proceedings of the workshop on chemical aspects of rice grain quality

All of this notwithstanding, the subject of grain quality has not been discussed in detail at any of the annual International Rice Research Conferences and symposia held at IRRI grain qu

PROCEEDINGS OF

THE WORKSHOP ON

CHEMICAL ASPECTS OF RICE GRAIN QUALITY

1979 INTERNATIONAL RICE RESEARCH INSTITUTE

LOS BAÑOS, LAGUNA, PHILIPPINES

P.O BOX 933, MANILA, PHILIPPINES

Correct citation: International Rice Research Institute

1979 Proceedings of the Workshop on Chemical Aspects

of Rice Grain Quality Los Baños, Laguna, Philippines The International Rice Research Institute receives support from a number of donors including the Ford Foundation, the Rockefeller Foundation, the European Economic Community, the United Nations Development Programme, the United Nations Environment Programme, the Asian Development Bank, the International Development Research Centre, the World Bank, and the international aid agencies of the following governments: United States, Canada, Japan, United Kingdom, Netherlands, Australia, Federal Republic of Germany, Iran, Saudi Arabia, New Zealand, Belgium, Denmark, and Sweden

The responsibility for all aspects of this publication rests with the International Rice Research Institute

FOREWORD

The characteristics of the rice plant covered by the term

grain quality to a large extent determine market price and

do not care for the taste, texture, aroma, or appearance of a newly developed rice variety, any other outstanding characteristic

importance as developing nations become more prosperous and as producing countries achieve self-sufficiency in rice, for both

of these conditions produce discriminating consumers

All of this notwithstanding, the subject of grain quality has not been discussed in detail at any of the annual

International Rice Research Conferences and symposia held at IRRI

grain quality are published in various periodicals in different

Quality was convened at IRRI (October 23-25, 1978) (a) to

critically review the present state of knowledge on the subject, (b) to review the status of rice quality evaluation in breeding programs in selected countries, (c) to examine existing methodology for estimating quality, (d) to recommend priorities for research

3-day workshop was attended by 28 breeders and chemists from 11 countries and IRRI

The proceedings of this Workshop give evidence that the

basic reference on the subject of the grain quality of rice for

are already being scheduled by the workshop participants

We wish to express our thanks to the workshop committee, which consisted of W R Coffman, G S Khush, B O Juliano

(chairman), J S Nanda, and M D Pathak

N.C BRADY Director General

Contents

Foreword

Opening remarks

RICE GRAIN RESEARCH

The Genetic Evaluation and Utilization program of the International Rice Research Institute

Rice grain quality evaluation and improvement at IRRI

IRRI’s efforts to improve the protein content of rice

J S NANDA and W R COFFMAN

Genetic studies on the grain quality of rice

Effect of environment on protein and amylose content of rice

The chemical basis of rice grain Quality

The nutritional value of rice in comparison with other cereals

M D PATHAK

G S KHUSH, C M PAULE, and N M DE LA CRUZ

T T CHANG and B SOMRITH

K A GOMEZ

B O JULIANO

B O EGGUM

COUNTRY REPORTS

Rice grain quality evaluation in Australia

Studies on quality of rice in Bangladesh

Rice breeding for grain quality in France

Status of rice breeding for grain quality in India

Rice grain quality evaluation in Japan

H.SUZUKI, H IKEHASHI, and K KUSHlBUCHl

Rice grain quality evaluation in the Philippines

F E MERCA, T M MASAJO, and A, D BUSTRILLOS

Rice grain quality evaluation in Spain

S BARBER and E TORTOSA

Rice grain evaluation in Sri Lanka

Physicochemical properties of Thai rice varieties and methodology used

in quality improvement

Components of rice quality: their identification, methodology, and stage

of application in United States breeding programs

REVIEW OF METHODOLOGY

Outlook for rice milling quality evaluation systems

S BARBER and C BENEDITO DE BARBER

Methodology of assessing appearance of the rice grain, including

chalkiness and whiteness

Gelatinization temperature of rice starch and its determination

Amylose analysis in rice – a review

Amylography and alkali viscography of rice

Assessing parboil-canning stability of rice in varietal improvement

programs

Gel consistency and viscosity of rice

Quality tests for waxy (glutinous) rice

Sensory assessment of cooked milled rice

Use of the Texturometer for measuring the texture of cooked rice

Instron measurement of cooked-rice texture

Use of the Viscoelastograph for measuring the texture of cooked rice

Tests for parboiled rice

H IKEHASHI and G S KHUSH

Priority research problem areas for assessment of grain quality in

rice-breeding programs – workshop committee report

Collaborative testing – report of the workshop chairmen

Appendix A – Participants and authors

Workshop will foster

In 1960, when IRRI was first established, primary attention was given to increasing rice yields The productive potential of tropical rices had not yet been determined, and many feared that the tropics were permanently saddled with lower yields than could

be achieved in the temperate zones Consequently, increasing yields was the primary focus, not only of IRRI scientists, but

of those in national programs as well

Even as late as the 1970s, when widespread drought and floods drastically reduced food grain levels, the world's primary emphasis was on the quantity of food produced and not on its quality Once again the worry was how the food could be produced and not so much its acceptability as a food product

