Partial Defoliation ofVitis viniferaL. cv. Cabernet Sauvignon/99 Richter: Effect on Root Growth, Canopy Efficiency; Grape Composition, and Wine Quality

Abstract

<i>Vitis vinifera</i> L. cv. Cabernet Sauvignon/99 Richter was grown under field conditions. The effect of partial defoliation (33%) in the lower half of the canopy at berry set stage, and thereafter at pea-size and veraison, respectively, on root development, distribution, and composition as well as on canopy efficiency, yield, grape composition, and wine quality was investigated. Defoliation evidently stimulated occurrence of fine and extension roots, which may have increased the absorptive capacity of the root system. Root number decreased with increasing depth and roots occurred predominantly in the top 800 mm of the soil profile. Starch was the principal carbohydrate storage form in the roots, irrespective of root size. Starch synthesis appeared not affected by root age. Sucrose and organic acid patterns were similar. Citric and tartaric acids were the main organic acids in roots, followed by malic acid. Elevated sugar and organic acid levels were found in roots of treated vines. The results demonstrate that the remaining leaves of partially defoliated vines were able to sustain normal metabolic functions in the roots. Canopy density was efficiently reduced by partial defoliation, leading to increased light penetration, fruit exposure, and photosynthetic activity of mature and old leaves. Although partially defoliated vines had much less leaf area per gram fresh berry mass at ripeness, yield increased considerably with defoliation at pea-size and veraison. Root density, yield, and cane mass were related. Grape total soluble sugar content was unaffected, but titratable acidity increased and the pH of the must decreased with partial defoliation. Ostensible increases in wine constituents (anthocyanins, phenolics), color density, cultivar character intensity, and overall wine quality were found in wines from treated vines.