Effects of shoot number on berry and wine composition (cv. Malbec)

Abstract

A field experiment was conducted to study the effects of shoot number per plant on canopy microclimate, yield components, vegetative growth, berry and wine composition on cv. Malbec vines. The experiment was installed during 2012 season in a commercial vineyard planted in 2000 and located in Luján de Cuyo, Mendoza (Argentina). Vines were spur-pruned and trained in a vertical shoot positioning system (VSP). Four pruning treatments with different number of buds per vine (b vine^-1) were established in winter: T38, T28, T22 and T16 with 38, 28, 22 and 16 b vine^-1 respectively. During early spring, shoot removal was performed to retain only those shoots from the counted buds left during winter pruning. Total leaf area (TLA), berry weight, and yield were measured. Grapes were harvested and wines of each replicate were elaborated, berry and wine composition were analyzed.

No differences in TLA were found among treatments. Vines with fewer shoots grew more laterals and reached similar TLA than those with more shoots. Yields were higher in the T38 (6.2 kg vine^-1) and T22 (6.5 kg vine^-1) than in T16 (4.8 kg vine^-1) whereas T28 showed intermediate values (5.8 kg vine^-1). In the following spring, T22 presented a higher number of flowers per cluster that the other treatments. The leaf area-fruit ratio (LAFR) varied from 0.9 m² kg^-1 (T38, T28, and T16) to 0.75 m² kg^-1 (T22), but no statistical differences were observed. Ravaz Index was higher in the T38 (11.3) and lower in the T16 (7.4). Wine analysis showed that there was an increase in tannins, totals anthocyanin, and total phenols concentration in T16 and T22 suggesting a microclimate effect on berry composition. In conclusion, these results showed that decreasing shoot number from 38 to 22 generated an increase in wine polyphenols concentration without affecting yield. Wine composition was similar between T16 and T22,

but the latter had a much lower yield. Even with no differences in the LAFR, there were differences in berry and wine composition. These results suggest that the distribution of leaf area within the canopy space and type of leaf area (leaf area from main shoots and leaf area from laterals) should be incorporated or taken into account when interpreting this equilibrium indexes.