of an aqueous acid, such as sulfuric acid, with steam distillation, produces furfural. The pentosans present in rice hull are hydrolyzed into pentoses, which are dehydrated into furfural (C5H 40 2) after losing 3 moles of water per mole of pentose. Sharma and Sahgal (1982) used superheated water at 185°C and 1.165 MPa in the acid hydrolysis of rice hull with sulfuric acid (less than 0.5 molar) in a batch reactor. The yield of furfural was 7-9% after heating the mixture for 1-2 hr. The furfural was recoverd by steam distillation.

RICE HULLS

285

Pressing aids

Rice hulls have been used by the food industry as filter (or flow) aids for fruit juices, beverages, wines, etc. The more important areas of concern are yields, contamination problems, and sterilization. In connection with yields, performance (yield comparisons-cake moisture) data should be developed for a given variety of fruit, using particle size and ripeness as parameters. Methods of cleaning in preparation of the hull must conform to legal standards. The procedures for sterilization and cleaning must be cost-effective. Rice-hull utilization may be expanded to areas other than fruit- and vegetable-juice filtration. Water purification

Rice-hull char can be used as an aid in filtration, adsorption, or coagulation of impurities in water. It can compete with diatomaceous earth as a filtering aid. Rice-hull char can compete with active carbon as an absorption medium. Theoretically, rice-hull char is relatively inert. It may have a lower efficiency than active carbon when judged on a comparative weight basis. Actually, the performance of rice-hull char ranges from poor to excellent in adsorbing some organic compounds. Rice-hull ash clears turbid water by acting as a nucleation site. Suspended colloidal impurities become attached to the site and are subsequently "swept out" of suspension as the ash particle settles. Rubber compounding

Rice-hull derivatives (silicates) can be effectively used in rubber compounding, particularly as a reinforcement and as a nonskid additive. For usage by the rubber industry, it must be supported by an adequate program for evaluating the advantages of utilizing rice-hull silica. Initially, a very fine particle material must be prepared in the desired carbon-silica ratio. Then its characteristics must be determined for various rubber formulations. Reinforcement specifications will be required, and advantages should be clearly determined. Colloidal silicas are used to reinforce nonblack rubbers, and carbon-free rice-hull ash could be similarly used. Where particle size is too large or unsatisfactory properties are exhibited, rice hull offers a potential for replacing a portion of the expensive colloidal silica. Rice-hull char can be used as a reinforcement in black rubbers. It is possible that mixtures of carbon black and rice-hull ash could provide superior properties or lower cost compared to carbon black by itself. Rice-hull silica can be utilized to enhance antiskid and abrasive wearing qualities.

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The silica ash produced from rice hull by the Mehta and Pitt process (1974) is in the form of a soft material, characterized by high surface area and cellular structure. The absence of any characteristic peaks of crystalline silica phases in the X-ray diffraction pattern shows that the silica is in a noncrystalline form. Rubber compounds containing 50-100 parts of ash by weight of 100 parts of rubber show mechanical properties that are generally superior to those given by commercially available ground silica or clay fillers. Properties of rubber compounds containing rice-hull ash are comparable to those obtained by using medium thermal blacks as reinforcing agents. Based on a synthetic rubber (SBR 1502), the relative mechanical properties from different reinforcing fillers are compared in Table 12-5. The strength and the elastic and hardness characteristics of rubber compounds made with rice-hull ;ash are further improved by slight modification of the compound compositions, such as introducing silane or using a combination of ricehull ash and a commercial carbon black (HAF Black). Advantages of using rice-hull ash as a filler are that it incorporates readily into the rubber compounds and that the curing times are somewhat quicker compared to those of carbon blacks. The usefulness of rice-hull ash is not limited to the styrene-butadiene type of synthetic rubber (SBR). Good-quality rubber products based on several other types of synthetic rubbers have also been made. It was a surprising discovery that when 60 parts of ash by weight were added to 100 parts of natural isoprene rubber, a product with unexpectedly superior mechanical properties was obtained. The resulting isoprene rubber can have 207-kg/cm2 (2950-psi) tensile strength and 63-kg/cm2 (900-psi) elastic modulus at 300% strain level (Mehta and Pitt 1974). Single-cell proteins

Rice hull has also been used as substrate for microorganisms to produce single-cell proteins (Chan et al. 1979; Shieh et al. 1980). A fermented rice hull feed for livestock and poultry involved pulverizing the hull, sterilizing it by steaming or boiling, swelling polysaccharides by alkali, inoculating the cooled product with microorganisms, mixing the culture at 65-75°C for 12 hr, and drying the fermented product (Sakurai, 1977). The fermented hull had higher crude protein than raw hull (16.6 vs. 4.7% at 14% moisture) as a result oflower crude fiber (25.8 vs. 36.1%) and extensive polysaccharide hydrolysis. Sodium silicate

The silica content of rice hulls varies from 18.8-22.3% (Table 12-1). The silica from rice hulls may serve the food industry better than bentonite and diatomaceous earth because of minimal amount of unwanted elements other than silica.

~

18.3 28.8 63 36

22.5

63.3

65 42 13.5

-

54.8 510

79.4 480

Commercial Medium Thermal Silica, 100 Parts"

62 41 18.2

45.3

21.4

106.8 610

100 Parts" RHA

a

The proportion of the reinforcing agent is based on 100 parts of rubber by weight. Source: Hsu and Luh (1980).

Tensile strength, kg/cm2 Elongation, % Modulus at 100% strain, kg/cm2 Modulus at 300% strain, kg/cm2 Shore hardness number Bashore rebound, % Compression set, %

Commercial Medium Thermal Black, 100 Parts"

(RHA)

54 49 18.5

37.3

14.8

68.2 500

50 Parts" RHA

RICE ASH

Table 12-5. Effect of Different Reinforcing Agents on the Properties of Rubber Compounds

60 50 27.2

55 49 16.6

51.3

17.9

130.8 550

30 Parts" RHA and 25 Parts HAF Black

52.0

17.2

95.6 460

50 Parts" RHA and 0.25 Parts Silane

OF THE MEHTA PROCESS

288

RICE: UTILIZATION

Based on overall operation cost, a sodium silicate plant utilizing rice hulls is more feasible than a conventional plant. This plant should be able to produce sodium silicate at an equivalent cost per MT slightly more cheaply than a normal plant. Transportation and labor costs must be lowered, however, and all the available steam should be utilized. Two unconventional processes, the wet-air oxidation process and the fluidized bed reactor process for making sodium silicate from rice hulls, appear feasible. Steel industry

Rice hull and its derivatives have been utilized by various segments of the steel industry (Beagle 1974). Material responsive to particular use requirements must be available at competitive prices. Some of its current use stems from the remarkably high refractory capability and good insulation qualities offered by rice hulls. Hydrolytic products

Rice hulls have been hydrolyzed with hydrochloric acid, sodium hydroxide, and sulfuric acid under various conditions of temperature and pressure. The resulting hydrolyzate can be used for the growth of microorganisms. The pentosan fraction of rice hulls (16.1% of total dry weight) can be extracted with 11% HCl at l10°C for 3 hr. A concentration of 20% NaOH extracted 72.8% of the pentosan at 80°C. The yield (96.2%) was improved by using 0.4% H 2S04 at 134°C at 2.1 kg/cm 2 for 3.5 hr. More severe conditions resulted in decomposition of the sugars. Rice hulls have been hydrolyzed in a two-step procedure by Dmitrenko (1976), who used 0.4-0.6% H 2S04 in a continuous procedure at 170-190°C. Yeast was grown under nonaseptic conditions, yielding 210-221 kg of dry yeast per metric ton of bone-dry forestry waste. Savinykh et al. (1969) obtained a yield of 51.5% on the growth of Candida tropicalis on the basis of the sugar content. Rice-hull utilization process

Mehta and Pitt (1974, 1976) described a low-cost process for large-scale disposal of rice hulls. The primary product of this process is a special silica material suitable for making acid-resistant hydraulic cements and reinforcing agents for rubber. Heat energy is an important by-product of this process. The paddy milling operation yields hulls at the rate of about one-fifth the weight of paddy. Typically, the hulls consist of about 36% cellulose,

RICE HULLS

289

5

10

TO GRINDING SYSTEM

----z~41:~~

-$~

Figure 12-1. Flow diagram of a 1ypical plantfor producing rice-hull ash and steam: (1) Underground ash silo, (2) dust collector, (3) preheated water, (4) boiler, (5) steam, (6) furnace, (7) surge bin, (8) feeder, (9) air, (10) exhaust or drying system, (11) water, (12) fan, and (13) screw feeder. (From Mehta and Pitt.)

20% lignin, and 20% ash. The ash is derived mainly from the opaline silica present in the cellular structure of hulls. The combustion of organic matter released about 3200 kcallkg of heat energy. Mehta and Pitt (1974, 1976) reported on a large-scale process for disposal of rice hulls. The process consists of burning the organic matter to produce heat energy under conditions such that the residual ash, which is essentially silica, continues to be amorphous. Mehta and Pitt developed an industrial furnace that can burn the hull continuously at relatively low temperatures. The burning time and temperature are controlled so that the cellular structure of the hull is generally not disrupted and the silica thus produced is in a reactive form. Burning the hull under various conditions changes the end characteristics of the material. This process is unique in that it removes most of the organic matter without significantly altering the silica structure. A flow diagram of a typical plant equipped with a steam boiler is shown in Fig. 12-1. From the furnace, the hot gases containing the rice-hull ash are taken to a tube boiler and, finally, to a multiclone type of separator, which separates the ash from the gases. The processing equipment is simple and can be fabricated locally. The refractory-lined furnace looks like an inverted cone, into which hulls are

290

RICE: UTILIZATION

sucked as a result of negative pressure conditions, which are maintained by a fan. After the initial start and when the temperature in the furnace is high enough, the hulls burn by themselves. Individual plants can burn hulls at the rate of 0.5-10 MT/hr. Bigger units can produce large quantities of hot air for crop drying and steam for the generation of electrical energy. After utilization for electrical generation, the low-pressure steam can be used for parboiling or other foodprocessing operations. Smaller units may be more practical in areas where there are a large number of small rice mills. Such units may not be equipped with boilers, especially if the initial capital cost is to be kept low. In such cases, heat energy can be utilized in the form of by-product hot gases, which can be used for partial or complete drying of paddy. REFERENCES

Allen, R. J., and Mosley, R. H. 1981. Mobile pyrolyzer for converting agricultural wastes to synthetic fuels. In Agricultural Residue Management. A Focus on Rice Straw, edited by J. E. Hell. Residue Management Task Force, Davis, CA: Univ. of California Press, pp. 101-110. Barber, S., Benedito de Barber, C., and Tortosa, E. 1981. Theory and practice of rice by-products utilization. In Cereals: A Renewable Resource. Theory and Practice, edited by Y. Pomeranz and L. Munck. St. Paul, MN: AACC, pp. 471-488.

Bartha, P., and Huppertz, E. A. 1977. Structure and crystallization of silica in rice husk. In Proceedings of Rice By-products Utilization International Conference, Valencia, Spain, 1974, edited by S. Barber and E. Tortosa. Valencia, Spain: Inst. Agroquim Techno!. Aliment., pp. 89-98. Beagle, E. C. 1974. Basic and applied needs for optimizing utilization of rice husk. In Proceedings of Rice By-Products Utilization International Conference, Valencia, Spain, Vol. I, edited by S. Barber and E. Tortosa. Valencia, Spain. Beagle, E. C. 1978. Rice-husk conversion to energy. Agricultural Service Bulletin 31. Rome: FAO. Bungay, H. R. 1985. Progress and perspectives of new biomass industries. In Biotechnology in International Agricultural Research, Los Banos, Philippines: IRRI, pp. 319-326. Chan, W. U., Chang, M. Y., Shu, W. H., and Fan, C. C. 1979. Pretreatment of cellulosic agricultural wastes and its effect on fermentation for single cell protein (SCP) production. Taiwan Food Industry Research and Development Institute Report 135. Chopra, S. K. 1981. Cementitious Binder from Rice Husk: An Overview. New Delhi: Cement Research Institute of India. Choudhury, N.H., and Juliano, B. 0. 1980. Lipids in developing and mature rice grain: Phytochem 19:1063-1069. Choung, C. C., and McManus, W. R. 1976. Studies on forage cell walls, III. Effect of feeding alkali-treated rice hulls to sheep. J. Agric. Sci. 86:517-530. Cruz, I. E. 1983. Producer gas from agricultural residues: Its production and

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utilization in internal combustion engines. In Proceedings of the FAOIFHI Regional Technical Consultation on Agricultural Wastes and Solar Technologies for Energy Needs in Farms, Suzhou, China, and Cabanatuan City, Philippines, 1982. Bangkok: Thailand, FAO, pp. 39-65. Dmitrenko, L. A. 1976. Comprehensive processing of raw vegetable substances. Proceedings of Conference on Single Cell Protein of the U.S./USSR Working Group, MIT, Cambridge, MA, March 24-26. FAO. 1974-1975. Rice Bulletin. Crop Forecast. 1974-1975. Rome: FAO. Ghose, T. K. 1981. Cellulose conversion. In Advances in Food Producing Systems for Arid and Semiarid Lands Part A., edited by J. T. Manassah and E. J. Briskey. New York: Academic Press, pp. 255-266. Ghose, T. K., Pannir Selvam, P. V., and Ghosh, P. 1983. Catalytic solvent delignification of agricultural residues. Organic catalysis. Biotechnol. Bioeng. 25:2577-2590. Govindarao, V. M. H. 1980. Utilization of rice husk-A preliminary analysis. J. Sci. Ind. Res. 39:495-515. Grist, D. H. 1975. Industrial use of rice products. In Rice. 5th Ed. London: Longmans. Guggolz, J., Saunders, R. M., Kohler, C. 0., and Klopfenstein, T. J. 1971. Enzymatic evaluation of processes for ruminant feeds. J. Anim. Sci. 33:167-170. Hamad, M. A. 1981. Thermal characteristics of rice hulls. J. Chern. Techno/. Biotechnol. 31:624-626. Hamad, M. A., El Abd, H. A., and Farag, L. M. 1982. Pyrolysis-combustion process of high ash agricultural residues. In Waste Treatment and Utilization. Theory and Practice ofWaste Management, Vol. 2, edited by M. Moo-Young, C. W. Robinson, and G. J. Faquhar. Oxford, England: Pergamon Press, pp. 123-131. Hamad, M.A., and Khattab, I. A. 1981. Effect of the combustion process on the structure of rice hull silica. Thermochim. Acta 48:343-349. Hanafi, S., Abo-El-Enein, S. A., Ibrahim, D. M., and El-Hemaly, S. A. 1980. Surface properties of silicas produced by thermal treatment of rice-husk ash. Thermochim. Acta 37:137-143. Hartman, L., and Lago, R. C. A. 1976. The composition of lipid from rice hulls and from the surface of rice caryopsis. J. Sci. Food Agric. 27:939-942. Hiroshi, I., Yoshiaki, T., Nobuhito, T., and Yukio, M. 1975. Improving the nutritive values of rice straw and rice hulls by ammonia treatment. Japan. J. Zootech. Sci. 46:87-93. Houston, D. F. 1972. Rice Chemistry and Technology. St. Paul, MN: AACC. Houston, D. F., Allis, M. E., and Kohler, G. 0. 1969. Amino acid composition of rice and rice by-products. Cereal Chern. 46:527-537. Hsu, W. H., Lin, K. C., Wu, C. Y., and Huang, F. M. 1976. Conversion ofagrocellulosic wastes to animal feed. I. Alkali treatment of rice hulls to improve nutritive value. Taiwan Food Industry Research and Development Institute Research Report 93. Hsu, W. H., and Luh, B.S. 1980. Rice hulls. In Rice: Production and Utilization, edited by B. S. Luh. Westport, CT: AVI, pp. 736-63. Huntanuwatr, N., Hinds, F. C., and Davis, C. L. 1974. An evaluation of methods for improving the in vitro digestibility of rice hulls. J. Anim. Sci. 38:140-148.

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IRRI. 1988. World Rice Statistics 1987. Los Bafios, Philippines: IRRI. Jones, J.D. 1954. Refractory insulators and porous media from vegetable sources. Can. Ceram. Soc. 23:99-101. Juliano, B. 0. 1985. Rice hull and rice straw. In Rice: Chemistry and Technology, edited by B. 0. Juliano. Westport, CT: AVI, pp. 689-755. Kearl, L. C. 1982. Nutrient requirements of ruminants in developing countries. International Feedstuffs Institute, Utah Agricultural Experiment Station, Utah State Univ., Logan, UT: Utah State Univ. Press. Leonzio, M. 1966. The contents of lignin as a by-product during the elaboration of rice. Riso 15:219-223 (in Italian). Lignex Products Group of Canada. 1980. Rice husk board process. Vancouver: Hawker Siddeley Canada. Maheswari, R. C., and Ojha, T. P. 1977. Fuel characteristics of rice husks. In Proceedings of the Rice By-Product Utilization International Conference, Valencia, Spain, 1974. Vol I. Rice Husk Utilization, edited by S. Barber and E. Tortosa. Valencia: Inst. Agroquin. Tecnol. Aliment., pp. 67-76. McManus, W. R. 1983. Structure of the plant cell wall in relation to its biodegradability. In The Utilisation of Fibrous Agricultural Residues. Australian Development Assistance Bureau Research and Development Seminar 3, Los Banos, Philippines, 1981, edited by G. R. Pearce. Canberra: Australian Government Public Service, pp. 14-32. McManus, W. R., and Choung, C. C. 1976. Studies on forage cell walls. II. Conditions for alkali treatment of rice straw and rice hulls. J. Agric. Sci. 86:453-470. Mehta, P. K., and Pitt, N. 1974. A new process of rice husk utilization. In Proceedings ofRice By-Product Utilization International Conference, Valencia, Spain, 1974, Vol. I. edited by S. Barber and E. Tortosa. Valencia, Spain: Inst. Agroquim. Techno!. Aliment. Mehta, P. K., and Pitt, N. 1976. Energy and industrial materials from crop residues. Resource Recov. Conserv. 2:23-38. Mikkelsen, D. S., and Sinah, M. N. 1961. Germination inhibition in Oryza sativa and control by preplanting soaking treatments. Crop Sci. 1:332. Miller, D. E., and Eisenhauer, R. A. 1982. Agricultural by-products and residues. In CRC Handbook of Processing and Utilization in Agriculture. Vol. 2. Part I. Plant Products, edited by I. A. Wolff. Boca Raton, FL: CRC Press, pp. 691-708. Minson, D. J. 1963. The effect of pelleting and wafering on the feeding value of roughage. Brit. Grassland Soc. Rev. J. 18:39-44. National Academy of Science. 1971. U.S. and Canadian feeds. In Atlas of Nutritional Data. National Academy of Science, Washington, DC. Neish, A. C. 1965. Coumarins, phenylpropanes, and lignin. In Plant Biochemistry, edited by J. Bonner and J. E. Varner. New York: Academic Press. Pitakarnnop, N. 1983. Production and evaluation of rice husk briquettes in Thailand. In Proceedings of the FAOIFHI Regional Technical Consultation on Agricultural Wastes and Solar Technologies for Energy Needs in Farms, Suzhou, China, and Cabanatuan City, Philippines. 1982. Bangkok: FAO, pp. 120-128. Ranjhan, S. K. 1983. Economic evaluation of various processing methods for improving the nutritive value of fibrous agricultural residues for backyard

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ruminant production systems in South and South-East Asian countries. In The Utilisation of Fibrous Agricultural Residues. Australian Development Assistance Bureau Research and Development Seminar 3, Los Baftos, Philippines, 1981, edited by G. R. Pearce, Canberra: Australian Government Public Service, pp. 157-165. Ranjhan, S. K., and Beagle, E. C. 1978. Utilization of rice hulls for animal feeding. Egyptian Technical Cooperation Programme Consultant Report 6/EGY/03/ /.Rome: FAO. Rexen, F. 1981. Industrial utilization of straw. In Cereals: A Renewable Resource. Theory and Practice, edited by Y. Poneranz and L. Munck. St. Paul, MN: AACC. Rusoff, C. L., Frye, J. B., and Epps, E. A. 1956. A look at uses for rice hulls. Hulls fed to cattle produce no ill effects. Rice J. 59(4):28. Sakurai, J. 1977. Utilization of rice by-products in Japan. In Rice By-Product Utilization International Conference, Valencia, Spain, 1974. Vol.4. Rice Bran Utilization: Food and Feed, edited by S. Barber and E. Tortosa. Valencia, Spain: Inst. Agroquim. Tecnol. Aliment., pp. 101-113. Sasaki, T., Sato, Y., and Kainuma, K. 1979a. Saccharification of rice hull glllcoxylan. Nippon Shokuhin Kogyo Gakkaishi 26:493-497. Sasaki, T., Sato, Y., Nakagawa, S., Shiraishi, M., and Kainuma, K. 1979b. Crystallinity and enzymatic hydrolysis of cryomilled rice hull cellulose. Nippon Shokuhin Kogyo Gakkaishi 26:523-529. Sasaki, T., Tanaka, T., Nanbu, N., Sato, Y., and Kainuma, K. 1979c. Correlation between X-ray diffraction measurements of cellulose crystalline structure and the susceptibility to microbial cellulase. Biotechnol. Bioeng. 21:1031-1042. Schule, F. H. 1971. Steam power plants for husk. Hamburg: Schule Manufactures. Sharma, D. K., and Sahgal, P. N. 1982. Production of furfural from agricultural wastes by using pressurized water in a batch reactor. J. Chem. Techno/. Biotechnol. 32:666-668. Shieh, C. H., Barnett, S.M., and Hira, A. U. 1980. Production of enzymes and single cell protein from rice hulls. In Food Processing Engineering. Vol. 2. Enzyme Engineering in Food Processing. edited by P. Linko and J. Larinkari. London: Applied Science Publishers, pp. 289-294. Shukla, B. D., Ojha, T. P., and Gupta, C. P. 1983. Engineering properties of rice husk boards. Agric. Mech. Asia Africa Latin Am. 14(3):52-58. Singh, R., Dhindaw, B. K., and Maheswari, R. C. 1977. Nature of silica in rice husk ash for the production of pure silicon. Rice Process Eng. Cent. Rep. 3(1):8-12. Singh, R., Maheshwari, R. C., and Dhindaw, B. K. 1981. Production and analysis of white ash. Agric. Mech. Asia Africa Lat. Am. 12(3):57-64. Thomas, R. S., Basa, P. K., and Jones, F. T. 1972. Silicon tetrachloride synthesis from rice hulls: Transmission and scanning electron microscope study. Proceedings of the 30th Annual Meeting of the Electron Microscopy Society of America. Baton Rouge, LA: Claitor's Publishing Division. Thomas, R. S., and Jones, F. T. 1970. Microincineration and scanning electron microscopy: Silica in rice hulls. Proceedings of the 28th Annual Meeting of the Electron Microscopy Society of America. Baton Rouge, LA: Claitor's Publishing Division.

