Screening soybean genotypes for high temperature tolerance by in vitro pollen germination, pollen tube length, reproductive efficiency and seed yield

High temperature stress is a major environmental stress and there are limited studies elucidating the impact of high day and night time temperature on reproductive processes in soybean. Twelve soybean genotypes were grown at day/night temperatures of 30/22, 34/24, 38/26 and 42/28 °C with an average temperature of 26, 29, 32 and 35 °C, respectively under green-house conditions. High temperature stress significantly increased duration of flowering and decreased number of flowers and pods formed as compared to ambient temperature. When plants were grown at elevated temperature pollen germination, pollen size and pollen tube length were declined leading to reduced reproductive efficiency which ultimately resulted reduction in seed yield. The average seed yield was maximum (13.2 g/plant) in plants grown under ambient temperature condition. Seed yield was declined by 8, 14, 51 and 65% as the plants were grown at 30/22, 34/24, 38/26 and 42/28 °C as compared to plants grown under ambient temperature conditions, respectively. The genotypes such as NRC 7 and EC 538828 showed less reduction in yield and stable reproductive biology as compared to other genotypes. It is concluded that for heat tolerance in soybean, breeding efforts needs to be focused on improving the reproductive efficiency.