Temperature during seed filling and soybean seed germination and vigour

Two soybean [Glycine max (L.) Merrill] cultivars were grown in a phytotron at temperatures of 27/22, 33/28, and 38/33 degrees C (day/night, 10 h day) during seed filling to investigate the effect of temperature on seed germination and vigour. Some of the seeds produced at 33/28 and 38/33 degrees C were smaller, wrinkled, and shriveled, and had poor quality. Most of these seeds would be removed during conditioning and would nor affect the final quality of the seed lot. Standard germination of seeds with no visual abnormalities (i.e., normal seeds that were not wrinkled or shriveled) developing at 33/28 degrees C was 98% or higher, but seed vigour was reduced as shown by an average accelerated ageing germination of 71% (97% at 27/22 degrees C) and an average electrical conductivity of 8.2 mS m(-1) g(-1) (5.9 mS m(-1) g(-1) at 27/22 degrees C). Standard germination and vigour of normal seeds developing at 38/33 degrees C were low. The effects of temperature on seed quality were similar for seeds harvested when all pods on a plant were mature and for seeds harvested when each pod reached physiological maturity, suggesting that the effect of temperature occurred during seed development, not after physiological maturity. High temperatures (33/28 degrees C and higher) during seed development reduced soybean seed quality which may explain lower duality in the absence of mechanical injury or seedborne disease.