Evaluation and Documentation of Genetic Resources in Cereals

ADVANCES IN AGRONOMY, VOL. 44

EVALUATION AND DOCUMENTATION OF GENETIC RESOURCES IN CEREALS A. B. Damania Genetic Resources Unit International Center for Agricultural Research in the Dry Areas (ICARDA) Aleppo, Syria

I. 11. 111. IV . V. VI. VII.

Introduction Evaluation of Cultivated Wheat Evaluation of Cultivated Barley Genetic Resources from Ethiopia Evaluation of Wild and Primitive Forms of Wheat and Barley Documentation of Genetic Resources Summary and Conclusions References

I. INTRODUCTION Agriculture is a relatively recent historical phenomenon having begun just over 10,000 years ago in the near East and later in Central America. Through the increase of food after the beginning of the agricultural (neolithic = food producing) revolution, the human species has incredibly multiplied its own population at the expense of the rest of the world’s biota (Reed, 1969). Early farmers initiated a series of partly conscious selections that have resulted in the landraces we see today. Plant breeding activity did not begin until the mid-1800s. This activity gathered pace after the turn of the century and breeders such as Strampelli were already using wild and primitive forms in breeding programs following the rediscovery of Mendel’s work (Maliani and Bianchi, 1979). Vavilov (1926) was the first to realize the need for a broad genetic base for crop plant improvement. But after the Second World War, massive aid projects led to the development of high-yielding cultivars that began steadily replacing the local varieties (landraces), thus narrowing the genetic base of several vital crops such as wheat, barley, and rice. By the 1960s, an urgent need was expressed in two symposia (Frankel and Ben87 Copyright Q 1990 by Academic Press, Inc. All rights of reproduclion in any form reserved.

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nett, 1970; Frankel and Hawkes, 1975a) to preserve the older more variable germplasm and wild relatives, which began to be referred to as genetic resources. The term “genetic resources” per se excludes breeding lines and recently released varieties (Frankel and Hawkes, 1975b), which are composed of gene combinations rather than the genes themselves. The two symposia also thoroughly reviewed the need for immediate and systematic exploration and collection on a worldwide scale of genetic resources of food and other commercial crops. An International Board for Plant Genetic Resources (IBPGR) was formed in 1972 by the Technical Advisory Committee of the Consultative Group on International Agricultural Research to undertake the plant collection and conservation recommended by the symposia. With the establishment of the IBPGR, collection and conservation of representative samples of genetic variability in landrace populations were accelerated and a large number of samples began to accumulate in the cold stores of the major genebanks. Genetic resources merely stored safely are of little value to plant breeders unless they are evaluated and the resulting data made widely available. Evaluation is, therefore, an essential link between conservation and use. In fact, Frankel (1987) categorically stated that genetic resources have been utilized without elaborate characterization, but never without evaluation. The next step was to evaluate the collected samples to identify sources of useful traits in order that the material be better utilized than in the past. The evaluation process for large collections follows several distinct stages: (a) seed multiplication and preliminary evaluation; ( 6 ) systematic evaluation of the entire collection; and (c) further evaluation of selected accessions (Chang, 1985). The utilization aspect of genetic resources was recently reviewed by Brown et al. (1989), wherein factors that are likely to limit or facilitate this process are discussed. Genetic resources workers discriminate between “characterization” and “evaluation” (Erskine and Williams, 1980; Hawkes, 1985), although this fact is not widely known. Characterization is defined as recording information only once on those traits that are highly heritable, easily visible, and expressed in all environments, for example, grain patterns and isozyme profiles. Characterization provides a standardized record of readily observable morphological characters that, together with passport (origin) data, identify an accession in the genebank. Evaluation, on the other hand, is the assessment of more variable traits for potential use in breeding, such as plant height, time to maturity, disease resistance, and protein content. This is done in several ways: growing the material in different environments, exposing it to various abiotic and biotic stresses, assessing grain quality, and selecting the best lines for the desirable attri-

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butes. “Preliminary evaluation” refers to screening that is frequently carried out during multiplication, at a single location and without the use of replicates prior to the incorporation of the samples into the collection (Damania et al., 1983; Erskine and Williams, 1980). The information generated by characterization and evaluation not only improves utilization of the germplasm but also rationalizes storage space by identifying duplicates and eliminating redundant germplasm. In spite of the wide recognition given to the importance of conserving and evaluating genetic resources (Frankel and Bennett, 1970; Hawkes, 1971, 1983; Frankel and Hawkes, 1975a; Harlan, 1975; Plucknett et al., 1983; Holden and Williams, 1984; Rogalewicz, 1985), little was known about the variability in the primitive forms, old landraces, and wild relatives of cereals and much work still remains to be done. Detailed evaluation of stored populations of different origins allows an understanding of the patterns of variability. The population structure of a species is defined as the totality of ecological and genetical relationships among individual members that may coevolve as a result of gene exchange, but may also diverge under localized forces of evolutionary change (Jain, 1975). Landraces and primitive cultivars are products of many years of crop evolution, and it is vital to preserve their genetic composition during and after evaluation. Cases have been reported where polymorphic cereal populations have undergone radical changes in their genetic composition in one growing cycle (Shevchuk, 1973). However, in the case of samples collected from village markets or those that are subjected to biased sampling methods, it is sufficient to safeguard and maintain their genes and not necessarily their gene frequencies within populations. It is now widely recognized that extensive surveys of geographic areas for genetic variability and computerized documentation of the evaluation results are needed for the utilization of large collections of cereal genetic resources. The problems of describing geographic variability data and development of statistical methods for categorizing sets of population samples from diverse localities have been discussed by Gabriel and Sokal (1969), and the analysis of variability between and within genotypes and environments has been discussed by Freeman and Dowker (1973). Computers with appropriate statistical packages have greatly facilitated this task of documentation. This chapter reviews the status of evaluation and documentation of genetic resources of wheat and barley. The work of a multidisciplinary team of evaluators that include germplasm scientists, taxonomists, cytogeneticists, pathologists, biochemists, and physiologists is presented, followed by conclusions and suggestions for future avenues of research.