In spite of this continued emphasis on yields, those who best understand food consumption patterns have encouraged

attention to grain quality As soon as IR8, the first of the modem varieties released by IRRI, became widely grown, its grain weaknesses were as conspicuous as its high yield

capabilities The "white belly", chalky appearance, short grain and hardness after cooking were negative quality characteristics that prevented IR8 from being a choice quality rice A

counterpart release of the University of the Philippines College

of Agriculture, C4 (C4-63G), while it lacked IR8's yield vigor, was much more acceptable to Filipino consumers because of its

"quality" characteristics At IRRI banquets and luncheons we sometimes serve C4 rather than our own varieties

Plant breeders have an acute awareness of consumer quality preferences A survey of the genetic traits sought by breeders

in India in their new rice varieties showed grain quality to be exceeded only by yield potential as a desired characteristic of

2 Chemical aspects of rice grain quality

the new rices they develop The generally accepted practice by breeders of crossing the high-yielding modern lines and

varieties with lower yielding local varieties having known

desirable quality characteristics is added evidence of the

significance given to grain quality in modern rice-improvement programs

But grain quality is not always easy to describe and

identify And research on grain quality is no simple activity

In the first place, it is not always easy to identify and

quantify the characteristics or combinations of characteristics that are responsible for human preferences which are popularly equated with grain quality Second, there is uncertainty about the relationship between nutritional quality and human

preferences A food is not nutritionally superior just because people prefer it At the same time, the nutritional quality of

a food that humans do not accept may not be too important Thus human preferences and nutritional value must both be considered The third complicating factor influencing grain quality research is the lack of tools or methods for measuring grain quality It is especially difficult to reduce to quantitative chemical and physical terms the parameters that characterize good grain quality, whether it be in terms of human preference

or nutritional value Even the taste panel approach to obtain

an integrated estimate of consumer preference has some weaknesses

In spite of these difficulties, it would be incorrect to leave the impression that no progress has been made in combining

in modern rice varieties good grain quality and high yield potential Scientists in national research programs and at IRRI have been successful in producing high-yielding rices with good grain quality, high consumer acceptability, and resistance to six or more major insect pests and diseases Furthermore,

chemical and physical methods for quantifying at least some elements of grain quality have been developed Several such methods are now routinely used here at IRRI, permitting us to evaluate thousands of experimental lines annually And research

is underway to develop practical techniques for evaluating the protein level and quantity of new rices as well as the ability

of humans to fully utilize the nutritional potential of the more protein-rich rices These research efforts are supplemented with biochemical studies which are adding to our knowledge about how grain constituents, such as starch and protein, are

interrelated in the rice grain

Studies of rice grain quality continue to point toward the need for interdisciplinary inputs for effectively improving and evaluating this grain quality The chemist, biochemist,

nutritionist, and food scientist must work together to better identify those characteristics which make for good grain quality

Opening remarks 3

They can then turn to the plant breeder with clear specifications for what characteristics must be bred into modern rices The plant breeder, in turn, must couple his activities with those of the agronomist, the entomologist, the plant pathologist, and the engineer, each of whom is concerned with cultural and/or pest management activities that may have a bearing on grain

food quality

Workshops such as the one you are attending permit an

effective interchange among scientists from different disciplines Research accomplishments on the chemical aspects of grain

quality will be exchanged at this workshop We hope there will also be time to give some attention to the future We at IRRI are especially seeking your advice about research priorities in relation to not only our own activities but to the collaborative research we should do with you or with scientists elsewhere in the world Our manpower and financial resources are limited, but the nature and scope of the research to be accomplished may make it possible for us to attract the interest of others,

thereby multiplying the work that can be done

We thank you sincerely for taking time to participate in this workshop and wish you success in your presentations and discussions

Rice grain research

THE GENETIC EVALUATION AND UTILIZATION PROGRAM OF THE

INTERNATIONAL RICE RESEARCH INSTITUTE

M D PATHAK

The Genetic Evaluation and Utilization program uses

an interdisciplinary approach to rice varietal

improvement Scientists of different disciplines

work as equal partners, each contributing expertise

in his respective area Varieties coming out of this

program are credited to the entire GEU team On a

broader scale, the GEU program activities at IRRI

envisage an international GEU network for rice

improvement Efforts already under way towards

this objective include a series of cooperative and

collaborative programs that promote dissemination

and evaluation of GEU materials under diverse

agroclimatic, pest, and disease conditions, and

a GEU training course at IRRI

INTRODUCTION

Rice is the staple food of over half of the world's

population Classified primarily as a tropical and subtropical crop, it is cultivated as far north as 49° and as far south as 35°, and from sea level to an altitude of 3,000 meters It is grown under diverse water regimes; as an upland crop, where there

is no standing water and the rains are the sole source of

moisture; or under lowland conditions wherein water derived from rain or irrigation systems is impounded in the field On slopes

it is cultivated in terraces, and in valleys or other low-lying areas, deepwater rice is grown in several feet of standing water

It is grown under a wide range of temperature, soil, pest , and disease conditions

Throughout approximately 5,000 years of cultivation

rice plants have adapted to these diverse conditions However, most varieties possessing these specialized attributes are tall and leafy and lodge easily when grown under improved agronomic conditions Thus, their potential for effectively utilizing natural soil fertility or added fertilizers is limited This discouraged the farmers from adopting improved agronomic

practices and, as a consequence, rice yields in the tropics and subtropics ranged only between 1.5 and 2 tons per hectare

