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

摘要

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 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 and thus providing critical knowledge for managing vineyards in a changing climate. Introduction Temperature is a primary environmental factor that plays a key role in affecting several plant physiological processes including phenology, vegetative growth, flowering and fruit set, crop development, yield and quality. The relatively recent trend towards higher average growing season temperatures in premium viticultural regions worldwide has heightened the importance of understanding the viticultural consequences of these temperature shifts (Schultz, 2000; Soar et al., 2008; Webb et al., 2007). When extreme temperatures (daily maximum temperatures greater than 35°C) were included in one study predicting the effects of future climate change on winegrape production in the United States, areas currently marginally suitable to grapevine production were almost eliminated while the acreage of premium grape growing regions decreased up to 81% (White et al., 2006). While an increase in the average growing season temperature is likely to have negative effects on crop yield and quality, short episodes of extreme temperatures are expected to be even more detrimental particularly at key phenological stages of plant development such as flowering and fruit set (Ferris et al., 1998; Hedhly et al., 2005; Prasad et al., 1999).Studies on grapevine reproductive development in controlled environments have shown that high temperatures are detrimental to reproductive performance and consequently yield. Comparing pre- and post-budburst exposures to elevated temperatures (>30°C) for approx. two weeks per period, Petrie and Clingeleffer (2005) found that flower number per inflorescence was 18% lower than at ambient conditions as a result of the pre-budburst heat treatment than in the post-budburst treatment, where a 15% reduction was observed. Similar results were obtained by Keller et al. (2010), who found nearly a one-third reduction in flowers per inflorescence when buds were exposed to warmer conditions (up to 40°C) from pre-bud swell to when the flowers were first visible. Higher temperatures applied after budburst (until fruit set) advanced the phenology of berry set and had a negative effect on flower number per inflorescence (Buttrose and Hale, 1973). High daytime temperatures of 35-40°C around flowering were also detrimental to fruit set and ovule fertility, and resulted in fewer berries per cluster (Ebadi et al., 1995a; Ewart and Kliewer, 1977; Kliewer, 1977). In Pinot Noir, there was a 23% decrease in fruit set and 21% decrease in ovule fertility when the maximum day-time temperature was 35°C compared to a maximum day-time temperature of 25°C (night temperatures were held constant at 20°C; (Kliewer, 1977)). Keller et al. (2010) reported a 6% increase in fruit set when the ambient temperature at budburst of 10°C was increased to 15°C, whereas a similar temperature increase from 14°C to 19°C resulted in a 12% increase in fruit set. Pollen germination is a temperature-sensitive process in most fruiting plants. In grapevines, Staudt (1982) found that pollen germination in vitro was reduced at a temperature of 15°C, while at a higher temperature of 28°C, pollen germination and subsequent tube growth was at its optimum. This temperature optimum for pollen germination was also found in Cabernet Sauvignon (Rajasekaran and Mullins, 1985). Pollen tube growth commences approx. 30 min after pollination (Staudt, 1982) and is also a temperature-dependent process. Studies on a number of horticultural crops have shown th