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Ulrey, D. G. 1966. Rice hull products and method. U.S. Pat. 3,259,501. July 5. U.S. Food and Drug Administration. 1966. Ammoniated rice hulls. Federal Register31,4,955. FDA, U.S. Dept. ofHealth, Education and Welfare, Washington, DC. Watson, C. A., and Dikeman, E. 1977. Structure of the rice grain shown by scanning electron microscopy. Cereal Chern. 54:120-130. Yoshida, S. 1981. Fundamentals of Rice Crop Science. Los Banos, Philippines: IRRI.

13 Rice Oil Chuan Kao USDA-FGIS

Bor S. Luh University of California, Davis

Rice has relatively low lipid content compared to other common cereal grains or leguminous seeds. Rice lipid is usually called oil because of its unsaturation and liquid nature at room temperature. The oil content of dehulled rice (brown rice) may vary from 1 to 4%, depending on the rice variety and growing conditions. Most of the rice oil is concentrated in the pericarp, the aleurone layer, and the germ of the rice kernel. The fragments of these tissues are combined to form the by-product bran or polish after the rice is milled (also called polished or whitened). The bran contains 15-20% oil while the wellpolished rice (mainly endosperm) has less than 1%. Except for the X-M process, which extracts the rice oil from the whole kernel, all other commercial rice oil producers use bran for oil extraction. The oil so produced is usually called rice bran oil or RBO. The X-M process will be discussed later. Weiss (1983) reported that RBO was sold on a local basis in areas where it was produced. The world production of rough rice was estimated to be about 490 million tons in 1989 (USDA-FAS, 1989). If all the oil in the rice bran is extracted, 4-5 million tons of edible oil can be produced. This is about the same as world peanut oil production. Although in certain countries, notably Japan, India, and Burma, the RBO has already made a significant 295

296

RICE: UTILIZATION

contribution to the edible oil supply, social and technological difficulties have so far prevented full exploitation elsewhere. Efforts to solve the technical problems, however, are being pursued in most rice-producing countries, including the United States (Randall et al. 1985), India (Bhattacharyya et al. 1987), Spain (Barber and Benedito de Barber 1982), the Philippines (Juliano 1983), Taiwan (Chang and Huang 1983), Korea (Kim et al. 1987), and Japan (Zhao et al. 1987). The chemistry and technology of rice bran are presented in Chapter 14 of this book. This chapter will cover oil determination, composition, characteristics, processing, and utilization. DETERMINATION

The main purpose of determining the oil content of rice in the United States is to check the milling degree. Milling degree is an important quality factor of milled rice (head rice and brewer's rice; see Chapter 10). It measures the severity of the polishing process by estimating the residual bran/germ on the rice. According to the USDA procedure, the milling degree is determined by comparing the sample to three standards called official interpretive line samples. The method, though convenient, is not very accurate because the standards are not tied to any definitive chemical/ physical property and are thus subject to change (Kao 1986). Since oil is one of the major components of the bran/germ and has well-defined chemical/physical properties, it becomes a useful indicator of the milling degree. There are two types of oil data determined by the industries, the surface oil and the total oil. The surface oil procedure uses petroleum ether to extract whole-kernel rice (head rice) for exactly 30 min. The substance extracted is considered surface oil. This method is fast and is preferred by the parboil rice industry. The total oil procedure extracts ground samples with the same solvent for 2.5 hr or longer, and the substance extracted is considered total oil. This method is widely used to check the oil content of the brewer's rice. The USDA Federal Grain Inspection Service has been interested in using a near-infrared (NIR) technique to determine the total oil content in rice because of its speed and accuracy. This technique involves the developing of a calibration equation and testing the accuracy of the equation. The calibration equation is derived by correlating the solvent extraction data with the NIR spectral data by multiple linear regression statistics. The calibration constants developed for long- and medium-grain rice are shown below.

RICE OIL

297

CALIBRATION CONSTANTS

Wavelength, nm

Long-grain

Medium-grain

16SO 2100 21SO 2310

62.66 -S4.04 -112.90 149.20

37.75 -9S.45 -93.SO 151.SO

The correlation coefficient R between the NIR determined values and the solvent extraction values was about 0.98. The root mean square of the difference, also known as standard error of prediction (SEP), was 0.10-0.15% (Kao 1988). COMPOSITION

Crude RBO, that is, n-hexane-extracted RBO, contains glycerides, free fatty acids, phospholipids, glycolipids, sterols, tocopherols, waxes, etc. (Barber and Benedito de Barber 1982; Sayre 1988). Their compositions are discussed below. Glycerides

The chief component of the RBO is triglycerides, which make up about 80% of the crude RBO. Because of strong lipolytic activity in the bran, substantial amounts of the triglycerides will be hydrolyzed to diglycerides, monoglycerides, and free fatty acids (ffa) under hot and humid conditions. This is the main reason why the RBO deteriorates during storage. Three fatty acids: palmitic, oleic, and linoleic, constitute more than 90% of the fatty acid portion of the glycerides. The rest of the fatty acids are myristic, palmitoleic, stearic, linolenic, and arachidic (Table 13-1). Table 13-1. Fat1y Acid Composition of Rice Bran Oil

Fatty Acid

Composition

Rice Bran Oil, %

Myristic Palmitic Palmitoieic Stearic Oleic Linoleic Linolenic Arachidic

(CI4: 0) (CI6: 0) (Cl6: 1) (CIS: 0) (CIS: 1) (CIS: 2) (CIS: 3) (C20: 0)

0.1- 1.0 I2.0-1S.O 0.2- 0.6 1.0- 3.0 40.0-50.0 20.0-42.0 0.0- I.O 0.0- 1.0

Source: Lu and Williams 1965.

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RICE: UTILIZATION

Aoyagi et al. (1985) reported that rice bran stored at higher temperatures (30-40°C) showed a considerable increase in acid value, whereas peroxide value remained unchanged. In brown rice similarly stored, both the acid and the peroxide values remained stable. Successive fractions of rice grains obtained by abrasion were stored separately; outer layers were more strongly hydrolyzed than inner ones, suggesting that the distribution of the lipolytic activity was predominantly in the outer layer of the grains.

Phospholipids Crude RBO contains about 2% phosphatides, which is relatively high compared to other vegetable oils. The phosphatides are the principal components of gum or lecithin. Phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol are the predominant classes (Adhikari and Adhikari 1986).

Glycolipids Crude RBO contains about 1% glycolipids. This group of compounds form the major part of starch lipids (Juliano 1983; Azudin and Morrison 1986; Perez et al. 1987). The main component fatty acids of the starch lipids are palmitic, oleic, linoleic, and linolenic acids, and the component sugars are galactose and glucose. Glycolipids associate closely with starch and protein and affect the cooking property of the rice as well as the flavor of sake brewed thereof (Ishikawa and Yoshizawa 1974).

Sterols and Oryzanol Sterols represent the typical nonsaponifiable matter of the rice oil. These include free sterols, esters, sterylglycosides, and acylsteryl glycosides and may constitute up to 5% of the oil weight. The most abundant sterol is {3sitosterol, which makes up about 50% of the total sterol. Jeong et al. (1984) used TLC to separate the nonsaponifiable matter into three fractions and identified each fraction with GLC and GC-MS. Ten sterols were confirmed as 4-desmethylsterol, nine as 4-monomethylsterol, and four as 4,4-dimethylsterol. Oryzanol is a valuable component of the nonsaponifiable portion. Seetharamaiah and Prabhakar (1986) reported that soap stock obtained from alkaline refining of the oil contained 1. 3-3.1% oryzanol. It could be effectively extracted with diethyl ether. The optimum pH for the extraction was 9.5. The oryzanol could be purified by an alumina column and crystallized in methanol-acetone (2: 1). The recrystallized material had a melting point of 133-139oC and absorption maxima at 230, 290, and 314 nm. This compound has an antioxidation property similar to that of vitamin E and is claimed to promote human growth, facilitate blood circulation, and

RICE OIL

299

7r--------------------------------------. 6

5 cf!.

•

High wax bran

D Low wax bran

4

X

C'il

3:

3 2

40

10

50

Temperature oc Figure 13-1. Temperature effect on wax extraction.

stimulate hormonal secretion. A pharmaceutical preparation known as OZ has been developed from oryzanol in Japan (Yokochi 1974; Okada and Yamaguchi 1983). Wax

RBO contains variable amounts of wax (2-5%), depending on the extraction method and the origin of the bran. Figure 13-1 shows the temperature effect on the extractable wax from high- and low-wax rice brans. The solubility of the wax increased exponentially with the temperature. Rice wax is insoluble in acetone or isopropyl alcohol, has iodine value 11-12, melting point 82-84°C, and a light-tan color (Chang et al. 1980). It is, however, soluble in hot hexane. It has a tendency to settle to the bottom of the tank where the oil is stored. Yoon and Rhee (1982) separated the tank settlings into hard wax and soft wax. The hard wax had a melting point of 79 SC and was composed of saturated fatty alcohols of C24, C26, and C30, saturated fatty acids of C22, C24, and C26, and n-alkanes of C29 and C31. The soft wax had a melting point of 74°C and was composed of saturated fatty alcohols of C24 and C30, saturated fatty acids of C16 and C26, and n-alkanes of C21 and C29. Belavadi and Bhowmick (1988), however, found that fatty alcohol from C24 to C38 were all present in the wax. Comparison of data before and after alkaline hydrolysis showed that the wax contained only 33% monomeric esters; the remainder may be present as polymeric esters as found in carnauba wax.

300

RICE: UTILIZATION

Table 13-2. Tocopherol Content of Crude Rice Bran Oil (mg/100 g Oil) TOCOTRIENOLS

TOCOPHEROLS

a

Ester Free Total

3.8 49.1 52.9

{3

0.4 1.5 1.9

'Y

0.2 6.1 6.3

a

'Y

0.2 27.9 28.1

0.1 38.1 38.2

/'j

2.2 2.2

Total

4.7 124.9 129.6

Source: Kato et al. 1981.

Tocopherols Rice germ and bran have a relatively high content of tocopherols. These compounds are known for their antioxidation properties and are able to prevent oxidative degradation of the oil. Kato et al. (1981) found that atocopherol, a-tocotrienol, and y-tocotrienol constituted the major part of this group. Table 13-2 shows that ,8-tocopherol and 8-tocotrienol and the ester forms were relatively small. Saker et al. (1986) studied the components of wheat, maize, and rice germ oils and found that the tocopherol contents of these oils were in the range of 32-67 mg/100 g, which is somewhat lower than Kato's value. RICE-OIL PROCESSING

The purpose of rice-oil processing is to isolate the oil from the bran and convert it into high-quality edible oil. The processing steps usually include the following: cleaning, heat treatment, drying, extraction, dewaxing, degumming, deacidification (refining), decolorization (bleaching), deodorization, and winterization (Fig. 13-2).

Cleaning The raw bran is cleaned by screening and aspiration to remove foreign materials, paddy kernels, hulls, broken rice, etc., which have low oil content or may contaminate the products.

Heat Treatment Heat treatment is used to free the lipids from other components in oil seeds to facilitate oil extraction. The major function of heat treatment of rice bran, however, is to inactivate the lipolytic enzymes (lipases) present in native bran. Lipases catalyze the hydrolysis of glycerides into free fatty

RICE OIL

301

Impurity

Solvent

Wax Degumming agent

Phosphatides (Lecithin)

Alkali

Soap stock

Kaolin Steam/vacuum

Distillate (Tocopherol)

Stearin

Figure 13-2. Flowchart for rice-bran-oil production.

acids and glycerol and cause the reduction of oil yield during refining. Hot air, steam, and microwave energy have been used to heat the bran (Chang et al. 1980; Rhee and Yoon 1984; Chakraverty and Devadattam 1985). Generally speaking, steam is more effective than hot air or microwave energy in destroying the lipolytic enzymes, and all heat treatments require adequate mixing to prevent localized overheating or underheating. Extrusion cooking has been studied extensively because of its versatility and high output rate. Studies showed that extrusion-cooked bran was more stable and had larger particle size than brans treated otherwise (Chang et al. 1980; Huang and Chang 1983; Sayre et al. 1985). Kim et al. (1987) compared solvent extraction characteristics of rice bran pretreated by hot air, steam, or extrusion and found that the extruded bran had a significantly higher solvent percolation rate than the steamed or air-heated samples.

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RICE: UTILIZATION

,-... 11.0

• Extrusion 0 Hot air drying b. Steam cooking

Q)

0

~ 6.0

Ol

0

::- 3.3

6 0

:::::1

1.8

"'0

·v;

Q)

0:: ~ 0

1.0 0.5

\., •,

·-..

........

20

·--·--·--·--·--·--·--·--~-L~ 40 60 80 100 • 120 140

Percolation Time (minutes) Figure 13-3. Effect of different heat treatments on rice-oil extraction rate.

The extraction time to reach 1% residual oil was shortened by about 90% (Fig. 13-3). An experimental extruder for small rural rice mills to stabilize rice bran as soon as it is produced was developed in Taiwan (Chang and Huang 1983). The extruded bran showed little increase in free fatty acids for at least 10 days and was suitable for storage or for transport to a large-scale oil-extraction plant. The fine particles that tend to plug up the filter during extraction were greatly reduced, and the extraction efficiency was improved. Randall et al. (1985) reported that the optimum temperature for extrusion was 130°C. After the extrusion, the bran temperature should be maintained at 97-99°C for an additional 3 min to allow sufficient time for enzyme inactivation. The moisture content of the bran should be adjusted to 12-13% before extrusion. After extrusion or steaming, the bran moisture has to be reduced to less than 10% to retard microbial growth. Extraction The earliest method of oil extraction used high pressure to squeeze the oil out of the oil-rich materials. Both the screw press and the hydraulic press were once very popular for extracting the oil from peanuts, cotton seeds, soybeans, sesame etc. This method was rather inefficient, however, especially for low-oil-content stock like rice bran. The solvent extraction method can extract 95-99% of the oil in the raw material and is ideal for

RICE OIL

303

Figure 13-4. Continuous countercurrent RBO extractor.

rice-oil extraction. Many organic solvents are suitable for oil extraction; however, n-hexane has become the most popular organic solvent in modern oil-extraction plants because of its efficiency, safety, and availability. Based on construction, there are three types of extractors: batch type, battery type, and continuous type (Chang et al. 1980). The batch type uses one or more extractors in which the raw material is placed; the hexane from the solvent tank is pumped to the extraction vessel, and the solvent level is maintained to percolate the bran. The miscella (oil solution) is filtered and pumped to the evaporator for oil separation and solvent recovery. The battery type of extractor is a semicontinuous or batch countercurrent system. The fresh solvent is applied to only one batch while the micella obtained is used to treat the contents of all other extraction vessels in a countercurrent pattern. The continuous type of extractor has a countercurrent extraction tube in which the oil-rich bran enters into the head end and the defatted bran exits from the tail end while the fresh solvent enters into the tail end and the micella exits from the head end. Inside the tube is a mixing conveyor to keep the bran and solvent mixed and to move the bran ahead. The wet defatted bran is desolventized, dried, and cooled. The micella is pumped to a distillation plant in which the oil and solvent are separated. The products are defatted bran and crude RBO (Fig. 13-4). Solvent Extractive Rice Milling

This process carries the commercial name X-M Rice Milling Process, which combines the conventional rice milling (polishing) and the solvent extraction of the rice oil (Hunnell and Nowlin 1972). Brown rice, free from

304

RICE: UTILIZATION

hull and other impurities, is spray-coated with warm rice oil (0.5 wt % of brown rice) and tempered for 4 hr. This treatment is designed to soften the bran to facilitate its removal during the succeeding solvent extractive milling. The treated rice is fed to duo-stage mills and irrigated with recycled micella from the settling tank while the milling takes place. The concentration and temperature of the micella are carefully controlled to minimize rice breakage. The milled rice is transported to a vibratory screen, where it is washed with fresh hexane to remove the adhering bran. After draining, the rice is transferred to a desolventizer. The desolventizer is a vertical tower in which the product cascades from top to bottom through two sections. During this time, the residual liquid hexane is evaporated by the countercurrent flow of the warm mixture of solvent vapor and inert gas. The dried rice is cooled and transported to grading, storage, or packaging areas. The micella-bran slurry is transferred to a settling tank for the bran to settle, and the clarified micella is pumped to the duo-stage mills. A series of two horizontal centrifuges are used to separate the bran from the micella and to wash the bran sequentially with dilute micella and fresh hexane. The hexane-damp bran cake from the second centrifuge is discharged through a venturi to a superheated hexane vapor stream for desolventizing. The desolventized bran and the hexane vapor are separated in a cyclone, and the dried bran is purged with warm inert gas prior to pneumatic conveyance to storage or bagging station. Recovery of the third product, rice oil, begins with the removal of residual fine bran particles. The micella from the first horizontal centrifuge contains some very fine, slow-settling bran particles. It has an oil concentration of 11-14%. Solubilized with the oil is the rice wax fraction, which amounts to as much as 3-5% of the total oil. The micella stream passes through a bank of liquid cyclones to remove any remaining bran particles. The micella is then cooled to precipitate part of the wax in the oil. Water and silicate floccing agent are added to the cooled micella stream just prior to the centrifugation. The fine bran particles and about half the wax fraction are removed in this operation. The clarified micella is then distilled in a standard stripper-evaporator to obtain a clear medium-brown rice oil containing 1-2% wax. Traditional supplies of crude RBO have suffered from problems of high refining losses resulting from high levels of free fatty acids, the presence of wax fraction, and finely suspended bran particles. X-M processing has greatly reduced these negative characteristics. Since the X-M process extracts the oil from the whole-grain rice, the oil yield is expected to be higher than that from the bran alone. Table 13-3 shows that X-M oil and conventional RBO have the same general composition.

RICE OIL

305

Table 13-3. Comparison of Conventional Rice Bran Oil and X-M Rice Oil Conventional Properties Specific gravity at 25°C Iodine number Saponification value Unsaponifiable matter, % Fatty acid ester composition, % Myristic Palmitic Stearic Oleic Linoleic Linolenic Arachidic

0.916- 0.921 99-108 181-189 3.0 - 5.0 0.4 12.0 1.0 40.0 29.0

- 1.0 -18.0 - 3.0 -50.0 -42.0 1.0 Trace

X-M 0.917-0.920 100-105 188-192 2.0 0.49 13.8 2.01 43.6 36.6 1.77 0.91

Source: Hunnell and Nowlin (1972).

The X-M plant at Abbeville, Louisiana, owned by Riviana Foods, had been in operation for about 20 years before its shutdown in 1982. Among the causes for the shutdown were depreciated equipment, excessive solvent loss, uneconomical plant scale, and a mediocre plant site in the city (Kohley 1989). Supercritical carbon dioxide has been studied to extract the oil from the bran. The operating pressure varied from 150 to 350 kg/cm 2, and temperature was held at 40°C. Fractions obtained at higher pressures contained less free fatty acids and waxes or unsaponifiables. Phosphorus and iron contents were very low, and the oil color was lighter than that extracted with hexane. This extraction method may simplify some steps of the succeeding refining procedure (Zhao et al. 1987). Dewaxing

Rice bran oil contains substantial amounts of wax, which is not found in other vegetable oils. The wax has a relatively high melting point and must be removed for the oil to be suitable for human consumption. The simplest method to remove the wax is to cool the oil in a settling tank. The wax crystallizes and precipitates to the bottom and can be removed by filtration or centrifugation. Other methods of dewaxing include crystallization of the wax from micella at low temperature (Bhattacharyya et al. 1983; Martovshchuk et al. 1982), addition of electrolytes, ionic or nonionic surfactants (Sah et al. 1983), tripolyphosphate or application of an electrostatic field (Martovshchuk et al. 1982).

