Wild Emmer Wheat Populations Research Articles

Sympatric speciation of wild emmer wheat driven by ecology and chromosomal rearrangements

In plants, the mechanism for ecological sympatric speciation (SS) is little known. Here, after ruling out the possibility of secondary contact, we show that wild emmer wheat, at the microclimatically divergent microsite of "Evolution Canyon" (EC), Mt. Carmel, Israel, underwent triple SS. Initially, it split following a bottleneck of an ancestral population, and further diversified to three isolated populations driven by disruptive ecological selection. Remarkably, two postzygotically isolated populations (SFS1 and SFS2) sympatrically branched within an area less than 30 m at the tropical hot and dry savannoid south-facing slope (SFS). A series of homozygous chromosomal rearrangements in the SFS1 population caused hybrid sterility with the SFS2 population. We demonstrate that these two populations developed divergent adaptive mechanisms against severe abiotic stresses on the tropical SFS. The SFS2 population evolved very early flowering, while the SFS1 population alternatively evolved a direct tolerance to irradiance by improved ROS scavenging activity that potentially accounts for its evolutionary fate with unstable chromosome status. Moreover, a third prezygotically isolated sympatric population adapted on the abutting temperate, humid, cool, and forested north-facing slope (NFS), separated by 250 m from the SFS wild emmer wheat populations. The NFS population evolved multiple resistant loci to fungal diseases, including powdery mildew and stripe rust. Our study illustrates how plants sympatrically adapt and speciate under disruptive ecological selection of abiotic and biotic stresses.

Variation in Stripe Rust Resistance and Morphological Traits in Wild Emmer Wheat Populations

Wild emmer wheat (Triticum dicoccoides), the tetraploid progenitor of cultivated wheats, is indigenous to the Near East Fertile Crescent. An important center of distribution is found today in and around the catchment area of the upper Jordan Valley in Israel and surrounding regions. In the current study, the field stripe rust resistance and morphological traits were analyzed using 98 sample accessions that represented the geographical distribution of wild emmer populations in Israel and its vicinity. The resistance tests at two field locations revealed that the majority of the wild emmer accessions possess quantitative resistance against stripe rust. This could be due to the high frequency of Yr36 in the wild emmer populations. The identification of potentially novel stripe rust resistance in this set of germplasm is highly significant. In total, 11 morphological traits were examined in this study. Wide range of natural variation was revealed in the tested morphological traits. Most of the morphological traits had significant correlations with climate variables, indicating that the local environmental conditions have a profound effect on shaping the genetic structure of wild emmer wheat. Our results suggest that wild emmer wheat has the enormous potential to improve stripe rust resistance and various important agronomical traits in wheat.

Retrotransposon-Based Genetic Diversity Assessment in Wild Emmer Wheat (Triticum turgidum ssp. dicoccoides)

Wild emmer wheat (Triticum turgidum ssp. dicoccoides) is the wild ancestor of all cultivated tetraploid and hexaploid wheats and harbors a large amount of genetic diversity. This diversity is expected to display eco-geographical patterns of variation, conflating gene flow, and local adaptation. As self-replicating entities comprising the bulk of genomic DNA in wheat, retrotransposons are expected to create predominantly neutral variation via their propagation. Here, we have examined the genetic diversity of 1 Turkish and 14 Israeli populations of wild emmer wheat, based on the retrotransposon marker methods IRAP and REMAP. The level of genetic diversity we detected was in agreement with previous studies that were performed with a variety of marker systems assaying genes and other genomic components. The genetic distances failed to correlate with the geographical distances, suggesting local selection on geographically widespread haplotypes (‘weak selection’). However, the proportion of polymorphic loci correlated with the population latitude, which may reflect the temperature and water availability cline. Genetic diversity correlated with longitude, the east being more montane. Principal component analyses on the marker data separated most of the populations.

Evolution and Adaptation of Wild Emmer Wheat Populations to Biotic and Abiotic Stresses.

