Acta Hortic. 1263. ISHS 2019. DOI 10.17660/ActaHortic.2019.1263.39 XXX IHC – Proc. Int. Symp. on Ornamental Horticulture: Colour Your World Eds.: R. Kamenetsky-Goldstein et al. 295 Origin of the Rhododendron kaempferi related species and cultivars estimated by SSR analysis S. Yamamoto 1,a , T. Nakamura 2 , K. Koiwai 2 , M. Miyano 2 , E. Iizuka 3 , A. Nakayama 3 , Y. Kurashige 4 , N. Kobayashi 5 and T. Handa 3 1 Organization for the Strategic Coordination of Research and Intellectual Properties, Meiji University, Kawasaki, 214-8571, Japan; 2 Graduate School of Agriculture, Meiji University, Japan; 3 School of Agriculture, Meiji University, Japan; 4 Niigata Prefectural Botanical Garden, Niigata, 956-0854, Japan; 5 Faculty of Life and Environmental Science, Shimane University, Matsue, 690-8504, Japan. Abstract 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. Keywords: hybrids, genetic introgression, microsatellite INTRODUCTION The genus Rhododendron (Ericaseae) consists of more than 1000 species. More than 30 native azalea species have been recognized in Japan (Yamazaki, 1996). Sixteen species have been classified as section Tsutsusi and it was divided into two subsections, Scabra and Tsutsusi by morphological characteristics (Yamazaki, 1996). These species are hybridized and many cultivars have been produced since the Edo era (1603-1867; Yamazaki, 1996). Rhododendron kaempferi var. kaempferi Planch. (= R. kaempferi) is classified in subsection Tsutsusi. This species is widely distributed in mountains and suburban forests in Japan. R. transiens Nakai was classified in subsection Tsutsusi by morphological characteristics (Yamazaki, 1996). Distribution of this species was recorded only in the edge of suburban forests of Kanto region which surrounds area of Tokyo. Our previous study (Miyano et al., 2013, 2014; Koiwai et al., 2014) suggested that origin of R. transiens and R. × hannoense considered as interspecific hybrid of R. kaempferi and other species or cultivars. There are several native species and cultivars related to R. kaempferi, such as R. komiyamae Makino and R. kaempferi var. mikawanum Makino. However, relationships and phylogeny of these species are not revealed. In this study, we evaluated the genetic relationships and estimated the origin of R. kaempferi var. mikawanum and R. komiyamae with the species of subsections Scabra and Tsutsusi by microsatellite (SSR) markers. a E-mail: sho.cactus@gmail.com