SOYBEAN MOTHER PLANT EXPOSURE TO TEMPERATURE STRESS AND ITS EFFECT ON GERMINATION UNDER OSMOTIC STRESS

High temperature reduces quality of soybean seed developed at different positions on the plant. The objective of this research was to study the quality of seed produced under different temperature regimes located at different position in the canopy. Soybean plants grown in pots were transferred at first pod stage to three growth chambers fixed at 18/10, 25/15 and 32/20 degrees C day/night temperature having 13/11 hrs day/night length. The plants remained in growth chambers until physiological maturity. Seeds harvested from each growth chamber were exposed to osmotic stress having osmotic potential of -0.5 MPa and unstressed control. Both stressed and control treatments were germinated in three growth chambers fixed at 18, 25 and 35 degrees C. Seed developed at lowest temperature (18/10 degrees C day/night) had maximum germination. Germination decreased linearly with increased day/night temperature and lowest germination was recorded at highest temperature of 32/20 degrees C (day/night). Seed developed at bottom position was heaviest and had better germination compared with seed developed at middle and top position. Seed germination was highest at 25 degrees C and took fewer days to 50% germination than 18 and 25 degrees C. Osmotic stress decreased germination and delayed days to 50% germination than control. It can be concluded that optimum temperature for seed development was 18/10 degrees C (day/night) whereas best germination temperature was 25 degrees C.