Baños, Laguna, Philippines M D Pathak, director, Research and Training Coordination, International Rice Research Institute, Los

8 Chemical aspects of rice grain quality

compared with yields of 4 to 6 tons per hectare in most of the countries in temperate areas, where short-statured varieties are grown following improved agronomic practices

Scientists in the early 1960s realized these weaknesses of the typical indica varieties They changed the architecture

of the rice plant to a short and stiff-strawed, heavy-tillering plant with moderately upright leaves and insensitivity to

changes in day length This plant type was developed to make more efficient use of sunlight, water, and nutrients

In recent years many rice varieties with improved

characteristics have been released in the developing countries, but still the lack of varieties adapted to local conditions appears to be a main cause of low rice yields The short and stiff-strawed, non-lodging, nitrogen-responsive and non-

photoperiod-sensitive varieties, exemplified by IR8, have

demonstrated that truly high yields of rice can be obtained in the tropics and subtropics and in several areas have effected substantial increases in rice production However, much of the rice in developing countries is grown under such adverse

conditions as high incidence of pests and diseases, drought, inundated conditions, problem soils, and suboptimum temperatures,

to which most of the newer varieties are not adequately adapted

As a consequence their cultivation has expanded to only about

25 to 30 percent of the rice area, which is apparently better suited to these varieties In many of these areas, the newly

replacing these earlier high-yielding varieties that lack

resistance

THE GEU PROGRAM

To further expand the use of modern high-yielding varieties and to provide stability at higher yields even in their current areas of production, it is essential to incorporate into them theegenetic resistance or tolerance to the various adverse

conditions under which they are grovn To accomplish this, coordinated effort by scientists representing different

disciplines is necessary Although IRRI scientists have always worked together in such studies, to extend the interdisciplinary team approach a formal Genetic Evaluation and Utilization (GEU) program was initiated on November 19, 1973 This program

embodies an Institute-wide approach to evaluating and utilizing the genetic potential of the rice plant It is subdivided into various problem areas, and an interdisciplinary team consisting

of a plant breeder (PB) and one or more problem-area scientists (PA) provides leadership for each problem area (Fig 1) Their objectives and general operational pattern are:

1 joint planning and review, with continuing coordination

of improving rice varieties suitable to different

agroclimatic conditions;

The CEU program of IRRI 9

1 The building of modern rice varieties Disease and insect resistance and superior

agronomic characteristics are the core for all varieties developed through the Genetic

Evaluation and Utilization (GEU) program Plant breeders (PB) and problem-area scientists (PA) are working together to incorporate the genetic ability to withstand other production constraints

IRRI and elsewhere;

10 screening of hybrid materials;

11 field evaluation and selection of breeding lines, including yield trials;

12 evaluation of selected collections and breeding lines

of international nurseries;

10 Chemical aspects of rice grain quality

13 dissemination of genetic materials;

identify materials with broad adaptability

The plant breeders continue to be the common core of the

contribute primarily through screening and testing and through special host-parasite studies (Fig 2) The system allows not only an integration of the inputs of various problem-area

specialists, but the multidiscipline and multilocation testings act as safeguards against the release of varieties more

susceptible to certain problems than the existing ones

The general scope of various GEU problem areas is briefly described as follows

Germplasm collection and maintenance

Rice germplasm on a worldwide basis is collected to

increase seed stocks, characterize and preserve the samples, properly catalog the accessions, identify and remove duplicates, provide duplicate storage to other seed banks, rejuvenate seed stocks when needed, and provide seed to various researchers throughout the world

Agronomic characteristics

Agronomic characteristics of the improved rice plant that ensure productivity and adaptability under varying cultural and ecological conditions are studied The main characteristics to

2 General operational procedure of GEU

The GEU program of IRRI 11

be investigated are: dwarf and semidwarf statures, high

tillering capacity, relatively short, dark-green and upright

leaves, early vegetative vigor, appropriate growth durations, photoperiod response, threshability without grain shattering, and susceptibility to sprouting

Grain quality

Grain size and shape, milling quality and recovery ability

of head rice, absence of white areas, appropriate amylose

content (waxy, low, medium and high amylose contents), gel

consistency, and cooking and eating quality are studied

Physicochemical qualities preferred by consumers, and the effect

of environmental conditions on these qualities are described Simple, rapid, reliable tests for these characteristics are

developed The effect of various preharvest and postharvest

operations on grain quality (e.g., time of harvest, parboiling) are determined

Disease resistance

Techniques are standardized and the rice germplasm is

evaluated for resistance to common diseases The nature and causes

of resistance, inheritance to resistance, and diverse sources

of resistance are studied Stability of resistance (horizontal resistance) , international disease nurseries to determine

pathogen, races, and the effect of environmental factors on

resistance are being investigated

Insect resistance

Sources of resistance to common insect pests in the rice

antibiosis, tolerance) and cause (biophysical, biochemical) of varietal resistance, insect biotypes, and genetics of resistance to the current insect populations and to new biotypes are determined Isogenic and multigenic resistant lines are developed, as are lines resistant to several insect pest species