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II. EVALUATION OF CULTIVATED WHEAT The evaluation of cereal genetic resources collections goes back to the time when their value to crop improvement began to be appreciated by the breeders. Cultivated wheat has been the most extensively evaluated crop among cereals, which is in keeping with the prominent position it enjoys in terms of production tonnage and importance as a food crop. Qualset and Puri (1973) evaluated heading time in a world collection of durum wheat (Triticumdurum Desf.) and presented results for each geographic area from which samples were analyzed. They found a wide range of heading time in about 3700 samples studies and identified those that were highly photosensitive. Puri and Qualset (1978) also researched effect of seed and seeding rate on yield and other characteristics of durum wheat and found a positive correlation between large seed size and yield. In another study, geographic patterns of phenotypic diversity for qualitative traits of more than 3000 samples of durum wheats were evaluated in the United States Department of Agriculture (USDA) world collection at Tulelake, California, by Jain et al. (1975). Observations were recorded on leaf sheath glossiness, glume pubescence and color, awn color, kernel color, and basal spike node fertility. Variability for each character was found usually within each geographical region. Although Jain et al. (1975) admit that the collection was small and not representative, they found centers of diversity among material from Ethiopia, India, and the Mediterranean countries. Some of the areas known to be important sources of genetic resources were poorly represented in the study, a fact emphasizing the need for intensification of efforts in exploration and conservation. Spagnoletti Zeuli and Qualset (1987) have reported an evaluation study on the same durum wheat entries for spike characters. Five clusters were delineated among 26 country origins and an east to west clinal pattern was detected that represented a gradient in unimproved to improved types. In a previous study, Porceddu (1976) evaluated 2400 wheat landraces from the world collection of durum wheat and recorded information on growth habit, beginning of shooting, heading time, culm length, and number of elongated internodes. Distinct differences were found to exist among samples from different countries. Multivariate analysis showed that samples from Mediterranean countries were very similar, probably due to old trade links. Similarity in other samples from Cyprus, Egypt, Jordan, and Palestine was also noted. Another discovery was the significant similarity between accessions from Turkey and the United States. This was attributed to the history of transport of germplasm from Turkey and subsequent inclusion in U.S. varieties. Konzak et al. (1973) also evaluated wheaL germplasm from Turkey for reaction to mildew at

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Pullman, Washington, U.S.A., and estimated yellow berry content of the grain produced. Porceddu and Scarascia-Mugnozza (1983) carried out similar studies for ascertaining variability in landraces of durum wheat from Algeria, Ethiopia, and Italy and found that there was clear separation between Ethiopian and Italian material, but Italian landraces were more variable among themselves than Ethiopian ones and material from Algeria was more variable than both the other two. Hence, differences among landrace populations from the same country were highly significant for all 1 1 characters studied, except kernel weight and spike density. Using multivariate analysis also, Kosina ( 1980) evaluated structure and caryopsis quality of some hybrids of spring wheat. Ehdaie and Waines (1989) described genetic variability in T. aestiuum from Iran. They concluded that local landraces, such as those found in Iran, could be improved by selection for shorter genotypes with fewer tillers per plant, but with larger and heavier grains. Morphological and physiological variability in T. aestiuum collected from Afghanistan was also reported comprehensively by Tani and Sakamoto (1987). There are traits, such as resistance to diseases and tolerances to certain types of soils, for which variability can only be observed at particular sites. Such traits are economically important and every effort must be made to record and document them by carrying out evaluation at sites where the incidence of that particular stress is the greatest, such as the so-called disease “hot spots.” For example, for screening against resistance to Septoria tritici (leaf blotch), ICARDA uses a humid and high-rainfall site located on the Mediterranean coast in Syria in addition to artificial inoculation. For experiments on tolerance to salinity, a drought-affected site on the shores of salt lake Jabboul in northern Syria is used. Jana et al. (1983) evaluated 3000 durum wheat accessions from various countries at this site, and 10 lines were found to be highly tolerant to combined stresses of salinity and drought. However, it is known that salinity is highly variable in the field and if experiments do not comprise several replicates, laboratory confirmation with tests such as chlorophyll influorescence (Smillie and Nott, 1982) may be used to help identify salt-tolerant lines. Selected bread wheat and barley plants from landraces grown in Nepal and Pakistan were examined and variability for certain qualitative traits described by Witcombe (1975). Barley from Nepal was found to be more variable than barley from Pakistan, whereas in the case of wheat the reverse was true. Murphy and Witcombe (198 I ) further analyzed landraces of wheat from northern India by growing single plants under glasshouse conditions in Wales, U.K. Multivariate analysis of data on quantitative traits was used to distinguish between introduced material and indigenous germplasm on the basis of means recorded on single plants. This data

