Effects of timing and intensity of elevated temperatures on reproductive development of field-grown Shiraz grapevines

Aim: To investigate whether timing and duration of exposure to elevated temperatures impact the reproductive development of field-grown Shiraz grapevines. Methods and results: The reproductive responses of Shiraz grapevines (Vitis vinifera L.) to two levels of elevated temperatures at budburst and flowering were investigated in an irrigated vineyard in the Barossa Valley (South Australia) over two consecutive growing seasons. Custom-built under-vine ‘tents’ and closed flow-through chambers enclosing a set of grapevines in the field were used to raise canopy temperatures above ambient. Higher temperatures at flowering resulted in lower yields due to decreased fruit set in 2007-08, while yield was virtually unaltered the following year despite the lower fruit set. Two indicators of grapevine reproductive performance, Coulure Index and Millerandage Index that quantify abscised and underdeveloped berries, respectively, were calculated to be higher as a result of the heat treatments in both seasons. Stigma receptivity, pollen germination, and pollen tube kinetics were generally lower in vines grown under the tents. Conclusion: Flowering and fruit set are strongly influenced by temperature changes during this period of development. Significance and impact of the study: This is one of the first field based studies to demonstrate that extreme temperatures (>35°C) during the flowering period detrimentally effect fruit set and final yield, thus providing critical knowledge for managing vineyards in a changing climate.Vinay Pagay and Cassandra Collin