THE EFFECT OF HIGH-TEMPERATURE ON KERNEL DEVELOPMENT IN WHEAT - VARIABILITY RELATED TO PRE-HEADING AND POSTANTHESIS CONDITIONS

In wheat, mean temperatures greater than 15-18 degrees C following ant hesis can result in a decrease in kernel weight at maturity, and breed ing for high temperature tolerance during kernel filling could provide a significant increase in yield in large parts of the Australian whea t belt. The response of kernel filling to high temperature, however, v aries from planting to planting and this variation has been shown to b e related to both pl e-heading and post-anthesis conditions. Thus high temperature (27/22 degrees C) or law light (50% shade) during ear dev elopment can reduce the response of the developing grain to high tempe rature (30/25 degrees C) following anthesis. In contrast, low light du ring kernel filling enhances the response to high temperature, resulti ng in a relatively greater reduction in kernel size. The latter respon se 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 i n light penetration of the canopy. This Variation in response to high temperature, although not appearing to change the order of tolerance a cross cultivars, can create difficulties in selecting for high tempera ture tolerance over a number of generations, and can account for the a pparent low heritability (h(2) = 0.2) of high temperature tolerance de termined here from a cross between the cultivars Kalyansona and Pinnac le.