Influence of Pre- and Postveraison Water Deficit on Synthesis and Concentration of Skin Phenolic Compounds during Berry Growth of Vitis vinifera cv. Shiraz

Abstract

The effects of various degrees of water deficit on the synthesis and concentration of skin phenolic compounds (flavan-3-ols, anthocyanins, and flavonols) on growing Shiraz berries were studied. Different periods and levels of water stress were applied to a model system of cultured vines in containers. Treatments consisted of two levels of early water deficit between anthesis and veraison (S1 = strong, S2 = medium) and a late strong water deficit between veraison and harvest maturity (S3). Biosynthesis of phenolic compounds, expressed per individual berry, appeared to depend on the level of water deficit and on the stage at which it was applied. Biosynthesis of flavonols was greater for S2 and S3 than for the control and S1; biosynthesis of flavan-3-ols (total tannins) was reduced in the early water deficit samples; and biosynthesis of proanthocyanins and anthocyanins increased only for S3, the late water deficit treatment. In all cases, water deficit increased the degree of tannin polymerization. Berry size was reduced by the application of different water deficits: S1-, S2-, and S3-treated berries attained 47, 68, and 85%, respectively, of control berry weight. Berry size reductions increased the skin-to-pulp weight ratio and, consequently, the concentration of the different phenolic compounds within the berry skin, which was always greater in the water-deprived berries than in the control berries (except for total tannins in the case of S1). These results confirm two types of berry responses to water deficit: an indirect and always positive effect on the concentration of phenolic compounds due to berry size reduction and a direct action on biosynthesis that can be positive or negative depending on type of phenolic compound, period of application, and severity of water deficit.