Analysis of Genetic Diversity in Synthetic Wheat Assemblage (T. turgidumxAegilops tauschii; 2n=6x=42; AABBDD) for Winter Wheat Breeding

An unconventional genetic resource for bread wheat improvement is the diploid D genome donor to bread wheat; Aegilops tauschii (2n=2x=14, DD). Bridge crossing the Triticum turgidum/Aegilops tauschii results in synthetic hexaploid (SH) wheats; the most common method of wheat improvement that efficiently utilizes the diversity of this diploid wheat progenitor of the primary gene pool. SH wheats exhibit spring or winter growth habits, depending on the parental durum germplasm. This study focuses on the molecular diversity among 58 winter synthetic hexaploid wheat (WSH) combinations that have been produced to facilitate winter wheat breeding programs. Genetic diversity and genome-wide linkage disequilibrium (LD) were investigated for all D-genome chromosomes using SSR markers. LD analysis based on 71 microsatellite loci represented a mean marker density of 7.1 cm. A total of 738 alleles ranging from 3 to 20 per locus were characterized in WSHs. The mean PIC and MI values were 0.61 and 3.41, ranging from 0.14 to 0.86 and 0.02 to 9.6, respectively. The analysis of molecular variance and Wright's fixation index further established significant genetic diversity among different clusters and durum groups leading to the conclusion that diversity within WSHs is well validated. The population structure also partially validated the cluster analysis by forming eight (K=6) sub-populations. The variable patterns of LD independent of the genetic distance (cm) in some cases provided critical information for these re-synthesized winter wheat genetic resources for their future deployment and association mapping studies. Molecular analyses, thus, have established ample diversity that is present within these winter SHs and generated information for effectively introducing new diversity from these unique genetic resources into the prevalent winter wheat germplasm.