AFLP markers for characterizing the azuki bean complex

Azuki bean [Vigna angularis (Willd). Ohwi & Ohashi] is an important crop in East Asia. However, little is known about the wild and weedy relatives and their relationship with the cultigen. This study was conducted to obtain information on the population genetic diversity of the azuki bean complex germplasm and relate this information to breeding, conservation, and evolution in this complex. Germplasm from a wide geographic distribution in Japan was analyzed. Amplified fragment length polymorphism (AFLP) markers were used to characterize the cultigen, wild, weedy, and complex populations. The relationships among 41 populations and 27 individual plants from an additional three populations were analyzed by principal component (PCA) and cluster analyses. The Mantel test was used to determine the relationship between genetic diversity and geographic location. Genetic diversity was less in the cultigen (Ha = 0.35) than wild populations (Ha = 1.19). The wild and weedy types were more dispersed than the cultigen on a PCA plot, which is a reflection of their greater genetic variation. Most weedy populations studied were more closely related to the cultigen than wild populations, but the magnitude of differentiation measured as the between-group diversity (H(D)), was very similar between wild, weedy, and cultivated populations (range 0.50-0.56). Low but significant association was observed between AFLP genetic similarity and geographic distance. The complex population analyzed displayed greater genetic diversity than the wild and weedy populations from the same area and thus are a logical primary target for both ex-situ and in-situ conservation. The greater genetic variation in the wild and weedy relatives of azuki bean suggest they may be useful for crop improvement. Weedy azuki beans, which generally appear to be a distinct ecotype rather than an escape from cultivation, may be easier to use in breeding than wild azuki beans.