|Authors: ||M. Keller, L.J. Millis, J.M. Tarara, J.C. Ferguson|
|Keywords: ||Vitis vinifera, vigor, leaf area, fruit set, yield components, fruit quality|
Bud temperature during budbreak of mature, field-grown ‘Cabernet Sauvignon’ vines was modified 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 decreased with decreasing 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.
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