Shortening the period from crossing to the seedling stage through ovule culture of interspecific crosses of azalea (Rhododendron spp.)

To establish a technique of obtaining azalea (Rhododendron spp.) seedlings precociously, ovules (immature seeds) from a diallel cross among 5 species and 1 variety were cultured in vitro. Adding 50 mg · liter^-1 GA₃ to the medium accelerated ovule germination, so that in the fastest case, 3 months after crossing (3 MAC) ovules from 20 crosses germinated, but the germination rates were low and less than 30%. When ovules 4 MAC were cultured, seedlings were obtained from all crosses; more than 50% of seedlings from crosses with R. kiusianum and R. kaempferi as seed parents were obtained within 1 and 2 months after culturing. These results indicate that by exposing ovules of 4 MAC to 50 mg · liter_-1 GA₃, one can obtain hybrid seedlings precociously; the period from crossing to the seedling stage was 1.5 to 2.5 months shorter than with 6 MAC cultured seeds.