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analysis method was used to detect modern varieties so they could be excluded from genebanks as genetic resources. However, variability studies based on observations of quantitative traits on single plants in a controlled environment are inconclusive and should be verified by field studies before an inference is drawn. Damania et al. (1985) evaluated populations of wheat and barley landraces from Nepal (Triticum aestivum and Hordeum vulgare L.) and the Yemen Arab Republic (T. turgidum L. and H . distichum L.) for morphological variability and days-to-heading under field conditions using sufficiently large samples. Observations were recorded for 18 characters on 50 randomly selected plants from each landrace. There were significant differences in variability among regions in the Yemen and river valleys in Nepal, as well as among landraces in the same regions or river valleys. It was concluded that landrace variability within primary or secondary centers of diversity could not be fully evaluated without growing the plant material in the field under conditions similar to the original habitat, although an initial impression of the extent of variability can be obtained through the application of polyacrylamide gel electrophoresis (PAGE) of seed proteins (Damania et a / ., 1983). Variability in high-molecular-weight glutenin subunits in landraces of hexaploid wheats from Afghanistan was also evaluated by Lagudah et al. (1987) using PAGE. The variability seemed to be independent of the altitude and geographical location of the collection site. A world collection of bread wheat (T. aestivum L.) maintained by the USDA was systematically analyzed for protein and lysine content by Vogel et al. (1973). Lewontin (1974) has expounded the advantages of electrophoretic surveys of proteins as measures of genetic diversity and reviewed the technical limitations and conceptual opportunities offered to plant biologists using this technique. Wheats can also be evaluated for quality and study of genomes and genotypes with the use of PAGE (Konarev et al., 1979). Kobrehel and Gautier (1973) studied peroxidase patterns of primitive and modern wheats by PAGE and found that brownness in macaronis can be associated with the compositions of the peroxidases. Damania (1985) demonstrated the usefulness of this technique in evaluating landraces of hexaploid wheats and their possible utilization in improving the bread-making quality of modern varieties. However, predictions on good or poor gluten quality based solely on presence or absence of certain bands in an electrophoretic gel may not be conclusive. It has been pointed out that the band with relative mobility (Rm) 45 and the band of Rm 42, which were indicators for good pasta and bread-making qualities in durum and bread wheat, respectively, were merely genetic markers, whereas other proteins (low-molecular-weight glutenins) were responsible for gluten viscoelasticity (Pogna et al., 1988).

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Information on the genetic variability of a sample is extremely useful and the eventual objective of every evaluator should be to describe the variation on the basis of a list of differences between and within samples in the sequence of nucleotides in the deoxyribonucleic acid (Erskine and Williams, 1980). At present, the study of storage protein (prolamins) variants by electrophoresis is the most convenient and rapid method available for detecting genetic differences at the DNA level in a cereal collection (Damania et al., 1983). Documentation of data derived from electrophoretic studies of storage proteins in cereal genetic resources has been reviewed by Konarev et al. (1979). However, it may be argued that heterogeneity in storage proteins alone is of little value to the breeders or genetic conservationists because its correlation with any single agronomic character is obscure. Nevertheless, these markers can perhaps monitor the relative genetic diversity with a greater degree of accuracy (Brown, 1978; Damania, 1983) than field studies with an inadequate number of traits. A prescreening procedure for identification of the ploidy levels and chromosomal aberrations, such as deletions with the use of electrophoresis, has been described by Damania (1985). This technique can also be used as a tool for elimination of duplicate germplasm stocks (Damania and Somaroo, 1988).

Ill. EVALUATION OF CULTIVATED BARLEY Barley is one of the most dependable cereal crops in harsh environments. It is grown in semiarid areas as well as in cold, short-season areas. Local varieties and landraces of barleys occupy nearly 80% of the cultivated areas in West Asia and North Africa and these should be collected before they are lost. Ward (1962), in one of the early efforts to characterize a large number of germplasm samples, evaluated 6200 lines from the USDA world collection of barleys and recorded observations on seven qualitative characters. He concluded that only a very small portion of the potential genetic diversity in barley was represented in the collection. Farmers still rely on barley landraces that have a stable performance in the dry areas and rarely outyield modern homogeneous varieties (Ceccarelli et al., 1987). The variability within these landraces is large and compares well with that within populations of its wild relative, Hordeum spontaneum, growing in the same region (Jana and Pietrzak, 1988). Variability for agronomic traits in landraces of barley has been evaluated by several workers. De Pace et al. (1978) crossed a set of six old Italian wheat varieties (female parents) with five breeding lines from the International Wheat and Maize Improve-

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ment Center (CIMMYT). The F3 progenies were grown in the field and variability for flag-leaf size, heading, and maturity time was recorded on single plants. It was concluded that utilization of genetic resources distant from the present varieties is advantageous as it permits breakage of linkage groups. The Cereal Improvement Program at ICARDA collected barley landraces from 33 locations in the drier regions of Syria and Jordan (Weltzien, 1982a). On subsequent evaluation it was found that some samples from Syria had a definite cold requirement to induce flowering (Weltzien, 1982b), indicating that under local conditions this trait may contribute to yield stability by preventing winterkill of early-planted material. Information of this kind is valuable for a crop improvement program, not only by showing which characteristics contribute to adaptation but also by indicating the degree of plasticity present in the indigenous landraces for which varietal improvement may be undertaken. Tolbert et al. (1979) carried out a diversity analysis on the USDA world collection of barleys and Ceccarelli et al. (1987)evaluated genetic diversity of barley landraces from Syria and Jordan for agronomic, morphological, and quality traits. Considerable diversity was observed between as well as within collection sites. Single-plant progenies were identified with larger yields and more desirable expression of agronomic characters than the original landraces. On the other hand, Murphy and Witcombe (1986) performed discriminant and reciprocal averaging analysis on single plants of covered and naked barleys from the Himalaya and confirmed their difference in a multivariate way. Sixteen populations of two-rowed barleys from the Yeman Arab Republic were screened for loose smut (Ustilago nuda) disease and found to be highly resistant when compared to the six-rowed barley landraces from Nepal (Damania and Porceddu, 1981). Incidence of diseases varies depending on climatic factors and inferences made of natural infestation in a single season should be avoided as they can be misleading. In another screening of landrace material, van Leur et al. (1989) tested 280 barley lines collected from different sites in Syria and Jordan. Large variability in response to four disease-yellow rust, scald, powdery mildew, and covered smut-was observed. No consistent association between the environmental conditions of the collection site and the level of resistance of the landrace lines could be found. Variation of flavonoids between barley lines was studied and found to be greatest in the Near East (Afghanistan and Iran) and Ethiopia (Frost et al., 1975). Allard et al. (1970) reviewed some studies on enzyme variability in a world collection of barleys and reported on the geographical distribution of different enzyme variants and factors responsible for the development and maintenance of the observed variability in the samples.

