Effect of leaf to fruit ratio on grape and wine composition in a minimally pruned vineyard

Abstract

There is some evidence that sugar accumulation is retarded in minimally pruned vines. This may be caused by an excessive yield (i.e. low leaf to fruit ratio) that could affect grape enological quality.  Our goal was to evaluate the effect of crop load on grape and wine composition for Cabernet Sauvignon under minimal pruning during two seasons (2011-12 and 2012-13). The vineyard was located in San Juan, Argentina. Treatments imposed at veraison were based on the % of cluster thinning: control (C) 0%, T1 50% and T2 75%. The leaf to fruit ratio (LFR) (m² kg^-1) required for maximum level of total soluble solids (24 Brix) ranged from 0.8 to 1.3 m²  kg^-1. Yield components (cluster weight, number of berries per bunch and berry weight) were not significantly affected by cluster thinning in both seasons. The anthocyanin content in berry skins varied between seasons (522 mg kg ^-1 in 2013 and 854 mg kg^-1 in 2012), while no effects of treatment nor season were observed in the wines. Berry skin total polyphenol index (TPI) was not affected by cluster thinning nor season, and both had impact on TPI in wine. In 2011-12 TPI was higher than 2012-13. Control had lower values (36) compared with T2 (48). Relationships among LFR and anthocyanins and TPI in skins and wine were weak. Our results suggest that in San Juan vineyards under minimal pruning, the growing season had a stronger influence on fruit and wine quality than the LFR.