Yield Responses of Late Maturing Soybean Cultivars to High-temperature Treatment

Abstract

Climate warming may reduce soybean yield due to the increase in temperature during the reproductive growth period. The temperature during the reproductive growth period of the late-maturing cultivars is seasonally lower. However, there may be inter-varietal differences among these cultivars in the yield response to the increase in temperature. The major late-maturing cultivars, 'Fukuyutaka' and 'Tanbaguro', were grown in a temperature-gradient chamber, and subjected to the ambient temperature in the early growth period. Then temperature-gradient treatment was given from shortly before flowering to the beginning of seed filling. Average temperatures during the treatment period ranged from 25.1–27.1°C in 2014 and 25.6–29.1°C in 2015 The difference between the high-temperature and control plots was 2.0C° in 2014 and 3.3C° in 2015. High-temperature treatment decreased the seed per pod and hundred-seed weight in both varieties, but decreased the harvest index (HI) to a greater extent in 'Tanbaguro' than in 'Fukuyutaka'. Only in 'Tanbaguro', did the high-temperature treatment reduce the percentage of fertilized embryo sacs and seed growth rate which may have contributed to the greater reduction in HI,. The photosynthetic rate decreased after the high-temperature treatment. These results suggest that in late-maturing soybean cultivars HI and photosynthetic activity decrease with a 2 to 3.3 degree increase in temperature, and that there is a cultivar difference in the extent of HI decrease.