Vines are thought to 'shutdown' in response to heatwaves. This syndrome includes, hypothetically, disruption of photosynthesis and arrest of berry growth and sugar accumulation. Observations in the field are inconclusive, however, because affected vines lack proper controls for comparison. Using heating chambers in the field, we compared the dynamics of berry growth and sugar accumulation in Shiraz vines exposed to three consecutive days of high daytime temperature (6 to 7°C above ambient) with unheated controls. Heat episodes were aligned with the beginning of a weekly irrigation cycle and applied in one of four phenological windows, namely post-fruitset, pre-veraison, veraison and pre-harvest. Heat did not affect the dynamics of berry growth andsugar accumulation at any stage. Vines up-regulated stomatal conductance in response to high temperature, and this response might have contributed to the maintenance of photosynthesis and berry growth.
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