Effects of Geitonogamy on the Seed Set of Magnolia obovata Thunb. (Magnoliaceae)

The effects of geitonogamy on the seed set of a protogynous hermaphroditic tree, Magnolia obovata Thunb., were investigated by electrophoretic allozyme analysis and pollination experiments. The multilocus outcrossing rates (tm) estimated in 1995 and 1997 by using four polymorphic loci were 0.39 and 0.42, respectively, indicating that more than half of the seeds are produced by geitonogamous selfing. Manual pollination demonstrated that the follicle set per fruit (frequency of ripe carpels) and seed set per fruit from self‐pollination were 2.6 and 3.8 times less than those from cross‐pollination, respectively, and the frequency of aborted seeds from self‐pollination was significantly higher than that from cross‐pollination. There was no significant difference between self‐ and cross‐pollination in the fruit set and the frequency of remnant ovules (ovules unfertilized or aborted before endosperm development). These results indicate that inbreeding depression is a primary factor reducing the seed set of self...