The structure of wild and domesticated emmer wheat populations,gene flow between them,and the site of emmer domestication

The domestication of emmer wheat (Triticum turgidum spp. dicoccoides, genomes BBAA) was one of the key events during the emergence of agriculture in southwestern Asia, and was a prerequisite for the evolution of durum and common wheat. Single- and multilocus genotypes based on restriction fragment length polymorphism at 131 loci were analyzed to describe the structure of populations of wild and domesticated emmer and to generate a picture of emmer domestication and its subsequent diffusion across Asia, Europe and Africa. Wild emmer consists of two populations, southern and northern, each further subdivided. Domesticated emmer mirrors the geographic subdivision of wild emmer into the northern and southern populations and also shows an additional structure in both regions. Gene flow between wild and domesticated emmer occurred across the entire area of wild emmer distribution. Emmer was likely domesticated in the Diyarbakir region in southeastern Turkey, which was followed by subsequent hybridization and introgression from wild to domesticated emmer in southern Levant. A less likely scenario is that emmer was domesticated independently in the Diyarbakir region and southern Levant, and the Levantine genepool was absorbed into the genepool of domesticated emmer diffusing from southeastern Turkey. Durum wheat is closely related to domesticated emmer in the eastern Mediterranean and likely originated there. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Photosynthetic performance in wild emmer wheat,Triticum dicoccoides: ecological and genetic predictability

Summary In a twin study, we have shown that wild emmer wheat, Triticum dicoccoides, the progenitor of all cultivated wheats, harbours important genetic variation (Vg) in photosynthetic characteristics. This Vg resides within and between populations and ecogeographical regions in Israel, which is the center of origin and diversity of wild emmer wheat. Here we analyzed, by univariate and multivariate methods, the significant differentiation of variation in photosynthetic characteristics of 107 genotypes from 27 populations of wild emmer in Israel, distributed in three ecogeographical regions including central, xeric (northern cold and eastern warm) marginal, and mesic (western) marginal populations. The highest photosynthetic efficiency was displayed by populations of the xeric marginal region, but most variation for photosynthetic capacity occurs between accessions within ecogeographical regions and populations. Genotypes and populations of T. dicoccoides having high photosynthetic capacity can be identified by climatic factors and isozyme markers. The identification by genetic markers, if substantiated by testcrosses, can facilitate the maximization of conservation, in situ or ex situ, and utilization of these photosynthetic genetic resources for improvement of hexaploid wheat (T. aestivum).     

Wheat storage proteins: diversity of HMW glutenin subunits in wild emmer from Israel

Summary The diversity of HMW glutenin subunits in the tetraploid wild progenitor of wheat, Triticum turgidum var. dicoccoides was studied electrophoretically in 231 individuals representing 11 populations of wild emmer from Israel. The results show that (a) The two HMW glutenin loci, Glu-A1 and Glu-B1, are rich in variation, having 11 and 15 alleles, respectively, (b) Genetic variation in HMW glutenin subunits is often severely restricted in individual populations, supporting an island population genetic model, (c) Significant correlations were found between glutenin diversity and the frequencies of specific glutenin alleles and physical (climate and soil) and biotic (vegetation) variables. Our results suggest that: (a) at least part of the glutenin polymorphisms in wild emmer can be accounted for by environmental factors and (b) the endosperm of wild emmer contains many allelic variants of glutenin storage proteins that are not present in bread wheat and could be utilized in breeding varieties with improved bread-making qualities.     

