SOYBEAN SEED COMPOSITION UNDER HIGH DAY AND NIGHT GROWTH TEMPERATURES

High diurnal temperatures often affect development of soybean [Glycjne max (L.) Merr.], but little is known about the relative influence of high day and night temperatures on the chemical composition of the see d. This study was conducted to determine the effects of combinations o f high day and night temperatures during flowering and pod set (R1-R5) , seed fill and maturation (R5-R8), and continuously during the reprod uctive period (R1-R8) on soybean seed oil, protein, and fatty acid com position. Day/night temperatures of 30/20, 30/30, 35/20, and 35/30 deg rees C were imposed on the soybean cultivar Gnome 85 in growth chamber s. The day/night temperature combinations during R1-R5 had little effe ct on the oil and protein concentration and the fatty acid composition of seed produced. As mean daily temperature increased from 25 (30/20) to 33 (35/30)degrees C during R5-R8 and 25 (30/20) to 33 (35/30)degre es C during R1-R8, and oil concentration decreased and protein concent ration increased. Increased day temperature during R5-R8 and R1-R8, av eraged across the two night temperatures, increased oleic acid and dec reased linoleic and linolenic acids. When night temperature was increa sed at 30 degrees C day temperature during R5-R8 and R1-R8, oleic acid decreased and linoleic acid increased. When night temperature was inc reased at 35 degrees C day temperature during R1-R8, oleic acid increa sed, and linoleic and linolenic acids decreased. These results indicat e the importance of high day and night temperatures during seed fill a nd maturation in the oil, protein, and fatty acid composition of soybe an seed.