306

RICE: UTILIZATION

Degumming

The gumming substances in the crude RBO are primarily polar lipids with surface-active properties, and their presence causes losses during neutralization because of the formation of emulsions. This leads to poor separation of soap stocks, entrainment of oil in the soap stock and residual soap in the neutral oil. The common method of degumming involves the hydrolysis of the gums at 60-80°C with a small quantity (0.5-1.5%) of degumming agents, followed by gum removal with filtration, settling, or centrifugation. Different degumming agents, such as water, phosphoric acid, oxalic acid, sulfuric acid, and nonionic surfactants, have been studied with varying degrees of success (Bhattacharyya et al. 1983; Kim et al. 1985). Deacidification

Deacidification and refining were reciprocally used by some authors to describe the process of removing the acidity from RBO. The most common method of deacidification is to neutralize the free fatty acids with a calculated amount of caustic soda. The free fatty acids are converted to sodium salts (soap stock), which is separated by settling or by centrifugation. It is at this stage that most problems have been met in the past. High refining losses, as much as 10 times the free fatty acid content, have been encountered as a result of difficulties in separating the soap from the oil. The cause of the high refining loss is not entirely clear although the concentration of caustic soda, mixing time, and temperature have been known to affect the characteristics of the soap stock formed (Cornelius 1980). Micella alkali refining, where neutralization of the oil is carried out in a hexane solution, is widely used for refining RBO of high acid content (Chang et al. 1980; Wang 1984; Bhattacharyya and Bhattacharyya 1985; Bhattacharyya et al. 1986). The principle of micella alkali refining is to let the free fatty acids react with caustic soda while they are dispersed in the solvent. The entrainment of neutral oil by the soap stock formed can be greatly reduced. Besides the neutralization, various deacidification methods have been investigated, including steam distillation (Kim et al. 1985), alcohol extraction (Bhattacharyya and Bhattacharyya 1983; Bhattacharyya et al. 1987), and reesterification (Moon and Rhee 1980; Bhattacharyya and Bhattacharyya 1987). Bleaching

The green coloration resulting from the milling of immature rice can be removed without difficulty by using activated acidic clay (Lynn et al. 1968). Other pigments in the RBO can also be removed. About 3-5%

RICE OIL

307

(based on oil weight) of the clay is added to the oil. The mixture is agitated and heated to l20°C for about 20 min. After cooling, the earth is removed by filtration, and a clear golden oil can be obtained (Akiya 1967). Deodorization

The combination of high-vacuum and steam purging is a most efficient method for removal of odors from the RBO. The process involves blowing live steam through the heated oil at 220-250°C under vacuum (3-5-mm Hg pressure). Volatile compounds such as peroxides, aldehydes, and ketones, either with objectionable odors or with pleasant flavors, are stripped off during this process. After deodorization, the oil is cooled down under vacuum to about 50°C. The deodorized oil is essentially tasteless and odorless (Cornelius 1980). Winterization

Winterization is carried out to remove saturated glycerides, commonly known as stearins, which have relatively high melting points and only a limited solubility in the unsaturated glycerides. The process consists of chilling the RBO very slowly in a large tank and holding it at soc or lower for a number of days. The saturated glycerides crystallize out and are separated by filtration. The separated stearins are not discarded but can find use as the solid fat fraction in margarine or shortening formulations. Considerable development work has been done to determine the optimum cooling rates, holding times, and filtration techniques to give rapid winterization with good yield (Lynn et al. 1968; Yokochi 1974). UTILIZATION OF RICE BRAN OIL

Rice bran oil can be used for edible or industrial purposes. Only highquality RBO is used for edible purpose. The richness of polyunsaturated fatty acids is considered beneficial for the prevention of arteriosclerosis and heart disease. Rice bran oil has better oxidative stability than its competitive products such as soybean oil or cotton seed oil because of its high tocopherol and low-linolenic-acid contents. Rice bran oil was found to have better thermostability than double-fractionated palm olein. When both were heated at 180°C for 50 hr, the free-fatty-acid content of the palm olein increased from 0.23 to 1.30 whereas that of the bran oil increased from 0.17 to 0.64 (Fig. 13-5, Yoon et al. 1987). Available evidence showed that RBO performed well in frying tests, giving low peroxide, foam, free fatty acid, and polymer formation (Lynn et al. 1968; Kim and Yum 1983). The winterized RBO is suitable for making

308

RICE: UTILIZATION

1.4 . . . . . . . - - - - - - - - - - - - - - - - - - - - - - ,

1.2

e

Palm oil D Rice bran oil

0.8 ~

~ 0.8 LL LL

0.6

Heating Time (hours) Figure 13-5. Comparison of RBO vs. palm oil.

mayonnaise or salad dressing because of its cold temperature stability, color and flavor compatibility, and ability to form stable emulsions with other ingredients. The stearin separated by winterization can be used in margarine and shortening formulations. As mentioned earlier, oryzanol has been used in pharmaceutical preparations to promote human growth and hormonal secretion. Low-grade RBO is not suitable for human consumption. It can be used in animal feed formulations or for producing solidified oil, stearic and oleic acids, glycerine, and soap. It can also be chemically modified to become antirust, anticorrosion, or lubricating agents. Rice wax was reported to have a structure similar to carnauba wax and can be used in confectionery, cosmetics, shoe polish, auto wax, or industrial coating purposes (Chang et al. 1980). REFERENCES

Adhikari, S., and Adhikari, J. 1986. Indian rice bran lecithin. J. Amer. Oil Chern. Soc. 63(10):1367-1369. Akiya, T. 1967. Edible rice bran oil in Japan. Japan. Agric. Res. Quart. 2(3):27-31. Aoyagi, Y., Koyama, S., Kamoi, 1., and Obara, T. 1985. Studies on rancidity of rice bran. Part 1. Changes of rice bran oil on storage. Nogaku Shuho 30(2):100-106.

Azudin, M. N., and Morrison, W. R. 1986. Non-starch and starch lipids in milled rice. J. Cereal Sci. 4:23-31. Barber, S., and Benedito de Barber, C. 1982. Improvement of rice bran for better

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309

utilization of its lipid fraction. Proceedings of 7th World Cereal and Bread Congress, Prague, pp. 961-66, New York: Academic Press. Belavadi, V. K., and Bhowmick, D. N. 1988. An investigation of rice bran oil tank settling. J. Amer. Oil Chern. Soc. 65(2):241-245. Bhattacharyya, A. C., and Bhattacharyya, D. K. 1983. Refining of high ffa rice bran oil by alcohol extraction and alkali neutralization. J. Oil Techno!. Assoc. India 15(2):36-38. Bhattacharyya, A. C., and Bhattacharyya, D. K. 1985. Refining of high ffa rice bran oil by mixed solvent-alkali neutralisation process. J. Oil Techno!. Assoc. India 17(2):31-32. Bhattacharyya, A. C., Majumdar, S., and Bhattacharyya, D. K. 1986. Edible quality rice bran oil from high ffa rice bran oil by micella refining. J. Amer. Oil Chern. Soc. 63(9):1189-1191. Bhattacharyya, A. C., and Bhattacharyya, D. K. 1987. Deacidification of high ffa rice bran oil by reesterification and alkali neutralization. J. Amer. Oil Chern. Soc. 64(1):128-131. Bhattacharyya, A. C., Majumdar, S., and Bhattacharyya, D. K. 1987. Refining of high ffa rice bran oil by isopropanol extraction. Oleagineux 42(11):431433.

Bhattacharyya, D. K., Chakrabarty, M. M., Vaidyanathan, R. S., and Bhattacharyya, A. C. 1983. A critical study of the refining of rice bran oil. J. Amer. Oil Chern. Soc. 60(2):467. Chakraverty, A., and Devadattam, D. S. K. 1985. Conduction drying of raw and steamed rice bran. Drying Techno[. 3(4):567-583. Chang, S. C., Saunders, R. M., and Luh, B. S. 1980. Rice oil: chemistry and technology. In Rice: Production and Utilization, edited by B. S. Luh, Westport, CT: AVI, pp. 764-89. Chang S.C., Sun, C. T., and Liu, T. Y. 1980. Development of rice bran oil I. Food Industry Research and Development Institute Research Report 172. Taiwan. Chang, S.C., You, Y. H., Sun, C. T., and Liu, T. Y. 1980. Development of rice bran oil II. Refining of rice bran oil. Food Industry Research and Development Institute Research Report 193. Taiwan. Chang, S.C., and Huang, C. S. 1983. Rice bran treated by extrusion-cooking for oil extraction. Food Industry Research and Development Institute Research Report 290. Taiwan. Cornelius, J. A. 1980. Rice bran oil for edible purposes: A review. Tropical Sci. 22(1):1-26.

Huang, C. S., and Chang, S.C. 1983. Treatment of rice bran by extrusion-cooking for oil extraction-An experiment prior to large-scale demonstration and extension. Food Industry Research and Development Institute Research Report 293. Taiwan. Hunnell, J. W., and Nowlin, J. F. 1972. Solvent extractive rice milling. In Rice Chemistry and Technology, edited by D. F. Houston. St. Paul, MN: AACC. Ishikawa, T., and Yoshizawa, K. 1974. Studies on changes of lipids in sake brewing. II. Changes oflipids in the process of washing, steeping and steaming of rice used for sake brewing. Nippon Nogei Kagaku Kaishi 48:337-341. Jeong, T. M., Yang, M.S., and Hah, B.S. 1984. Sterol composition of rice bran oil. J. Korean Agric. Chern. Soc. 27(2):119-128.

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Juliano, B. 0. 1983. Lipids in rice and rice processing. In Lipids in Cereal Technology, edited by P. J. Barnes. New York: Academic Press, pp. 305-330. Kao, C. 1986. Determination of rice milling degree with near infrared reflectance method. Proceedings of 21st Rice Technical Working Group, Houston, TX. College Station, TX: Texas A&M University. Kao, C. 1988. Determination of total rice oil content with NIR instruments. Proceedings of 22nd Rice Technical Working Group, Davis, CA. Kato, A., Tanabe, K., and Yamaoka, M. 1981. Esterified tocopherols and tocotrienols in rice bran oil, soybean oil and sesame oil. Yukagaku 30:515-516. Kim, C. J., Byun, S.M., Cheigh, H. S., and Kwon, T. W. 1987. Comparison of solvent extraction characteristics of rice bran pretreated by hot air drying, steam cooking, and extrusion. J. Amer. Oil Chern. Soc. 64(4):514-516. Kim, G. S., and Yum, C. A. 1983. Studies on the properties and frying performance of domestic rice bran oil. Korean J. Food Sci. Techno!. 15(1):77-89. Kim, S. K., Kim, C. J., Cheigh, H. S., and Yoon, S. H. 1985. Effect of caustic refining and steam refining on the deacidification and color of rice bran oil. J. Amer. Oil Chern. Soc. 62(10):1492-1495. Kim, S. K., Yoon, S. H., Kim, C. J., and Cheigh, H. S. 1985. Effect of oxalic and phosphoric acid on degumming of rice bran oil. Korean J. Food Sci. Techno[. 17(2): 128-130.

Kohley, D. 1989. Personal communication. Lu, T. C., and Williams, V. R. 1965. The effect of length of storage on the fatty acid composition of rice lipids. Proceedings of lOth Rice Technical Working Group. Davis, CA. College Station, TX: Texas A&M University. Luh, B. S. (Ed.) 1980. Rice: Production and Utilization. Westport, CT: AVI. Lynn, L., Steen, G. J., and Anderson, R. M. 1968. New rice oil. Food Techno[. 22:1250-1252.

Martovshchuk, E. V., Arutyunyan, N. S., and Martovshchuk, V.I. 1982. Characteristics of different methods for the extraction of waxes. Maslo-Zhir. Prom-st. 10:20-23. Moon, S. H., and Rhee, J. S. 1980. Study on reesterification of rice bran oil containing high free fatty acids and glycerol. Korean J. Food Sci. Techno/. 12(3): 193-199.

Okada, T., and Yamaguchi, N. 1983. The anti-oxidation and pharmaceutical properties of oryzanol. Yukagaku 33:305. Perez, C. M., Juliano, B. 0., Pascual, C. G., and Novenario, V. G. 1987. Extracted lipids and carbohydrates during washing and boiling of milled rice. Staerke 39(11):386.

Randall, J. M., Sayre, R. N., Schulz, W. G., Fong, R. Y., Mossman, A. P., Tribelhorn, R. E., and Saunders, R. M. 1985. Rice bran stabilization by extrusion cooking for extraction of edible oil. J. Food Sci. 50:361-364. Rhee, J. S., and Yoon, H. N. 1984. Stabilization of rice bran by microwave energy. Hanguk Sikpum Kwahakhoechi 16(1):113-19. Sah, A., Agrawal, B. K. D., and Shukla, L. S. 1983. A new approach in dewaxing and refining rice bran oil. J. Amer. Oil Chern. Soc. 60(2):466. Saker, A., Fahmy, A. A., and Roushdi, M. 1986. Evaluation of some chemical components in wheat, maize and rice germ oils. Egypt Grasas y Aceites 37(3): 134-136.

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Sayre, R.N., Nayyar, D. K., and Saunders, R. M. 1985. Extraction and refining of edible oil from extrusion-stabilized rice bran. J. Arner. Oil Chern. Soc. 62(6): 1040-43. Sayre, R. N. 1988. Rice bran as a source of edible oil and higher value chemicals. Presented at the American Association of Cereal Chemists 73rd Annual Meeting, Oct. 12, 1988, San Diego, CA. St. Paul, MN: AACC. Seetharamaiah, G. S., and Prabhakar, J. V. 1986. Oryzanol content oflndian rice bran oil and its extraction from soap stock. J. Food Sci. Techno/. 23(5):270-273. USDA-Foreign Agriculture Service (FAS). World Agriculture Production, 1989. Wang, W. L. 1984. Improvement of rice oil refining-Micella alkali refining on pilot scale. Food Industry Research and Development Institute Research Report 341. Taiwan. Weiss, T. T. 1983. Food Oils and Their Uses. Westport, CT: AVI. Yokochi, K. 1974. Rice bran utilization. Proceedings of International Conference on Rice By-Products of Utilization, Valencia, Spain. Vol. III. Valencia: Institute for Agricultural Chemistry and Food Technology, Valencia, Spain. Yoon, S. H., Kim, S. K., Kim, K. H., Kwon, T. W., and Teah, Y. K. 1987. Evaluation of physicochemical changes in cooking oil during heating. J. Arner. Oil Chern. Soc. 64(6):870-873. Yoon, S. H., and Rhee, J. S. 1982. Composition of waxes from crude rice bran oil. J. Arner. Oil Chern. Soc. 59(12):561-563. Zhao, W. Q., Shishikura, A., Fujimoto, K., Arai, K., and Saito, S. 1987. Fractional extraction of rice bran oil with supercritical carbon dioxide. Japan Agric. Bioi. Chern. 51(7):1773-1777.

14 Rice Bran: Chemistry and Technology Bor S. Luh University of California, Davis S. Barber and C. Benedito de Barber Instituto de Agroquimica Y Tecnologia de Alimentos, CSIC

INTRODUCTION

Rough rice, or paddy, consists of a white starchy endosperm kernel surrounded by a tightly adhering bran coat, an adhering germ with the total enclosed within a loose outer hull or husk. All rice is milled before consumption, producing hull, bran, germ, and white rice. Although a small amount of rice is consumed as brown rice, which still contains the bran and germ, white rice is the principal food staple of over 2.5 billion people worldwide. Rice bran and rice germ are rich in protein, lipids, dietary fiber, vitamins, and minerals. These qualities lead to a high demand for them as feed (Piliang et al. 1982). The quantity of bran and germ available from rice-milling operations throughout the world is about 30 million MT/year. Except for some limited exceptions, neither bran nor germ is consumed as food. This is due to the high fiber content and possible hull contamination and to the rapid development of rancidity caused by lipase and lipoxidase activities after milling. Recent progress in rice bran stabilization by extrusion cooking has improved the shelf life of the product (CFTRI 1983; Randall et al. 1985; Saunders 1990). 313

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RICE MILLING AND RICE BRAN PRODUCTION

Milling methods vary from simple hand-pounding with a mortar and pestle to large-scale processing in highly mechanized mill plants. Hand-pounding still accounts for a major percentage in many important areas. The remaining technologies can be classified under two major categories, depending on whether hulling and whitening are carried out in one or several steps. The Engleberg huller is widely used to remove hull and bran in a single operation. Hull and bran are discharged together with the broken rice (Barber and Benedito de Barber 1980).

Bran from Shellers The most common machines used in hulling paddy rice are the underrunner disk huller and the rubber-roll huller, which is gaining popularity. Both machines produce sheller bran. It may include a small proportion of pericarp, some germ, and small fragments of endosperm as well as dust. The underrunner disk huller performs the work. The paddy is forced between two horizontal cast iron disks that are lined with an abrasive coating. Pressure and friction are applied to remove the hull. Even though the clearance between the disks is adjusted to the optimum conditions, some damage to the pericarp and germ cannot be avoided. The rubberroll huller, when properly adjusted, does not damage the pericarp and rarely removes the germ from the caryopsis. The paddy grains are caught under pressure between the two rubber rolls and the hull is stripped off. Consequently, bran from the rubber-roll huller basically consists of hull fragments and impurities and contains almost no germ. The underrunner disk huller produces 1-2.5% bran with reference to paddy rice. The rubberroll huller gives productions lower than 0.5%. The discharge from the huller is a mixture of brown rice, paddy, hulls, bran, dust, broken rice, and immature paddy grains, Bran, dust, and small broken rice are separated by sieving. An airstream passing through it separates the bran and dust from the brokens. The industrial hullers hull only 80-95% of paddy in a single pass. After separation of hulls, bran, dust, and brokens in the hull separator, a mixture of brown rice and paddy remains; the paddy is then separated in a paddy separator.

Bran from Whiteners In the process of whitening, the pericarp, tegmen, aleurone layer, and germ are removed from brown rice. The bran is made up largely of fragments of the above coverings, plus some starchy endosperm, bits of the caryopsis and, occasionally, some particles of hull.

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In removing bran from brown rice, two kinds of machines are widely used: (1) the abrasive type of whitening machines, either vertical, like the European cono mills, or horizontal, the Japanese design; and (2) the friction type of whitening machines, like the Japanese horizontal jet pearler. In the abrasive machines, brown rice is whitened as it passes through the clearance between an abrasive roller and a wire screen (European mill) or perforated cylinder (Japanese mill). The abrasive roller, with sharp edges of vitrified particles, acts as a blade to cut and remove small bits of the bran layer from the brown rice. The abrasive type of whitening machines have a high peripheral roll speed and a low pressure charge to grains. In the vertical whitening cone, the bran passes through the wire screen and drops into the bottom of the cone housing, from which it is scraped by a rotating scraper and unloaded. Air sucked through the machine serves to cool the system but will remove some bran, which is recovered by cyclone separation. In the abrasive type of horizontal whitening machine, jet air is blown through the hollow part of the main shaft into the milling chamber and, as it cools the rice grains, blows off the bran adhered to the whitened kernels. In the friction type of whitening machines, the Japanese jet-pearler type, brown rice is whitened on a different principle. Pressure is applied to the grains as they pass through the clearance between the screen and the milling roller; the bran layer of the brown rice is loosened and peeled off by means of friction caused by the action of grains rubbing together under pressure. Jet air is blown through the hollow part of the main shaft through the rice grains. It blows off the adhered bran and removes the freed bran as it leaves the machine through the perforated screen. The multipass whitening process is gaining in popularity because it produces higher head rice output than the single-pass whitening process. The process of polishing removes from the already whitened rice any fine particles adhering to the grain, just as the kernel acquires a glossy appearance. The two types of polishing machines more widely used, the vertical cone polisher and the horizontal polisher, are based on the same principle. A cone or a cylinder is mounted on a shaft and is housed in a screen casing. The space between the cone or cylinder and the screen forms the polishing chamber. The cone or cylinder is provided with leather strips on the surface, and the polishing is accomplished by the rubbing effects produced by these leather strips when the shaft revolves. The detached loose flour-polish-is sucked out of the machine and recovered in a cyclone system. In some countries, calcium carbonate is used as a milling aid, usually 0.25% with reference to the paddy rice. No matter how well a whitener machine works, some breakage of the grain is unavoidable. Grain fragments of various sizes are produced. The

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finest fragments pass, along with the bran and the germ, through the perforations of the wire screen or cylinder of the milling chamber openings of 1.30 x 1.25 mm.

