The Influence of Recovery Temperature on the Effects of a Brief Heat Shock on Wheat. I. Grain Growth

Abstract

The responses of wheat yield to moderately high (20-32ºC) and very high temperatures (> 32ºC) have been studied separately in the literature, but not in combination, despite the fact that this is usually how elevated temperatures occur in the field. In this study, controlled environment conditions were used in order to examine the interaction of moderately high and very high temperatures during grain filling and their effect on wheat yield. Specifically, we wished to test the hypothesis that cooler conditions would facilitate greater recovery of grain growth following a brief exposure to very high temperature. To this end, wheat was exposed to either 21/16 or 40/16ºC (day/night) from 15-19 days after anthesis and subsequently grown under one of three moderately high temperature regimes until maturity: 21/16, 27/22 or 30/25ºC. For all moderately high temperature treatments, a brief 'heat shock' significantly reduced mature individual kernel mass by 17%, on average. In the absence of 'heat shock', increasing moderately high temperature progressively reduced mature individual kernel mass by ca 2.5% for each 1ºC increase in average daily temperature. After a 'heat shock' event, however, there was not a progressive decline in mature individual kernel mass with increasing moderately high temperature. A short period of very high temperature applied early in grain filling therefore reduced the response of wheat to subsequent moderately high temperatures. We conclude that the reduction in yield caused by 'heat shock' is not alleviated by cool post-shock conditions.