Genetic polymorphisms of α- and β-amylase isozymes in wild emmer wheat,Triticum dicoccoides,in Israel

Summary - and -amylase isozyme diversity was studied electrophoretically by thin-layer polyacrylamide gel isoelectrofocusing in the tetraploid wild emmer wheat, Triticum dicoccoides, the progenitor of all cultivated wheats. We analyzed 225 plants from 23 populations encompassing the ecological spectrum of T. dicoccoides in Israel. The results were as follows: (a) Band and multilocus genotype polymorphisms abound and vary within and between the four amylase components: malt, green (-amylases), and dry and germinating seeds (-amylases). (b) The number of bands of malt, green, and dry and germinating seeds were 20, 6, 11 and 13, respectively, generating 40, 6, 51, and 51 patterns or multilocus genotypes (MGP), respectively. The MGPs vary drastically within and between populations, from monomorphic in some populations with a single pattern to highly polymorphic ones, (c) Mean H _e values for malt, green, and germinating and dry seeds are 0.053, 0.055, 0.088, and 0.077, respectively; mean number of bands per individual was 11.8, 4.4, 7.6, and 4.0, respectively, (d) The percentages of 50 bands and 148 multilocus genotype patterns (MGP) (in parenthesis) were classified into widespread, sporadic, and localized: 84.4 (10.8), 8.9 (12.2), 6.7 (77.0), respectively. Notably, 89.2% of the patterns were not widespread, but sporadic and localized, (e) The mean value of genetic distances among populations (Nei's D) for the four amylase groups is D = 0.136, 0.175, 0.288 and 0.307, respectively, not displaying geographical correlates. (f) Most of the - and -amylase diversity is between populations (G _st = 68–75%). (g) Significant environmental correlates occur between either bands or patterns and climatic diversity (water and primarily temperature factors). (h) Significant associations of multilocus amylase bands occur across Israel. Like-wise, significant gametic phase disequilibria, D, occur within populations and are positively correlated with climatic variables, primarily that of temperature, (i) Discriminant analyses correctly classified (95–100%) the 23 wild emmer populations into their ecogeographical region and soil type. (j) Autocorrelation analysis showed that there is no correlation between bands and geographic distance and excluded migration as a major factor of amylase differentiation.These results suggest that diversifying climatic and edaphic natural selection rather than stochastisity or migration is the major evolutionary force driving amylase differentiation at both the single and multilocus levels. Furthermore, wild emmer harbors high levels of - and -amylase diversity both as single bands and as multilocus adaptive genetic patterns. These are exploitable both as genetic markers for quantitative loci (QTLs) and as adaptive genetic resources to improve wheat germination and growth through classical breeding and/or biotechnology.     

Natural selection of allozyme polymorphisms: a microgeographical differentiation by edaphic,topographical, and temporal factors in wild emmer wheat (Triticum dicoccoides)

Summary Allozymic variation in proteins encoded by 47 loci was analyzed electrophoretically in 1983/4 and 1984/5 in 356 individual plants of wild emmer wheat, Triticum dicoccoides, from a microsite at Tabigha, north of the Sea of Galilee, Israel. Each year the test involved two 100-meter transects, each equally subdivided into basalt and terra rossa soil types, and comparisons were based on 16 common polymorphic loci. Significant genetic differentiation, genetic phase disequilibria, and genome organization according to soil type were found over very short distances. Our results suggest that allozyme polymorphisms in wild emmer wheat are partly adaptive, and that they differentiate at both single and multilocus structures primarily from environmental stress of such ecological factors as soil type, topography, and temporal changes, probably through aridity stress.     

Genetic diversity for drought resistance in wild emmer wheat and its ecogeographical associations

Wild emmer wheat (Triticum turgidum spp. dicoccoides (Körn.) Thell.), the tetraploid progenitor of cultivated wheat, is a potential source for various agronomical traits, including drought resistance. The objectives of this study were to characterize (1) the genetic diversity for drought resistance in wild emmer wheat, and (2) the relationship between drought responses of the wild emmer germplasm and the ecogeographical parameters of its collection sites. A total of 110 wild emmer accessions consisting of 25 populations and three control durum wheat cultivars were examined under two irrigation regimes, well-watered (’wet’) and water-limited (’dry’). Wide genetic diversity was found both between and within the wild emmer populations in most variables under each treatment. A considerable number of the wild emmer accessions exhibited an advantage in productivity (spike and total dry matter) over their cultivated counterparts. Most wild emmer wheat accessions exhibited a greater carbon isotope ratio (δ¹³C, indicating higher water-use efficiency) under the dry treatment and higher plasticity of δ¹³C relative to the cultivated controls, which may have contributed to the drought adaptations in the former. The most outstanding drought-tolerance capacity (in term of productivity under the dry treatment and susceptibility indices) was detected in wild emmer populations originated from hot dry locations. The results suggest that wild emmer has the potential to improve drought resistance in cultivated wheat.     