Germ and Bran Separation The combined streams coming out from the whitener machines consist of a mixture of bran, germ, starchy endosperm particles, and hull fragments. Sieving in combination with an airstream is used to accomplish separation of major fractions-bran, germ, and brokens of various sizes. In many countries, the commercial bran includes the germ. In Italy and Spain, the separation of the germ is a common practice. In Spanish mills, the mixture of by-products from the whitener machines pass through the rotating hexagonal reel and the germ separator. The former, a rotatory sieve, with a mesh of approximately 0.8 mm (No. 20 ASTM standard), allows bran, fragmented germ, and germs of smaller size to pass through. The germ separator combines oscillating sieving and pneumatic force to separate particles differing in size and density. It comprises a first sieve, with openings of 0.8 mm, to remove residual bran; a second screen with openings of 1.5 mm to separate the germ, and a third screen, with perforations of 2 mm, to separate small from large brokens and kernels of small size that might be present. An airstream is sucked through the germ fraction discharge, removing light impurities such as bran and hull. Further purification of the germ fraction can be achieved by pneumatic separation.

HISTOLOGY AND HISTOCHEMISTRY OF COMMERCIAL RICE BRAN

Papers dealing with outer layers of the caryopsis have been published (Barber et al. 1972 a,b, 1976; Little and Dawson 1960; Saio and Noguchi 1983). The rice caryopsis is a fruit in which the seed occupies the greatest part. It is covered by two florescent glumes: the lemma, which is the largest and has an awn or beard, and the palea. Two small sterile lemmas, the rachilla and the pedicel, can be present in the paddy rice to be milled. In the process of milling, the caryopsis becomes disclosed, showing the pericarp or outermost layer. Immediately under the pericarp, the seed covering known as the testa by some authors and as the tegmen by others, the aleurone layer and the starchy endosperm are located. The germ remains in a cavity in the lower abdominal area of the caryopsis, stuck to the endosperm and outwardly covered by the aleurone layer, the seed coat and the pericarp and, externally, by the lemma. The whitening process is intended to remove the pericarp, the

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Table 14-1. Types of Discrete Particles Identified in Spanish Commercial Rice Bran SIMPLE PARTICLES

Type

Composition

COMPOUND PARTICLES

Type

a

Fragments of florescent glumes

b

Fragments of sterile glumes

j

c

Fragments of trichomes

k

d

Fragments of pedicel

e

Fragments of pericarp

m

f

Fragments of starchy endosperm

n

g

Germ, whole or fragments

0

h

Fragments of fibers

Composition

Fragments of pericarp and seed coat Fragments of seed coat and aleurone layer Fragments of pericarp, seed coat, and aleurone layer Fragments of pericarp, seed coat, aleurone layer, and starchy endosperm Fragments of starchy endosperm and aleurone layer Fragments of germ, flattened cell layer, and starchy endosperm Fragments of germ, aleurone layer, seed coat, and pericarp

Published with permission (Barber and Benedito de Barber 1980).

tegmen, the aleurone layers, and the germ, although parts of the starchy endosperm are also separated. Pineda (1976) observed 15 kinds of discrete particles (Table 14-1), and a few small fragments of the abrasive coating of the cono mills were identified in commercial bran. Type a Particles: Fragments of Florescent Glumes

Type a particles have irregular polygonal shapes and are of variable size, usually ranging from 25 to 40 f.L, although a few fragments can reach 2.5 x 1.5 mm; the thickness of cross sections varies from 80 to 120 f.L· Most particles come from longitudinal fragmentation of the hull. Its outer surface is rough and wrinkled, covered by entire and/or broken trichomes, whereas its inner surface is plain. In a cross section cut, four layers

can be seen: an external epidermic layer, an esclerenchymatic layer, a parenchymatic layer, and an internal epidermic layer. An extracellular layer, the cuticle, is present outside the epidermis. The external epidermic layer is made up of thick-walled epithelial cells (30-80 x 20-10 f.L for those of the palea and 60-90 x 50-120 f.L for those of the lemma), which are radially elongated and axially oriented. in rows. The esclerenchymatic layer is composed of two to four layers of thick-walled (4-6-JL) cells,

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200-610 p,long for those of the lemma and 150-630 p,long for those of the palea. The parenchymatic layer is made up of several layers of cells. Cells are of two types, tangentially elongated and short, with sizes varying from 20 to 30 x 10 to 15 p,, and thin cell walls (2 p,). Among the parenchymatic cells, tube and cross cells are placed. The internal epidermis (6-12 p, thick) is formed by three thin-walled isodiametric cell layers, tangentially oriented. Between the esclerenchymatic and parenchymatic layers, the vascular bundles are located. Carbohydrates are present in the cell walls of type a particles. Cellulose is the major carbohydrate, along with hemicelluloses, mainly pentosans. Lignin appears to be intermingled with the cellulose of the cell walls and is chemically combined with hemicelluloses. Proteins are apparently absent, as shown by the mercuric chloride-bromophenol blue reagent. Black Sudan stains intensely the particle outer surface, indicating the presence of wax and cutin (Pineda 1976). Silica is abundant in the extracellular cutin-silica layer, the outer epidermis, and the esclerenchymatic layer. Type b Particles: Fragments of Sterile Glumes

The sterile glumes are boatlike, with the forward end sharp-pointed and the rear end U-shaped. Fragments of sterile glumes, not numerous in bran, are of variable sizes and, occasionally, they are more than 2 mm long. The surface is plain. The trichomes are less frequent and are smaller than those in the lemma and palea. The thickness of the fragments varies from 60 to 120 p,. Their histological structure is simpler than that of florescent glumes. In cross section, there is an outer epidermis, an inner epidermis and, between them, a parenchymatic layer. The outer epidermis consists of a single layer of rectangular cells from 50 to 70 x 5 to 10 p,, tangentially elongated, with thick outer walls (3 p,), coated externally by a thick (5 p,) cuticle. The inner epidermis has similar characteristics. The intermediate parenchymatic tissue consists of two to four cell layers. The cells are variable in size (20-70 x 7 p,). Type c Particles: Trichome Fragments

The entire trichome is conic, transparent, uncolored, and empty. In commercial bran of short-grained varieties, entire trichomes and fragments, varying from 100 to 350 p, in length with a maximum diameter of 30 p,, have been detected. In the cell walls of trichomes, carbohydrates were detected with the PAS (periodic acid-SchifO method, lignin with Schiff s reagent, and lipids, only in cross sections (Pineda 1976) with Black Sudan.

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Type d Particles: Pedicel Fragments

Fragments of pedicel are scarce in bran. They are cylindrical fragments of variable sizes, up to 2-3 mm, with grooved surfaces. Their cell walls react positively to stain tests for carbohydrates, lignin, and silica, and negatively for proteins and silica. Type e Particles: Pericarp Fragments

Type e particles have an elongated shape, variable size-generally no more than 800 ~A--and a thickness of 6-8 IL· The pericarp tissues can be strongly compressed so that it is difficult to distinguish their characteristic constitutive layers. They are visible in some varieties only. Six layers, five of which are transversely elongated, can be distinguished. Because of their high differentiation, these layers can be subdivided into epidermis, hypodermis, cross cells, and tube cells, in that order, moving inward. The epidermis consists of a single layer of cells, transversely elongated, with sinuous end walls. Cells in noncompressed pericarp fragments vary in size from 5 x 3 to 20 x 10 IL· On the outer walls of the epidermal cells, there is a thin cuticle. The hypodermis is composed of several layers of parenchymatic cells, partially crushed, transversely elongated, with dimensions varying from 15 x 80 to 5 x 12 IL· Two to five layers of elongated cross-cells of 6-IL width and 1-2-~A- depth, arranged in files and rows, give the tissue, along with the parenchymatic layers, a netlike look. Finally, the tube cells, with a long and approximately cylindrical shape, 3-5 IL in diameter, lie with their long axes parallel to the long axis of the caryopsis. The mean thickness of pericarp cell walls is 2 IL· (Little and Dawson 1960). Carbohydrates have been identified in the pericarp: cellulose and hemicellulose. Also present are lignins, proteins, lipids-cutin and/or wax, phytin, anthocyanins (Chang and Bardenas 1965), and silica. Pericarp cell walls, mainly those of epicarp, contribute notably, along with the seed coat, to higher fiber content of rice bran. Starch is apparently absent. Lignin has been detected in pericarp cell walls. It is abundant in the epidermis. Schiff's staining failed to detect it in tube cells, even though the cells are lignified. Pericarp cell walls can be stained with typical protein reagents. Staining with Hg-BPB is positive in hypodermis and tube cells and negative in epidermis. On the free surface of pericarp, lipids, cutin, and probably wax can be detected with Black Sudan. Type f Particles: Starchy Endosperm Fragments

Typefparticles are one of the most abundant types. Size varies from 1 x 1.5 to 30 x 15 IL· The largest particles are usually components of subaleurone endosperm. These are parenchymatic cells with lumina full of com-

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pound starch granules and protein bodies. The smallest particles come from the caryopsis nucleus and are cell fragments. The cells are either . polygonal, generally irregular pentagons or hexagons in cross section, or slightly elongated. Those of the central core have isodiametric shapes ranging in size from 45 x 50 to 80 x 105 11-· The mean thickness of endosperm cell walls is about 0.25 11-· In the starchy endosperm, starch, cellulose, hemicellulose, proteins, and lipids have been detected. Cellulose and hemicellulose are located in the cell walls and starch in the lumen. Starch granules are polygonal, usually five-sided, and compound. Sizes of individual granules range from 0.3 to 13 11-· Starch granules are small (2-4 JJ-) in subaleurone cells and larger (5-9 JJ-) in cells of the kernel nucleus. Size of compound granules varies from 12 x 10 to 20 x 10 11- in the short grain. Proteins occur as protein bodies about 1 11- in size in the inner cells; as cementing material between protein bodies and compound starch granules (Del Rosario et al. 1968); and as a lipoprotein membrane surrounding individual starch granules. Type g Particles: Entire Germ or Fragments of Germ

Whether or not it is degermed at the mill, commercial rice bran always contains entire germ and fragments of germ. These fragments can easily be distinguished from other particles. The most conspicuous fragments are (1) entire plumule, (2) coleoptile, (3) entire coleoptile and plumule, (4) primary root with root cap and part of coleorhiza, and (5) scutellum and epiblast (see also particles n and o). The histology and histochemistry of rice germ have been the subject of detailed studies (Barber et al. 1972 a,b). The germ (Fig. 14-1) is composed of the embryonic axis (which includes the plumule, the coleoptile, the primary root and the hypocotyl) and the tissues surrounding it (the scutellum, the coleorhiza, and the epiblast). The germ is covered by the aleurone layer, the tegmen, and the pericarp. The plumule has two to three embryonic leaves.lt is igloolike in shape, 0.3 mm in diameter and 0.4 mm in height. The embryonic leaves have polyhedral thin-walled parenchyma cells, isodiametric (7JJ-) in cross section and elongated in longitudinal section. They are covered by the upper and lower epidermis and coated by a 0.1-0.2-wthick cuticle. The provascular bundles of the leaves have polygonal cells in cross section of about 4 JJ-, and rectangular cells in longitudinal section of about 4 x 11 11-· The apical meristem has isodiametric cells (4 JJ-). The coleoptile covers the plumule and has a pore in its apex. It is 0.11-0.18 mm thick and is composed of 9-12 layers of polygonal cells. It is covered by an outer

Ge

Hv

Ep

Cr

(B)

(A)

, ·~ (C)

••

Figure 14-1. Histology and histochemistry of commercial rice bran: (A) and (B) longitudinal sections of germ; (C) various types of bran particles; (D) type k particle, composed of pericarp (Pe), seed coat (fe), and aleurone (AI). AI, aleurone layer; Cl, coleorhiza; Co, coleoptile, Cr, wrinkle; En, endosperm; Ep, epiblast; ES, scutellum, Ge, epitheliar gland; Hv, provascular bundle; Ma, apical meristem; Pe, pericarp; PI, plumule; Ra, primary root; Te, seed coat.

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epidermis with a 1.1-1.3-~-t-thick cuticle and an inner epidermis with a 0.5~-t-thick cuticle. The primary root is cylindrical, about 300-350 1-L in diameter and 0.45 mm in length. It is composed of several tissues arranged in radial symmetry: a 6-10-~-t-thick cuticle (thinner, 1.5 /-L, in apical) meristem, the epidermis and subepidermis (a single layer each of prismatic cells, of 11 x 23 1-L and 7 x 14~-t, respectively), the exodermis (two layers of cells of various sizes), the cortex (70 1-L thick, 5-7 layers of round cells of 10-20 1-L in size), the endodermis (a single layer of prismatic cells, of 6 x 5 ~-t), the pericycle (1-2 layers of cells), and the central cylinder (vascular cylinder), which consists of the protophloem, the protoxylem, the metaxylem, and the parenchymatic cells. The tip of the primary root is protected by the calyptra or root cap (about 40 1-L high). The hypocotyl joins the primary root and the plumule. It is made up of pro vascular bundles surrounded by parenchymatic cells. The scutellum is located between the embryonic axis and the endosperm. The greatest part of the scutellum is composed of polygonal parenchymatic cells, 14 to 28 1-L in longitudinal section. The scutellum is surrounded externally by an epidermis that is modified to form the scutellar epithelium in the area next to the endosperm; this consists of radially elongated, thin-walled cells arranged in palisade and some epithelial glands. A provascular bundle extends into the scutellum from the plumule. The epiblast is fused to the scutellum and surrounds the coleoptile. Its thin-walled cells are parenchymatic, polygonal, and isodiametric (about 6 ~-t) in cross section, and elongated (7-12 ~-t) in longitudinal section. Starch, hemicellulose, cellulose, lipids, proteins, basic and sulfur amino acids, tryptophan, and ash have been identified histochemically in rice germ. Germ-cell walls react positively to PAS (periodic acid-Schift) reagent for total carbohydrates and to cellulose and hemicellulose tests; cell walls of the primary root and cuticles of the primary root, coleoptile, and scutellum appear to be rich in hemicellulose. Cuticles of the epidermis of plumule, coleoptile, primary root, and scutellum react positively with PAS (Pineda 1976). The cytoplasm of the cells of the embryonic axis and of surrounding tissues contains simple starch granules; these are not abundant (1-16 per cell) but are round and of variable size (0.5-5~-t). Granules are more numerous in the scutellum and coleorhiza and are apparently absent in the epidermic layers. The tissues of the germ were stained with Black Sudan. Lipids occur in the cytoplasm as globules of diverse size (0.5-4 ~-t); they are abundant in the coleoptile and scutellum and scarce in the plumule, primary root, andhypocotyl. The cuticle of the epidermis of plumule, coleoptile, primary root, and scutellum reacts positively to Black Sudan.

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The cytoplasm and the nucleus, including the plasmatic membrane, react positively to a bromophenol blue test for proteins. In the cytoplasm of parenchyma cells of plumule, coleoptile, primary root, scutellum, and coleorhiza, tiny protein granules (0.51 p.,) and dispersed proteins are detected; the cytoplasm of the respective epidermis cells shows only dispersed proteins. Provascular bundles are weakly stained with bromophenol blue. Proteins are absent in the cuticles. The tissues containing proteins react positively to naphthol-yellow for lysine, hydroxylysine, histidine, arginine, and terminal amino groups and to DDD (2,2'-dihydroxy-6,6' dinaphthyl disulfide) for tryptophan. The germ contains minerals distributed throughout. The plumule and the primary root are more intensely stained than the coleoptile; minerals are abundant in the scutellum, particularly in the cell layers near the endosperm. The structure of rice scutellum has been examined by scanning electron microscopy (Tanaka et al. 1976). Scutellar cells contain many rounded particles, around 2-3 f.L in diameter, covered with a membranous coat that resembles aleurone particles of the aleurone layer. Particles in both tissues are characterized by a high magnesium content and potassium salts of phytic acid. Type h Particles: Fibers

Fibers originate from knots of the panicula base and are scarce. Some are very long (1 em or even more), ribbonlike, and twisted. They do not show a definite cellular structure; between two thick, almost parallel walls, they show a cavity about 30 f.L wide. Fibers react positively to PAS stain for carbohydrates and negatively to stains for lignin, proteins, lipids, and silica. Type i Particles: Fragments of Pericarp and Seed Coat

These particles and those of type k are the major components of commercial bran. They are rolled or bent flakes with a smooth, shining surface and a round inner surface of different sizes, between 200 and 300 f.L· In particles with compressed tissues, the thickness ranges from 10 to 15 p.,. The histological and histochemical particularities of pericarp have been described above (see under Type a Particles). The seed coat (tegmen or testa) consists of (1) the fatty cuticle; (2) the spermoderm, which is located next to the pericarp; and (3) the perisperm, which is next to the aleurone layer. In commercial bran, only the cuticle and a layer (2-6 f.L thick) containing the remains of the inner integument and nucella, have been detected. The cuticle, 1 to 3 f.L thick, is occasionally discontinuous. The tegmen in the germ area is thinner. Some commercial bran particles consist only of pericarp and cuticle.

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The seed coat, except the cuticle, reacts positively to the PAS test for carbohydrates and to the Hg-BPB test for proteins. Cellulose is the major constituent of cell walls. The cuticle absorbs Black Sudan, but the remains of the inner integument and nucella are stained very weakly. The integument and nucella contain lignin. Neither the pericarp nor the seed coat reacts positively to the silica test (Yoshida et al. 1971). Type j Particles: Fragments of Seed Coat and Aleurone Layer

This is a type of particle not abundant in commercial bran. These particles contain only one layer of aleurone cells. Generally, neither the seed coat nor its constituent layers are removed alone during milling. Although a part of the endosperm, aleurone cells come out of the caryopsis preferably stuck to the seed coat (particles j and k) rather than with the starch endosperm (particle m). The size ofj particles ranges from 100 to 300 f.L in length and from 15 to 20 f.L in width. The seed coat is around 6 f.L thick. The characteristics of the seed coat are described under Type i Particles. Aleurone cells are predominantly polygonal. Those from the ventral side are almost perfect rectangles, and those from the dorsal side are irregular hexagons (Del Rosario et al. 1968). They are nucleated parenchymatic cells, with cell walls around 1-3 f.L thick, rich in protoplasmatic constituents. Aleurone cells are around 25-30 f.L long and 6-10 f.L thick. The aleurone layer on the germ is thinner, and its cells are smaller. The aleurone cells contain the aleurone grains or aleurone particles. These have been isolated as a white ivory powder from rice bran using differential centrifugation in nonaqueous media. Its yield ranges between 2 and 3 wt% of the bran fraction used (2-4 wt% in bran/unpolished grain). Subcellular aleurone particles are spherical grains about 1-3 f.L in diameter. They exhibit no strata structure and, instead, show embedded electrondense bodies. The cell walls and lumina of aleurone cells react positively to carbohydrates. Starch granules smaller than 5 f.L have been detected. Aleurone cell walls are stained by reagents for cellulose and hemicellulose or pectin. Staining with Hg-BPB indicates the presence of proteins in the aleurone cells. A weak, pale staining suggests the presence of dispersed protein material in the lumen. The Hg-BPB reagent shows a thin cuticle along the inner border of aleurone cell walls (Pineda 1976). Isolated aleurone grains showed no iodine reaction, and no starch granules were recognized under a transmission electron microscope. Protein content was 11.7%; protein solubility in water was 6.03%; 0.5 M NaCl, 0.60%; 0.05 M HCl, 0.25%; and 0.2 M NaOH 2.19%. Gamma, and gamma2 globulins are localized in the aleurone cells, as shown by means of a fluorescent-antibody technique; the same globulins appear to exist in the scutellum (Hori-

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koshi and Morita 1975). Acid-soluble organic phosphorus amounts to 97.3% of the total phosphorus, and almost all of it exists as phytic acid. The aleurone particle is the accumulation site of phytic acid in rice grain. The distribution of 3H -myoinositol administered to ripening grains of rice was followed by microradioautography, and the 3H was found exclusively in aleurone particles (Tanaka et al. 1974). The electron-dense materials embedded in the aleurone particles of mature rice grains are potassium and magnesium salts of phytic acid (Ogawa et al. 1975). The phosphorus and protein content of the protein bodies in the endosperm and the aleurone particles differ sharply. Protein bodies are rich in protein (about 60%) and very low in phosphorus (0.5%). About 6% of the total protein in the protein bodies is water-soluble whereas, in the aleurone particles, 70% of the total protein is water-soluble. Other Types of Bran Particles (k-o)

Type kparticles are composed ofpericarp, seed coat, and aleurone layers. Reported sizes range between 130 x 50 and 560 x 105 J.L. Most particles have one to two aleurone cell layers; few have five to seven. Presumably, this has a bearing on the fact that Japonica varieties have one to two aleurone cell layers in the ventral side of the caryopsis and five to seven in the dorsal side. Aleurone cells appear generally intact. In some particles, the lipid cuticle of the seed coat appears interrupted; then the pericarp and seed coat are around 20 J.L thick. Particles of type 1 include pericarp, seed coat, aleurone layer, and starchy endosperm, and they are scarce. Their size ranges generally between 400 x 260 and 735 x 200 J.L. Particles of type m are composed of a starchy endosperm and aleurone layer. Their size varies; generally it is less than 95 x 60 JL. Particles of type n include germ, flattened cells layer, and starchy endosperm. Usual sizes range between 690 x 320 and 410 x 225 J.L. Germ, mainly scutellum, is the major component. The layer of flattened cells is around 5-20 J.L thick. Particles of type o include germ, aleurone layer, seed coat, and pericarp. They are scarce and of various sizes (Pineda 1976). General histological and histochemical characteristics of anatomic layers constituting particles k through o (Table 14-1) coincide with those described in preceding sections. CHEMICAL CONSTITUENTS OF BRAN, POLISH, AND GERM Proximate Analysis of Bran and Polish

