A Comparison of the Effect of High Temperature on Grain Development in Wheat and Rice

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Abstract
Grain weight at maturity of the wheat cultivar Banks was reduced by about 5% for each 1 °C rise in daily mean post-anthesis temperature in the range from 17.7 to 32.7 °C, using grain weight at 17.7 °C as the base. In contrast, the rice cultivar Calrose had a stable grain weight up to 26.7 °C and above that showed a 4.4% drop in weight per 1 °C increase in mean post-anthesis temperatures up to 35.7 °C, using grain weight at 26.7 °C as the base. In both wheat and rice there was a reduction in the duration of grain growth with increasing temperature up to a mean of 26.7 °C. In this range rice, but not wheat, showed a compensating increase in the rate of dry-matter accumulation. Above 26.7 °C the rate of dry-matter accumulation fell in both species, although this was more stable in rice than in wheat. In wheat the duration of grain growth continued to decrease at temperatures above 26.7 °C, but showed little change in rice up to 35.7°C, the maximum tested. These data are discussed in relation to the physiological, biochemical and physical constraints that may act to regulate grain development in wheat and rice at high temperature.