Genetic diversity among wheat germplasm pools with diverse geographical origins

Since a significant level of genetic erosion and latent vulnerability has been recognized in some major crop species, more efforts have been made to expand their genetic bases. Systematic quantification and management of genetic diversity are requested to optimize exotic and elite germplasm resources and to further facilitate wheat improvement programs. The objectives of this research were to: (1) analyze RFLP characteristics and their association with coefficient of parentage for measures of genetic diversity in Eastern U.S. soft winter wheat lines, (2) investigate the genetic nature and phylogenetic relationships of Triticum tauschii and landraces of T. aestivum found in China using RFLPs, and (3) determine patterns of genetic diversity in world germplasm collections with different origins using RFLPs and morphological characters.; RFLP variation was very limited for the 22 Eastern U.S. soft wheat lines. The highly pedigree-related soft white winter wheat lines (mean coefficient of parentage (COP) = 0.51) was much less genetically diverse than the soft red winter wheat lines with mean COP of 0.15. Insertions and/or deletions might play an important role in the origin of DNA polymorphisms. As measures of genetic relationships, RFLP-based genetic similarity (GS) significantly correlated with COPs for all genotype pairs (r = 0.73**).; As compared to the Southwest Asian gene pool of T. tauschii, the Chinese T. tauschii pool showed a low frequency of polymorphism. In spite of a narrow genetic base, the Chinese landraces of common wheat were divided by the cluster analysis of RFLP-based GS matrix into two subgroups: Xinjiang Rice wheat for one group and Tibetan Weedrace, Sichuan White and Yunnan Hulled wheats for the other. The Chinese landraces were more related to the Southwest Asian T. tauschii than to the Chinese T. tauschii on the basis of RFLP-based mean GS. An eastward decline of RFLP diversity from Southwest Asia was apparent for both T. tauschii and landrace pools of T. aestivum.; Each of the 21 germplasm pools of common wheat grouped by geographical or institutional origins of 338 accessions showed significant level of genetic uniformity. RFLP variation was highest in the Turkish landrace pool. The Eastern U.S. soft red winter wheat pool revealed the highest RFLP diversity in the advanced germplasm pools. RFLP-based genetic relationships among accessions or germplasm pools were largely determined by their common geographical origins, breeding history and/or coancestry. In spite of significant variation (p {dollar}<{dollar} 0.01) among germplasm pools for all examined morphological characters, morphology-based standard taxonomic distance estimates were poorly correlated with the RFLP-based GS estimates (r = {dollar}-{dollar}0.15{dollar}rmsp{lcub}NS{rcub}).{dollar}...