Effect of high temperature on the rate and duration of grain growth in field-grown Sorghum bicolor (L.) Moench

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Abstract
Sorghum was sown at six dates in a tropical environment and grown under high water and nutrient supply. For each sowing, mean temperature during grain-filling was relatively stable, but across sowings it ranged from 24.6 to 30.2¦C. The effect of this variation on the following was examined: the linear rate of grain growth, the duration of the effective grain-filling period, the rate of increase in harvest index during grain-filling, the rate of development of black layer (as an indicator of maturity) and final grain yield. Contrary to previous findings from controlled environment experiments, the rate of grain growth increased linearly with temperature to 30¦C. However, the duration of grain-filling and the rate of development of black layer were not closely related to mean temperature. Final grain yield was not necessarily adversely affected by high temperature during grain-filling. Also, high grain yield was not necessarily associated with long duration of grain-filling. Similar to the rate of grain growth, harvest index increased linearly during grain-filling. The rate of increase in harvest index was not significantly related to temperature, with a mean value across sowings of 0.0185 day-1. An important implication of the linear increase in harvest index is that grain yield accumulation can be estimated from the crop biomass at any stage of grain growth without knowledge of grain number or the rate of grain growth.