Differential Responses to High Temperatures of Starch and Nitrogen Accumulation in the Grain of Four Cultivars of Wheat

Plants of four cultivars of wheat were exposed during the grain-filling stage in two different experiments to brief episodes (10 or 20 days) of high temperature. About the same number of degree-days above a standard temperature were accumulated in both experiments. While the cultivars differed in detail in their responses, final single grain weight in all cases was reduced by elevating the temperature, and to about the same extent (14%) in both experiments. The numbers of B-type starch granules (but not of A-type) were substantially reduced by warming, but this reduction did not appear to account wholly for the smaller weight of starch per grain resulting from elevated temperature. Nitrogen content per grain was not affected by the warm conditions and, in the experiment with the short duration at the high temperature differential (33/25°C day/night as compared to 21/16°C), percentage nitrogen was significantly increased by warming from 2.61 to 3.05%. It is concluded that starch and nitrogen accumulation in the grain have differing susceptibilities to brief episodes of high temperature during grain-filling.