Effectiveness of three-way crossing for the breeding of yellow-flowered evergreen azalea

For the purpose of obtaining yellow-flowered evergreen azaleas, single and three-way interspecific crosses between evergreen azaleas and Rhododendron japonicum f. flavum were compared. In single cross, although many seeds were obtained from R. eriocarpum x R. japonicum f. flavum, the seedlings from immature ovule were albino or pale-green plants. They were withered away at acclimation. In R. kiusianum x R. japonicum f. flavum, green seedlings were observed, but number of ovules contained in one capsule was very small. In three-way cross, (R. kiusianum x R. eriocarpum) x R. japonicum f. flavum, many viable seeds were contained in one capsule, and about 15% of the seedlings were green leaf colored. These results suggest that three-way cross is one of the useful breeding methods for creating the new yellow-flowered evergreen azalea. Isozyme analysis revealed that most of seedlings were zygotic origin without distinction of their leaf colors, but some green seedlings indicated the same genotypes as the seed parents. Therefore, it is important to confirm hybridity of the seedlings by isozyme technique.