Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 6/16/2005
Publication Date: 8/30/2005
Citation: Keller, M., Mills, L.J., Tarara, J.M., Ferguson, J.C. 2005. Effects of budbreak temperature on seasonal shoot and fruit growth in grapevines. Acta Horticulturae. 689:183-188. Interpretive Summary: It is important to understand the basic physiology of the development of grapevine shoots and grape berries in the vineyard environment. From this basic knowledge, further applied research can be conducted with the goal of developing management practices that optimize yields for wine grape growers. Maximum yield is not necessarily a goal of wine grape production; growers and wineries work to achieve high quality grapes at economically sustainable yields. The balance between vegetation and fruit (green shoots and grape berries) influences both yield and quality. Temperature is an environmental variable that has major effects on both shoot and fruit development in the grapevine. Thus, an experiment was conducted to determine the effects of dormant bud temperature on subsequent shoot growth and number of flowers and grape berries produced. Dormant buds were exposed to cool, ambient, warm, and hot temperatures. Warming the buds before budbreak (shoot emergence) resulted in an increased rate of shoot growth throughout the season and higher fruit yield at harvest. There were only minor differences in grape quality between grapes from heated buds and those from chilled buds. The experiment suggests that spring temperatures before budbreak can have lasting effects on grapevine vegetation during that season, but only minor and indirect effects on fruit growth and yield.
Technical Abstract: Bud temperature of mature, field-grown 'Cabernet Sauvignon' vines was modified during budbreak using a forced-convection cooling/heating system. Four temperature regimes were applied individually to 10 exposed buds in 2002 and 2003: cool (ambient-5°C), ambient, warm (ambient+5°C), and hot (ambient+10°C). Treatments were applied from the beginning of sap flow until individual flowers were visible on inflorescences. Increasing bud temperature advanced budbreak and dramatically accelerated shoot growth. Differences in shoot development initiated during budbreak remained throughout the season and were due to greater vigor of the main shoot, stimulation of lateral growth, and increased leaf-area development. However, there was no consistent treatment effect on the number of flowers per cluster. Fruit set decreased with increasing flower number, but also increased with increasing bud temperature. Despite the decrease in the number of berries per cluster with lower bud temperature, bud cooling also reduced berry weight compared with other treatments. Therefore, the hot treatment resulted in 2.5-fold greater yields per shoot than the cool treatment. Differences in fruit composition were comparatively minor, but grapes from the cool treatment had the highest concentrations of sugar, acidity, and color, whereas those from the hot treatment had the lowest sugar, acidity, and color. These results suggest that differences in temperature during budbreak may dramatically alter seasonal vegetative growth, while effects on reproductive growth are minor and may be indirect due to differences in shoot growth.