Protein content

Improving the protein content of milled rice, while

maintaining grain yield, grain quality, and other desirable

characteristics, is attempted The effects of genotypes,

environment, and their interactions on protein content are

determined The effect of protein content on grain quality and the inheritance of protein content are studied

12 Chemical aspects of rice grain quality

Drought resistance

Varieties are screened for drought resistance Drought resistance is evaluated at different stages of plant growth The physiological base of drought escape, avoidance, tolerance, and recovery in different varieties is determined The effect

of drought on plants is studied The role of root elongation, stomatal spacing, rolling of leaves, and the presence of a waxy layer on leaf surfaces in drought tolerance is studied

Drought-resistant lines are bred; selected lines and

breeding materials are evaluated under different agroclimatic conditions International upland rice trials are conducted

Tolerance to adverse soil conditions

Varieties are screened for their tolerance to common

adverse soils Plant characters giving tolerance to adverse soils and their inheritance are determined The effects of different agroclimatic conditions on the tolerance of plants to adverse soils are studied, and breeding for tolerance to adverse soils is carried out

Deepwater and flood tolerance

Factors limiting grain yields of deepwater rice are

determined, and the "improved plant type" for deepwater rice is conceptualized

Rice varieties are screened for their ability to elongate with increasing depths of water and tolerance to submergence The mechanism and inheritance of deepwater and flood tolerance are studied and lines are bred for deepwater and flood

tolerance Emphasis will be on developing semidwarf and

intermediate-height varieties with "elongation genes" for growing

in 1 to 5 m of water, including other desirable attributes, such as appropriate photoperiod sensitivity and resistance

to pest, diseases, adverse soils, drought, and other common problems

Temperature tolerance

Rice varieties are screened (at vegetative and reproductive stages) for their tolerance to high and low temperatures The effects of nonoptimum temperatures on plant growth, sterility, and other yield components are studied The inheritance of temperature tolerance is investigated and lines are bred for this character

The GEU program of IRRI 13

HOW GEU OPERATES

The GEU approach enables scientists of different

disciplines, working as a team, to contribute their expertise

to the improvement of rice The plant breeders/geneticists maintain the rice germplasm and provide it to various problem- area scientists (such as plant pathologists, agronomists,

entomologists, soil chemists) for screening against appropriate problems The screening is done primarily by problem area

scientists but in close collaboration with the plant breeders All hybridization work is centralized and is done by breeders Each cross is given a number, and the list of crosses is

available to all interested scientists upon request Subsequent screening of breeding materials and specialized studies, such

as on the genetics of various attributes, pests, and pathogen races, are conducted in collaborative efforts as shown in Fig 2

The GEU team at IRRI is working on 26 different attributes

of the rice plant in addition to the appropriate plant type

(Table 1) This requires a large number of crosses, some of which are quite complex Scientists at IRRI make about 5,000 crosses per year, which generates the need for the evaluation

of about 50,000 progenies per year (Fig 3) Such a massive screening requirement is met by evaluating the hybrid materials against problems for which rapid screening procedures are

available, such as blast disease, bacterial leaf blight, brown planthopper, and green leafhopper The selected lines are then tested against problems whose screening procedures are slow

or more complicated Then they are tested in a series of

field experiments at IRRI, in farmers' fields in the Philippines, and under various agroclimatic conditions in collaboration with scientists in other countries The entire screening is conducted jointly by problem-area scientists and plant breeders

COMPUTERIZED DATA

The diverse and large quantity of data generated by this screening and hybridization procedure has been made possible through the use of the computer All data on the screening of parents and the hybrid materials are sent by the scientists to the statistician, who appropriately codes them and stores them

on tape These data are available to all scientists upon request

To assist the scientists in the final selection of promising breeding lines to be grown in yield trials in the field, the statistician provides them with computer printouts of the reaction

of the test lines to the major problems against which they have been screened This is done as a routine However, any

scientist can at any time request similar information on the germplasm collection or hybrid(s) in which he has interest

14 Chemical aspects of rice grain quality

Table 1 List of characters being incorporated in improved rice

grassy stunt virus

ragged stunt virus

arid areas coastal areas zinc deficiency iron toxicity aerobic soils iron deficiency manganese toxicity aluminum toxicity FLOOD TOLERANCE

DEEPWATER AND FLOOD TOLERANCE TEMPERATURE TOLERANCE

OPERATIONS COMMITTEE

A six-person operations committee including plant breeders, problem-area scientists, and statisticians coordinates the GEU program, including the crossing and screening, the associated system of data collection, recording, and reporting The

committee arranges for providing the seed of breeding materials

to concerned scientists, arranges for field planting, and

integrates the overall varietal improvement program

To facilitate communication among the scientists working

on GEU, the entire GEU group meets on the first Tuesday of every month to review progress and to plan future strategies

Scientists working on various problem areas also meet in smaller groups for similar discussions