Microclimatic stress and adaptive DNA differentiation in wild emmer wheat, Triticum dicoccoides

 Genetic diversity was examined by RAPD-PCR analysis in 118 registered individuals of wild emmer wheat, Triticum dicoccoides, from a microsite at Yehudiyya, northeast of the Sea of Galilee, Israel. The test involved two climatic microniches in the open oak-park forest of Quercus ithaburensis: (1) sunny between trees and (2) shady under the trees’ canopies. Comparisons were based on 97 loci amplified by 20 oligonucleotide primers. Significant genetic differentiations were found at single-, two- and multilocus structures between the neighbouring shady and sunny niches. These DNA polymorphisms appear to be associated with microclimatic stresses. The pronounced niche-effect on the significance of linkage disequilibrium and niche-specific linkage disequilibrium may suggest that natural selection directed the two-locus associations. The structure of the multilocus associations also mainly results from natural selection, and not by chance from population subdivision, or founder effects. These findings are largely parallel to the previous allozymic results at single-locus and multilocus levels. Both the DNA and the allozymic results suggest that microclimatic selection appears to play an important role in DNA differentiation as well as in protein polymophism. Received: 30 October 1998 / Accepted: 2 November 1998     

MIGRATION PATTERNS AND THE DEVELOPMENT OF MULTILOCUS ASSOCIATIONS IN A SELFING ANNUAL,TRITICUM DICOCCOIDES

Migration patterns in wild emmer wheat, Triticum dicoccoides, were inferred from single-locus and multilocus genetic distributions based primarily on expectations derived from single-locus and multilocus cline theory. Populations from five collections displayed a large amount of multilocus structuring, as indicated by high values of gametic-phase disequilibrium between pairs of loci and by high values of multilocus associations. Analyses of the distributions of individual alleles, however, indicated that alleles had apparent independent centers of origin and that at least some independent dispersal within regions occupied by ecotypes or races of wild emmer had occurred. The distribution of the degrees of multilocus association suggests that there has been a net migration of the northern or Qazrin race south and west into the pocket occupied by the Yehudiyya race. The results suggest that ecotypic differentiation may be independent and may antedate electrophoretically determined differentiation in these populations. There is no convincing evidence that the multilocus associations represent coadapted complexes; rather they appear to involve associations of mutant alleles that have been accentuated and preserved by low recombination rates and gene-flow barriers within previously differentiated ecotypes.     

Patterns and impacting factors of gene evolutionary rate between wild and cultivated emmer wheat (Triticum turgidum)

Tetraploid emmer wheat (Triticum turgidum L., BBAA) is the founder progenitor of bread wheat, providing the valuable genetic resource and gene pool for wheat improvement. However, the evolutionary trajectory of tetraploid wheat, especially the evolutionary fate of different types of genes has not been well studied. In this study, the rate of non-synonymous substitution (d_N) and synonymous substitution (d_S) was calculated by comparing the orthologs between the wild emmer and cultivated durum wheat at the whole genome and subgenome levels to obtain the positively selected genes (PSGs) and negatively selected genes (NSGs). Then, mutation rate, gene length, exon number, GC content, codon bias, and expression level were comprehensively investigated and compared between the PSGs and NSGs. Within both wild emmer and cultivated durum wheat, PSGs between A and B subgenome displayed shorter gene and exon lengths as well as fewer exon numbers compared with NSGs, whereas from wild emmer to cultivated durum wheat, PSGs showed longer gene length and more exon numbers. Furthermore, PSGs displayed much higher expression levels and stronger codon usage bias, but lower genetic diversity compared with NSGs. Finally, two PSGs TdER1-6B, and TdLC7-2A, were found to play the crucial roles in regulating grain width and plant height of tetraploid wheat, respectively. This study systematically investigated the evolutionary, structural, and functional difference between PSGs and NSGs in tetraploid wheat, which will contribute to a better understanding of the selective mode and evolutionary trajectory during wheat domestication and evolution.     

