Inheritance of Fall Flowering on Cross between Rhododendron oldhamii Maxim. and Evergreen Azalea Species Native to Japan

Abstract

Flowering habits of progenies from crosses between Rhododendron oldhamii and evergreen azalea species native to Japan were investigated to clarify the inheritance of a fall flowering trait from R. oldhamii. The flower bud appearance date of the parents was the earliest in R. oldhamii and latest in R. eriocarpum and R. yedoense var. yedoense. Regarding fall flowering, all flower buds bloomed within the year in R. oldhamii. Some of the flower buds bloomed in R. kiusianum and R. tosaense, but no flowering was observed in other species. Fall flowering among F₁ seedlings was observed in all cross combinations. In addition, the frequency of fall flowering seedlings tended to be higher in the cross using evergreen azalea species with earlier flower bud emergence as a pollen parent. When an F₁ seedling of R. oldhamii × R. kiusianum was crossed with another strain of R. kiusianum, the first flowering dates of progenies were distributed continuously from July to March. These results revealed that the non-dormancy of the flower buds of R. oldhamii is dominantly inherited, and that flowering within the year is influenced by the date of flower bud appearance.