The GEU program of IRRI 15

3 Growth of the IRRl GEU program,

16 Chemical aspects of rice grain quality

EARLY-GENERATION TESTING AND OTHER COLLABORATIVE EXPERIMENTS

IRRI decided to discontinue the practice of naming

varieties starting in 1975 This was done primarily to

encourage scientists working in different regions to name the varieties best suited to their conditions Every effort is

made to provide them with materials from the various breeding programs The data obtained from these experiments are

very valuable, as they provide information on the broad

adaptability of certain rice strains, the suitability of a plant type under diverse agroclimatic conditions, and the occurrence of pest races/biotypes Some of the common avenues of providing these materials are:

scientists This allows selection of the lines best adapted to various agroclimatic conditions and that possess resistance to the common pest and disease problems Evaluation of these lines at other locations helps identify lines with broad adaptability

2 Supplying other breeding materials to scientists in national programs During 1978 a new scheme was initiated Under this scheme 10 to 15 rice breeders in selected national programs are invited to participate in the actual selection of breeding materials growing at IRRI Two such groups of scientists are brought to IRRI each year one in April and one in October- November These scientists are free to select as many lines as they wish, and the seed of the selected lines is sent to them soon after the crop is harvested

experiments are designed to determine the stability of resistance/ tolerance of select rices under different agroclimatic conditions The differences in their performance could be due to race/biotype variations in the pests, chemical composition of soils, or the effect of specific environmental conditions on the rice plant Collaboration with scientists working in developed countries is also sought for detailed studies in identifying these factors Collaborative research projects have the following

distinguishing features

(i) Collaborative projects are concerned with specific research goals that cannot be achieved solely by researchers at Los Baños These projects may require environments, pests,

research expertise, and/or facilities not present at Los Baños or

in the Philippines They will include basic research through which we can gain an understanding of the processes, phenomena, and mechanisms of performance

The GEU program of IRRI 17

(ii) Collaborators on these projects are carefully selected, keeping in mind the more rigorous criteria, such as enviroment, facilities, staff competency, and support for this type of

research While we do not refuse to collaborate with any

scientist who seeks such collaboration, we encourage collaboration with those who satisfy the more rigorous criteria

(iii) Each year, at either the International Rice Research Conference or through some other convenient meeting or mechanism, the data on collaborative experiments are reviewed, and specific annual work plans are developed in consultation with overseas collaborators

4 International Rice Testing Program (IRTP) The IRTP serves to effectively link the national and international rice improvement programs around the world in a testing network of select parents and improved breeding lines IRRI plays the

coordinating role by soliciting materials from various scientists, and providing them, along with appropriate methodology and

record books, to cooperating scientists It also compiles data and disseminates the data of these tests Access to a wide

array of breeding material helps identify elite breeding lines with broad resistance to various stresses Screening tests for specific diseases and insects provide information on the strain and biotype variations among the insect pests and pathogens IRTP provides an excellent testing ground to rice scientists for their own breeding materials because, during a single season, the materials can be subjected to diverse pressures in various

environments

Three broad categories of IRTP nurseries are composed of:

1 yield trials;

2 general observational nurseries;

3 specific stress nurseries (environments, disease, and insects)

The yield trials include promising, advanced material and help to identify varieties with wide adaptability and regional suitability The general observation nursery, composed of

several breeding lines from different sources, is subjected to diverse stresses and serves as a potential source for identifying lines with broader resistance that can be followed up by yield tests and/or utilized as donors The specific stress nurseries include both breeding lines and donor varieties, and these,

besides helping identify potential donors for individual stresses, reveal genetic variation (biotypes and strains) in insect pests and pathogens Table 2 lists the various nurseries tested in

1978

18 Chemical aspects of rice grain quality

Table 2 Utilization of entries from 1975 trials in 1976

national programs

Nursery a

30

19

17

13

Medium; IURYN = International Upland Rice Yield Nursery; IRON = International Rice Observational Nursery; IURON = International Upland Rice Observational Nursery; IRBN = International Rice Blast Nursery; IRSHBN = International Rice Sheath Blight Nursery; IRTN = International Rice Tungro Nursery; IRBPHN = International Rice Brown Planthopper Nursery; IRGMN = International Rice Gall Midge Nursery; IRSATON = International Rice Salinity and Alkalinity Tolerance Observational Nursery; IRCTN = International Rice Cold Tolerance Nursery; and IRDWON = International Rice Deep Water Observational Nursery

The GEU program of IRRI 19

Several of the entries in these nurseries have been formally named as varieties in different countries, but a large number are being used in hybridization and for crossing, or for further yield evaluations

One of the important components of IRTP's activities is the organization of monitoring tours involving groups of rice scientists from different countries who jointly review the

international nurseries and national research programs of

importance in selected countries The tours provide an informal forum for the exchange of ideas among the scientists and their

an effective supplement to the data from IRTP nurseries in

formulating future plans

GEU training program

A formal GEU training program was initiated at IRRI in 1975 with a group of 16 trainees This course is now being offered twice a year with about 25 trainees in each group It is a

multidisciplinary and skill-oriented program that emphasizes the practical aspects of rice improvement and stresses the need for interdisciplinary cooperation When possible, a team from a particular research station, composed of a plant breeder, a

pathologist, and an entomologist, and representatives of other disciplines, is trained simultaneously They are given a 2- week condensed course on rice production and 3-1/2 months

training in various theoretical and practical aspects of GEU work They work together to plan crosses and develop breeding strategies to be implemented when they return to their countries The training prepares scientists at the local level to utilize the products of the GEU Program and to develop or strengthen their own program National programs have shown tremendous enthusiasm for this training