Microsatellite polymorphism in natural populations of wild emmer wheat,Triticum dicoccoides,in Israel

Diversity in 20 microsatellite loci of wild emmer wheat, Triticum dicoccoides, was examined in 15 populations (135 genotypes) representing a wide range of ecological conditions of soil, temperature, and water availability, in Israel and Turkey. An extensive amount of diversity at microsatellite loci was observed despite the predominantly selfing nature of this plant species. The 20 Gatersleben wheat microsatellites (GWM), representing 13 chromosomes of genomes A and B of wheat, revealed a total of 364 alleles, with an average of 18 alleles per GWM marker (range: 5–26). The proportion of polymorphic loci per population averaged 0.90 (range: 0.45– 1.00); genic diversity, He, averaged 0.50 (range 0.094– 0.736); and Shannon’s information index averaged 0.84 (range 0.166–1.307). The coefficients of genetic distance between populations were high and averaged D=1.862 (range 0.876–3.320), an indication of sharp genetic divergence over short distances. Interpopulation genetic distances showed no association with geographic distance between the population sites of origin, which ruled out a simple isolation by distance model. Genetic dissimilarity values between genotypes were used to produce a dendrogram of the relationships among wild wheat populations by the unweighted pair-group method with arithmetic averages (UPGMA). The results showed that all the wild emmer wheat populations could be distinguished. Microsatellite analysis was found to be highly effective in distinguishing genotypes of T. dicoccoides, originating from diverse ecogeographical sites in Israel and Turkey, with 88% of the 135 genotypes correctly classified into sites of origin by discriminant analysis. Our present microsatellite results are non-random and in agreement with the previously obtained allozyme and RAPD patterns, although the genetic-diversity values obtained with microsatellites are much higher. Significant correlates of microsatellite markers with various climatic and soil factors suggest that, as in allozymes and RAPDs, natural selection causes adaptive microsatellite ecogeographical differentiation, not only in coding, but most importantly in non-coding genomic regions. Hence, the concept of ”junk DNA” needs to be replaced by at least partly regulatory DNA. The obtained results suggest that microsatellite markers are useful for the estimation of genetic diversity in natural populations of T. dicoccoides and for the tagging of agronomically important traits derived from wild emmer wheat. Received: 27 February 2001 / Accepted: 22 March 2001     

Molecular identification of a new powdery mildew resistance gene <Emphasis Type="Italic">Pm41</Emphasis> on chromosome 3BL derived from wild emmer (<Emphasis Type="Italic">Triticum turgidum</Emphasis> var. <Emphasis Type="Italic">dicoccoides</Emphasis>)

Powdery mildew caused by Blumeria graminis f. sp. tritici is an important wheat disease in China and other parts of the world. Wild emmer (Triticum turgidum var. dicoccoides) is the immediate progenitor of cultivated tetraploid and hexaploid wheats and thus an important resource for wheat improvement. Wild emmer accession IW2 collected from Mount Hermon, Israel, is highly resistant to powdery mildew at the seedling and adult plant stages. Genetic analysis using an F₂ segregating population and F_2:3 families, derived from a cross between susceptible durum cultivar Langdon and wild emmer accession IW2, indicated that a single dominant gene was responsible for the resistance of IW2. Bulked segregant and molecular marker analyses detected that six polymorphic SSR, one ISBP, and three EST-STS markers on chromosome 3BL bin 0.63–1.00 were linked to the resistance gene. Allelic variations of resistance-linked EST-STS marker BE489472 revealed that the allele was present only in wild emmer but absent in common wheat. Segregation distortion was observed for the powdery mildew resistance allele and its linked SSR markers with preferential transmission of Langdon alleles over IW2 alleles. The resistance gene was introgressed into common wheat by backcrossing and marker-assisted selection. Since no designated powdery mildew resistance gene has been found on chromosome 3BL, the resistance gene derived from wild emmer accession IW2 appears to be new one and was consequently designated Pm41. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Grain zinc, iron and protein concentrations and zinc-efficiency in wild emmer wheat under contrasting irrigation regimes

