Origin of the Rhododendron kaempferi related species and cultivars estimated by SSR analysis

More than 30 native evergreen azalea species have been recognized in Japan, from which many cultivars have been produced since the Edo era (1603-1867). Rhododendron kaempferi var. kaempferi Planch. (= R. kaempferi) is classified in subsection Tsutsusi and widely distributed in mountains and suburban forests throughout Japan. There are several native species and cultivars closely related to R. kaempferi. Our previous study revealed that the origin of R. transiens and R. × hannoense are considered as interspecific hybrids of R. kaempferi and other evergreen azalea species and cultivars. Recently, we also applied SSR analysis to other R. kaempferi related species and cultivars such as R. komiyamae and R. kaempferi var. mikawanum. Cluster analysis showed that R. komiyamae and R. kaempferi var. mikawanum were related to R. kaempferi and not related to other evergreen azalea species, which means they originated from R. kaempferi and not from hybridizing with other azalea species. From the results of SSR analysis using R. kaempferi and its related species and cultivars, we propose three models of establishment of R. kaempferi related species and cultivars: 1) natural mutation, 2) interspecific hybridization between wild species, and 3) hybridization between wild species and cultivars.