The composition of rice bran depends on a variety of factors associated with the rice grain itself and the milling process. Major factors associated with the rice grain are varietal and environmental variability in (1) average

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chemical composition, (2) distribution of chemical constituents, (3) thickness of anatomical outer layers, (4) size and shape of grains, and (5) resistance of grains to breakage and abrasion. Major factors associated with the milling process are (1) processing methods and machines, and (2) milling conditions as they affect degree of milling. Bran products obtainable from different alternatives of processing rice are (1) those from one- step milling, i.e., "huller bran," and (2) those from multistep milling, such as (a) sheller bran from hulling, (b) bran partially degermed or with all of its accompanying germ, including or not including polishings, (c) polish, and (d) germ from whitening. Data published on the composition of bran vary within a range. Because of frequent variations in bran composition, it is a market practice to guarantee a limit composition (Barber and Benedito de Barber 1985a). Bran from the hulling step differs in composition from that produced in the whitening steps. It is lower in protein and fat content and higher in fiber and ash content. The composition of sheller bran depends on the type of sheller. The underrunner disk huller produces bran of higher protein and fat content and lower fiber content than the rubber-roll huller. The type of machine used in the hulling step also has an influence on the composition of the bran removed in subsequent whitening. The rubberroll huller produces undamaged brown rice, from which a bran richer in fat will be removed. The underrunner disk huller removes some germ and the outermost layers, rich in oil, which will not be incorporated into the bran. The type of whitening machine used is another source of variation of the chemical composition of bran. The friction type of machines produce bran of higher fat content than the abrasion type. Kernel layers at various depths differ greatly in chemical composition. Because the removal of bran may range from 4 to 14%, the bran from the last cones is higher in NFE (nitrogen-free extract) and lower in protein, fat, fiber, and ash. In industrial practice, bran from successive whitening cones is combined into a single product; polishings are sometimes an exception. Rice polish composition is not too far from that of rice bran in protein and fat, but it is lower in fiber and ash content and higher in NFE content. The unequal removal of bran layers as a result of the irregular geometrical shape of the caryopsis and of the rough and difficult-to-control abrading/friction action in the whitening machine greatly contributes to minimum compositional differences. Large differences exist in the homogeneity of milling. These can be measured objectively and have been shown to occur in commercial milling. The use of calcium carbonate (10.25-kg calcium carbonate/100-kg

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paddy) as a milling aid can influence the chemical composition of bran. Chemical Constituents of Bran and Polish Carbohydrates

Starch, which occurs abundantly only in the endosperm, has been identified in the germ and the aleurone layers and is apparently absent in the pericarp and seed coat. Commercial bran contains a fair amount of starch due to the endosperm present. Reported values range from 10 to 55% (dry basis). The starch content of bran increases from the first to the last whitening machine (Table 14-2). Free sugars are apparently absent in pericarp, tegmen, and aleurone layers. Nevertheless, reported values for total sugars content of rice bran range from 3 to 5%, moisture-free basis; presumably the contribution of germ and endosperm is significant. Nonreducing sugars are more abundant than reducing sugars, the ratio being 3: 1 to 4: 1. Glucose, fructose, and sucrose have been reported to be present in rice bran; raffinose has been found in the 80% ethyl alchohol extract of bran and polish. Bran is rich in cellulose and hemicelluloses. Data for crude cellulose of 10 samples of Italian bran partially degermed at the mill site ranged from 9.64 to 12.80%. Corresponding values for rice polish were 2.10-5.25%. Pentosans ranged from 8.59 to 10.87% in bran and from 3.15 to 6.01% in polish (Leonzio 1967). The hemicelluloses are a complex fraction not readily resolved into polysaccharides of single sugar units. Hemicellulose B of bran has been reported to contain 67.9% reducing sugars, primarily pentoses (59.6%). Xylose, arabinose, galactose, and uronic acid were identified as major components, with the first two predominating. The hemicelluloses of bran polish have been found to contain 0.1% water-soluble fraction and 1% 0.5 N sodium hydroxide extractable fraction. The former had an arabinose : xylose ratio of 1.8 and contained galactose and protein; the latter contained arabinose and xylose in a 1 : 1 ratio as major components, as well as galactose and minor amounts of glucose. The 4 and 24% KOH-soluble fractions of hemicellulose, as well as the a-cellulose fraction (residue from alkaline extractions) of bran (including germ) and polish, have a similar qualitative sugar pattern. They contain galactose, glucose, mannose, arabinose, and xylose. Lignin

Lignin content ranged from 7.70 to 13.11% in the bran, and from 2.01 to 4.42% in the polish. It decreased from the first to the fourth cone: 12.79, 8.41, 5.94, and 4.28%, dry basis, free of fat.

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Table 14-2. Proximate Analysis and Some Chemical Constituents of Rice Bran and Polish and Other Cereal Brans0 RICE

Constituent

Crude protein, % N X 6.25 Crude fat,% Crude fiber, % Available carbohydrates, % Crude ash,% Calcium, mg/g Magnesium, mg/g Phosphorous. mg/g Phytin phosphorus, mg/g Silica, mg/g Zinc, f.Lg/g Thiamin (B 1), f.Lg/g Riboflavin (B 2), f.Lg/g Niacin, f.Lg/g

Bran

Polish

Wheat Bran

Rye Bran

12.0-15.6 15.0-19.7 7.0-11.4

11.8-13.0 10.1-12.4 2.3-3.2

14.5-15.7 2.9-4.3 6.8-10.4

14.6 2.6 6.6

34.1-52.3 6.6-9.9 0.3-1.2 5-13 11-25 9-22 6-11 43-258 12-24 1.8-4.3 267-499

51.1-55.0 5.2-7.3 0.5-0.7 6-7 10-22 12-17 2-3 17;60 3-19 1,7-2.4 224-389

50.7-59.2 4.0-6.5 1.2-1.3 5.6 9-13 10 2 105 5.4-7.0 2.4-8.0 181-550

58.0 4.2 0.9-1.2 7.2-10.5 6.9 56 2.5 0.2 22.6

Adjusted to 14% moisture level. Data compiled from the National Academy of Science (1971); Gohl (1981).

a

Proteins and other nitrogen compounds

The nitrogen content of bran varies from 1 to 3%, dry basis. The nitrogen content is usually multiplied by the factor 5.95 for conversion into protein content. In the feedstuff industry, the conversion factor 6.25 is widely used (Table 14-2). The largest part of rice-bran nitrogen is protein nitrogen. Nonprotein nitrogen accounts for about 16% of the total nitrogen and for about 11% of rice polish nitrogen. Major free amino acids in bran are glutamic acid (7-31%), alanine (11-16%), and serine (5-15%). Other nitrogen compounds reported are guanine, xanthine, adenine, hypoxanthine, histidine, ammonia, dimethylamine, trimethylamine, cytosine, nicotinic acid, guanidine, betaine, choline, uracil, allantoin in rice polish, flavine adenine dinucleotide (0.93 ppm), and flavine mononucleotide (0.69 ppm). The amino acid composition of rice bran varies within wide limits (Table 14-3). Sheller (underrunner disk) bran, bran, and polish were remarkably similar in amino acid content. The protein content of bran (including germ) and polish of high- and low-protein rice varieties are as follows: bran, 13.3-15.5% and

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Table 14-3. Amino Acid Composition of Rice Bran and Polish and Other Cereal Brans0 RICE

Amino Acid

Bran

Polish

Wheat Branb

Alanine Arginine Aspartic acid Cystine Glutamic acid Gycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tryosine Valine Ammonia

6.5- 7.0 8.6- 9.1 10.0-11.0 2.5- 2.8 14.6-15.0 5.8- 6.2 2.9- 3.7 2.9- 4.5 7.6- 8.4 5.3- 6.0 1.9- 2.5 4.9- 5.3 4.6- 6.1 5.1- 6.0 4.2- 4.6 0.6; 1.4 3.5- 3.8 5.4- 6.6 1.9- 7.6

6.5; 6.6 8.9; 9.0 9.7;10.7 2.7; 2.8 16.1;17.6 5.6; 5.7 2.8; 2.9 2.9; 4.2 7.2; 8.4 4.6; 5.1 2.4; 3.0 4.6; 5.0 4.2; 5.7 4.9; 5.9 3.9; 4.4 1.4 3.8; 4.3 4.8; 6.2 2.2; 6.5

5.7; 3.8 8.1; 5.9 8.5; 6.1 2.8; 1.9 21.2;16.8 6.7; 4.6 3.2; 2.5 3.4; 2.7 6.8; 5.1 4.5; 3.4 1.7; 1.0 4.3; 3.1 6.5; 5.7 5.0; 4.3 3.7; 2.9 1.7 3.3; 2.4 3.2; 3.7 2.1

Rye Branb

Oat Bran

5.4 6.3 7.5 1.9 27.9 5.4 2.2 3.7 6.8 4.1 0.4 4.6 4.9 4.5 3.3

5.1 6.8 8.6 2.4 21.1 5.4 2.2 3.8 7.4 4.1 2.1 5.1 6.2 4.8 3.4

2.7 5.3

3.5 5.5

2.5

Expressed in g/16 g of N. U.S. Dept. of Health, Education, and Welfare/FAO (1968, 1972).

a

16.0-17.4%; and polish, 12.2-14.1% and 17.9-19.0%. The major protein fractions in bran are albumin and globulin; the major protein fraction in polish is glutelin. Prolamin is the minor fraction in both cases. The mean ratio of albumin globulin : prolamin : glutelin for the six Philippine samples is 37: 36: 5: 22 for bran (including germ) and 30: 14: 5: 51 for polish. The albumin-globulin fraction of bran has been resolved by gel filtration in Sephadex G-100 into three components with molecular weights of 2.0 x 105 , 0.8 x 105 , and 0.3 x 105 • The globulin fraction has also been fractionated by Sephadex G-200 chromatography into three components: gamma globulin, with a molecular weight of 1.5 x 105, is the major one (Morita and Yoshida 1968). Cytochrome C and a blue protein have been isolated and found to be the major soluble basic proteins of bran (Morita and Ida 1968; Morita et al. 1971). The blue protein is a copper containing glycoprotein, with an estimated molecular weight of 18,300, which occurs predominantly in the aleurone layer but rarely in the embryo and other parts of the kernel.

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Enzymes

Rice bran is abundant in various enzyme systems (Barber and Benedito de Barber 1980). The following enzymes have been reported to be present: a-amylase, ,8-amylase, ascorbic acid oxidase, catalase, cytochrome oxidase, dehydrogenase, deoxyribonuclease I, esterase, flavin oxidase, aand ,8-glucosidase, ferredoxin NADP reductase, glutamic acid decarboxylase, glutamine synthetase, glutathion reductase, ,8-glycerophosphatase, invertase, lecithinase, lipase (Aizono et al. 1976; Shastry and Rao 1976; Shibuya et al. 1975), lipoxygenase (Shastry and Rao 1975), pectinase, peroxidase (Barber et al. 1977a,b), phosphatases, phytase, polyphenoloxidase, protease, and succinate dehydrogenase. The more important enzymes related to rice-bran stability are lipase, lipoxygenase, and peroxidase. The germ and outer covers of the caryopsis are the site of higher enzymatic activities. Amylolytic activities (mg maltose/10 g) of rice milling products are brown rice, 39; milled rice, 15; bran, 320; polishings, 250; and germ, 310. The catalase activity ratio for brown rice: brown rice free of germ: milled rice was found to be about 40: 16: 1. Proteolytic activities of degermed brown rice (1), bran (5.9% of 1), polish (4.6% of 1), and germ were 1.7, 17.4, 4.9, and 31.8 hemoglobin units/g rice, dry basis. Enzymes in rice bran might also be of microbial origin. Among the enzymes, lipase merits most attention because it affects the keeping quality of rice bran. Minerals

Phosphorus is one of the major mineral constituents of bran (Table 14-4). Also present in decreasing order are potassium, magnesium, and silicon. The concentration of mineral elements in bran varies with the degree of milling and growing environment. Some elements (P, K, Mg) increase initially and decrease with deeper milling; others (Ca, Mn, Fe) exhibit an early sharp decrease. A decreasing concentration gradient occurs in subaleurone layers (Kennedy and Schelstraete 1975). The distribution of phytate and mineral elements in endosperm, germ, and pericarp plus aleurone in rice has been reported by O'Dell et al. (1972). Phosphorus in bran occurs as phytic acid, nucleic acid, inorganic phosphate, carbohydrate, and phosphatide. The reported values, calculated as percentages of the total phosphorus, are 89.9, 4.4, 2.5, 2.3, and 1%, respectively. The largest part of phosphorus is linked to inositol as the calcium-magnesium salt of myoinositol hexaphosphate or phytin. Bran may contain about 1.8% of phytin. Phytin phosphorus contents for brangerm range between 2.2 and 2.6%.

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Table 14-4. Inorganic Constituents of Rice Bran

Constituent

Content, ppm (dry basis)

Aluminum Calcium Chlorine Copper Iodine Iron Magnesium Manganese Mercury Phosphorus Potassium Selenium Silicon Sodium Sulfur Tin Titanium Zinc

53.5-369 140-1,310 510-970 0.37 5 130-530 8,650-12,300 110-877 0.3 14,800-28,680 13,650-23,960 0.170 1,700-16,300 0-290 80 17.6-41.3 26 80

Source: Barber and Benedito de Barber (1980).

Vitamins

Bran is abundant in vitamins of the B group and tocopherols and is poor in vitamin A and C (Table 14-5). The variation in vitamin content reflects rice variety, degree of milling, and possible hull contamination. In the United States, bran for food consumption is devoid of hull and, thus, the vitamin content would be expected to be at the high end of the range listed here. Vitamins are not uniformly distributed within the grain. The greatest concentration is found in bran, where the major part of the B vitamins in the grain is located. The pattern of distribution is not identical for all the vitamins. For instance, nearly 80% of the nicotinic acid and only 35% of the thiamin has been found to occur in the pericarp plus aleurone layer. In the germ (scutellum plus embryo), about 2.5% ofthe nicotinic acid and over 55% of the thiamin are located. Concentration levels of some vitamins, like pantothenic acid and folic acid, in rice polish may be higher than in rice bran. Although the vitamin content differs among rice varieties and, to a lesser extent, with location of growth, major causes of variations are the

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Table 14-5. Vitamin Content of Rice Bran Vitamin

Content, ppm (dry basis)

Vitamin A Thiamin Riboflavin Niacin (nicotinic acid) Pyridoxine Pantothenic acid Biotin Inositol Choline p-Aminobenzoic acid Folic acid Vitamin B12 Vitamin E (tocopherols)

4.2 10.1 27.9 1.7 3.4 236 - 590 10.3 32.1 27.7 71.3 0.16- 0.60 4627 -9270 1279 -1700 0.75 0.50- 1.46 0.005 149

Source: Barber and Benedito de Barber (1980).

uncontrolled proportion of germ and polish and the differences in the degree of milling. Vitamins occur in bran in free or combined form: 75% of riboflavin was reported to be in esterified form, with 89% of the folic acid, 49% of the pantothenic acid, and 86% of the niacin in the bound form. Pyridoxine was also found in free and combined form. Chemical Composition of Rice Germ

Literature on rice germ is less abundant than that on bran. Rice germ is characteristically richer in proteins (17.3-26.4%) and fat (16.6-39.8%) but lower in fiber (1.98-15.10%) than bran. Commercial germ available in Spain, however, always contains 20-30% impurities, most frequently endosperm and hull fragments. Ash (6.07-10.8%) is an important component. Since rice germ accounts for 20% or more by weight of rice bran (Japonica rice), germ removal affects bran composition, particularly decreasing the fat content (Barber and Benedito de Barber 1980). Sugars

Total sugar content of germ differs widely. They vary from 8 to 25% (Fossati et al. 1976). Reducing sugars range from 1 to 11.63%. Pentosans and Lignins

Pentosans in germ amount to about 7% by weight and lignin about 3-6% (Leonzio 1967). The level of pentosan in the germ is intermediate between that of bran (9.65%) and polish (4.60%). Lignin content is much lower in the germ than in the bran (10.35%) but is similar to that in the polish (3.15%).

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Nitrogenous Compounds

Nonprotein nitrogen in rice germ is about 13% of the total nitrogen, intermediate between bran and polish (Baldi et al. 1976). Total free amino acids range from 24.3- to 106.0-mg amino N/100-g germ. Rice embryo contains about four times more amino N than bran. The major free amino acids are alanine (14%), aspartic acid (12%), proline (29.5%), and serine (12%). Polyamines occur in appreciable quantities in rice germ: cadaverine, 133 ppm; putrescine, 69 ppm; spermidine, 153 ppm, and spermine, 141 ppm (Moruzzi and Caldarera 1964). Amino acid composition of rice germ protein varies widely (Baldi et al. 1976). Rice germ contains more lysine than the bran. The protein fractions in rice germ have been shown to be high in the brine-soluble fraction, the mean albumin-globulin: prolamin : glutelin ratio being 71: 1:28 (Baldi et al. 1976). In contrast, 17.4% albumin and 20.0% globulin have been reported for Japanese rice embryo protein (Morita and Yoshida 1968). The brine-soluble fraction in Italian rice was much higher in the germ than in the bran and lowest in the polish. Much as with bran globulin, embryo globulin has been fractionated into three components by Sephadex G-200 chromatography. The f fraction, with a molecular weight of 1.5 x 105, is the major one (Morita and Yoshida 1968). Gamma-globulin has, in turn, been fractionated into three components by diethylaminoethyl Sephadex A-50 chromatography (Sawai and Morita 1970a). The molecular dimension and chemical characteristics of one of these gamma fractions have been reported (Sawai and Morita 1970b; Horikoshi and Morita 1975). Hemoproteins (cytochrome C and peroxidase 556 as major constituents) and some other cromoproteins (flavoproteins and a blue protein) have been isolated from rice embryo, purified, and partially characterized (Morita and Ida 1968, 1972). Minerals

Rice germ is high in phosphorus and low in calcium, sodium, and silicon. In pure germ, 75% of the total phosphorus is present as phytate phosphorus. In pericarp and aleurone, 91% of the total phosphorus is phytate P (O'Dell et al. 1972). Vitamins

The values reported for most of the vitamins of the rice germ fall within the ranges reported for bran (Table 14-6). The exceptions are thiamin, which is more abundant in the germ, and niacin, which is more abundant in the bran.

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Constituent, y/ g, dry basis

Content

Vitamin A (carotenes) Thiamin Riboflavin Niacin (nicotinic acid) Pyridoxine Pantothenic acid Biotin Inositol Choline p-Aminobenzoic acid Folic acid Vitamin B 12 Vitamin E (tocopherols)

1.3 45.3 - 76.0 2.7 5.0 15.2 - 99.0 15.2 - 16.0 13.2 - 30.0 0.26- 0.58 3725 -6400 2031 -3000 1 0.9 4.3 0.001 87.3

Source: Juliano (1972).

Processed Rice Brans The composition and properties of various processed rice brans-parboiled, stabilized, defatted, dephytinized, and adulterated-have been reviewed by Barber and Benedito de Barber (1980) and Saunders (1990). Parboiled rice bran is higher in oil content than raw bran but lower in thiamin and riboflavin. Differences in composition between raw and parboiled brans depend on the degree of milling and on parboiling conditions (Benedito de Barber et al. 1977). Removal of oil from regular bran by pressing or solvent extraction brings about proportional increases in the concentration of all major constituents except water. Bran from the solvent-extraction milling process (X-M process, Hunnell and Nowlin 1972) has been reported to be higher in protein content and lower in fiber content than expected from the simple removal of fat. Dephytinized bran has a lower ash and nitrogen-free extract (NFE), and higher protein, lipids, and crude fiber content than regular bran (Table 14-7). Some rice bran may be adulterated with hulls, corncobs, peanut shells, wood, sawdust, and clay. Urea is used to increase the nitrogen content. Hulls, the most frequent adulterant, increase the lignin, silica, and ash content of bran. PHYSICAL PROPERTIES OF RICE BRAN Information on the physical characteristics and properties of bran is necessary for appropriate processing of the by-product in stabilizing, drying, handling, and storage.

