Effect of temperature and soil moisture status during seed development on soybean seed isoflavone concentration and composition

Soybean [Glycine max (L.) Merr.] seed isoflavone concentration has been shown to be highly dependent on environmental conditions, but isoflavone concentrations have not been studied under controlled conditions to quantify the effects of specific factors. To determine the effect of air temperature and soil moisture status during soybean seed development on seed isoflavone concentration and composition, soybean plants were grown in the greenhouse under intermediate (18/28 degrees C), 9.5 h night/14.5 h daytime temperatures with high soil moisture conditions. Beginning at the R6 growth stage plants were subjected to either intermediate (18/28 degrees C), low (13/23 degrees C), or high (23/33 degrees C) 9.5 h night/14.5 h daytime temperatures with either low or high soil moisture conditions. Two French cultivars, Imari and Queen, and three U.S. cultivars, Dwight, Jack and Loda, all in maturity group 11 were studied. The overall results show that low temperatures and high soil moisture conditions produced the highest seed isoflavone concentrations with changes in temperature having the larger effect. The changes in daidzein and genistein concentrations were similar to changes in total isoflavones but the glycitein concentration was much less affected. The three U.S. cultivars were much less responsive to soil moisture than the two French cultivars. All five cultivars showed a two- to threefold increase in total isoflavone concentrations at the low temperature regime compared to the high temperature regime. Plant height was greatest under the intermediate temperatures; whereas, low temperatures and low soil moisture hastened maturity. Seed size was not significantly affected by any treatment. Soil moisture and air temperature have clear effects on the isoflavone concentrations in mature soybean seeds, but the ranking of all the cultivars based on average isoflavone concentration remained the same with all treatments. Environmental factors can have a large effect on isoflavone concentration, but the potential for isoflavone production is largely under genetic control.