RICE GRAIN QUALITY EVALUATION AND IMPROVEMENT AT IRRl

All IRRI breeding materials are evaluated for milling

recovery, grain size, shape, and appearance, and for

include developing improved germplasm with high total

and head rice yields, translucent and medium long to

long slender grains, intermediate amylose content,

intermediate gelatinization temperature, and soft gel

consistency Most of the improved varieties and

breeding lines developed to date have high amylose

content are generally preferred by consumers in the

tropics and subtropics Therefore, we are now

emphasizing the development of improved gemplasm

with intermediate amylose content We are also

developing some breeding lines with aroma and grain

elongation ability similar to those of the Basmati

rices

The development of improved germplasm with superior milling and cooking qualities is one of the most important objectives of

addition, grain size, shape, and appearance must also be taken into account because they largely determine the market

acceptability of milled rice Thus, all of our breeding

materials are evaluated for three components of grain quality

as follows :

1 milling recovery;

2 grain size, shape, and appearance;

3 cooking and eating characteristics

MILLING RECOVERY

Milling yield of rough rice is the estimate of the quantity

of head rice and of total milled rice that can be produced from

a unit of rough rice It is generally expressed as a percentage

To determine the milling yield, a given sample of clean rough

Plant Breeding Department, International Rice Research Institute, Los Baños, Laguna, Philippines G S Khush, plant breeder, C M Paule, senior research assistant, and N M de la Cruz, research assistant,

22 Chemical aspects of rice grain quality

rice is passed through a shelling device to remove the hulls from the kernels The dehulled or brown rice is then milled to remove the bran and the embryos The endosperm in the form of whole or broken kernels is separated from bran and embryos Generally, the hulls form 20 to 22% of the rough rice, although variation of 18 to 26% has been recorded Bran and embryos constitute another 8 to 10% Thus, from a given sample of rough rice about 70% milled rice is obtained The milled rice is separated into broken and whole grains with a sieving device The proportion of whole grains is known as head rice recovery and is expressed as percentage of rough rice Thus, if from a sample of 100 g of rough rice 70 g of milled rice is obtained and 20 g of this is broken, head rice recovery is 50%

We start assessing the milling yields of the breeding lines

as soon as they are entered into observational or replicated yield trials, generally starting with F5 or F6 A 125-g rough rice sample is dehulled and milled in a McGill Miller No 2 (Adair 1952), and various components such as hulls, bran, and broken and whole grains are weighed to determine the milling yields and head rice recovery

The head rice recovery may vary from as low as 25% to as high as 65% Head rice recoverability is an inherited trait, although environmental factors such as temperature and humiditv during ripening and postharvest handling operations are known

to influence grain breakage during milling Head rice recovery

is also dependent upon grain size, shape, and appearance In general, varieties and breeding lines with long or long bold grains and those having chalky grains give lower head rice yields Varieties having medium long, slender, and translucent grains give the best head rice yields Of the IR varieties, IR8 and IR5, which have bold and chalky grains, give the lowest head rice yields, whereas IR20, IR26, IR36, and IR42 give very high head rice yields (Table 1)

GRAIN SIZE, SHAPE, AND APPEARANCE

Preferences for grain size and shape vary from one group of consumers to another Some ethnic groups prefer short bold grains, some have a preference for medium long grains, and long slender grains are prized by others In general, long grains are preferred in the Indian subcontinent, but in Southeast Asia the demand is for medium to medium long rices In temperate areas short grain varieties are prevalent There is a strong demand for long-grain rice in the international market

We begin to characterize our breeding materials for grain size and shape from the F3 generation Ten unbroken milled

high high high high low high high waxy high high high high high high high

soft hard medium hard soft medium hard soft soft soft hard medium hard medium

24 Chemical aspects of rice grain quality

kernels are measured and on the basis of average length are classified into the following categories

Length in mm More than 7.50 6.61 to 7.50 5.51 to 6.60 Less than 5.50 For grain shape the following scale is used

Length/width ratio Over 3.0

2.1 to 3.0 1.1 to 2.0 1.0 or less

Of the IR varieties, IR5, IR8, IR20, IR26, IR30, IR40, and IR42 have medium grains; IR22, IR24, IR28, IR32, IR34, IR36, and IR38 have long, slender grains; IR29 has medium, slender grain (Table 1)

Grain appearance is largely determined by endosperm opacity, the amount of chalkiness, either on the dorsal side of the grain (white belly) or in the center (white center), and the condition

of the "eye" In some varieties the grain tends to break more frequently at the "eye" or pit left by the embryo when it is milled Rice samples with damaged eyes have poor appearance and low market value Similarly, the greater the chalkiness, the lower the market acceptability The starch granules in the chalky areas are less densely packed than those in translucent

the starch granules Therefore, the chalky areas are not as hard as the translucent areas and the grains with chalkiness are more prone to breakage during milling