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Table 14-7. Gross Chemical Composition of Dephytinized and Defatted Dephytinized Bran Constituenta

Untreated Rice Bran

Dephytinized Rice Bran

Defatted Dephytinized Rice Bran

16.6 19.7 7.5 10.7 45.6

17.2 25.4 14.1 3.2 40.1

21.3 2.7 17.0 4.0 55.0

Protein Fat Crude cellulose Ash NFE

Percentage, dry basis. Source: Barber and Benedito de Barber (1980).

a

Particle-size distribution of bran varies within a wide range. Data have been published for bran from friction vs abrasion types of milling machines, different cones (Barber and Benedito de Barber 1977), raw vs. heat stabilized rice (Barber and Maquieira 1977), and defatted bran and germ (Barber and Benedito de Barber 1980). They include the following findings: 1. Friction-type machines produce a bran of larger particle size than the abrasion type. 2. There is no clear relationship between fineness and cone number; nevertheless, the percentage of fine particles increases in the bran fraction of deeper layers. Distribution patterns for brans from different mills differ remarkably. 3. Moist-heat stabilization brings about agglomeration of rice bran particles (Table 14-8). Table 14-8. Particle-Size Distribution of Raw and Heat-Stabilized Brans0 Meshb

>18 18- 30 30- 50 50- 80 80-100 24, 27-28, 62, 73, 77-78 Genetic control of grain size, 26 Genetic diversity, reinstating in major cultivars, 77-79 Genetic Evaluation and Utilization (GEU) Program, 52, 66, 69 Genetics, 23-101 nitrogen use efficiency differences, 141 Germination and temperature, genetic factors, 34-35 temperature limits for, 120 Gibberella fujikuroi, 198, 199-200 Gibberella moniliformis, 199 Gibberellic acid, 413 response of dwarfs to, 25 Gleyic cambisols, and upland rice culture, 124 Globulin, 402, 404-5 Glucose, 401

427

Glucosidases, 412 Glutamic acid, 406 Glutelin, 402, 405-6 Gogo-rantja culture, 146, 163 Governmental subsidy and pricing policy, and growth in production, 6 Grain genetic control of size, 26 genetic studies of, 30-31 Grain blast, 202 Grain quality, 40-42 and drying conditions, 320-21 of Japanese varieties, 60 shape, 31 type, and breakage on milling, 369-70 Grain rot, 194-95 Grain yield correlation with protein content, 42 and plant type, 28 Grasses, 128 Grassy stunt virus, 222, 225-27 breeding for resistance to, 53 brown planthopper vector for, 239 epidemic, 188 resistance breakdowns in hybrids, 69-70 resistance to, 38, 78 Green leafhoppers, 130, 244-47 biological control studies, 152 resistance to, 39-40, 53 Green Revolution, 23, 51, 171-72, 178, 238 and rice leaffolder epidemics, 256 second, in China, 74 semidwarf indicas used in the, 54 Green smut. See False smut Growing season, extension of, 173 Growth and ecological adaptation, 32-37 rates, factors affecting, 6 responses to low temperatures, 34 Growth duration genetics of, 32-33 and plant height, 28 Growth hormones, hybrid seed production using, 74

Habataki cultivar, 60 Haploid plants, 45 Harvested area, by ecosystem, less developed countries, 133 Harvest index (HI), 77 effect of climate on, 21 and plant height, 27 and plant type, 28 and yield, 83

428

INDEX

Harvesting, 313-18 of broadcast seeded rice, 157 with drill seeding, 159-60 factors affecting breakage, 364-65 timing of, 153 upland rice, 169-70 Heading stage, 18-19 and need for solar energy, 122 and temperature, 121 Head rice, 311-12 Head yield, 313-14 and checking, 325 defined, 348 and tempering, 328 Heat, generation in bulk storage, 337 Heat summation units, 121 Helminthosporium oryzae, 204 damage to upland rice, 164 resistance to toxin of, 81 Helminthosporium sigmoideum, 219 Hemicellulose, 401 Herbicides, 129, 146, 155, 159, 306-7 damage to rice plants by, 299, 302 and drill seeding, 159 for dry-seeded and flooded rice systems, list, 306 for irrigated transplanted rice, 152 in paddy floodwater, 296 for preemergence weed control, 130 for transplanted rice weed control, 295 for upland rice culture, 166 list, 298 and water management, 145 for water-seeded rice weed control, 157, 301-4 and weed management, 292-93 Heritability estimates of economic traits, 31-32 of recessives for dwarfism, 27 Heterobeltiosis, 74 Heterosis, 73 High-yield varieties (HYVs), 23, 52 in India, 65 and rice gall midge infestation, 251 traits of, 28 Hirschmaniella oryzae, 229 Histidine, 406 Histosols, 127 Hoja blanca virus breeding for resistance to, 63 and brown spot, 205 in Colombia, 59 resistance to, 38 Hopperburn, 239 Hordeum vulgare, host toP. fuscouaginae, 197 Horizontal resistance to the BPH, 244

Hoshiyutaka cultivar, 60 Hoyoku cultivar, 59 Hsien type. See Indica race Hull, 390 characteristics, and dormancy, 35-36 colors, genes controlling, 25 Hulling, defined, 347-48 Humic-gley soils, and upland rice culture, 124 Husked rice. See Brown rice Hybridization Porteresia coarctata trials, 80 probes, 50 seed companies' work on, 64 Hybrids, 73-76 cytoplamic male-sterile, 60-61 economic constraints on use of, 76 intergeneric, 80 japonica!indica, 60-61 sativa x australiensis, 80 spontanea x sativa, 80 tropical indica x Ponlai, 68-69 tropical indica x semidwarf indica, 68-69 and yield, China, 58-59 Hydromorphic soils, 124 in West Africa, 165 Hysteresis in EMC, 318

Impact sheller, 352 Importing regions, 4, 8-9 Inceptisols, 127 phosphorus deficiency in, 149 Incomplete grain filling, healing by parboiling, 368 Increase in production, rate of from 1979-1988, 2 southern and southeastern Asia, 2-3 Indented disk separators, 349-50, 359-60 India change in production (1979-1988), 2 extremes of moisture in, 7 government support and yield, 6 rice breeding experiments in, 65 Indica race, 20, 47, 51, 105 crosses with dwarfs, 25 hybrids, 60, 68-69 linkage groups, 42 shattering in, 35 Individual kernel drying, 329-30 Indonesia breeding experiments in, 66 change in production (1979-1988), 2 government support and yield, 6 IPM success in, 131 pest control in, 79

INDEX

Inhibitor genes dominant, for tall height, 25 recessive, for short height, 25 Insect damage, inhibiting in stored rice, 337-38 Insecticides for brown planthopper control, 240, 244 cost of, 237 overuse of, 66 proper use of, 79 for rice gall midge control, 252 for rice water weevil control, 255-56 secondary pest outbreaks following use of, 239 for seed feeder control, 261 for stem borer control, 250 for water weevil control, 254 Insect pests, 130-31, 237-68 control methods, 152-53 damage to upland rice, 165 of stored rice, 269-85 Insect resistance, 39-40, 53, 67 See also Resistant cultivars Instituto Columbiana Agropecuaria (ICA), 59 Integrated Pest Management (IPM), 131, !53 disease management technology, 188 Intercropping, 174, 175 Intergeneric hybrids, 80 International Rice Germplasm Center (IRGC), 53 International Rice Research Institute (IRRI), 1, 52, 57-58, 105, 121, 123, 144, 164, 238 breeding at, 68-71 harvester types, research on, 315 puddling's effects, research on, 13 7 weed control research, 129 International Rice Testing Program (IRTP), 52, 64 International trade, 7-8 Internode elongation, 17 Intervarietal hybrid, sterility of, 47-49 Iron in brown rice, 410 deficiency, 166 requirement of rice, 166 uptake, and water condition, 126 Irradiated mutants, 25 Irrigation, 119, 146-60 constraints on yields, 175 importance of, 133 lowland rice culture, nitrogen transformation processes in, 143 and monsoon dependence, 105, 108

429

rotational method of, 147 yields in the wetland ecosystem, 5 Iso-loss line, additive leaffolder and stem borer damage, 257 Jagannath mutant, 65, 73 Japan breeding experiments in, 59-61 change in production (1979-1988), 3 government support and yield, 6 high yield from, 51 Japanese varieties, segregation for photoperiod and temperature response, 34 Japonica race, 20, 47, 51, 105 linkage groups, 42 sd 1 gene, 59-61 shattering in, 35 Jauanica race, 51, 105 shattering in, 35 Jikkoku cultivar, 59 Kakatiya cultivar, ROM resistance of, 251-52 Karyotype, 47 Oryza sativa, 43 Keng rice. See Sinica race Kernel size, and breakage on milling, 37071 Kernel smut, 63 Kokumasari variety, 59 Korea blast disease in, 79 breeding experiments in, 61 Koshihikari hybrid, 60 Kresek, symptom of BB infestation, 191 Land preparation for direct seeding onto flooded fields, !56 for drill seeding, 158 mechanizing, 176 regional variations, upland rice culture, 167 and weed control, 287-88 upland culture, 298 Lasioderma serricorne, 269-71 Latheticus oryzae, 270 Latin America, rice varieties by ecosystem, 135 Leaf blight epidemic, maize in the United States, 78 symptom of bacterial blight, 191 Leaf elongation, and temperature, 120 Leafhopper, as a vector for tungro, 223-25

430

INDEX

Leaf streak, genetic resistance to, 37 Leaves characteristics, wetland rice, 55 development of, 15-16 genetic control of characteristics, 28-29 senescence patterns, 19-20 Lecithin in milled rice, 400 Leersia hexandra, ROM host, 252 Leersia sayanuka, weed host to Xanthomonas cinnamoha, 192 Legume crops, 176 Lepidoptera, 278 pests of stored grain, 273 Leptocorisa, 260 Lesser grain borer, 274 Lethal genes, 48 Level terrain for lowland rice culture, 125 Life cycle of the green leafhopper, 245 of the rice plant, 13 Lindane for storage insect control, 281 Linkage groups, 42, 47 Linked traits, for adaptation to adverse conditions, 57 Lipase, 412 Lipid bodies, 391 Lipids, 406 bound, 399-400 Liposcelis divanatorius, 271 Lissorhoptrus oryzophilus, 130, 253-56 Lodging resistance and plant height, 27, 28 trade-off with drought tolerance, 168-69 Lolium perenne, host toP. fuscovaginae, 197 Loonzian. See Brown rice Lophocateres pusillus, 270 Losses, financial and intangible, in contaminated product, 272 Lowland rice culture ammonia volatilization in soils, 142 direct seeded, 145-46 and nitrogen fertilizer application, 149 soils suitable for, 125-27 and weed competition, 130-31 and zinc deficiency, !51 Low-temperature stress, and sheath rot, 211 Lysine, 402 distribution of, 403 Lysocephalin in milled rice, 400 Lysolecithin in milled rice, 400 Machinery settings, and breakage, 379 Madagascar, changes in production, 4 Magnaporthe grisea, 202

Magnaporthe salvinii, 220 Magnesium in brown rice, 410 nutrient amounts in brown rice, 408 Mahsuri cultivar, brown spot resistance, 207 Maintainer line in hybridization research, 76 Malathion for storage insect control, 281 Male sterility in Chinese wild rice, 24 gene for (ms), 48-49, 72-73 Maliarpha separatella, 248, 249 Manganese in brown rice, 410 and brown spot, 205, 207 uptake, and water condition, 126 Manifold system for aeration of stored rice, 339 Manzeb, for brown spot control, 207 Market, international, 104 Market price international, 8 and real price of rice, trends in, 9 Mars cultivar, 63 Maternal influence on chalkiness, 40 MCPA, 2,4-D weed control in dry-seeded, flooded culture, 306 in water-seeded culture, 30 I Mechanization, new technology in, 176-78 Meiosis in asynaptic plants, 44 in autotetraploids, 46 Melibiose, 401 Mendelian genes, 26-27 Mepronil, sheath blight control with, 216 Merchant grain beetle, 277 Metals removal during cleaning, 350 toxicity in upland rice production, 16566 Methoxychlor for storage insect control, 281 Methyl bromide, fumigation with, 282 Metica I semidwarf, 59 Microvelia atronlineata, effect of insecticides on, 244 Microwave drying, 366 Milled rice, 311 consumer preferences in, 380 insect infestability of, 272 proximate analysis of, 397 Milling, 347-88, 395 Minerals, 408 in brown rice and its fractions, 410 Mitochondrial genes, 49 Moisture conservation, and puddling, 136

INDEX

Moisture content and breakage, by variety of rice, 364 changes in, and cracking, 334-35 during harvesting, 314 measures of, 312 and milling yields, 371-72 and optimum soil conditions, 138-39 Moisture stress and capacity of the soils to retain water, 165 effects of, 138 and upland rice production, 163 varietal differences in tolerance to, 139 See also Relative humidity Molecular cytogenetics, 50 Molinate weed control in dry-seeded, flooded systems, 306 in water-seeded culture, 301 Mollusks, crop damage by, 132 Monosomic plants, 46-47 Monozet, for sheath blight control, 216 Morphologic traits, 24-27 Moths, 278 Mulching and moisture conservation, 164 for Sclerotium oryzae control, 221-22 Multiple cropping and the brown planthopper, 240 early-maturing types for, 69-70 and insect pests, 239 and vulnerability to pests, 78 Mutations breeding from, 73 endosperm, 40-41, 60 induced, 62 by irradiation, 25 Myanmar (Burma), breeding experiments in, 66 Myo-inositol-1-phosphate synthetase, 412

Najas guadalupensis, 290 Nakataea sigmoidea, 220 Narrow brown leaf spot, 209-11 breeding for resistance to, 63 National Agriculture Research Center (Japan), 60-61 National Fertilizer Development Center, u.s., 149 Nato cultivar, optimum drying conditions for, 365 Natural enemies of BPH, 244 Near infrared measurements of milling effects, 381 Neem (insecticide), 244, 247 Nematode diseases, 227-29

431

Nephotettix cincticeps, 246 transmission of tungro virus by, 224-25 N ephotettix nigropictus, 244 transmission of tungro virus by, 224-25 Nephotettix virescens, 130, 244 transmission of tungro virus by, 224-25 Newbonnet cultivar, 63 Newton's law of cooling, analogy to thinlayer drying of small grains, 331 Niacin, 409 Nilaparvata baberi, vector for grassy stunt virus, 226 Nilaparvata lugens, 130, 239, 244 vector for grassy stunt virus, 226 Nilaparvata maeander, 239 Nilaparvata malay anus, 244 Nilaparvata muiri, vector for grassy stunt virus, 226 Nira cultivar, optimum harvesting conditions, 364 Nitrification-denitrification, as a nitrogen loss mechanism, 142 Nitrogen and the brown planthopper, 240 loss of, 141-42 midseason application guide, 158-59 response of insect pests to, 238 responsiveness and plant type, 28 and upland rice culture, 165-66 Nitrogen fertilizer balance sheet, 148 and emergence of bacterial blight, 189 and false smut, 208-9 and resistance to blast, 204 responses of upland rice, 168-69 and responsiveness to irradiance, 123 role, with brown spot, in 1942 famine, 207 and sheath rot, 211 and stem rot control, 220 See also Fertilizers Nitrogen fixation, 141 in flooded soils, 127 microbial, in a flooded soil, 56 Nitrogenous compounds, caryopsis, 402-6 Node blast, 201-2 Nonwaxy rice starch, 400-401 North America, changes in production, 4

Notched belly imperfections, 21 Nucellus, 391, 395 Nuclear magnetic resonance (NMR), measurement of lipids in rice, 381 Nutrients availability, and puddling, 137 from crop residues, 125-26 and fertilizer use efficiency, 139-40

432

INDEX

Nutrients (cant. ) from flooded soil, 108 leaching of oxidized forms, 125 Nutritional value, 40-42 and protein content, 396, 402 Nutsedge, as a competitor to upland rice, 167

Oebalus pugnax, 130, 260 Oligogenes breakdown of, 38 for disease resistance, 38 inheritance of plant height, 27 Oochikara cultivar, 60 Organic manures, and HYVs, 151 Ornithine, 406 Orseolia oryzae, 250-53 Oryseolia oryzivora, 250-53 Oryzaephilus mercator, 270, 277 Oryzaephilus surinamensis, 270 Oryza glaberrima, !05 crosses with Oryza sativa, 48 shattering in, 35 Oryza sativa, I 05 amylose fraction, gene controlling, 40 brown spot susceptibility, 206 chromosome complement of, 42-43 ecogeographic races of, 51 genetic diversity of, 51-52 host toP. fuscovaginae, 197 infection by Xanthomonas cinnamoha, 192 reproduction of BPH on, 240 shattering in, 35 sterility in interspecific crosses with 0. glaberrima, 48 Ovary culture, 80 Overmilling. See Deep milling Overproduction in Japan, 59-60 Oxadiazon, 159 upland rice culture weed control, 298 for weed control, transplanted rice, 295 Oxisols, 127 phosphorus deficiency in, 149 Oxyflurofen for weed control in upland rice, 298 Oxygen exchange from atmosphere to soil, 126 soil levels of, 137 Oxytetracycline, for control of P. fuscovaginae, 198 Paddy rice, drying rate constant k, 331. See also Rough rice Paddy separators, 352-55 Pakistan, change in production (19791988), 3

Palorus ratzeburgi, 270 Panicle blast, 202 Panicle initiation, 16-17 nitrogen fertilizer topdressing at, 156 and nitrogen topdressing, 144 Panicle number, and tiller number, 29-30 Panicles additive gene action controlling, 30 characteristics in wetland rice, 55 critical need for solar energy, 122 genetic control of character, 26 heritability of characteristics, 31 and temperature, 121 Pantothenic acid, 409 Parathion, methyl, for seed feeder control, 261 Parboiled rice, 395-96 breakage of, 361-62 drying of, 366 effect of humidity on head yield, 373 milling of, 359, 368 physical changes in, 411 vitamin content of, 408 Parenchyma cells, endosperm components, 392 Parthenogenetic females, RWW, California and Japan, 254 Pedigree selection for breeding experiments, 72 Pencycuron, for sheath blight control, 216 Pendimethalin dry-seeded, flooded systems, weed control, 306 upland rice culture, weed control, 298 Percolation losses and puddling, 136 rate, and productivity, 109 Pericarp, 390-91, 395 dormancy of, 36 glutelin of the, 405 Peroxidase activity, 412 Peru, changes in production, 4 Pesticides for control of storage insects, 281-83 Pest management chemicals for, 187 water drainage for, !58 Peta cultivar, crosses with semidwarfs, 27 pH changes in flooded soils, 126 and phosphorus sources, 149 range in soils, 124 in upland soils, 165-66 and water management, 142-43 and zinc deficiency, 159 Phalguna cultivar, RGM resistance of, 251-52 Phenoxy herbicides, 159

INDEX

Philippines change in production (1979-1988), 3 government support, and yield, 6 Phleum pratense, host toP. fuscovaginae, 197 Phorate for rice gall midge control, 252 Phosphate fertilizer, placement for weed control, 306 Phosphine, fumigation with, 283 Phospholipase, 412 Phospholipids, 406 in milled rice, 400 Phosphorus, 144, 205, 207 banding and upland rice culture, 169 in brown rice, 402, 408, 410 deficiency of, 149-50 and direct seeding onto flooded fields, !57 Phosphorylase, 411-12 Photoelectric sorting, 361-62 Photoperiod, 121-22 breeding plants insensitive to, 23 critical, for panicle initiation, 33 effect on development, 21 optimum, defined, 32 and segregation for temperature responses, 34 Photoperiod-sensitive phase (PSP), 32 Photoperiod sensitivity cultivar variations in, 122 of deepwater rice cultivars, 162 genetic basis of, 54 inheritance patterns, 32-33 of male sterility, 76 and panicle development, 17 Photosynthesis genetic code for enzymes involved in, 49 in the reproductive and ripening phases, 109 Physicochemical properties, 396-411 Physiological diseases, 132 Phytase activity, 413 Phytin, 402 Phyzopertha dominica, 275 Piperophos for weed control, 155 in upland rice culture, 298 Pirimiphos methyl, for storage insect control, 281 Plant growth, 13-22 Plant height, 27-28 heritability of characteristics, 31 inhibitor genes, 25 Planthoppers, 130 as vectors for grassy stunt virus, 226 See also Brown planthopper; Whitebacked planthopper; Zigzag planthopper Planting, and harvest preparation, 314-15

433

Plant regeneration in somatic cell culture, 81 Plant spacing, 137-38 Plant type, component traits, 28 Platygaster oryzae, 253 Plodia interpunctella, 270, 275, 278 Plow sole, 125 Polishing, 359-61 Pollen culture, 70-71, 80 Pollination, 19 Ponlai type, 54. See also Sinica race Population growth, 4 and agricultural production index, 8-9 and need for rice, 82-83, 171 and projected rice production, 237 and rice consumption, 9-10 Porteresia coarct at a, 80 Postharvest management, 311, 318 Potash fertilizers. See Potassium Potassium, 144 in brown rice, 408, 410 deficiency of, 150 and direct seeding onto flooded fields, 157 and sheath rot, 211 Precipitation distribution, and yield, 109 and yield, I 08 Preharvest quality, 313-14 Prelude cultivar, optimum harvesting conditions, 364 Pretilachlor, for weed control, transplanted rice, 295 Pributycarb, for weed control, transplanted rice, 295 Processing effects on the caryopsis, 395-96 stages of, 311-12 Production annual, world, 237 by country and region, 106-7 by ecosystem, less developed countries, 133 factors affecting increases in, 23 and growing period, 172 overview and production, 1-11 technology, future outlook, 170-78 world levels of, 1-2 regional distribution, 104 Projections of the need for rice, 10, 170, 237 Prolamin, 402, 405 change during grain development, 410 Propanil weed control in dry-seeded, flooded systems, 306 in upland rice culture, 298 in water-seeded culture, 301 Propiconazole, for brown spot control, 207

