The Effect of High Temperature on Kernel Development in Wheat: Variability Related to Pre-Heading and Post-Anthesis Conditions

In wheat, mean temperatures greater than 15-18�C following anthesis can result in a decrease in kernel weight at maturity, and breeding for high temperature tolerance during kernel filling could provide a significant increase in yield in large parts of the Australian wheat belt. The response of kernel filling to high temperature, however, varies from planting to planting and this variation has been shown to be related to both pre-heading and post-anthesis conditions. Thus high temperature (27/22�C), or low light (50% shade) during ear development can reduce the response of the developing grain to high temperature (30/25�C) following anthesis. In contrast, low light during kernel filling enhances the response to high temperature, resulting in a relatively greater reduction in kernel size. The latter response suggests that the slightly greater sensitivity to high temperature of grains from plants allowed to tiller freely in comparison with the responses observed using single culms, may be related to differences in light penetration of the canopy. This variation in response to high temperature, although not appearing to change the order of tolerance across cultivars, can create difficulties in selecting for high temperature tolerance over a number of generations, and can account for the apparent low heritability (h2 = 0.2) of high temperature tolerance determined here from a cross between the cultivars Kalyansona and Pinnacle.