The genetic bottlenecks associated with plant domestication and subsequent selection in man-made agroecosystems have limited the genetic diversity of modern crops and increased their vulnerability to environmental stresses. Wild emmer wheat, the tetraploid progenitor of domesticated wheat, distributed along a wide range of ecogeographical conditions in the Fertile Crescent, has valuable "left behind" adaptive diversity to multiple diseases and environmental stresses. The biotic and abiotic stress responses are conferred by series of genes and quantitative trait loci (QTLs) that control complex resistance pathways. The study of genetic diversity, genomic organization, expression profiles, protein structure and function of biotic and abiotic stress-resistance genes, and QTLs could shed light on the evolutionary history and adaptation mechanisms of wild emmer populations for their natural habitats. The continuous evolution and adaptation of wild emmer to the changing environment provide novel solutions that can contribute to safeguarding food for the rapidly growing human population.

Chloroplast DNA haplotype variation within two natural populations of wild emmer wheat (Triticum turgidum ssp. dicoccoides) in southern Turkey

Wild emmer wheat (Triticum turgidum ssp. dicoccoides) is the progenitor of cultivated emmer wheat (ssp. dicoccum) and durum wheat (ssp. turgidum conv. durum). Because of its full interfertility with domesticated emmer wheat, this wild species can serve as one of the most important genetic resources to improve durum as well as bread wheat. To elucidate the magnitude of genetic variation within a population of wild emmer wheat, variation of chloroplast DNA was investigated using 91 plants, in total, collected from two natural habitats in southern Turkey. Allelic variation at 24 microsatellite loci in the chloroplast genome was investigated using these samples. Allelic variations were observed at 15 microsatellite loci. The number of alleles per locus was the same in the two populations, ranging from 1 to 4 with an average of 2.17. The estimated diversity indices (H) were also very close ranging from 0.00 to 0.70 with an average of 0.28 and 0.29 for the two populations. Based on the observed allelic variation at all chloroplast microsatellite loci, a total of 23 chloroplast haplotypes (plastotypes) were identified. Only two plastotypes were shared in common between the two natural populations, indicating that the two populations are highly differentiated. Furthermore, uneven micro-geographic distribution of plastotypes was found within each population, suggesting limited rate of migration (seeds dispersal rate) in this species. Our study demonstrated the presence of a high level of genetic diversity between and within highly structured populations of wild emmer wheat in southern Turkey.

SNP-revealed genetic diversity in wild emmer wheat correlates with ecological factors

BackgroundPatterns of genetic diversity between and within natural plant populations and their driving forces are of great interest in evolutionary biology. However, few studies have been performed on the genetic structure and population divergence in wild emmer wheat using a large number of EST-related single nucleotide polymorphism (SNP) markers.ResultsIn the present study, twenty-five natural wild emmer wheat populations representing a wide range of ecological conditions in Israel and Turkey were used. Genetic diversity and genetic structure were investigated using over 1,000 SNP markers. A moderate level of genetic diversity was detected due to the biallelic property of SNP markers. Clustering based on Bayesian model showed that grouping pattern is related to the geographical distribution of the wild emmer wheat. However, genetic differentiation between populations was not necessarily dependent on the geographical distances. A total of 33 outlier loci under positive selection were identified using a FST-outlier method. Significant correlations between loci and ecogeographical factors were observed.ConclusionsNatural selection appears to play a major role in generating adaptive structures in wild emmer wheat. SNP markers are appropriate for detecting selectively-channeled adaptive genetic diversity in natural populations of wild emmer wheat. This adaptive genetic diversity is significantly associated with ecological factors.

Adaptive polymorphism of tetrameric alpha-amylase inhibitors in wild emmer wheat

α-Amylase inhibitors are attractive candidates for the control of seed weevils as these insects are highly dependent on starch as an energy source. Wheat tetrameric α-amylase inhibitor (WTAI) is a mixture (60 kDa) of 3 units: WTAI-CM2 plus 2 WTAI-CM3 plus WTAI-CM16, where none of the subunits is active on its own. A total of 334 gene sequences were obtained from 14 populations (131 accessions= genotypes) of wild emmer wheat. The frequencies of SNPs in WTAI-CM2, WTAI-CM3 and WTAI-CM16 were 1 out of 87.6, 101.4, and 108.0 bases, where 5, 5 and 4 SNPs were detected in the coding sequence, respectively. The nucleotide sequence of each unit of tetrameric α-amylase inhibitors were much more conserved than that of dimeric or monomeric inhibitors. The wild emmer wheat populations showed diversity on three WTAI loci, both between and within populations. It was revealed that WTAI were naturally selected for across populations by a ratio of dN/dS as expected. The results of purifying and positive selection hypothesis (p<0.05) also showed that the sequences of WTAI were contributed by natural selection, which ensures the protein function conservation as well as the inhibition diversity with insects amylase enzyme. Ecological factors, singly or in combination, explained a significant proportion of the variations in the SNPs. Ecological factors have an important evolutionary role in gene differentiation at these loci, and tetrameric α-amylase inhibitors are obviously adaptively selected under different environments.

