Capsule set, seed productivity and germination in interspecific crosses among evergreen azaleas

Crossability among seven evergreen azaleas (Rhododendron spp.) in subsection Tsutsusi was compared. Capsule set was observed in all the crosses. Number of seeds per capsule was lower in the crosses with R. kiusianum or R. serpyllifolium than in other crosses, and small flowers with short style and small ovary may be the reason for lower number of seeds. Number of seeds per capsule was maximum when male/female style length ratio (SLR) was around 0.7. The number gradually decreased as the increase of SLR, and above 2.2 of SLR resulted in < 200 seeds, approving the relationship between SLR and number of seeds per capsule. The seeds germinated very well in the most crosses. In the crosses with R. serpyllifolium, however, unilateral cross incompatibility was observed.