Ripening habit of buckwheat.

In buckwheat (Fagopyrum esculentum Moench), the diverse ripening times of seeds and the remarkable seed shattering can make it difficult to determine the optimum harvest time. To provide basic information for the improvement of the ripening habit of buckwheat by breeding and cultural methods, we monitored the changes in the numbers of mature (brown) and immature (green) seeds at each raceme of buckwheat plants in the field during the course of seed maturation. A determinate line was used in addition to an indeterminate one (wild type), since the former had previously been reported to display more uniform ripening. Seed weights were also determined to estimate yields. Seed discoloration proceeded from the main stem to branches, and from basal to apical racemes regardless of genotypes or years. Seed shattering progressed in a similar pattern. In contrast to these consistent habits, differences in maturation speed were seen between years. Seed discoloration progressed slightly slower in 1997, while seed shattering began much earlier, compared with that in 1998. Consequently, in 1997, seed shattering began before all seeds had matured in most plants, while in 1998, this phenomenon was observed in fewer plants. Seed yields accordingly increased slowly until reaching maximum levels, followed by rapid decreases in 1997, relative to 1998. Growth habit (determinate vs. indeterminate) appeared to have little influence on ripening. These results are the first to clearly demonstrate that seed shattering can start before all seeds mature in buckwheat, regardless of growth habit. And that the rates of seed ripening and seed shattering are independent and vary among years.