The possession of cpDNA of Rhododendron ripense Makino in evergreen azalea cultivars

In Japan, great numbers of evergreen azalea cultivars have been bred since the Edo era (1603-1867) based on the genetic diversity of the various species in the genus Rhododendron (Ericaceae), the subgenus Tsutsusi section Tsutsusi. The several varieties out of them had been brought to Western countries and utilized for breeding materials of pot and garden azalea. R. ripense Makino endemic to the west part of Japan is one of the best ornamental performance species with high adaptability to environmental conditions. We have focused on the genetic contribution of R. ripense to azalea cultivars and developed the PCR-RFLP marker of cpDNA identification based on the species-specific sequence of trn L-F region. As a result of R. ripense cpDNA specific maker in Japanese groups, most of the large-flowered cultivars have cpDNA of R. ripense and the small-flowered cultivars have cpDNA of non-R. ripense type. Furthermore, almost all Western pot azalea cultivars possess R. ripense cpDNA type. These results indicate the cytoplasmic contribution of R. ripense not only to Japanese large-flowered cultivars but also to all the pot azalea cultivars. Although R. simsii has been recognized as the ancestral species of pot azalea, R. ripense should be remarked as the cytoplasmic parent of the pot azalea cultivars.