Genesis of grain yield in buckwheat (Fagopyrum esculentum Moench) with a special attention to the low seed set

This paper reviews five years of research conducted in Belgium on the genesis of the low grain yield in buckwheat (Fagopyrum escultentum cv. "La Harpe"). Detailed observations were made on the evolution of flowers during the whole flowering period in field trials and under controlled conditions. Treatments involved different times of sowing, seeding rate and defoliation rates, modifications of flower numbers (removal of entire inflorescences or racemes), hand pollinations, honeybee pollination, application of osmotic stress, comparison among different photoperiod regimes). The morphogenesis of the inflorescences was examined. The genesis of seed numbers appeared to be very much affected by drastic reductions of flower numbers that occur soon after full display of the corolla whatever the position of the flower and the time of its appearance in the raceme. Seed set remained low for all the treatments applied and the environmental conditions tested even if no pollen transfer limitation was detected. Position of a raceme had a higher effect on flower number than on seed set. Relation to environmental stress occurring at well defined critical stages is unlikely. The causes of this low seed set remain unclear but appear to be due to the flowers themselves, as poor fertility could be due to abnormalities of ovaries and/or anthers.