Evolutionary relationship between a wild ancestor of common buckwheat Fagopyrum esculentum subsp. ancestrale and a self-compatible relative F. homotropicum based on microsatellite variability

Information on the genetic variation of crop wild relatives is important for their utilization and in situ and ex situ conservation. Cultivated common buckwheat Fagopyrum esculentum subsp. esculentum has two wild relatives, wild common buckwheat ( F. esculentum subsp. ancestrale ) and F . homotropicum . We evaluated the genetic diversity within and among natural populations of these species using microsatellite markers. Genetic diversity values averaged over loci within wild common buckwheat populations ranged from 0.503 to 0.668, which were higher than those of F . homotropicum that ranged from 0.138 to 0.333. F . homotropicum showed a high level of genetic differentiation among populations ( F ST = 0.606), whereas the corresponding estimate for wild common buckwheat was much lower ( F ST = 0.272). These contrasts between species are largely consistent with differences in their mating system; common buckwheat exhibits heterostylous self-incompatibility and F. homotropicum exhibits homostylous self-compatibility. A phylogenetic analysis and Bayesian clustering revealed that local populations of wild common buckwheat were divided into northern and southern groups. F . homotropicum was not monophyletic as some populations were closely related to the southern group of wild common buckwheat. These results strongly suggest that the self-compatible species F . homotropicum diverged multiple times from wild common buckwheat. Our study indicates that both wild relatives of cultivated common buckwheat retain a substantial level of genetic diversity and are potentially useful genetic resources for the genetic improvement of cultivated common buckwheat.