The impact of single nucleotide polymorphism in monomeric alpha-amylase inhibitor genes from wild emmer wheat, primarily from Israel and Golan

BackgroundVarious enzyme inhibitors act on key insect gut digestive hydrolases, including alpha-amylases and proteinases. Alpha-amylase inhibitors have been widely investigated for their possible use in strengthening a plant's defense against insects that are highly dependent on starch as an energy source. We attempted to unravel the diversity of monomeric alpha-amylase inhibitor genes of Israeli and Golan Heights' wild emmer wheat with different ecological factors (e.g., geography, water, and temperature). Population methods that analyze the nature and frequency of allele diversity within a species and the codon analysis method (comparing patterns of synonymous and non-synonymous changes in protein coding sequences) were used to detect natural selection.ResultsThree hundred and forty-eight sequences encoding monomeric alpha-amylase inhibitors (WMAI) were obtained from 14 populations of wild emmer wheat. The frequency of SNPs in WMAI genes was 1 out of 16.3 bases, where 28 SNPs were detected in the coding sequence. The results of purifying and the positive selection hypothesis (p < 0.05) showed that the sequences of WMAI were contributed by both natural selection and co-evolution, which ensured conservation of protein function and inhibition against diverse insect amylases. The majority of amino acid substitutions occurred at the C-terminal (positive selection domain), which ensured the stability of WMAI. SNPs in this gene could be classified into several categories associated with water, temperature, and geographic factors, respectively.ConclusionsGreat diversity at the WMAI locus, both between and within populations, was detected in the populations of wild emmer wheat. It was revealed that WMAI were naturally selected for across populations by a ratio of dN/dS as expected. Ecological factors, singly or in combination, explained a significant proportion of the variations in the SNPs. A sharp genetic divergence over very short geographic distances compared to a small genetic divergence between large geographic distances also suggested that the SNPs were subjected to natural selection, and ecological factors had an important evolutionary role in polymorphisms at this locus. According to population and codon analysis, these results suggested that monomeric alpha-amylase inhibitors are adaptively selected under different environmental conditions.

Divergent diversity patterns of NBS and LRR domains of resistance gene analogs in wild emmer wheat populations

Disease resistance (R) genes are intriguing in their evolution and diversity patterns because of their constant interactions with evolving pathogens. In this study, we demonstrate the use of resistance gene analog (RGA) markers to estimate genetic diversity among 13 populations (118 genotypes) of Triticum dicoccoides collected along a natural aridity gradient in Israel. The diversity patterns of 204 markers derived from two R-gene domains, nucleotide binding site (NBS) and leucine-rich repeat (LRR), were compared and contrasted. Diversity patterns of NBS domain markers differed significantly from those of the LRR domain. NBS markers showed higher between-population diversity (Fst=0.58), while LRR markers showed higher within-population diversity (Fst=0.35). Gene diversity (He) values were twofold higher in the LRR domain than in the NBS domain (0.144 vs. 0.067). LRR He values were correlated with precipitation in the spring (r=0.8, p=0.01), while NBS He values showed no correlation with any ecogeographical variable. The evolutionary and applicative inferences of these findings are discussed. The current study demonstrates that RGA profiling is an excellent tool for studying diversity of R genes in natural plant populations.