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In any survey of the distribution of genetic variability within a crop species of economic value, or its wild relatives, the most obvious pattern that emerges is the variability associated with broad geographical regions (Allard, 1970). It is important to sample not only the broadest geographical variability but also to have samples from the extremity of distribution of the species, that is, the marginal areas. According to the hypothesis of “peripheral diversity” put forward by Yamashita (1980), it has been suggested that there is considerable accumulation of diversity where a species has reached its geographical limits as a result of physical or climatic barriers that it cannot traverse. This variability needs to be collected, followed by evaluation for economically useful traits.

IV. GENETIC RESOURCES FROM ETHIOPIA A mention must be made of the very substantial amount of variability in genetic resources still to be found in Ethiopia (Porceddu and Perrino, 1973; Mengesha, 1975) and the considerable evaluation studies carried out on this material. This region of Africa has been often quoted as a secondary center of diversity of tetraploid wheats, and Vavilov (1932)was able to find a high amount of variability among and within samples. Porceddu et al. (1973) described 145 morphologically different phenotypes in a collection of tetraploid wheats from Ethiopia. The influence of altitude on yield and quality in cereals in Ethiopia was reported by Alkamper (1974). Bekele (1984) carried out an extensive evaluation study on populations of 153 tetraploid and 72 hexaploid wheats, respectively, collected from several regions in Ethiopia; 633 1 and 2700 individual plants were studied for 11 morphological characters. Jain et al. (1975) emphasized the importance of both regional and local patterns of genetic variability to genetic resources conservationists as well as to plant breeders. Analyses of regional patterns of variability for characters to determine the relative contribution of various regions to genetic resources showed differences in the level of importance of useful germplasm material. Polymorphism in characters was higher for tetraploid than hexaploid wheats, indicating that Ethiopia is almost certainly a center for diversity for tetraploid wheats. The contribution to total variability varied among characters and in both forms the contribution to the total phenotypic diversity was highest at the lowest level (within localities), followed by the differences among populations in a region, and among regions themselves. Qualset (1975) discussed optimal sampling strategy for germplasm possessing a single desirable trait in a center of diversity, using disease resistance in Ethiopian barleys as an example. The identity of genes in barley

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accessions from Ethiopia when compared with genes in primitive barley samples from the area of origin in the fertile crescent of the Middle East would provide evidence for the migration of this crop from the primary center of origin to Ethiopia. Negassa (1985a) evaluated the Ethiopian barleys for resistance to powdery mildew, studied the patterns of phenotypic diversity in a collection, and suggested that the Arussi-Bale highlands in Ethiopia was the secondary center of origin for H . vulgare (Negassa, 1985b). In another significant evaluation work, Negassa (1986) studied a collection of 293 entries of tetraploid and hexaploid wheats from Ethiopia. Some characters showed clinal variability, whereas others had localized concentrations. More significantly, a gene center for grain quality was identified in southern Ethiopia and this was confirmed by Dominici e f a / . (1988), who found lines with gliadin (storage protein of wheat) banding patterns not reported before from Ethiopian wheat landraces through an electrophoretic study. During 1967-1968, Kyoto University organized a collecting mission that covered Ethiopia (Sakamoto and Fukui, 1972).The principal objective was to investigate the variability pattern of cultivated plants and collect samples of their local strains. Seven hundred and seven accessions of wheat and barley were collected. Preliminary observations and analysis of variance on morphology and spike coloration have been published. Report of such information after evaluation of collected material is very useful for planning future collecting activities and every expedition must follow this example. The Ethiopian gene center certainly appears to be harboring interesting material when germplasm with such a high level of variability has already disappeared from other centers of diversity. Hence, further collections could be made to conserve genetic resources before the expanding human population and deforestation lead to genetic erosion.

V. EVALUATION OF WILD AND PRIMITIVE FORMS OF WHEAT AND BARLEY Wild relatives and primitive forms are those from which the present crop plants were domesticated and that continue to survive in conjunction with the cultivated species or by themselves as weeds. Several of these forms have become tolerant to biotic and abiotic stresses in their natural habitats, thus enhancing their value to agriculture as additional sources of genetic variability. However, their usefulness to plant breeders depends on their cytogenetic affinity and barriers to hybridization, the amount of

