Evolution of flowering, ripening and seed set in buckwheat (Fagopyrum esculentum Moench):: quantitative analysis

Buckwheat is characterised by a low grain yield despite an abundant formation of flowers through a long period of time. To understand the genesis of this low final yield (around 2000-2500 kg ha(-1) in our weather conditions of Belgium), we studied, during 3 years in the field, the evolution of flowering and ripening of inflorescences or spikes located on the main stem of buckwheat plants of cultivar "La Harpe". We applied different treatments of defoliation (partial and complete) and partial removal of inflorescences of the main stem in order to modify the availability of photosynthates and to reduce the competition between kernels. In all cases, whatever the treatment, there was a drastic reduction of the grain number relative to the number of flowers formed, seed set being very low, around 20-30%. Cumulative curves of development stages of flowers and kernels show clearly that complete flower senescence occurring early after full display of the corolla accounted for most of the low grain set, whatever the treatments and the trials. The critical stage of grain is clearly just after flowering and is not influenced by change in sink-source relations due to defoliation or removal of inflorescences parts. In a given inflorescence, the extent of this early senescence increases progressively from the base (near the peduncle) to the top of the inflorescence. A drastic reduction of competition between inflorescences and kernels (through partial removal of inflorescences) has only a negligible effect on final grain yield per plant, indicating a strong compensation by the remaining kernels. Thus, the limitation is associated to a strong sink restriction appearing only in some flowers and probably linked to internal flower structure and fertilization. (c) 2004 Elsevier B.V. All rights reserved.