Effect of flowering season on the compatibilities of interspecific single, three way, and double crosses among Hibiscus syriacus, H. sinosyriacus, and interspecific hybrids (H. syriacus x H. par

摘要

To study the cause of seasonal changes of compatibilities in crosses among H. syriacus, H. sinosyriacus, and interspecific hybrids H. syriacus x H. paramutabilis, stigma receptivity, pollen tube growth and the relationship between the number of pollen tubes in the stylar tissue and fruit and seed setting were investigated in early- (July), middle- (August), and late- (September) flowering season of H. syriacus. In interspecific single crosses between cultivar of H. syriacus and H. sinosyriacus, high seasonal fruit and seed setting varied, depending on the combinations. The peak of fruit and seed setting was lowest during the late-flowering season. However, pollen viability and stigma receptivity were higher in the late season than in the middle season. In early- and mid-flowering seasons, numerous pollen tubes penetrated into ovaries between 12 and 24 h after pollination, but in the late-flowering season, a few pollen tubes penetrated into the ovaries between 24 and 48 h after pollination. The decreased number and delay of pollen tube penetration into the ovary resulted in low fruit and seed setting in the late-flowering season. A few viable seeds were produced only in the early-flowering season in the three-way and double interspecific crosses.No viable seed was obtained in late-flowering season. These results were closely related with slow pollen tube growth in the styles and low penetration of pollen tubes into the ovary in the late-flowering season.