434

INDEX

Protease, 412 Protectants for storage insect control, 281 Protein accumulation in developing grain, 408-9 distribution in milling fractions, 397 genetic control of content, 41-42 utilization in parboiled rice, 411 Protein bodies, 392-94, 402-3 timing of appearance, 408, 410 Proteoglycans, 401 Protoplasmic DNA uptake, 82 Protoplast fusion, 70-71, 81-82 Proximate analysis, 396-97 Pseudomonas, 188, 189 Pseudomonas fuscouaginae, 195-98 Pseudomonas glumae, 194-95 Pseudomonas oryzae, 190 Ptinidae, 270 Pubescence, genes controlling, 25 Puddling, 145 and direct seeding, 154-55 and land preparation, 154 for lowland rice culture, 134, 136-38 and weed type, 294 Pupae, susceptibility to fumigants, 282 Pyongyang variety, Korea, 61 Pyralid moths, 278 Pyrazoxyfen for weed control, transplanted rice, 295 Pyrethrins, for storage insect control, 281 Pyrethroids, for storage insect control, 281 Pyricularia oryzae, 200-204 Pyridoxine, 409 Pyroderces rileyi, 271 Pyrozolate for weed control, transplanted rice, 295 Pyrroline, 2-acetyl-1-, 407-8

Q-enzyme, 411-12 Quality of cooked rice, 41 from mixing-type driers, 323 Quantitative traits, genetics of, 27-32 Quarterly Bulletins of Statistics, 1 Quinalfos for rice gall midge control, 252

Radicle, 392 Raffinose, 401 Ragged stunt virus, 222 brown planthopper vector for, 239 Rainfall and upland rice yield, 162-64 Rain-fed ecosystems dryland yields, 5 lowland rice culture, 109, 134-46

moisture stress limitations, 138 and nitrogen transformation processes, 143 wetland yields, 5 yield constraints in, 56, 175 Ratna cultivar, stem borer resistance of, 250 Ratoon cropping, 20, 175 fertilizer for, 159 and tungro infection, 245 RD6 and RD15 cultivars from mutant breeding, 73 Recessive genes for dwarfism, 25 for floating ability, 36 for growth habit, 35 for panicle expression, 26 for photoperiod sensitivity, 33 for short height, 25 for water tolerance, 36 Recilia dorsalis, transmission of tungro virus by, 224-25 Reciprocal crosses, and pollen sterility, 73-74 Reciprocal translocation, 44 Recombinant DNA, 82 Recurrent selection, 73 Redox potential, nutrients affected by, 126 Regional distribution of rice production, 6 Reimei variety, 73 Relative humidity and P. oryzae infection, 203 and rice gall midge infestation, 251 and stress cracking, 372-73 See also Moisture stress Relay cropping, 175 R-enzyme, 411-12 Reproductive phase, 13, 16-19 photoperiod dependence of duration, 122 Republic of Korea (South Korea) change in production (1979-1988), 3 high yield from, 51 Residual insect infestations in storage areas, 279 Resistant cultivars to bakanae, 200 to blast infections, 204 to brown planthopper, 243 to brown spot, 207 for controlling bacterial blight, 192 to grassy stunt virus, 227 to green leafhopper, 246 to narrow brown leaf spot, 211 to rice gall midge, 251 to rice leaffolder, 260 to rice water weevils, 255 to stem borers, 250

INDEX

to stem rot, 221 to tungro virus, 225, 246 Resources, genetic, 51 Respiration of stored rice, 336-37 Return sheller, 355 Rexark variety optimum harvesting conditions, 364 temperature and milling breakage, 372 Rhizoctonia oryzae, 217 Rhizoctonia oryzae-sativae, 218 Rhizoctonia so/ani, 213-17 Rhyzopertha dominica, 270, 274 Riboflavin, 409 Ribonuclease, 412 Ribonucleic acid (RNA), 406 Rice: Chemistry and Technology, 40 Rice bran, defatted, from SEM processing, 378 Rice culture, 103-86 Rice Diseases (Ou), 187-236 Rice dwarf, GLH vectors for, 245 Rice flour, high protein, 382 Rice gall midge (RGM), 250-53 Rice Genetics and Cytogenetics, 23-101 Rice Genetics Newsletter, 25, 27, 37, 39, 42, 43, 47 ems sources, list, 49 Rice harvesters, 316-18 Rice, insect pests, 237-68, 269-85 Ricelands, classifications, 132-33 Rice leaffolder (RLF), 256-60 Rice oil, from SEM processing, 378 Rice plant, growth and development, 1322 Rice-processing machinery, 348-63 Rice root nematode, 229 Rice straw, nutrients returned to the soil, 126 Rice water weevil, 253-56 Ripening phase, 13, 19-20 Rockefeller Foundation, breeding experiments at, 71 Rodents, losses due to, 131 Roots development, and temperature, 121 and drought resistance, 36-37 pulling resistance heritability, 37 Rough rice, 320 defined, 347 drying, 318-33 EMC equation for, 319-20 harvest, 311-18 storage, 336-42 RTSV virus, role in tungro, 223 Rubber roll sheller, 351-52 Rusty grain beetle, 277

435

Sabog-tanim method, 163 Safety of aerosol-applied insecticides, 28182 Salinity in deepwater areas, 162 Saroc/adium oryzae, 211-13 Sasanishiki hybrid, 60 Sativalspontanea cross, 79-80 Saturn, moisture content and shelling, 371-72 Sawtoothed grain beetle, 277 Scalping machine, 349, 350 Scanning electron microscopy (SEM), structure of caryopsis, 389 Scirpophaga incertulas, 248, 249 cultivars resistant to, 250 Scirpophaga innotata, 248, 249 Sclerotia! fungal pathogens, 213-22 Sclerotium oryzae, 218-22 Screen separators, 349-50 Scutellum, 392 Sedges, 128 Seedbed preparation in dry seeding and flooding systems, 305 and weed management, 288-89, 294 Seed coat, 391 weight percent of the caryopsis, 390 Seed companies, work on hybrid development, 64 Seed-feeding insects, 260-61 economic thresholds for Oebalus pugnax, 258-59 Seeding for upland rice, 168 Seedling blast, 201 Seedlings growth, 15 respiration rate and grain size, 31 treatment with zinc, 151 Seed, weed free, 290 Selection for breeding experiments, 71-72 Self-sufficient regions, 5 Semidwarfs, 24, 59, 62-63 diseases of, 187 genetics of, 27 impact on total production, 3-4 and sclerotia! fungus incidence, 213 See also Cultivars; Genes; Green Revolution Semisterility, lines breeding true for, 48 Sesamia calamistis, 248, 249 Sesamia inferens, 248 Shading experiments in, 122-23 protection for upland rice, 164 Shakti cultivar, RGM resistance of, 251-52 Shallow-bed drying, model, 331-33 Shattering, 35 and grain moisture, 169 and temperature during ripening, 21

436

INDEX

Sheath blight, 213-17 genetic resistance to, 38 in Japan, 60 susceptibility of semidwarfs, 63 Sheath brown rot, 195-98 Sheath rot, 211-13 breeding for resistance to, 63 Sheath spot, 217 Shedding, 35 Shelled rice. See Brown rice Shelling, 351-52 defined, 347 Shifting import/export regions, production changes in, 5 Shiranui variety, 59 Shuttle breeding, 70 Siam 29 group, response of RGM to, 252 Silica, and P. oryzae infection, 204 Silicon in brown rice, 408, 410 Single-seed descent, 72 Sinica race, 51, 58 shattering in, 35 Sink formation, partitioning of energy for, 77 Sitophilus oryzae, 270, 275 Sitophilus zeamais, 270 Sitotroga cerealella, 270, 275 Sizing, 359-61 Smallfiower umbrella sedge, development stage and herbicide use, 304 Soaking temperature, effect on quality, 396 Sodium in brown rice, 410 Sogatella furcifera, 242 Soils characteristics of, 124-27 moisture tension and yield, 166 problem, 175-76 structure, and puddling, 136-37 type, and advantages of percolation, 109, 119 Solar radiation, 122-23 Solvent extractive milling (SEM), 377-79 Somaclonal variants, 81 Sorting, photoelectric, 361-62 South America, production in, 5-6 Southern and Southeastern Asia, production in, 2-3 Southern naiad, 290 Sowing, of upland rice, 168 Spacing for upland rice, 168 Spain, high yield from, 51 Sphaerulinia oryzina, 210 Spikelet, heritability of characteristics, 31 Spike-toothed cylinder harvester, 316-17, 318 Sporophyte, monosomics in, 47 Sri Lanka, breeding experiments in, 67-68

Starbonnet cultivar, 62, 63 moisture content and shelling, 371-72 Starch, 396-98 fractionation of, 400 granules, endosperm, 394 Starch synthetase, 412 Starchy endosperm, weight percent, 390 Steaming effect on quality, 396 before milling, and breakage reduction, 376 Stem borers, 130, 247-50 list, 248 resistance to, 39-40, 63 Stem maggots, resistance to, 39-40 Stem nematode, 227, 228 Stem rot, 218-22 in California, 63 resistance to, 38 Sterility following bacterial blight, 190 and chromosomal abberations, 44 in haploid plants, 45 intervarietal hybrid, 47-49 Stink bugs, 130 breeding for resistance to, 63 Stoners, 350 Storage, 336-42 changes due to, 410-11 and cracking, 336 and milling yields, 366-68 properties of undermilled rice, 380 protection afforded by the hull, 390 stability of SEM rice, 378 Straighthead, breeding for resistance to, 63 Streptomycin, for P. fuscouaginae control, 198 Striped stemborer, breeding for resistance to, 53 Stripe virus in Japan, 60 resistance to, 38 Stripper harvesters, 317-18 Sucrose, 401 Sugars, 401 Sulfur dioxide, experimental treatment of rough rice with, 376 Sun checking, and breakage, 364 Suncrack, 333-34 Surekha cultivar, RGM resistance of, 25152 Sustainability of riceland, 10 Sustainable rice production, 178-79 Synthetase, myo-inositol-1-phosphate, 412 Taichung Native 1 (TN!) variety, 54, 62 Taiwan, breeding experiments in, 54, 6667

INDEX

Taxonomy of Phytopathogenic Bacteria, 193

Tebonnet variety, 63 Teleomorphs G. fujikuroi, to F. moniliforme, 199 Magnaporthe grisea to Pyricularia oryzae, 202 Magnaporthe salvinii to Sclerotium oryzae, 220 Sphaerulinia oryzina to Cercospora oryzae, 210 Thanatephorus cucumeris to Rhizoctonia so/ani, 215 Temperature drying, and cracking, 336 and the drying rate constant k, 331 effect on breakage during milling, 372 effects on crop maturity, 20-21 as a limiting factor in rice culture, 11921

and maturation time, 33-35 and ripening time, 20 and tetraploidy, 46 Temperature sensitivity, 197, 211 genetic basis of, 54 of male sterility, 76 Tempering and breakage, 365-66 of partially dried rice, 325 Tenebroides mauritanicus, 270 Terpenoids, effect on BPHs, 243 Terraces for lowland rice culture, 125 Tetraploid plahts, 43, 46 Textural profile, soils and nitrogen applications, 148 and rooting depth, 165 and water penetration, 124 Thailand breeding experiments in, 68 change in production (1979-1988), 2 extremes of moisture in, 7 pest control in, 79 water tolerance studies, 36 Thanatephorus cucumeris, 215 Thiamin, 409 Thin-layer drying, simulation models, 33033 Thiobencarb for weed control, 159 in transplanted rice, 295 in upland rice culture, 298 in water-seeded culture, 301 Threshing, 153 of indica semidwarfs, 54 mechanization of, 177 Tillering, 15, 137 and evapotranspiration, 119 and flooding, 109 in indica semidwarfs, 54

437

and nitrogen topdressing, 144 quantitative studies of, 30 and temperature, 120 Tiller number, 15 and panicle number, 29-30 and planting density, 137 Tillers characteristics in wetland rice, 55 heritability of, 31 Tilling and rice growth, 125 and weed management, 288-89, 300 Tissue culture, 73, 80 Tocopherols, 406-7, 409 Tong-il variety, 3 Toxic substances, and anaerobic decomposition in flooded soils, 127 Trade policies, links to production, 177-78 Transfer methods, and breakage, 367 Transitory yellowing, GLH vectors for, 245

Transmission electron microscopy (TEM), structure of caryopsis, 389 Transplanting cost of, 154 critical air temperature for, 120 versus direct seeding, 15 irrigated, 147 in lowland rice culture, 134 and weed control, 293-97 Trap crop, protecting against GLH with, 247

Tray-type separator, 353-54 Tribolium audax, 270, 276 Tribolium castaneum, 270, 275, 276 Tribolium confusum, 270, 276 Tribolium destructor, 276 Tribolium spp., 276 damage to stored rice, 269-71 Trichoderma, and R. so/ani survival, 216

Triphenyltin acetate, for brown spot control, 207 Triploid plants, 45-46 Trisomy, 46 Triticum aestivum, host toP. fuscovaginae, 197 Triveni cultivar, resistance to BPH, 244

Tropical storms, and culture, 123 Tryptophan, distribution in the rice kernel, 382

Tungro virus, 222, 223-25, 246-47 breeding for resistance to, 53 control using varietal rotation, 66 epidemic, 188 GLH vectors for, 245 resistance breakdowns in hybrids, 69-70

438

INDEX

Tungro virus (cont.) resistance to, 38, 78 spherical form of, 38 Typhae stercorea, 270

Ufra nematode. See Stem nematode Ultisols, 127 phosphorus deficiency in, 149 United States breeding experiments in, 61-64 changes in production, 4 government support and yield, 6 high yield from, 51 production in, 5 smooth-hulled varieties grown in, 25 University of California, Davis, 315 Upland rice culture, 162-70 Africa and Latin America, 133-34 soils suitable for, 124-25 weed management, 297-300 and weed pests, 128-29 Urea basal incorporation into drained soil, 147-48 deep placement of, lowland rice culture, 149 fertilizer, demand for, 142 U.S.S.R., changes in production, 4 Ustilaginoidea virens, 208-9 Utilization, 8-9 Utri Rajapan cultivar, resistance to BPH, 244

Validamycin, for sheath blight control, 216 Valine, 406 Vascular disease, bacterial blight, 191 Vegetative phase, 13, 15-16 genetic basis of, 54 Vertical resistance to pathogens and insects, 38-40 Vertisols, 127 phosphorus deficiency in, 149 and upland rice culture, 124 Vietnam, brown planthopper in, 60 Vikram cultivar, RGM resistance of, 25152 Virus diseases, 222-27 insects as vectors of, 130 Vitamins, 408 A, B12• and E, 409 in brown rice and rice fractions, 409

Waika virus, 223-24. See also RTSV virus Water net requirement for, 119 requirement for, 103 resistance to deficit, 36-37 tolerance for excess, 36 Watergrass, 290 development stage and herbicide use, 303 Water management for drill seeding, 158 for rice water weevil control, 255 and seeding practices, 145 direct seeding onto puddled soil, 154 and stem borer activity, 249 for weed control, 130, 291-92, 295 in water-seeded rice, 300-301 Water mold complex, breeding for resistance to, 63 Water-seeded rice, 300-304 Water weevils, 130 breeding for resistance to, 63 Waxy character, heritability of, 40 Waxy rice, 408 amylose content, 399 starch of, 394, 400 Waxy starch granules, 398 Weather conditions, impact on world production, 2 Weed Control In Rice, 128 Weed management, 166-67, 287-309 and broadcast seeding, 155 chemical, and U.S. hybrids, 62 and direct seeding, 146 onto flooded fields, 156 with drill seeding, 159 for irrigated transplanted rice, 152 mechanizing, 176-77 and optimum spacing, 138 in rain-fed areas, 144-45 in water-sown rice, 157 and yields of deepwater rices, 161 Weeds, 128-30 as fodder for animals, 295 in dry-seeded flooded fields, list, 305 in transplanted rice fields, list, 296 in upland rice fields, list, 297 in water-seeded rice fields, list, 302 Weevils, as stored rice pests, 273-74 Wetland rice culture, and zinc deficiency, 151 Wet tillage (puddling), 125 Whitebacked planthopper, 242 resistance to, 39-40 Tainung resistance to, 67 White rice. See Milled rice

INDEX

Wild Abortive ems, 77 in China, 75-76 Wilted stunt virus, 226 Wire loop cylinders, 317 World Climate Research Program, predictions of, 83 World Crop and Livestock Statistics, I World production, trends in, 9 World Rice Statistics, I

Xanthomonas, 188, 189 Xanthomonas campestris, 191, 193 Xanthomonas cinnamoha, 192 Xanthomonas oryzae, 189-94 Xanthomonas oryzico/a, 193 Xylem vessel number, heritability for, 37 Yellow dwarf virus resistance to, 38 vectors for, 245 Yield and biomass, 83 breeding for, 54-56 ceiling, 76-77 and characteristics of wetland rice, 55 constraints in rain-fed ecosystems, 56 correlation with total solar radiation, 122 factors affecting, 50, 173 and flooding, 138 of F 1 hybrids, 74 and growth period, 172 of hand versus combine harvesting, 365 head, 313-14 and nitrogen uptake, 148 per plant, heritability of, 31

439

and plastic mulching, 222 and weed competition, upland rice, 166 weed control as a limiting factor, 297 See also Harvest index Yield losses from bacterial blight (BB), 190 from brown planthoppers, 241, 242 from C. suppressalis, 249 from hopperburn, 239 from rice gall midge damage, 251 from rice leaffolder damage, 257 from rice water weevils, 254 from sheath rot, 211 from stem rot, 218 Yield, regional, 104 in the developed countries, 177 and ecosystem, less developed countries, 133 by latitude, I 08 trends in Asia, 7 in the tropics and temperate zone, 123

Zea mays, host toP. fuscovaginae, 197 Zenith effect of humidity on head yield, 373 optimum drying conditions, 365 optimum harvesting conditions, 364 temperature and milling breakage, 372 Zigzag planthopper, resistance to, 39-40 Zinc in brown rice, 410 deficiency, 151 in alkaline soils, 159 tolerance to, 152 and direct seeding onto flooded fields, 157

INDEX

Abietic acid, HLR-Mickus process for adding, 38 Abrasive milling, 315 Abrasives, rice hulls as, 270 Absidia corymbifers, yellow rice-associated, 196 Absorbent qualities of hulls, 280 Acetaldehyde dehydrogenase, 258-59 Acetic acid, 265 acid-parboiling with, 41 concentration in fermentation, 259-60 tolerance, genetic property, 259 Acetification, 258-61 for producing rice vinegar, 256 submerged, 260-61 Acetobacter aceti for making vinegar, 254-

55

Acid parboiling, 41-42 Actinomycete, yellow rice-associated, 196 Activated carbon from hulls, 280-81 Activation energy for browning reactions, 172 of water removal, 172 Additives used in preparing quick-cooking rice, 137 ADP-glucose pyrophosphorylase, 385-86 Africa, rice cultivation in, 1

Agricultural uses of hulls, 274-76 Agrobacterium tumefaciens, gene transfer using, 386 Air-classification process, for flours, 17-18 Alanine in rice germ, 333 Albumin, 367 in bran and polish, 329 in rice germ, 333 Alcohol dehydrogenase, 258-59 Alcoholic fermentation for producing beverages, 206-19 for producing vinegar, 256 Aleurone, 321 phosphorus in, 333 Aleurone layer, 321 oil in, 295 phytic acid in, 373 type j particles, 324-25 Aleurone particles composition of, 373 phosphorus and protein content, 325 Alkali digestion test, 157 Alkaline extraction of bran, 342-44 flowchart, 343 yield and composition, 345 Alkali treatment, quick-cooking process, 136-37

397

398

INDEX

Amarillo (yellow rice), 196 American Association of Cereal Chemists (AACC), 21 American Frozen Foods, 230-31 Amino acids balance in composite flours, 20 enrichment with, 35-49 in milling fractions, 364-69 profile of rice vinegar, 263 in rice, beans, and soybean proteins, 164 in rice bran and polish, 329 in rice germ, 322-23, 333 in rice hulls, 273 in vinegar, 258 Aminopeptidase activity of Aspergillus oryzae, 264 in vinegar mash, 257, 262 Ammoniated rice hulls, nutritive value of, 277-78

Amulomyces, 197 Amylase, 202, 210 activation during steeping, 59 fungal, in fermentation, 206 a-Amylase content of milled rice, 16 in koji for vinegar, 257 in vinegar preparation, 253 J3-Amylase in koji-making, 204 Amylognim of starches for rice cakes, by source, 240 Amylographic gelatinization and quality, 102

Amylograph pasting curves long-grain varieties, 103-4 by mill type, for flours, 14-15 of rice flour, 11-12 Amylograph peak viscosity to measure the extent of steaming, 16 Amylomyces in fermentation starters, 201-2

Amylopectin, 3, 93 and gel formation, 189 and rice-cake character, 243-44 in waxy rice flour, 9 Amylose, 3, 369 and canned-rice characteristics, 148-51 and character of rice products, 6 and expansion during parboiling, 84 and freezing, 170-71 and gelatinization temperatures, 17 and gel formation, 189 and grain type, 51-52 in Jasmine rices, 106 and quality, 102, 103 and rice breads, 27-28 and subjective appeal, 148

