| It is well known that Aegilops tauschii(DD, 2n=14) is one of closest relative for common wheat, which is thought the source of wheat D genome. Thus,the study of genetic diversity, population differentiation and species evolution between Ae.tauschii and wheat germplasms have been caused much attention of wheat genetists and breeders.In order to evaluate the genetic diversity and relationship among different Ae.tauschii and wheat germplasms, we analyzed allelic profile using 140 genome simple-sequence repeat(SSR) markers representating193 Ae.tauschii and 130 wheat accessions. Moreover, based on linkage disequilibrium of pairwise loci and population structure analysis, the genotyping data of 140 simple-sequence repeat(SSR) markers with phenotypic data of 12 agronomic and kernel traits were used in association analysis. Comparisons were also conducted to discriminate the different alleles associated with agronomic traits between Ae.tauschii and wheat accessions. The main results were as follows:1. The genetic diversity of323 Ae.tauschii and wheat accessions were evaluated. A total of 1612 alleles ranging from 5 to 19 were identified at the 140 SSR loci in Ae. tauschii, compared with the 1057 alleles ranging from 3 to 13 in wheat. The PIC values in Ae. tauschiiranged from 0.561 to 0.937 and the rare alleles, with a frequency of less than 5%, was 424(32.3%). In contrast, the PIC values in wheat ranged from 0.371 to 0.912 and the number of rare alleles was 356(26.2%). The average Nei’s genetic diversity is 0.869 and 0.797 in Ae.tauschii and wheat, respectively, indicating a higher diversity in Ae. tauschii than in the D gonome of wheat.2. The Claritying Linkage Disequilibrium(LD) and population structure were evaluatedfor the populations of Ae.tauschii and wheat accessions.By populationstructure analysis, the193 Ae.tauschii were clustered into 6 main clusters. The130 wheat accessionswere clustered into 7 main groups. Theresult of UPGMA cluster was similar to population structure analysis. And the germplasms originating from the same region tended to be assigned to the same cluster.4.45% of the SSR markers showed insignificant LD(P< 0.01) in population of Ae.tauschii, compared with 3.72%in wheat.The attenuation of R2 value in Ae.tauschii followed equation of Y=-0.025ln(x)+0.114, and the LD extended 8.45 c M.The attenuation of R2 value followed equation of Y=-0.017ln(x)+0.116, and LD extended 6.53 c M in wheat accessions.3.The relationship between population and geographic differeniationof Ae.tauschii and wheat accessions was revealed. The results of AMOVA showed that significant portions(P<0.001)of the variation existed either in germplasms or among the populations of the two species. These evidence supports that the cluster of differentiation has sound genetic bases for both Ae.tauschii and wheat populations.The coefficient of genetic differentiation, genetic distance and clustering analysis of all accessions among subgroups of the two species showed the same rusults to AMOVA. Each subgroup of wheat population showed relatively smaller genetic distance with subgroup 3 and subgruop 4 of Ae.tauschii accesions,which mainly origined from European and western Asia. So, we can speculate that the origin of the D genome of wheat might be related to the Ae.tauschii of Europe and western Asia.4.The marker-trait association was tested for 12 important agronomic and kernel traits through the mixed linear model using the software TASSEL 2.1. In Ae.tauschii, a total of 271 marker-trait associations were identified(P≤0.05) with 101 different markers, and the R2 ranged of 0.68%-33.70%. In wheat accessions, a total of 370 marker-trait associations were identified(P≤0.05) with 73 different markers, and the R2 ranged of 0.92%~26.97%.The screened out 10 SSR loci was significantly associated with the 9 detected traits both in Ae.tauschii and wheat accessions. Ten SSR locis are cfd4-3D, gdm33-1D, gdm61-4D, gpw5020-2D, gpw5072-4D, gpw5133-4D, gpw5137-7D, gpw5179-6D, gpw5181-7D and gwm583-5D. Nine traits are plant height(PH),spike length(SL), flower dates(FD), heading dates(HD), grain length(GL), grain perimeter(GP),Grain Area(GA), grain Roundness(GR) and Thousand-kernel weight(TKW).6. The allelic effects of SSR loci were computed, which were significantly associated with traits in multiple environments. And a average positive(negative)allelic effect of a locus was culculatied to estimate the phenotypic effects. In Ae.tauschii and wheat accessions, 39 allelic loci discovered have different allelic effect(positive or negative) to 9 traits, indicating the potential of genetic recombination for breeding purposes. A same marker locus could associate with multiple traits with multiplealleles or a same allele correlating two related phenotypic traits. |
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