In many cultivars of Vitis vinifera periods of mild water stress during ripening are thought to increase grape quality for winemaking, even though yields may be negatively affected. Because abscisic acid (ABA) is involved in the signaling of water stress in plants, we examine the effects of the ABA signal being given without the concomitant water stress. ABA at 250 mg l -1 was sprayed weekly or biweekly from bud-burst until harvest onto the leaves of vineyard-grown plants of cv. Cabernet Sauvignon. For ABA-treated plants berry yield per bunch and per plant was significantly increased (1.5-to 2.0-fold) across three consecutive harvests (2005 through 2007). Number of berries per bunch and per plant was the primary basis for the significant crop increases, although bunches per plant also tended to increase (1.1-to 1.3-fold) across all three harvests. Other parameters assessed included number of internodes, shoot length, leaf area, leaf water potential at midday, photosynthesis, and stomatal conductance. These parameters showed no significant change with ABA treatment, although shoot length tended to be reduced, as was leaf area relative to control plants. The significantly increased fruit yields were thus accomplished without accompanying increases in leaf photosynthesis and leaf areas. Juice at harvest had equal levels of sugars (Brix) and somewhat higher levels of anthocyanins and total polyphenols relative to control values. The two latter trends continued for the resultant wine across two vintage years. In conclusion, three seasons of experimental trials have demonstrated that ABA application can significantly enhance yield per plant in the field-grown grape (cv. Cabernet Sauvignon) by favoring increased berry set without diminishing the quality of the fruit for winemaking use.

The production of grapevine secondary metabolites can be magnified by abiotic stresses or exogenous abscisic acid. Selected phenolic compounds were determined in grape and wine by gas chromatography/mass spectrometry with the aim to asses the physiological responses of plants submitted to water stress and hormonal treatments. Exogenous abscisic acids as well as postveraison water stress produce differential enhancements on phenolic accumulation on Cabernet Sauvignon grapes and such effects were reflected in wine. Resveratrol and malvidin were enhanced by both abscisic acid and water stress and the improvement produced by such factors was additive. On the other hand, the synthesis of gallic acid, (+) catechin, quercetin and caffeic acid was not stimulated by water deficit. Combined hormonal-water stress treatments produced three positive effects on wine quality; a) increments of blue compounds, b) increments of flavonols and flavan 3-oles that favor copigmentation of wines, c) higher antioxidant compounds concentration with the consequent health benefits.

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