Studies On Reproductive Biology Of Magnolia Grandiflora (Magnoliaceae)

Magnolia grandiflora belongs to subgenus Magnolia (Magnoliaceae). Through field investigation, this thesis studied the floral characters, insect-pollination, breeding system and embryonic development of Magnolia grandiflora by bagged artificial pollination, pollen viability test, stigma receptivity test, pollen-ovule ratio, OCI observation, normal paraffin and other methods. This research could provide es-sencial data for the stduy on reproductive characters and machanism of Magnolia grandiflora, and find out the differences in reproductive characters between Magnolia grandiflora and Magnolia denudata. From the perspective of reproduction, this thesis suggested the evolutionary relationship among genus Magnolia, and provided reproductive biological basis for systematic classification of Magnoliaceae. The main results were as follows:1. Full flowering stage of Magnolia grandiflora was from late May to mid-June. During the five-six days flowering period of an individual flower, pollen variability decreased over flowering stage. The optimal pollination period was in the first opening stage, and the stigma receptivity could last about four days.2. During the five-six days flowering period of an individual flower, two-times opening/closure flowering was observed in Magnolia grandiflora. After the flower re-opening, pollen grains released from dehisced anther, and stigmas was still receptive for a short time.This phenomenon could provide an opportunity for self-pollinating, and was an important difference in reproductive characteristics between Magnolia grandiflora and Magnolia denudata.3. Magnolia grandiflora has a mixed mating system, and is self-compatible to some extent. The differences between subgenus Magnolia and subgenus Yulania in self-compatibility resulted in the differences in fruit set ratio, seed set ratio and mating system.4. Protogyny in Magnolia grandiflora lies in a mechanism that determines the anther dehiscence stage, thus reducing interference between pollen and stigmas and self-pollination.5. The comprehensive interaction of breeding syetem and embryonic development contributed to carpels development of Magnolia grandiflora, which was relatively stable. The differences in caepels development may play an important role between subgenus Magnolia and subgenus Yulania.