REPRODUCTIVE DETERIORATION IN BUCKWHEAT (FAGOPYRUM-ESCULENTUM) UNDER SUMMER CONDITIONS

To resolve the problem of low and unstable yield in buckwheat under unsuitable environmental conditions, five varieties were grown and compared in summer and autumn. Vegetative and reproductive growth characteristics were investigated, and embryo development was observed with Nomarski's differential interference contrast (DIC) microscopy. In summer, under high temperatures and longer day-length, autumn-type varieties showed faster vegetative growth and later reproductive development as compared to summer-types. In the autumn, with generally good climatic condition for buckwheat growth in southern part of Japan, the embryo sacs and zygotes of both types developed normally. At 3 days after pollination (DAP), the embryos reached the globular stage. In summer, however, mostly abnormal embryo sacs were observed 3 DAP, leading to incomplete development, failure of fertilization or abortion of embryo. The abnormal embryo sacs were classified into 6 types. Abnormality of either type occurred in 9 1-1 00 % of the tetraploids, which is higher than in the diploids (50-77 %). The present study, conducted to clarify the factors causing low seed set in buckwheat under summer conditions, provides detailed information for further breeding of environment-tolerant buckwheat. Diploid genotypes which are less sensitive to unfavourable conditions and, thus, show more efficient fertilization in summer, should be considered for use as breeding material in buckwheat.