The following scale is used for classifying endosperm

chalkiness of milled grain

Rice grain quality evaluation and improvement at IRRI 25

2 White center 0 none; 1 small, less than 10%;

5 medium, 10 to 20%; 9 large, more than 20%

1 White belly 0 none, 1 small, less than 10%;

5 medium, 10 to 20%; 9 large, more than 20%

26 Chemical aspects of rice grain quality

We start selecting for nonchalky grains from the earliest generation possible Only two of the IR varieties, IR5 and IR8, have chalky grains, and IR29 has opaque kernels characteristic

of waxy rice The rest have clear translucent grains (Table 1) Translucency is a heritable trait, and selection in early

generations is very effective in eliminating lines with chalky grains

COOKING AND EATING CHARACTERISTICS

Cooking and eating characteristics are largely determined

by the properties of the starch that makes up 90% of milled rice Several tests are conducted in our laboratory to determine the cooking characteristics of the rice varieties

Gelatinization temperature

Time required for cooking is determined by the

physical property of starch, is the range of temperature within which the starch granules begin to swell irreversibly in hot water Final gelatinization temperature ranges from 55° to 79°C Environmental conditions such as temperature during grain

ripening influence gelatinization temperature A high ambient temperature during grain development results in a starch with

temperature of rice varieties may be low (55 to 69°C),

intermediate (70 to 74°C), or high (75 to 79°C)

Gelatinization temperature is estimated by the extent of alkali spreading and clearing of milled rice soaked in 1.7% potassium hydroxide for 23 hours at room temperature (Little

et al 1958) Rices with low gelatinization temperature

disintegrate completely, whereas rices with intermediate

gelatinization temperature show only partial disintegration Rices with high gelatinization temperature remain largely

unaffected in the alkali solution

Although the gelatinization temperature and cooking time of milled rice are positively correlated (Juliano 1967),

gelatinization temperature does not correlate with the texture

of cooked rice (IRRI 1968)

There seems to be a distinct preference for rices with intermediate gelatinization temperature Thus, although IR8 and IR5 have the same amylose content and similar grain size and appearance, IR5 has greater acceptability scores as cooked rice than IR8 The gelatinization temperature of IR8 is low, that of

Rice grain quality evaluation and improvement at IRRI 27

IR5 is intermediate Similarly, IR36 and IR38 are identical in grain size and shape and amylose content but differ in

gelatinization temperature, has a better acceptability rating as cooked rice We evaluate our breeding lines in the pedigree

nurseries, observational yield trials, and replicated yield

trials for gelatinization temperature

Amylose content

Many of the cooking and eating characteristics of milled

rice are influenced by the ratio of two kinds of starches,

Amylose is almost absent from the waxy (glutinous) rices Such rices do not expand in volume, are glossy and sticky, and remain firm when cooked These rices are the staple food of people in northern and northeastern Thailand and Laos

Nonwaxy (nonglutinous) rices may have high (25 to 30%),

low (10 to 23%), or intermediate (20 to 25%) amylose content A great majority of the rices from Vietnam, Thailand, Burma, and the Indian subcontinent have high amylose content These rices show high volume expansion (not necessarily elongation) and a

high degree of flakiness They cook dry, are less tender, and become hard upon cooling

Low-amylose rices cook moist and sticky All of the

japonica varieties of temperate regions have low amylose content

A great majority of the varieties grown in the Philippines,

Malaysia, and Indonesia have intermediate amylose content

Intermediate-amylose rices cook moist and tender and do not

become hard upon cooling A recent survey conducted by IRRI

shows that the most preferred varieties in the areas where high- amylose rices are generally grown have intermediate amylose

We are convinced that intermediate-amylose rices are the

preferred types in most of the rice-growing areas of the world, except where low-amylose japonicas are grown Therefore,

development of improved germplasm with intermediate amylose

content is the most important objective of our grain quality

improvement program Except for IR24 and IR29, all IR varieties released to date have high amylose IR24 has low amylose and

IR29 is waxy However, we now have many improved breeding lines with intermediate amylose content Some of them are listed in

resistance to all major diseases and insects besides having high yield potential

28 Chemical aspects of rice grain quality

Table 2 Some improved plant-type IRRI rice selections with

intermediate amylose content

Ge 1 consistency IR4215-301-2-2-6

IR2061-465-1-4/IR2055-475-2 IR3264-13/IR1702-74-3//IR2055- 219-1-3

IR28/IR2053-521-1-1//IR36 IR28/IR2053-521-1-1//IR36 IR2053-521-1-1/IR2061-464-2-4- 5//IR36

IR2053-521-1-1/IR2061-464-2-4- 5//IR36

soft softmedium

soft

medium soft soft

soft

soft

We start screening the breeding materials for amylose

content from the F4 generation By that time, most of the lines with poor grain appearance and susceptibility to diseases and insects are discarded Analysis of amylose content is thus

observational and replicated yield trials are evaluated for

amylose content We determine the amylose content of our

breeding materials by the simplified method of Juliano (1971) using a Technicon AutoAnalyzer

Gel consistency

We observed that two varieties with the same amylose

content may have different acceptability scores For example, IR5 and IR8 have similar amylose content However, IR5 always scores higher for acceptability in panel tests conducted in the Philippines Recent work by our cereal chemists indicates that varieties having the same amylose content may be differentiated

Rice grain quality evaluation and improvement at IRRI 29

for differences in tenderness of cooked rice by the gel

the consistency of the cold 5.0% milled rice paste Within the same amylose group, varieties with softer gel consistency are preferred, and cooked rice is more tender Our breeding

materials are analyzed for gel consistency, starting with the

yield trials are evaluated for this trait Materials with soft gel consistency are preferred in the selection program Gel consistency for the IR varieties is given in Table 1 Most of the intermediate-amylose lines appear to have soft gel

consistency (Table 2)