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germplasm available for evaluation, and the desirable traits revealed, and whether repeated backcrossing is needed to eliminate undesirable traits introduced from the wild or primitive parent. The evaluation of wild relatives of crop plants, including wheat and barley, has also been reviewed by Harlan (1984). Many regions in the world have succeeded in improving crop production through the introduction of high-yielding varieties. However, these varieties have not met with great success in West Asia and North Africa because of their intolerance to an environment where moisture is limited and inputs are very low (Srivastava and Damania, 1989). To improve and stabilize cereal production in the drylands, characters such as earliness plus tolerance to drought, temperature extremes, low plant nutrients, and diseases need to be incorporated into varieties. The genes for these characters can probably be found in wild relatives and primitive forms that are well adapted to such environments through independent survival over a very long period of time. Wheat and barley plant breeders in developed countries consider landraces and primitive forms as unadapted germplasm and Hallauer and Miranda (1981) termed as exotics all germplasm that does not have immediate use without selection for adaptation to a given area. The exploitation of wild and primitive forms in wheat breeding has been insufficient for four reasons. First, collections of wild progenitors in the past have been fragmentary as well as scanty and material available in collections is not representative (Croston and Williams, 1981). Second, work on wild forms has primarily concentrated on evolutionary (Feldman and Sears, 1981) and taxonomic studies (Bowden, 1959; Chennaveeraiah, 1960; Morris and Sears, 1967; Kimber and Feldman 1987). Third, wild relatives are not well adapted to Europe and North America and hence are used mainly as single-gene donors. Finally, variability between and within populations of wild species has not been looked at in adequate detail and utilization has hardly commenced (Srivastava et al., 1988). The principal reason for utilizing wild species such as Aegilops, Agropyron, and Triticum dicoccoides Korn. in wheat breeding has been the transfer of genes for disease resistance, salinity tolerance, and highprotein content, respectively, when these desirable traits are not found in the available genetic stocks. However, confirmation of the sources of resistance and cataloging of genes for resistance should precede any attempt at transfer from the wild to the cultivated forms. This would involve collecting and evaluating in-depth relevant germplasm collections for genetic variability. In-depth evaluation would consist of replicated tests at different locations, resulting in genetic analyses and observations on traits such as disease resistance.

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It is also useful to gain knowledge of genetic relationships between the wild donor and cultivated recipient species because without ready crossability, desirable traits cannot be easily transferred. Thus, wild progenitors of the cultivated species should be considered an important source of variability for broadening the genetic bases of cultivated crops (Harlan, 1976; Hawkes, 1977; Lange and Balkema-Boomstra, 1988). Brown (1978) states that the genetic resources of wild relatives of crop plants should be systematically evaluated, for these sources of genes will supplement, and even rival, the primitive landraces in their effectiveness in crop improvement programs. There is an opinion among certain workers, especially those involved in breeding for favorable environments, that the variability in landraces of wheat and barley has been fully exploited and for further progress in introducing useful genes one should turn to wild relatives and other alien germplasm of the secondary and tertiary gene pools. Strampelli, working in Italy, was among the first plant breeders in Europe to utilize wild and primitive genetic resources, especially Triticum villosum Schur. and T . spelta L., to improve wheat in 1906 (Maliani and Bianchi, 1979). Elliot (1957) transferred stem rust resistance to common wheat from Agropyron elogatum and Riley et al. (1968) transferred yellow rust resistance from Aegilops comosa Sibth. to cultivated wheat by genetically induced homologous recombination. One of the most detailed evaluation studies of morphological, physiological, genetic, and cytological characteristics of Aegilops and Triticum species was carried out at the University of Kyoto (Kihara et al., 1965). A geographical survey of species of wheat and its wild relative Aegilops was conducted following the University of Kyoto expedition to Afghanistan, Iran, and Pakistan in 1955. Emphasis was placed on collecting Aegilops squarrosa L., the probable donor of the D genome to cultivated wheat; other species were also sampled whenever possible. There was evidence that bread wheat arose as a hybrid between cultivated emmer ( T . dicoccum Schub.) and A . squurrosu. This study was not only illustrated with photographs, but also contained valuable information on utilization of the germplasm. Cox et a/. (1989) evaluated 212 accessions of A. squarrosa from the University of Kyoto collection using polyacrylarnide gel electrophoresis and found gliadin diversity to be higher than in the D genome of cultivated bread wheat. Genetic variability in Aegilops species and primitive forms of wheat has been studied by several researchers (Hillel et al., 1973; Sharma et a/., 1981; Dhaliwal et al., 1986; Waines et al., 1987), whereas in the past more emphasis was placed on Triticum dicoccoides, the wild progenitor of wheat (Lawrence et al., 1958; Avivi, 1979) as reviewed by Poyarkova (1988). Also, Gerechter-Amitai and Stubbs (1970) found the source of resistance to yellow rust in T. dicoccoides from Palestine.

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In another evaluation of primitive and wild types of wheat comprising 75 accessions of T . boeoticum Boiss., T . araraticum Jakubz., and T . dicoccoides; 42 of T . urartu Tuman.; and 34 of A . squarrosa seeking resistance to leaf rust, Hessian fly, and greenbug, Gill et al. (1989) found that all species except T . dicoccoides had resistance to both leaf rust and Hessian fly. Only A . squarrosa contained some resistance to greenbug, T . boeoticum had an intermediate response, but all other species were susceptible. Multiple resistance lines to leaf rust and Hessian fly were identified, but only A . squarrosa had two lines resistant to all three pests. Hillel et al. (1973) evaluated A . longissima Schweinf. and A . speltoides Tausch, two loosely related species that differ in their mating systems, to assess the direct effect of the mating system on the amount of genetic variability. They found that for most of the 36 quantitative characters examined, the differences between populations, the total variances of the populations, and the mean within-species variances were greater in the selfer (longissima) than the outbreeder (speltoides). These differences were attributed to the low probability of a successful gene flow in A . longissima, with each isolated population adapted to a specific microenvironment. Ninety-three accessions of cultivated emmer wheat ( T . dicoccum), five each of two wild tetraploid wheats ( T . dicoccoides)and T . araraticum, and the cultivated varieties ‘Modoc’ ( T . durum) and ‘Anza’ ( T . aestiuum) were evaluated for plant height, seed weight, flour protein content, and flour lysine content, as well as several morphological and grain quality characters by Sharma et al. (1981). Variability among lines for each trait in different species was significant except plant height in dicoccoides and araraticum. Primitive and wild wheats were higher in protein and lysine content, but lower in spike weight and 1000-kernel weight than the two modern cultivars. It seems that selection for larger kernels has resulted in a drop in the protein content of seeds from the wild species to the modern wheats. Lawrence et al. (1958) also found higher protein and lysine contents in wild wheats than in cultivated bread and durum wheats, but only one accession of T . dicoccoides and T . monococcum L. were analyzed. Avivi (1978) evaluated 47 samples of T . dicoccoides for protein content in kernels and found it to be highly variable, ranging from 19% to 28%. Waines (1983) did a comparative study of primitive diploid wheats such as T . monococcum with modern polyploid varieties and advocated the former’s direct usage as commercial varieties. Among the several positive characteristics of diploid wheats mentioned were less extraneous genetic material, only seven linkage groups and hence easier to manipulate than polyploid wheats, greater ecogeographic distribution and hence wider adaptability, and resistances to pests and diseases. However, Waines (1983) did not fully evaluate grain quality aspects such as pasta and dough

