Investigations on the mechanism for avoidance of selfing and its ecological meaning in nut production of Fagaceae

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Artificial pollination with different mating patterns (outcross, self-, and non-pollination) was performed for Quercus serrate. The timing of abortion and the size and internal development of acorns from each mating type were investigated. Independently of pollination treatment, size of the one ovule began to increase and developments of remaining ovules were arrested at the period around 50-60 days after pollination (DAP). In the outcross acorns, further development of the ovule and remaining five ovules degenerated. Acorns were slowly developed and similarly dropped in every pollination treatment until 90 DAP. Almost all self- and non-pollinated acorns were rapidly aborted during the period 90-120 DAP. The results indicated that ovule abortion began at maternal initiative and completed in fertilization of the selected ovule with suitable pollen. The correspondence between the timing of abortion and the timing of rapid size growth and the development of storage organs suggests that this acorn-maintenance strategy may be the consequence of a maternal adaptation that allows better reproductive success under resource limitation. Paternity analysis of seeds obtained from controlled pollination showed the presence of conspecific competition and/or selection from pollination to maturation. Furthermore, the similar analysis for isolate the ovules from the premature acorns also showed that multiple ovules were fertilized and difference of in the contribution on fertilization, and identify that intra-specific interactions was possibly occurred in the pre-fertilization stage.