Grain elongation

Some varieties expand more in size than others upon cooking Lengthwise expansion (grain elongation) without increase in girth

is considered a highly desirable trait in some high-quality

rices Basmati rices of India and Pakistan, Bahra of Afghanistan, Domsia of Iran, Bashful of Bangladesh, and D25-4 from Burma

elongate 100% upon cooking

We are attempting to incorporate this characteristic into improved germplasm Evaluation for this characteristic

from crosses involving the parents having this trait are

evaluated Grain elongation appears to be a quantitative trait Our preliminary experience indicates that only a few hybrid lines approach the parents in degree of elongation The method of Azeez and Shafi (1966) is used for evaluating the degree of grain elongation

Aroma

Many high-quality preferred varieties are aromatic

Examples are the Basmati rices of India and Pakistan, Dulha bhog

of Bangladesh, Khao Dawk Mali of Thailand, Azucena and Milfor of the Philippines,` and Rojolele of Indonesia Scented rices

command high prices and are used on special occasions We are endeavoring to develop improved germplasm with the aromatic characteristic In most cases the Basmati rices are being used

as donor parents Breeding lines are evaluated for this trait

been developed (IRRI 1971) All IR varieties developed to date are nonaromatic However, several aromatic breeding lines are available

30 Chemical aspects of rice grain quality

IMPROVEMENT OF BASMATI RICES The Basmati rices of India and Pakistan are famous the world over There is a great demand for the Basmati rices in the

domestic markets in India and Pakistan and in the international markets They generally sell at twice the price of ordinary varieties These rices are characterized by intermediate amylose, intermediate gelatinization temperature, soft gel consistency, strong aroma, and a high degree of grain elongation Varieties with similar grain characteristics are grown in Afghanistan and Iran (Bahra and Sadri varieties) The Basmati, Bahra, and Sadri rices are tall in stature and are poor yielders Attempts to improve the yield potential of these varieties have been

largely unsuccessful

These varieties are poor combiners, and crosses involving them and dwarf parents have yielded poor plant-type progenies When backcrosses to the improved plant-type parents are made, grain quality characteristics are lost, as several of the

desirable traits (aroma, elongation, and intermediate amylose) are quantitatively inherited

Our strategy for combining the Basmati grain quality with high yield potential is to develop lines with improved plant type, having one or two components of Basmati grain quality Thus, we have developed breeding lines with high yield potential and aroma, high yield potential and grain elongation, and high yield potential and intermediate amylose content We are now

in the process of intercrossing these lines to develop gerplasm that combines high yielding ability with all of the components

of Basmati grain

REFERENCES Adair, C R 1952 The McGill miller method for determining the milling quality of small samples of rice Rice J

1967 Los Baños, Philippines 308 p

Rice grain quality evaluation and improvement at IRRI 31

1970 Los Baños, Philippines 265 p

Juliano, B O 1967 Physicochemical studies of rice starch and protein Intern Rice Comm Newslett (spec issue):93-105

Little, R R., G B Hilder, and E H Dawson 1958

Differential effect of dilute alkali on 25 varieties of milled white rice Cereal Chem 35:111-126

del Rosario, A R., V P Briones, A J Vidal, and B O Juliano

1968 Composition and endosperm structure of developing and mature rice kernel Cereal Chem 45:225-235

Sanjiva Rao, B., A R Vasudeva, and R S Subrahmanya 1952 The amylose and amylopectin content of rice and their

influence on the cooking quality of cereals Proc Indian Acad Sci 368:70-80

IRRl's EFFORTS TO IMPROVE THE PROTEIN CONTENT OF RICE

J S NANDA AND W R COFFMAN

Among cereals, the protein of rice is one of the most

nutritious However, the protein content of milled

rice is relatively low (about 7% at 14% moisture)

There appears to be little prospect of increasing

lysine content, but it should be possible to increase

protein content

A large portion of the total variability in protein

content is attributable to environment However,

true genetic differences in protein content do exist

Studies have shown the inheritance of protein content

to be complex, with low protein content being dominant Heritability values for protein content in the early

segregations are low

The use of natural variability and breeding techniques designed to reinforce genetic factors for high protein mntent have been moderately successful At IRRI,

there is some evidence of general progress in the

improvement of protein content in advanced breeding

lines as well as specific examples of breeding lines

that exhibited superior performance for protein

content over several seasons at yield levels

comparable to standard check varieties However,

after the extensive testing time required for

verifying the true increase in protein content,

such lines are no longer of varietal potential

INTRODUCTION

Milled rice is the staple food of tropical Asia It

zontributes 40 to 80 percent of the calories and 40 percent of the protein in the Asian diet Rice protein is one of the most nutritious of all cereal proteins It is rich in lysine (about 4%), its first limiting essential amino acid However, the protein content of milled rice is relatively low (about 7% at 14% moisture) Brown or dehulled rice contains about 8% protein

J S Nanda, visiting plant breeder, and W R Coffman, plant breeder, Plant Breeding Department,

International Rice Research Institute, Los Baños, Laguna, Philippines