Timing of Fruit Initiation and Seed Size in Soybean

Abstract

There is substantial variation in seed size (weight per seed) among the seeds produced by a soybean (Glycine max [L.] Merrill) plant. Five field experiments with two cultivars were conducted near Lexington, Kentucky, United States (38°N), to test the hypothesis that variation in seed size was related to the time of fruit initiation during the flowering period. All fruits ≥ 10 mm long on a plant were marked at three-day intervals, harvested at maturity, and separated by the time of marking before seed size was determined. There was substantial variation in seed size, but the time of fruit initiation accounted for only a small proportion of the variation. Fruits that initiated growth at different times often produced the same sized seeds, and there was always substantial variation in seed size among fruits initiated at the same time. The data provide little support to the hypothesis that seed size is related to the timing of fruit initiation. The data suggest that there may be several mechanisms responsible for the variation in seed size on soybean plants.