Molecular evolution of dimeric α-amylase inhibitor genes in wild emmer wheat and its ecological association

Backgroundα-Amylase inhibitors are attractive candidates for the control of seed weevils, as these insects are highly dependent on starch as an energy source. In this study, we aimed to reveal the structure and diversity of dimeric α-amylase inhibitor genes in wild emmer wheat from Israel and to elucidate the relationship between the emmer wheat genes and ecological factors using single nucleotide polymorphism (SNP) markers. Another objective of this study was to find out whether there were any correlations between SNPs in functional protein-coding genes and the environment.ResultsThe influence of ecological factors on the genetic structure of dimeric α-amylase inhibitor genes was evaluated by specific SNP markers. A total of 244 dimeric α-amylase inhibitor genes were obtained from 13 accessions in 10 populations. Seventy-five polymorphic positions and 74 haplotypes were defined by sequence analysis. Sixteen out of the 75 SNP markers were designed to detect SNP variations in wild emmer wheat accessions from different populations in Israel. The proportion of polymorphic loci P (5%), the expected heterozygosity He, and Shannon's information index in the 16 populations were 0.887, 0.404, and 0.589, respectively. The populations of wild emmer wheat showed great diversity in gene loci both between and within populations. Based on the SNP marker data, the genetic distance of pair-wise comparisons of the 16 populations displayed a sharp genetic differentiation over long geographic distances. The values of P, He, and Shannon's information index were negatively correlated with three climatic moisture factors, whereas the same values were positively correlated by Spearman rank correlation coefficients' analysis with some of the other ecological factors.ConclusionThe populations of wild emmer wheat showed a wide range of diversity in dimeric α-amylase inhibitors, both between and within populations. We suggested that SNP markers are useful for the estimation of genetic diversity of functional genes in wild emmer wheat. These results show significant correlations between SNPs in the α-amylase inhibitor genes and ecological factors affecting diversity. Ecological factors, singly or in combination, explained a significant proportion of the variations in the SNPs, and the SNPs could be classified into several categories as ecogeographical predictors. It was suggested that the SNPs in the α-amylase inhibitor genes have been subjected to natural selection, and ecological factors had an important evolutionary influence on gene differentiation at specific loci.

Genetic structure of wild emmer wheat populations as reflected by transcribed versus anonymous SSR markers

Simple sequence repeat (SSR) markers have become a major tool in population genetic analyses. The anonymous genomic SSRs (gSSRs) have been recently supplemented with expressed sequence tag (EST) derived SSRs (eSSRs), which represent the transcribed regions of the genome. In the present study, we used 8 populations of wild emmer wheat (Triticum turgidum subsp. dicoccoides) to compare the usefulness of the two types of SSR markers in assessing allelic diversity and population structure. gSSRs revealed significantly higher diversity than eSSRs in terms of average number of alleles (14.92 vs. 7.4, respectively), polymorphic information content (0.87 vs. 0.68, respectively), and gene diversity (He; 0.55 vs. 0.38, respectively). Despite the overall differences in the level of diversity, Mantel tests for correlations between eSSR and gSSR pairwise genetic distances were found to be significant for each population as well as for all accessions jointly (RM=0.54, p=0.01). Various genetic structure analyses (AMOVA, PCoA, STRUCTURE, unrooted UPGMA tree) revealed a better capacity of eSSRs to distinguish between populations, while gSSRs showed a higher proportion of intrapopulation (among accessions) diversity. We conclude that eSSR and gSSR markers should be employed in conjunction to obtain a high inter- and intra-specific (or inter- and intra-varietal) distinctness.

Drought resistance in wild emmer wheat: Physiology, ecology, and genetics

Drought is the main environmental stress limiting crop productivity and yield stability worldwide. Improving drought resistance of crop plants is considered a sustainable and economically viable solution to increasing agricultural productivity under diminishing water availability. The implementation of this solution requires wide explorations of potential genetic resources and in-depth understanding of their adaptive mechanisms and responses to water deficit. In this minireview we summarize the physiological, ecological, and genetic aspects of drought resistance in wild emmer wheat [Triticum turgidum ssp. dicoccoides (Korn.) Thell.] and discuss their implications on wheat improvement. A comprehensive survey of wild emmer wheat populations, collected across the aridity gradient in Israel, revealed wide genetic diversity for drought responses, with a considerable number of wild accessions exhibiting an advantage over durum wheat cultivars. A variety of adaptive traits associated with improved performances u...

