Genetic diversity patterns among phytophthora resistant soybean plant introductions based on SSR markers

Genetic diversity is low among elite Northern American soybean [Glycine max (L.) Merr.] breeding populations. Fewer than 20 soybean cultivars are responsible for 80% of the genes in public soybean culthars released in recent years. Diversifying the soybean germplasm base could introduce new genes for agronomic diversity as well. Recently, soy bean plant introductions (PIs) have been identified as additional sources of both partial and specific resistance to Phytophthora sojae M.J. Kaufmann & J.W. Gerdemann (syn. P. megasperma Drechs. f. sp. glycinea T. Kuan & D.C. Erwin). The objective of this study was to compare the genetic diversity present among soybean PIs resistant to P. sojae in relation to cultivars and breeding lines that represent U.S. breeding germplasm, and to develop guidelines for the genetic study and practical use of these resistant resources in applied breeding. Ninety-three accessions from South Korea, China, and Japan and 15 genotypes from the USA were evaluated for 52 simple sequence repeat (SSR) primer pairs. The South Korean material included 32 P. sojae resistant, 49 partially resistant, and 7 susceptible accessions. The SSR data were used to compute Nei's distance estimates. Clustering and multivariate analysis of Nei's distance estimates demonstrated that accessions from South Korea are genetically different from U.S. germplasm. These results indicate that the South Korean germplasm may contain alleles not present in U.S. cultivars, such as new alleles for P. sojae resistance. Additionally, this study identifies SSR markers that can be used to begin mapping P. sojae resistance alleles in South Korean germplasm.