Quantitative assessment of some factors limiting seed set in buckwheat

A healthy buckwheat (Fagopyrum esculentum Moench) plant produces numerous flowers but few seeds. The objective of this study was to investigate mechanisms responsible for the low frequency of seed set. Newly open and receptive flowers were pollinated at weekly intervals from 4 to 12 wk after seeding (WAS) on selected racemes of greenhouse-grown plants. Flower number, seed set, abortion. and anatomical observations of egg sacs and proembryos were analyzed. Although flowers formed continuously for 7 wk, the period of maximum seed set under controlled conditions was brief (1-2 wk). Competition within the same nutritional unit (raceme) did not account for low average seed set per raceme. Neither the number of flowers nor frequency of seed set was decreased when developing seeds were on the same raceme. Abortion (approximate to10%) was not a major factor limiting seed set. Eighty percent of the flowers failed to initiate seeds even under controlled growing conditions when hand pollinated. Approximately 20% of megagametophytes appeared to be defective at anthesis. The proportion of ovules containing a proembryo at 24 h after pollination (HAP) paralleled the proportion initiating seeds, indicating that fertilization is a limiting process. Pollen tube remnants were observed near the micropyle in 65% of the unfertilized ovules at 24 HAP. Lack of fertilization accounts for most of the reduction in seed set. appears to be caused by failure of the pollen tube to grow into the micropyle, and increases with plant age at pollination. Flowers that form late in the plant cycle contribute little to seed set and may be ignored in yield management decisions.