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products, which are vital to the success of any wheat variety, although one may tend to agree with him that exploratory research should be carried out to see if diploid wheats have a future as commercial varieties. Hordeum spontaneum C. Koch. is now recognized as the only progenitor of cultivated barley (Harlan, 1979). Wild barleys, H. spontaneum and H . murinum, and cultivated varieties from Afghanistan were collected by the Kyoto University Scientific Expedition. The morphological, physiological, and genetic characterization are described by Takahashi et al. (1965). Resistance to barley powdery mildew was also found in H. spontaneum, but the reaction was classified as being different from that of the cultivated forms. The overall diversity in this collection was reported to be low and the wild forms were less variable than the cultivated. Jana et al. (1987) studied genetic diversity in morphological characters in H. spontaneum and cultivated barleys from the Near East and also found that the latter were more variable than the former. However, it must be considered that this wild form in the near East has a long history of survival, has undergone millenia of natural selection pressures and therefore is better adapted to harsh environments (if not as variable as the cultivated landraces), and hence is a very valuable genetic resource for abiotic stress tolerance genes (Grando et al., 1985). An evaluation of H. spontaneum accessions was also carried out by Ceccarelli and Grando (1987) to assess the amount of useful genetic variability within this species. The results indicated that the progenitor is a useful source of genes for a number of economically important characters for breeding barley in the dry areas. Bakhteyev (1979) evaluated a collection of 77 samples of the same wild species originating from Iran, Iraq, and Turkey at an experimental farm in the Soviet Union. Considerable variability was observed in this study and the species merits breeders’ interest especially for adaptation to dry areas. Landraces of primitive wheats have been evaluated for several economically important traits. Blum et al. (1987) evaluated 13 accessions of T. compactum Host., a form of wheat cultivated in Syria and Palestine in the prepottery neolithic period (Renfrew, 1969), for grain quality. It was found, while comparing these with some modern cultivars of bread and durum wheat, that the latter were superior in all characters tested except protein content and quality. In a comparative study of wild and primitive forms of Triticum, Asins and Carbonell (1986) provided information for future use on intraspecific variability differences among species. Robertson et al. (1979) evaluated the genetic variability in primitive wheats for seedling root numbers, as it is well known that this character is probably responsible for drought resistance in wheats. Among the 16 species studied, the highest root numbers

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were found in T. durum and the lowest in T . araraticum; seed weight was positively correlated with root number. A test of progenies showed that this character was stable from one generation to the next over two environments. O’Toole and Bland (1987) have reviewed genotypic variation in root systems of cultivated wheat and Aegilops. Electrophoretic techniques also have been applied to the study of variability of storage proteins in wild and primitive forms of wheat (Cole er al., 1981; Damania er al., 1988) and barley (Jana et al., 1987). Using this technique, Nevo et al. (1979) showed that there was greater variability in wild and weedy barleys ( H . sponraneum) collected from Palestine than in a composite cross of cultivated barley that included more than 6000 varieties in its parentage. This result was surprising since cultivated barley is conspicuously more variable than its wild and weedy relatives from the Near East (Harlan, 1984). However, Jana and Pietrzak (1988) reported almost identical levels of variability between the two in material collected from Greece, Jordan, Syria, and Turkey. Nevo et al. (1982, 1988) studied genetic diversity within and between Turkish populations of wild emmer, T . dicoccoides, utilizing electrophoretic and statistical analysis, and reported that climatic selection played an important role in genetic differentiation of populations of this species and that the wild gene pool represents a significant genetic resource for utilization in wheat improvement. In another study of the same material, Nevo and Payne (1987) reported variability in seed storage protein and the use of certain high-molecular-weight glutenins for improvement of bread-making qualities of wheat. Variability for kernel proteins in 841 accessions of T . dicoccoides has been reported also by Mansur-Vergara et al. (1986) using gel electrophoresis. The protein content measured ranged from 15% to 25% with some accessions having high protein content as well as large kernel size. A high percentage of protein content was also reported by Srivastava and Damania (1989) in dicoccoides accessions from Syria and by Avivi (1978) in those from Palestine. In a study of 167 accessions of T . dicoccum from 23 different countries of origin using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Vallega and Waines (1987) identified a total of 20 alleles out of which 9 were different from those reported by earlier work. The newly discovered alleles enhance the genetic variability available to improve the industrial quality of wheats, and some of them may facilitate basic research on the relationship of industrial quality with highmolecular-weight glutenin subunit number. Success in future crop improvement depends largely on the ability to exploit existing genetic resources in wild relative and primitive forms,

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especially for less favorable environments. A better utilization and exploitation of these resources requires greater understanding of critical issues related to evolutionary pathways, geographical distribution, genetic diversity, and multicharacter associations. Variability studies, such as those described earlier, have provided this vital information. However, much more work needs to be done before evaluation can be instrumental in greater use of genes from wild relatives and primitive forms.

