The Effects of Figaron and Water Deficit on Seed Yield of Two Soybean Cultivars

Abstract

In tropical and subtropical regions, soybean (Glycine max L.) often encounters a temporary water deficit in summer. Application of auxin during the reproductive period, when a water deficit and high temperature cause pod abscission, is expected to decrease pod abscission and thus increase seed yield. The present study was conducted in a greenhouse to assess the effects of Figaron (synthetic auxin) under various conditions of water deficiency in two soybean cultivars, Fukushirome and Miyagishirome. The plants were supplied with 500–, 300–, 200–, or 100–mL water per pot (5 L) three times a day. Figaron (lOOmgL–1) was sprayed 10 days after opening of the first flower. The rate of photosynthesis and transpiration were greatly decreased by water deficit in both cultivars. Application of Figaron slightly increased the rates of photosynthesis and transpiration irrespective of the water condition, though it temporarily decreased the rates during the initial few days after Figaron application. Figaron decreased the abscission of reproductive organs and increased the percentage of pod set, irrespective of the water condition, resulting in increase of seed yield. However, seed yield was severely decreased by water deficit, and application of Figaron could not fully overcome the decrease of yield caused by a severe water deficit.