Micronutrient malnutrition, and particularly deficiency in zinc (Zn) and iron (Fe), afflicts over three billion people worldwide, and nearly half of the world’s cereal-growing area is affected by soil Zn deficiency. Wild emmer wheat [Triticum turgidum ssp. dicoccoides (Körn.) Thell.], the progenitor of domesticated durum wheat and bread wheat, offers a valuable source of economically important genetic diversity including grain mineral concentrations. Twenty two wild emmer wheat accessions, representing a wide range of drought resistance capacity, as well as two durum wheat cultivars were examined under two contrasting irrigation regimes (well-watered control and water-limited), for grain yield, total biomass production and grain Zn, Fe and protein concentrations. The wild emmer accessions exhibited high genetic diversity for yield and grain Zn, Fe and protein concentrations under both irrigation regimes, with a considerable potential for improvement of the cultivated wheat. Grain Zn, Fe and protein concentrations were positively correlated with one another. Although irrigation regime significantly affected ranking of genotypes, a few wild emmer accessions were identified for their advantage over durum wheat, having consistently higher grain Zn (e.g., 125 mg kg^?1), Fe (85 mg kg^?1) and protein (250 g kg^?1) concentrations and high yield capacity. Plants grown from seeds originated from both irrigation regimes were also examined for Zn efficiency (Zn deficiency tolerance) on a Zn-deficient calcareous soil. Zinc efficiency, expressed as the ratio of shoot dry matter production under Zn deficiency to Zn fertilization, showed large genetic variation among the genotypes tested. The source of seeds from maternal plants grown under both irrigation regimes had very little effect on Zn efficiency. Several wild emmer accessions revealed combination of high Zn efficiency and drought stress resistance. The results indicate high genetic potential of wild emmer wheat to improve grain Zn, Fe and protein concentrations, Zn deficiency tolerance and drought resistance in cultivated wheat.     

The distribution, natural habitats and availability of wild cereals in relation to their domestication in the Near East: multiple events, multiple centres

In this article we examine the natural habitats and distribution of the six wild cereals: Triticum urartu (wild urartu wheat), T. boeoticum aegilopoides (single-grained wild einkorn), T. boeoticum thaoudar (two-grained wild einkorn), T. dicoccoides (wild emmer wheat), Secale spp. (wild ryes) and Hordeum spontaneum (wild barley). A comparison of late Pleistocene/early Holocene archaeobotanical assemblages in the Near East with present-day distributions of wild cereals shows a good correlation. The regional variation in the archaeobotanical cereal assemblages and the ensuing domestication provide evidence that different cereal species were domesticated independently in different areas. Some sites were not situated near wild cereal habitats and a few were located outside the limits of distribution, even accounting for moister climatic conditions. I argue here that current models which try to explain the shift to farming have tended to over-emphasize the effect of the Younger Dryas climatic change. First, it would have had only a minor effect on cereal availability. Secondly, agriculture appears to have been established after the Younger Dryas. Thirdly, there is no evidence for a single centre of origin; agriculture arose in widely separated geographic and climatic regions. And fourthly, agriculture depends on stable climatic conditions which were not established until after the Younger Dryas.     

Diurnal rhythms of the chlorophyll a/b binding protein mRNAs in wild emmer wheat and wild barley (Poaceae) in the Fertile Crescent

The mRNAs encoding the chlorophyll a/b binding (cab) proteins of the light harvesting system were monitored in the wild cereals, wild emmer wheat,Triticum dicoccoides, and wild barley,Hordeum spontaneum, the progenitors of all cultivated wheats and barley, respectively. Significantly different mRNA levels were detected at different time points during the day, with generally low levels around sunrise, sunset and midnight, and maximum levels around noon. These results indicate that a diurnal control of thecab gene expression is present in these ancient species.     