VI. DOCUMENTATION OF GENETIC RESOURCES An efficient system for dissemination of evaluation data on genetic resources material held in genebanks is essential if it is to be of use to breeders. Databases of genetic resources information on world collections have been established and contain a formidable amount of evaluation information that needs analysis and documentation (Ford-Lloyd, 1978). For example, 12,129 accessions of barley from a world collection were evaluated by ICARDA at one location (Somaroo et al. 1986, 1988); there was significant variability among the landraces for such characters as days to heading, plant height, 1000-grain weight, protein/lysine ratio, and resistance to diseases. In recent years much effort has been devoted to making these databases as comprehensive and mutually compatible as possible. However, less effort is being channeled toward considering how the results of these studies might be put to use. This is because most users are interested primarily in a very restricted aspect of the data (Williams et af., 1980). Plant breeders may be interested in an immediate problem such as resistance to a particular pathogen or a specific agronomic trait. Alternatively, their interest may reflect locally prevailing environmental conditions. For example, breeders at ICARDA are not interested in plants adapted for favorable conditions, as such environments are not common in West Asia and North Africa, where the Center operates (Damania and Srivastava, 1989). However, an international genetic resources center might be expected to take a wider view and Williams et al. (1980) contend that genetic resources evaluation data presently stored in computer memory banks contain more information of practical value than is immediately apparent without proper analysis. A detailed study of network analysis of genetic resources data has been attempted (Williams et af.,1980; Robinson et af., 1980; Burt et al., 1980). Internationally agreed descriptor states are not used when evaluation data are exchanged between genetic resources workers. Considerable time

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and effort would be saved if a lengthy description of the method and intervals used for recording each character is avoided. The IBPGR has been convening small working groups of scientists for the purpose of arriving at an internationally agreed upon list of descriptors for describing information for wheat (IBPGR, 1985) and barley (IBPGR, 1982). However, experience has shown that it is too time-consuming to record observations on all descriptors mentioned in the descriptor lists, as the method of recording and the selection of characters are very much dictated by the region and the needs of local breeders at each institution concerned. It is also necessary to set out data in a standard format using a generally agreed upon series of descriptors and descriptor states for the crop. In this way the data can be entered into computers, retrieved, and exchanged among institutions with the least possible confusion and optimum efficiency (Hawkes 1985). For the purpose of utilization, systematic analysis and description of samples is useful in both distinguishing between populations and identifying duplicates, as well as in providing information on the extent of variation within a given germplasm collection. It is axiomatic that the more documentation on a collection, the greater the chance of its rational utilization. Information from the site where a particular sample was collected may be extremely important. For instance, at ICARDA, germplasm that is described as having a short maturity period receives immediate attention of the breeders as this trait is very useful to escape drought and high temperatures during grain filling in the dry areas. Therefore, information recorded by germplasm collectors at site would be very valuable later when the samples are evaluated. Peeters (1988) studied statistically a large barley germplasm collection at Cambridge and reported that despite extensive collecting activity in recent years and subsequent exchange between countries, combinations of characters have remained substantially different in germplasm by country gene pool. Material from the United States now contains more variability in toto than material from any other country. Subsequently, Peeters and Martinelli (1989) used hierarchical cluster analysis to classify entries from this collection according to their degree of similarity and concluded that this statistical analysis procedure could be used as a tool to classify entries to their respective gene pools even when no passport data are available. Often those responsible for entering data recorded at a collecting site into a computer data base believe that lengthy descriptive notes made at the collection site, for example, notes on disease observations or peculiarities of the habitat, are not relevant and hence should be omitted. Nothing could be more erroneous. Although it is recommended that passport data

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must not be encumbered with vast amounts of morphologicaldescriptions, it should certainly contain disease and habitat data and, more importantly, comments from the farmers as to the useful features that distinguish their material from the rest. Inadequate passport data very often inhibit effective utilization of collected germplasm. It has been repeatedly pointed out to collectors and genebank managers that passport data divulge extremely valuable and in many cases the only available information on the ecological adaptation of an accession and hence no effort should be spared to fill this important gap in documentation of germplasm (Frankel, 1987). Systematic description of samples for discrete traits has been limited to cataloging the phenotypic variation because of constraints in relating genotype with phenotype. Quantitative morphoagronomic traits are also currently used in characterization. These traits are controlled by several genes, each contributing a small effect that is quite often blurred by the environment. Consequently, the correlation between genotype and phenotype is obscured. Certain evaluation studies have used ranking as a method of describing results of economically important traits such as yield. This ranking may change from one site to another for some quantitative characters such as plant height and days to heading (Damania, 1983). Such unstable characters cannot be adequately described when studied at a single location. Thus, the concept of multilocation testing becomes imperative. We cannot commit ourselves to hard and fast rules regarding the selection of a representative sample, but it must be stressed that an evaluation that partially covers the total variability can only be of limited value at best. That is, if raw data are misinterpreted or incorrectly fed into the main data base, self-consistency is lost and the entire task becomes futile. Unfortunately, not all the samples assembled in our genebanks were collected with the aim of preserving genetic variability of populations in danger of extinction. On the contrary, several genetic resources collecting expeditions were targeted to filling certain gaps, such as finding resistant lines to specific stresses or studying relationships between wild and cultivated species. Therefore, genetic material from such expeditions represents only a fraction of the existing variability present in a particular area. This being so, it can provide useful genes for current breeding goals, but may be inadequate for tomorrow’s needs (Porceddu, 1976). The major collections of wheat and Barley now contain several thousand accessions. Such numbers may be too large for detailed evaluation. In response to this, there is a recent trend toward developing “core collections,” which are subsets upon which detailed evaluation work may

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be concentrated (Brown, 1989). The remainder of the large collection constitutes a reserve still maintained in storage and available when a desired trait cannot be found in the core (Chapman, 1989). The ability of genetic resources managers to respond to requests from breeders for material depends very much on the adequate description of the accessions and the ability to query the information in a computerized data base. Hitherto, insufficient emphasis has been placed on recording passport data, and their absence is a major constraint to curators in assessing the range of variability in their collections and in identifying gaps (Williams, 1989).

