Genetic diversity of the rice bean (Vigna umbellata) genepool as assessed by SSR markers

The genetic diversity of 472 rice bean accessions (388 cultivated and 84 wild) from 16 Asian countries was evaluated by 13 simple sequence repeat (SSR) markers. In total, 168 alleles were detected, and the numbers of alleles in cultivated and wild accessions were 129 and 132, respectively. The gene diversity in cultivated populations (0.565) was about 83% of that for wild (0.678) populations. Cultivated populations from Vietnam, Myanmar, Nepal, and India had the highest gene diversity (>0.5). East Asian accessions formed a distinct genepool. Indonesian cultivated accessions showed high genetic divergence from other cultivated populations and had the most similar genetic structure to wild accessions. In Nepalese cultivated accessions, many accessions from western regions were quite distinct from others and formed a specific group. These Nepalese accessions could be considered a unique gene source for rice bean breeding. In contrast, eastern Nepalese accessions showed an SSR profile similar to that of Southeast Asian rice beans. The present study represents the first comprehensive SSR analysis in cultivated and wild rice bean germplasm and clarifies geographical distribution of genetic profile that might be used to broaden the genetic base of currently grown rice bean cultivars.