Amylose/amylopectin ratio, 178-79 and rice flour product, 16 Anka fermented solid, 195, 199-201 Antioxidants in cereals oryzanol, 298-99 in Rice Krispies, 247 See also Butylated hydroxyanisole (BHA); Butylated hydroxytoluene (BHT) Antithiamin factor in bran, 352 Antitrypsin, in bran, 338 Apical meristerm, 321 Arak starter cultures, 197 Arare (cracker), 233 Arlesienne variety canned-rice characteristics, 150 effect of heating canned rice, 151 Arroz fermando (yellow rice), 196 Ascorbic acid, adding to cereal, 43 Asia, rice cultivation in, 2 Aspartic acid, in rice germ, 333 Aspergillus jiavus, yellow rice-associated, 196

Aspergillus oryzae, 205, 257, 262, 264 function in sake brewing, 213, 214, 217 in miso culture, 205 saccharification by, 198 Australia, rice exporting by, 5 Autoclave fermentation vessel for vinegar production, 258 Avorio process for parboiling, 73, 77

Baby foods, 186-89 broken rice used in, 10 formulated, 189 packaging, 189-92 rice polish used in, 353 Bacillus subtilis, yellow rice-associated, 196

Baking bran used in, 353 changes in raw rice during, 237-38 rice flours used in, 9-33 Balilla, canned-rice characteristics, 150 Bamboo leaf-wrapped rice, 245-46 Barley, production by region, 4 Basmati varieties, 94, 106 Bedding and litter, use of hulls for, 278 Belle Patna variety, utilization of, 149 BEPT. See Birefringence end-point temperature Beriberi, 35, 38 BHT. See Butylated hydroxytoluene (BHT)

INDEX

Bibingka (rice cake), 244 Biotin, changes with milling, 36 Birefringence end-point temperature (BEPT) and gelatinization temperatures, 17 of rice flour, ll Bitaibah (noodle), 243 Bleachiqg of rice oil, 306-7 Bluebelle variety, utilization of, 149 Blue Bonnet variety phosphorus distribution in, 371-72 popping characteristics, 179 processing for quick cooking, 128-29 utilization of, 149 Blue protein, Cu-containing glycoprotein, 329 Bostwick consistometer, baby food testing with, 189 Bran, 313-62 and cholesterol levels, 225 chemical constituents, 325-31, 335 color and quality, 95-96 defatted, 357 defined, 364 extrusion cooking, 338, 339 flavor and color, 348 fractionation, 341-48 functional properties, 349 heating after milling, 3 histology and histochemistry, 316-17 industry standards, 356 nutritional properties, 350-52 oil in, 295 from parboiled rice, 67 particles, 317-25 processes, 314-16, 337, 339-40 proximate analysis of, 325-27, 328 stabilization, 337-8, 340-41 standards, 356-7 sugars in, 370 utilization, 352-56 vitamins, 331-32 See also Rice-bran products Breads acid-leavened, 202-3 and flour characteristics, 14 Breakage, 9-10 and drying of parboiled rice, 63 during milling, 315-16 Breakfast cereals, II, 177-94 broken rice use in, 10 fortification with rice and minerals, 186 hot rice, 179 puffed rice, 180-83 puffing by extrusion, 183-84

399

ready-to-eat, 180 shredded rice, 184 Brewing, 178 broken rice use in, 10 shao-hsing wine, 210-13 Broken grades fabricating quick-cooking rice from, 137 flour from, 10 Browning reactions activation energies, 172 during drying, 62 during parboiling, 84 vacuum processing to prevent, 161-62 Brown Patna, 168 Brown Pearl, 168 Brown rice composition of, 365 defined, 364 flours, 15 storage problems of, 13 freezing properties of, 168 grades and requirements, U.S., Ill nutritional quality, compared with milled rice, 379-83 quick-cooking, 132, 139, 142 Bumping treatment, 128, 131 Burma, rice exporting by, 5 Butylated hydroxyanisole (BHA) antioxidant, 69 in cereals, 190 Butylated hydroxytoluene (BHT) antioxidant, 43, 69 in cereals, 190 Calci!lm, 375-76 distribution in the grain, 19 FDA (U.S.) standards for addition to rice, 47 fortification standards, 48 RDA in rice, 380 Calcium carbonate, milling with, 315 and bran composition, 326-27 Calcium:phosphorus ratio, 375-76 Calcium silicide manufacture from hulls, 280 California Pearl freezing properties, 167 for gun-puffing, 182 for puffed rice, 181 Calrose canned fried rice prepared from, 160-61 canning of, 165 characterization, 12 Candida tropicalis, growth on rice hull, 288

400

INDEX

Canned fried rice, 159-63 Canning, 147-67 flow diagram, 166 of rice pudding, 232 of soups, 158-59 varieties, 148 Carbohydrates, 369-70 in commercial bran, 327 in fibers, 323 in hulls, 271 in seed coat, 324 in type a particles, 318 Carboxymethylcellulose, use in rice breads, 28 Carrier, rice hull products as, 281 Carter Dockage Tester, 114 Caryopsis, 65, 316 enzymes in, 330 swelling during steeping, 59 variations in, 51 Cassava in fermentation starters, 201 eDNA for ADP-pyrophosphorylase, 385-86 for rice glutelin, 384-85 CeCoCo mill, 18 Cellulase in chiang mash, 204 Cellulose in bran, 327 in germ, 322 Central Food Technological Research Institute (CFTRI) (India), 71-72 Centrifugal fluidizing bed drier, quickcooking rice preparation, 141-42 Century Patna, 102 characterization, 12 Cereals ' production by region, 4 vitamin D fortification, 43 world-wide use of major, 3-4 See also Breakfast cereals Cesariot, canned-rice characteristics, 150 CFTRI process for parboiling, 71-72, 77 Chalkiness and grade, 115 and parboiling, 55 and quality, 99-100 Checking in quick-cooking processes, 138 Chein tsong snack food, 245 Chelating agents in rice vinegar, 262-63 Chemical characteristics of hulls, 271-74 of rice flour, 10 Chemical treatment of hulls, 276-78 in the quick-cooking process, 136-37 Chiang fermented paste, 195, 203-5

Chien tsong (bamboo leaf-wrapped rice),

245 China production, percentage, 177 rice exporting by, 5 Chinese red rice, 201 Chiou-chu preparation, 198 Cholesterol levels and bran, 225, 353-54 and fiber, 20 Chromoprotein in the embryo, 333 Chu chong tsaw (for red rice), 200-201 Chu (starter for fermentation), 198 Ciglon variety, canned-rice characteristics 150 Citric acid cycle, 265 Classification of rice crackers, 233-34 Cleaning of rice for parboiling, 55-56 Coleoptile, 321 Coleorhiza, 321 Color of bran, 348-49 of hulls, and quality, 91,95-96 of pericarp, and quality, 91 and quality, canned rice, 158 United States Standards for Rice, 113 Colored rice varieties, 94 Color sorting automated, 115 of parboiled rice, 67-68 See also Photoelectric sorting Compartment separators, 57 Composite flour for baking, 20-21 Composition of grains used for shao-hsing wine, 207 and quality after processing, 157 Compressing. See Bumping treatment Concrete building blocks, rice hull aggregate in, 279 Conditioning during drying, 63 Consistency of fermented grains, 196 Consumer acceptability, 89 of cookies with rice flour, 27 Continuous parboiling, 80 Cookies, 22-27 Cooking automatic equipment for, 143 loss of vitamins by, 37 and quality, 101-8 Copper, in bran, 329 Corn production by region, 4 starch use in rice breads, 28 waxy-type flours from, 17 Costs of freeze-dried rice, 172

INDEX

of pressure parboiling, 82 See also Economics Crackers, 226, 235-36, 238 fried (aghe arare), 234 momaka shell, 234 Cracking and drying of parboiled rice, 63 CRGA process for parboiling, 77 Crispix, 185 Crisp rice, 230 Crispy Cakes, 228 Crista!, canned-rice characteristics, 150 Cross-linkages in rice starch, 154-55 Crystal rice process, 73, 77 Cup Rice (instant), 122 Cutin in rice hulls, 273 in type a particles, 318 Cytochrome C, 329, 333 Cytochrome oxidase, in vinegar production, 258-59 Daily caloric intake, percentage rice, 3 Dairy cows, bran feed for, 356 Deacidification of rice oils, 306 Defatted rice bran, analysis, 357 Delignification of hulls, 271-72 Della variety, 94, 106 physical and chemical characteristics, 107 Delta variety canned-rice characteristics, 150 effect of heating canned rice, 151 Deodorizing rice oil, 307 Department of Agriculture, U.S., 90 Dephytinized bran, chemical composition of, 335 Diastase, processing with, 188 Dielectric heating, 79-80 Differential scanning calorimetry (DSC) to evaluate starches, 22 to measure gelatinization temperatures, 14-15 Differential thermal analysis (DTA) of rice hull, 282-83 Discoloration due to the maillard reaction, 62, 84 of parboiled milled rice, 59 and steaming, 61-62 See also Color DNA, complementary for ADP-pyrophosphorylase, 385-86 for rice glutelin, 384-85 Dockage, standards for, 113-14 Dosci (pancake-type product), 203

401

Dough improvers, use in rice-substituted wheat flours, 20-21 Drier blancher, 160 Dry fractionation of bran, 341 Dry-heat treatments, quick-cooking process, 131-32 Drying advantages of vacuum processing, 63 dielectric heating, 79-80 equipment for, 63-64, 160 infrared, 242 of parboiled rice, 62-63 pneumatic equipment,for stabilizing rice bran, 339-40 for quick-cooking rice processing, 78 Dry pack canned rice, 151-52 Dry soup mixes, quick-cooking rice in, 131 DSC. See Differential scanning calorimetry DTA. See Differential thermal analysis of rice hull Duribe variety, canned-rice characteristics, 150 Economics of parboiling, 81-82 of rice-oil production, 354 See also Costs Emulsifying capacity of bran, 349-50 Encapsulation to preserve flavors, 233 Endosperm, 321 nutritional quality, 363-95 Energy for extrusion cooking of bran, 339 hull utilization for, 269, 282-84 recovery from rice-hull disposal, 289-90 See also Fuel Engleberg huller, 314 Enrichment, 35-49 laws requiring, 48 Enthalpy value, as a measure of starch damage during grinding, 15 Environment during growth, and quality, 90-91 Enzymes in bran, 330 digestion to produce high-protein flour, 19 Epiblast, 321 Epidermis, 270 Epithellar gland, 321 Ethanol fermentation for making vinegar, 257-58 percentage in vinegar fermentation, 25960, 262 Extraction of oil from rice bran, 302-3

402

INDEX

Extruded products flavoring of, 232-33 fried rice snacks, 246-47 pellets for rice cakes, 227-28 precooked baby foods, 188-89 puffed rice, 183-84 quality, and bran content, 226 rice cakes, 228-29 ricelike, 142 Extrusion cooking, 20 in bran processing, 301-2 for bran stabilization, 338-39, 341 Face powder, rice starch in, 21 Fakau (rice cake), 244 ingredients, 245 Farinaceous foods, quick-cooking process, 129 Fat absorption by brans, 349-50 content of brans, 67 Fatty acids bran sources of, 351 polyunsaturated, in rice oil, 307 in rice bran oil, 297, 305 saponification of, in rice oils, 306 Federal Grain Inspection Service (USDA), 296 Feed bran for, 354-56 energy values of rice by-products, 352 rice bran and rice germ as, 313 Fermentation anaerobic growth of saccharolytic molds, 201 liquid state rice foods, 206 for rice cake preparation, 244 rice products, 195-223 rice vinegar preparation, 252-58 starters, 197-99 during steeping, 58 Ferric compounds phytate, 374 pyrophosphate, HLR-Mickus process for adding, 38 See also Iron Fertilizers, annual use of, 5 Fiberboard, rice hull utilization, 279-80 Fiber content, 370 and cholesterol levels, human, 20 of milled rice, 383 pericarp cell walls and, 319 type h particles, 323 Filtration in brewing, 212 rice hulls for, 285

Fissuring in dry-heat treatment, 132 in microwave processing, 139 in pre-cooking processes, 128 Flame sterilization, canned products, 16364 Flavor additives in extruded products, 232-33 of bran, 348-49 Florescent glumes, type a particles, 317 Flours, 9-33 from broken rice, 138 brown rice, 15 composite, for baking waxy-rice, 17 See also Rice flour Food and Drug Administration, U.S., 278 Food, bran in, 353 Fortification with amino acids, 43-46 of Rice Krispies, 247 Fractionation processes for bran, 341-48 flowchart, 347 yield and chemical composition, 348 Freeze-drying, 135-36, 171-72 general principles, 171-72 moisture absorption in fruit, 191 Freeze resistance of waxy rice-flour pastes, 11. Freeze-thaw treatment, quick-cooking process, 132-33 Freezing characteristics of the product, 169-71 and flour type, 17 process, 167-71 of rice, 167 technology, 167-69 Fried rice canned, 159-63 frozen, 169 Fructose, 369 in rice bran, 327 Fuel paddy hull as, 82 rice hull as, 282 See also Energy Fungi, as saccharifying agents, 198 Furfurals from hulls, 284 in roasted bran, 348 ,8-Galactosidase in chiang mash, 204 Gardner meter, tristimulus color measurement, 158 Gas-liquid chromatography, to identify rice vinegar components, 262

INDEX

Gelatinization, 152 and conditions during steaming, 61 defined, 22 during parboiling, 83 in the quick-cooking process, 129-30 Gelatinization temperature and grain type, 51-52 and quality, 102 of rice flour, 11-12 by mill type, 14-15 suitable for rice breads, 27-28 General Foods, 126, 128, 131, 142, 144 Genetic characteristics, and quality, 90 Germ, 321 chemical composition of, 332 nitrogenous compounds in, 333 oil in, 295 pentosans and lignins, 332 separation of, 316 size distribution of, 336 sugars, 332 type g particles, 320-23 vitamins in, 333-34 Glassine in cereal packaging, 192 y-Globulin in the embryo, 333 Globulins, 367 in bran and polish, 329 in rice germ, 333 Glucoamylase in koji for vinegar, 257 in vinegar preparation, 253 Glucose, 369 in rice bran, 327 Glutelin, 367, 384-85 in bran and polish, 329 in endosperm, 365 Glutinous rice in crackers, 235-36 for making shao-hsing wine, 207 for rice cake, 243 Glycerides removing from rice oils, 307 in rice bran oils, 297-98 Glyceryl monostearate, use in rice breads, 28 Glycolipids in rice bran oils, 297, 298 Grades, 89-119 brown rice, 111 milled rice, 110 of rice for parboiling, 56-57 rough rice, 112 special and numerical, 115-16 Grain gauge, 97 properties, for shao-hsing wine, 207 quality, 89-90, 91, 92-94 shape tester, 96-97

403

size and shape, 97-98 type and milling yields, 101 Granola snacks, 230 process flow diagram, 231 Green grains, and parboiling, 55 Growth medium for microorganisms, rice hull, 288 Guar gum, use in rice breads, 28 Gums as gluten substitutes in bread, 27 guar, use in rice breads, 28 locust bean, use in rice breads, 28 removing from rice oil, 306 Gun-puffed rice, 182-83 Harusame (noodles), 241-43 Heat-damaged kernels, 114 Heat of combustion for rice hull, 283 Heat-stabilized brans moisture content, 337 particle-size distribution of, 335 Heat treatment method, rice oil extraction from bran, 302 Hemagglutinin in bran, 352 Hemicellulase, use in preparing quickcooking rice, 137 Hemicelluloses in bran, 327 and pasting properties of starch, 12 Hemoproteins in the embryo, 333 n-Hexane extraction using, 303 for fractional sedimentation, 346-47 High-protein flour, 17-19 High-protein food flour, 17-19 from rice bran, 19 Hiochic bacteria classification of, 218 Lactobacillus homohiochi, 260 sake spoilage by, 217 Histology of commercial rice bran, 321 HLR-Mickus process for niacin fortification, 38 rice premix, 39 for thiamin fortification, 38 Hua Tiao, 213 Hong-ru wine, 219 Hot cereals, 179-80 Hua-tiao wine, 213 comparison of processes, 214 "Huller bran" composition, 326 Hulls, 269-94, 351 amino acids, 273 ash, analysis, 274 ash plant, 289

INDEX

404

Hulls, (cont.) carbohydrates, 271 chemical properties, 271 chemical treatment, 276 color and quality, 91, 95-96 composition, 271 cutin, 273 delignification, 271 inorganic component, 274 lignin and cutin, 272 lipid, 272 morphology, 270 organic acids, 273 physical properties, 270 physical treatment, 278 protein, crude, 272 reviews, 260 utilization, 274, 288 active carbon, 280 agricultural uses, 274 animal and poultry feeding, 274 bedding and litter, 278 building materials, 279 calcium silicide, 280 carrier, 281 cement, 281 colloidal usage, 282 fiberboards, 279 fuel, 282 fufural, 284 hydrolytic products, 288 industrial uses, 280 pressing aids, 285 rubber compounds, 285, 287 single cell proteins, 286 sodium silicate, 286 steel industry, uses by, 288 vitamins, 273 Hydration conditions, effect on properties of frozen rice, 170 Hydraulic cement utilizing rice hulls, 28182 Hydrophilic character of flour, and baking qualities, 24-25 Hydrothermal processing, 76 Hypocotyl in type g particles, 322

Idli, 15, 202-3 Image analyzers for grading by grain size,

97

India, percentage of world rice production, 177 Indica rice, 177 Indonesia, rice importing by, 5 Infrared drying, 242

Infusion, adding threonine and lysine by, 45-46 Insects and bran deterioration, 338 effects on parboiled rice quality, 54 Instant noodles, 241-43 manufacturing process, 241 Instant rice, 121 physicochemical properties of, 140 Institute of Nutrition of Central America and Panama, 45 lnstron press for measurement of firmness, 157 International market price, 5 International Rice Research Institute (IRRI), 365 Iodine-blue reaction (amylose), 157 IR-8 characterization, 12 protein in, 384 IR-480, protein in, 384 Iron, 376 availability in phytate, 374 changes with milling, 36 FDA (U.S.) standards for addition to rice, 47 pyrophosphate, 38-39 RDA in rice, 380 Italy, rice exporting by, 5 Ivory Coast, rice importing by, 5 Jadavpur University Process for parboiling, 72,77 Japanese Agricultural Standard (JAS) for rice vinegar, 261 Japan, rice exporting by, 5 Japonica rice, 177 Jasmine types, 94, 106 physical and chemical characteristics, 107 Kellogg Company, 181, 247 Kellogg, J. H., 230 Kernels composition, 364 damaged, 114 dimensions and grade, 96 quality characteristics, 91 Kneading dough for rice crackers, 238-39 Koji, 195, 204, 205 from bran, 353 for brewing sake, 213 for making vinegar, 254-55 preparation of, 198-99 for making vinegar, 256 for wine making, Taiwan, 213

INDEX

Kokuhorose types, 106 Kong-Yen Food Co., 260 Kuriowa technique for making vinegar, 254-55 Kyokay yeast, 252-53 L202 variety, physical and chemical characteristics, 107 LaBelle variety, characterization, 12 Lactobacillus function in sake brewing, 214 homohiochi, in vinegar production, 260 Latent heat of vaporization of water, 172 Layer cakes, 29 and flour characteristics, 14 from wet-milled flour, 16 Legumes as a protein source, 165 Lethal ratio, and processing times, 163 Lignins in bran, 327, 332 in hulls, 271-72 Lignocellulose in hulls, 271-72 Lipase, 202, 330 and bran deterioration, 337-38 in chiang mash, 204 inactivation by heating, 52, 67 inactivation in bran processing, 300-301 inhibiting with extrusion cooking, 20 in koji for vinegar, 257 and shelf-life of brown-rice flour, 15 and stability of rice oil, 3 Lipids, 370-71 distribution in the grain, 19 effect on retrogradation, 156 in germ, 322 in hulls, 272 See also Rice-bran products, oil; Rice oil Lipolytic fungi in fermentation starters, 202 Lipoprotein membrane, 320 Lipoxygenase, and stability of rice oil, 3 Lite Energy Rice Cake Machine, 226 Locust bean gum, use in rice breads, 28 Long-grain types California, 104 chemical and physical characteristics, 103-4 classes, types, and grades, U.S., 109 processing characteristics, 178-79 quality characteristics conventional, 105 Newrex/Rexmont-type, 105 scented, 93, 106 Lysine, 43-46, 164, 367, 368 deficiency in bran, 350

405

loss on parboiling, 76 in rice germ, 333 Macrominerals, 371-76 Magnesium, 375-76 fortification standards, 48 RDA in rice, 380 Magnolia variety, utilization of, 149 Maillard reaction, 62, 84 Malau (rice cakes), 226 Malek process for parboiling, 75, 77 Manucol SS LL alginate, use in rice breads, 28 Market price and brewers' use of rice, 10 international, 5 See also Economics Mash seed, 215 for shao-hsing wine, 210 Maturity, and chalkiness, 99 Meals-Ready-to-Eat (MRE) program, 155 Medium-grain types classes, types, and grades, U.S., 109 physical and chemical characteristics, 104 processing characteri