Resources of high-protein genotypes in wild wheat,Triticum dicoccoides in Israel: Predictive method by ecology and allozyme markers

Geographic variation of protein and seed characters of wild emmer wheat,Triticum dicoccoides in Israel and the associations with ecological and allozyme markers were tested in an attempt to derive predictive optimal guidelines for conservation and utilization in breeding programmes. The study involved 46 genotypes of wild emmer from 5 populations in Israel, 2 central and 3 marginal. These populations were tested earlier for allozymic variation (Nevoet al., Theor. appl. Genet. 62: 241–254, 1982). The results indicate that protein percentage, kernel and protein weight (the product of the former two values), vary both within, but particularly between, populations. Notably, the 3 marginal populations exhibit high protein content but low kernel weight, hence low protein weight as compared with the 2 central populations which displayed lower protein percentage but high kernel weight, hence higher protein weight. Three-variable combinations of climatic factors explain R squared=0.70 of the variance in kernel weight and R squared=0.60 of the variance in protein weight. Likewise, 3-variable combinations of allozyme genotypes explained significantly the spatial variances in protein percentage, kernel and protein weight (R squared=0.60, 0.69 and 0.54, respectively). We conclude that natural populations of wild emmer in Israel contain large amounts of yet untapped genes for elite protein and high seed weight. These could be effectively screened and utilized for producing high quantity protein wheat cultivars by means of effectively following ecological and allozymic markers as predictive guidelines in screening natural populations of wild emmer wheat.     

Geographical variation in heading traits in wild emmer wheat, Triticum dicoccoides. I. Variation in vernalization response and ecological differentiation

 Geographical variation in vernalization response and narrow-sense earliness was investigated for accessions of wild emmer wheat, Triticum dicoccoides, collected in Israel. Wide variation between and within populations was observed in both characters. The analysis of vernalization response showed that 2 accessions from Tabigha were of a strong spring growth habit, and thus wild emmer wheat was classified into four types, i.e., strongly spring type, moderately spring type, moderately winter type, and strongly winter type, according to their vernalization response. Whereas winter types were frequently found in most populations except that of Tabigha, the distribution of spring types was sporadic and restricted to warmer areas. It was thus suggested that spring type in T. dicoccoides might have evolved from a winter prototype as an adaptation to warmer conditions. Within moderately winter and moderately spring types, quantitative differences in vernalization response, measured as Dof₇₀/Dof₂₀ and Dof₂₀/Dof₀, were observed between populations. Inter- and intra-population variation in vernalization response could be explained to some extent by the difference in growing conditions at each habitat. It was clearly indicated that environmental heterogeneity caused ecogenetic differentiation in wild emmer wheat in Israel. Wild emmer wheat also varied considerably for narrow-sense earliness, ranging from 32.9 days to 69.5 days among accessions. However, it was difficult to explain its geographical variation simply by a linear relationship with environmental factors, and a nonlinear relationship and/or unknown microgeographic heterogeneity may be responsible. Received: 18 March 1996/Accepted: 13 December 1996     

Comprehensive evaluating of wild and cultivated emmer wheat (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L.) genotypes response to salt stress

Emmer wheat as the progenitor of common wheat, holds the genetic potentiality for improvement of wheat yield, quality and stress tolerance such as drought and salt. To comprehensively evaluate the salt tolerance of emmer wheat, a total of 30 traits including growth, physiology and photosynthesis related as well as K⁺ and Na⁺ content of 30 wild emmer and 14 durum wheat accessions were systematically investigated and compared between normal and saline conditions. Salt tolerance index (STI) based on multiple regression analysis of these traits was calculated and five wild emmer accessions showed high salt tolerance, which could be used as valuable resource for wheat salt tolerance improvement. Furthermore, wild emmer genotypes showed wider trait performance variation compared to durum wheat, indicating the higher genetic diversity in wild emmer wheat. Then, shoot Na⁺ content, shoot K⁺/Na⁺ ratio, root length and root surface area were identified as suitable indexes for salt tolerance evaluation. Na⁺ exclusion mechanism was found to be playing an important role in response to salt stress in emmer wheat. The salt tolerance in emmer wheat was systematically characterized here, which not only provided the elite germplasm for wheat improvement, but also provided the efficient method and some useful indexes for salt tolerance assessing.     