VII. SUMMARY AND CONCLUSIONS Genetically uniform cultivars are employed by cereal farmers in the major cereal-producing countries of the world. Because plant breeding is essentially a process for exploitation of genetic variability, breeders could also examine means of conserving already existing genetically variable germplasm as well as creating new varieties. Mak and Harvey (1982) have described the composite cross technique that creates, as well as exploits, genetic variability, using the USDA barley world collection as a model. This may be one of the ways to proceed for other cereal crops. When precise objectives of evaluation are known at the outset, the task becomes relatively simple. In the case of most wild and primitive forms, evaluation aims to reveal potentially useful variability for direct use in the breeding programs. This may necessitate initial characterization in nurseries and cataloging of passport information, followed by a more detailed field study in collaboration with the end-users of the germplasm. Inferences regarding geographical variability, even on the basis of evaluation of a world collection, cannot be considered truly representative as they represent findings based on the composition of a collection that may be comprehensive for some regions and deficient for others. Furthermore, variability studies based on collections made several years ago may not accurately reflect the variability to be found at present in the same area. It is presumed that, after observation of dramatic degradation of the environment and genetic erosion, there would be considerable decline in variability if not extinction of indigenous germplasm in several previously generich regions in the world (Hawkes, 1981). The utilization of germplasm collections in crop improvement for the major cereals has revealed the following:

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1. The use of exotic germplasm. The successful use of landraces and wild species in cereal improvement has been more extensive in the developed countries, which lack indigenous germplasm, than in the less developed countries. In recent years the International Agriculture Research Centers (IARC) have contributed substantially to generation and distribution of improved adapted germplasm with genes from landraces and wild forms to the national programs and other institutions, as the germplasm developed for more favorable environments has not succeeded in the dry areas. 2. Constraints to the use of exotic germplasm. Many plant breeders were reluctant to devote a greater part of their resources for the exploitation of landraces and wild species in the past. This was because the potential value of these germplasms for the stressed environments was not fully appreciated. However, in recent years, varieties targeted for lowinput, rain-fed agricultural systems possess genes from adapted landraces and even direct usage of selections of the best lines isolated from landraces have been recommended for release. 3. Support for plant genetic resources programs. Extensive use of landraces, primitive forms, and wild species will be more tenable for harsh environments when the process of conservation, evaluation, documentation, and exchange of germplasm is strengthened and adequately funded. Donor countries and international agencies could increase support for utilization of indigenous landraces and primitive forms in the recently established breeding programs of the developing world. 4. Use of computers and statistical program packages. Computer programs designed for analyzing a large quantity of evaluation data have greatly reduced the time and effort needed for arriving at tangible results. This in turn has led to the publication ofgermplasm catalogs, which have facilitated dissemination of information on genetic resources collections to actual users, allowing for greater utilization of the services rendered by genebanks. However, breeders prefer to receive a short list of accessions with specific traits to choose from rather than large genetic resources catalogs.

Electrophoretic techniques that permit rapid mass screening of samples are increasingly recognized as powerful research tools for the study of genetic variations in populations. A wider application of gel electrophoresis in the evaluation of plant genetic resources is expected. The use of restriction fragment length polymorphisms (RFLP) for evaluating genetic diversity has been described (Bernatsky and Tanksley, 1989), and is the best available means for detecting differences at the DNA level on samples of reasonable size. It would be useful if such techniques were utilized to a greater extent than at present on genetic resources collections.

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The breeding objectives of the developed countries, mostly located in favorable environments, are different from those of the West Asia and North Africa region. The advanced breeding programs in the former countries began utilizing exotic landraces about 100 years ago and have fully exploited them, so they no longer seek variability but only single genes from the wild relatives and grasses of the tertiary gene pool. The breeding objectives for West Asia and North Africa, on the other hand, are to develop varieties adapted to withstand harsh environments and low inputs. Hence, selections from landraces and crosses with wild and pnmitive forms are undertaken to produce well-adapted germplasm for targeted agroecological zones. In recent years, world collections of cereals have been evaluated by many scientists working in different countries who were searching for economically useful genes or gene combinations. Confidence has been expressed that such materials are a usable source of breeding stocks, although they still require thorough assessment. Large-scale evaluation, if carried out thoroughly, is an expensive, arduous, and time-consuming process. Therefore, it is imperative to carefully select the traits that one wishes to evaluate in consultation with the breeders. Further, not all material in a collection may be of immediate interest. Priorities need to be discussed and selection of the traits made on the basis of their importance to the actual user. Such a procedure will assure optimal utilization of physical facilities, manpower, and financial resources. Finally, breeding objectives change, sometimes rapidly, and hence evaluation needs to be adaptive to a certain extent to succeed. ACKNOWLEDGMENTS The author thanks Drs. W. Erskine, S. Ceccarelli, and J . Valkoun for their comments and suggestions on a draft of this review and the Government of ltaly for financial support.

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