Allelic diversity associated with aridity gradient in wild emmer wheat populations

The association between allelic diversity and ecogeographical variables was studied in natural populations of wild emmer wheat [Triticum turgidum ssp. dicoccoides (Körn.) Thell.], the tetraploid progenitor of cultivated wheat. Patterns of allelic diversity in 54 microsatellite loci were analyzed in a collection of 145 wild emmer wheat accessions representing 25 populations that were sampled across naturally occurring aridity gradient in Israel and surrounding regions. The obtained results revealed that 56% of the genetic variation resided among accessions within populations, while only 44% of the variation resided between populations. An unweighted pair-group method analysis (UPGMA) tree constructed based on the microsatellite allelic diversity divided the 25 populations into six major groups. Several groups were comprised of populations that were collected in ecologically similar but geographically remote habitats. Furthermore, genetic differentiation between populations was independent of the geographical distances. An interesting evolutionary phenomenon is highlighted by the unimodal relationship between allelic diversity and annual rainfall (r = 0.74, P < 0.0002), indicating higher allelic diversity in populations originated from habitats with intermediate environmental stress (i.e. rainfall 350-550 mm year(-1)). These results show for the first time that the 'intermediate-disturbance hypothesis', explaining biological diversity at the ecosystem level, also dominates the genetic diversity within a single species, the lowest hierarchical element of the biological diversity.

Spatio-temporal genetic variation in populations of wild emmer wheat, Triticum turgidum ssp. dicoccoides, as revealed by AFLP analysis

Genetic structure of natural populations of wild crop relatives has been the subject of many studies. Yet, most of them focused on the assessment of spatial genetic diversity, while information on long-term variation, affected by yearly changes, has been considered only in few cases. The present study aimed therefore, to estimate the spatio-temporal genetic variation in populations of wild emmer wheat, the progenitor of domesticated wheat, and to assess the contribution of spatial versus temporal factors to the maintenance of genetic variation in a population. Single spikes were collected in the years 1988 and 2002 from plants that grew in the same sampling points, from six different habitats in the Ammiad conservation site, Eastern Galilee, Israel. Seeds were planted in a nursery and DNA was extracted from each plant and analyzed by the AFLP method. Fourteen primer combinations yielded 1,545 bands of which 50.0 and 48.8% were polymorphic in the years 1988 and 2002, respectively. Genetic diversity was much larger within populations than between populations and the temporal genetic diversity was considerably smaller than the spatial one. Nevertheless, population genetic structure may vary to some degree in different years, mainly due to fluctuations in population size because of yearly rainfall variations. This may lead to predominance of different genotypes in different years. Clustering the plants by their genetic distances grouped them according to their habitats, indicating the existence of genotype-environment affinities. The significance of the results in relation to factors affecting the maintenance of polymorphism in natural populations is discussed.

Comparison of the genetic structure of populations of wild emmer wheat, Triticum turgidum ssp. dicoccoides, from Israel and Turkey revealed by AFLP analysis

The aim of the present study was to assess the genetic variation in several Israeli and Turkish populations of wild emmer wheat, Triticum turgidum ssp. dicoccoides, the progenitor of most domesticated wheat. Single spikes were collected in 2002 from 60 plants that grew in six different habitats in Ammiad, northeastern Israel (8–12 plants from each habitat), and in 1998 from 56 plants that grew in seven different habitats in Diyarbakir, southeastern Turkey (8 plants from each habitat). Seeds were planted in a nursery and DNA was extracted from every plant and analyzed by the fluorescent-based amplified fragment length polymorphism (AFLP) method. Seven primer combinations produced 788 discernible loci of which 48.6% were polymorphic in Israel and 40.5% in Turkey. The genetic diversity estimates P (frequency of polymorphic loci) and He (gene diversity) were higher in Ammiad than in Diyarbakir (means of P = 0.34 and He = 0.13 in Ammiad vs. P = 0.20 and He = 0.08 in Diyarbakir). Ammiad populations contained more unique alleles than Diyarbakir populations. The relative genetic diversity estimates (θ) values were 0.188 in Ammiad and 0.407 in Diyarbakir, suggesting better differentiation of the populations in Turkey. Genetic distance was larger between Israeli and Turkish populations than between populations of each country. The data indicate that the Israeli and Turkish populations are considerably diverged and that the Israeli populations are more polymorphic than the Turkish ones, having a larger within-populations genetic variation than among-populations one. The significance of the results in relation to the differentiation pattern of wild emmer in the Near East is discussed.

