Fruit Ripening in Vitis vinifera L.: Responses to Seasonal Water Deficits

Abstract

The response of fruit ripening to vine water status was investigated in a hillside Cabernet franc vineyard in the North Coast region of California. Treatments were imposed by drip irrigation at 2 x the standard practice rate (continual) to maintain high water status, by withholding water before (early deficit) or after (late deficit) veraison, or by withholding water throughout most of the season (full deficit). Midday leaf water potential of continual vines decreased from approximately-0.3 MPa before bloom to -1.13 MPa at veraison and to -1.32 MPa at harvest. Leaf water potentials of early deficit and late deficit vines were approximately 0.3 MPa more negative than continual vines at veraison and harvest, respectively. After veraison, water status of early deficit vines recovered to the level of continual vines. These moderate differences in water status at different phenological stages altered fruit composition at harvest. The concentrations of phenolics in juice and dermal extracts and of anthocyanins in dermal extracts were increased by all treatments which withheld water. Malate concentrations were significantly lower in treatments which imposed low vine water status before veraison. Low vine water status after veraison increased proline concentration significantly. There were no treatment effects on the onset of veraison, the duration of ripening, juice pH, or potassium levels, and little difference in °Brix or titratable acidity. Thus, irrigation to obtain seasonal water deficits may offer a cultural control of winegrape composition without significant effects on the time required to reach maturity.