Resistance of wild wheat to stripe rust: Predictive method by ecology and allozyme genotypes

From 114 accessions of wild emmer wheat from 11 sites in Israel, known for their allozymic variation (Nevo & al. 1982), individual genotypes were tested for resistance to one isolate of stripe rust both in the seedling stage in a growth chamber and in the adult plant stage in the field. The results indicate that resistance to stripe rust in seedlings and adults are significantly correlated (r_s = 0.40, p < 0.001). Genetic polymorphisms of resistance to stripe rust vary geographically and are predictable by climatic, as well as allozymic markers. Three variable combinations of rainfall, evaporation, and temperature explain significantly 0.40–0.53 of the spatial variance in disease resistance to stripe rust, suggesting the operation of natural selection. Several allozyme genotypes are significantly associated with disease resistance. We conclude that natural populations of wild emmer wheat in Israel contain large amounts of disease resistance genes. These populations could be effectively screened and then utilized by the phytopathologist for identifying resistant genotypes and producing new resistant cultivars.Patterns of Resistance of Wild Wheat to Pathogens in Israel II.     

Genetic diversity of wild emmer wheat in Israel and Turkey

Summary Allozyme variation in the tetraploid wild emmer wheat, Triticum dicoccoides, the progenitor of all cultivated wheats, was studied for the proteins encoded by 42 gene loci in 1815 plants representing 37 populations - 33 from Israel and 4 from Turkey - sampled in 33 localities from 1979 to 1987. The results showed that: (a) 6 loci (14%) were monomorphic in all populations, 15 loci (36%) were locally polymorphic, and 21 loci (50%) were regionally polymorphic. These results are similar to those obtained earlier on 12 Israeli populations. All polymorphic loci (except 4) displayed high local levels of polymorphism (>/ 10%). (b) The mean number of alleles per locus, A, was 1.252 (range: 1.050–1.634); the proportion of polymorphic loci per population averaged 0.220 (range: 0.050–0.415); genic diversity, He, averaged 0.059 (range: 0.002–0.119). (c) Altogether there were 119 alleles at the 42 putative loci tested, 114 of these in Israel, (d) Genetic differentiation was primarily regional and local, not clinal; 70% of the variant alleles were common (>/ 10%) and not widespread, but rather localized or sporadic, displaying an archipelago population genetics and ecology structure. The coefficients of genetic distance between populations were high and averaged D = 0.134; range: 0.018–0.297, an indication of sharp genetic differentiation over short distances, (e) Discriminant analyses differentiated Israeli from Turkish populations, and within Israel, between central and 3 marginal regions, as well as between different soil-type populations, (f) Allozymic variation comprised 40% within and 60% between populations, (g) Gametic phase disequilibria were abundant, their number being positively correlated (r_s = 0.60, P<0.01) with the humidity, (h) Multilocus organization was substantive, also positively correlated with humidity, (i) Allozyme diversity, overall and at single loci, was significantly correlated with, and partly predictable by, climatic and edaphic factors, (j) The distrubition of the significant positive and negative values and the absence of autocorrelations in the correlogram revealed no similar geographic patterns across loci, eliminating migration as a prime factor of population genetic differentiation. These results suggest: (I) during the evolutionary history of wild emmer, diversifying natural selection, through climatic and edaphic factors, was a major agent of genetic structure and differentiation at both the single and multilocus levels; (II) wild emmer harbors large amounts of genetic diversity exploitable as genetic markers in sampling and abundant genetic resources utilizable for wheat improvement.