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Environmental stress during reproductive growth of soybean Glycine max (L.) Merr. may reduce seed germination and vigor. Most studies of environmental influence on soybean seed germination and vigor have concentrated on the effects of drought, maximum day temperature, or average daily temperatured uring seed fill. This study was conducted to determine the effects of different combinations of day temperatures and night temperatures during reproductive growth on soybean seed quality. Day/night temperatures of 30/20, 30/30, 35/20, and 35/30°C were imposed at flowering and pod set (R1‐R5), seed fill and maturation (R5‐R8), and during the entire reproductive growth period (R1‐R8). High day and night temperature reduced soybean seed germination and seedling vigor. The extent of reductions in germination and vigor by high temperature was influenced by duration of temperature exposure and phase of reproductive growth. Temperatures during flowering and pod set exerted little influence on soybean seed quality. A combination of 35°C day temperature and 30°C night temperature during seed fill and maturation or 35°C day temperature from flowering to maturity decreased germination. Seedling vigor was reduced by 35/20, 30/30, and 35/30°C during seed fill and maturation and the entire reproductive period. Increase in night temperature from 20 to 30°C decreased seedling vigor at both 30 and 35°C day temperatures. These results suggest that Incational and seasonal differences in soybean seed quality may be induced by high temperatures during reproductive growth and indicate that night temperatures along with day temperatures are important in determining soybean seed quality.
Gibson et al. (Fri,) studied this question.