Introgression from Durum Wheat Landraces in Wild Emmer Wheat (Triticum Dicoccoides (Körn. ex Asch. et Graebner) Schweinf)

Introgression was detected within wild emmer wheat population in Jordan during the year 2000. Wild emmer wheat was found to occur in non-disturbed habitat, very close to cultivated durum wheat in northern parts of Jordan, and it was found in cultivated durum wheat in southern parts of Jordan. Random Amplified Polymorphic DNA (RAPD) test was constructed to assess natural introgression occurrence within wild emmer wheat population. Associated durum wheat land races from the vicinity of durum wheat fields were also collected. Shannon Diversity Index for wild emmer wheat populations was 0.46 and for durum wheat landraces was 0.45. The percentage of polymorphic loci for wild emmer wheat populations was 92.6. The close genetic distance between certain wild emmer wheat populations and durum wheat landraces provided proofs that massive introgression has occurred.

Variation in agronomically important traits in natural populations of wild emmer wheat, Triticum dicoccoides, in Israel

AbstractDiversity in agronomically important traits of wild emmer wheat, Triticum dicoccoides, the progenitor of most cultivated wheats, was examined in l60 genotypes representing 16 populations derived from a wide ecogeographical spectrum of climate, soil and water availability in Israel and Turkey. The analysis included 14 quantitative economic characters including heading date, culm length, biomass, grain yield and its components, and grain protein percentage.The results led to two major conclusions: (i) agronomically important traits varied genetically: ecogeographic diversity in these traits is dramatically displayed when populations are grown in a relatively standardized environment; and (ii) genetic diversity is revealed not only between, but also within populations. Thus, genotypes excelling in some of these characters were found in several populations.

Low genetic diversity in wild emmer (T. turgidum L. subsp. dicoccoides (Körn. ex Asch. et Graebn.) Thell.) from South-eastern Turkey revealed by Restriction Fragment Length Polymorphism

The present work was carried out to study genetic diversity among 17 populations of wild emmer wheat sampled from South-eastern Turkey, considered to be an important region for domestication of wheat. Eleven RFLP clones and 4 restriction enzymes combinations were used to probe the genomic DNA. A total of 151 polymorphic loci were obtained from the enzyme-probe combinations. The Genetic Distance (GD) values were from 0.019 (Gaziantep-3 and Sanliurfa-4) to 0.200 (Gaziantep-1 and K. Maras). Cluster analysis results showed that populations formed 2 clades within the dendrogram. Population Gaziantep-1 was unique and genetically most diverse from the remaining 16 populations. The results of average genetic distance (GD) among populations suggested that narrow genetic variability exist among 17 populations in the present study.

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. dicoccoidesand for the tagging of agronomically important traits derived from wild emmer wheat.

SPATIAL AND TEMPORAL GENETIC STRUCTURE OF WILD EMMER WHEAT IN JORDAN. I. PHENOTYPIC TRAITS

Natural populations of wild emmer wheat in Jordan represent a unique and sizable part of the species’ distribution in the Fertile Crescent. However, information on their genetic structure and diversity is limited. An understanding of the way genetic variation is partitioned among these populations is of primary importance for the ex situ sampling and in situ conservation of their genetic diversity. Fourteen categorical traits were used to characterize different phenotypes found in 12 wild emmer wheat populations in Jordan. They were scored in plants growing in 207 marked sampling sites and representing a wide range of observable variation. A strong effect of the heterogeneous habitats, encountered across collecting sites, was reflected in the magnitude and spatial distribution of phenotypic diversity. Several, and probably unique, first- and second-order associations among phenotypic traits reflect functional adaptation of the species to arid and semiarid Mediterranean environments. Phenotypic distances among populations were highly influenced by latitude and rainfall quotient (Q2) of collection sites. Spatial factors accounted for large portions (60.5–93.1%) of total variation in phenotypic diversity indices, suggesting strong provenance specificity. Temporal variation was less pronounced than spatial variation, and there were no drastic changes between years in frequencies of genotypes. Both spatial and temporal variation varied among populations.