A three-year survey on the impact of pre-flowering leaf removal on berry growth components and grape composition in cv. Barbera vines

Aims: Competitiveness in modern viticulture requires that vineyard management techniques used for crop regulation, besides being economically viable, would assure stable grape composition improvement across variability of genotypes and seasons. Pre-flowering basal leaf removal has previously been shown as an effective tool in controlling yield primarily through a reduced fruit-set. This study aims to evaluate the impact of early leaf removal on the differential growth of the various berry organs (skin, flesh and seeds) as well as the constancy of such effects across season variability and their impact on final grape composition. Methods and results: Pre-bloom defoliation (D) of the first six basal leaves on main shoots was applied to the field-grown Barbera cultivar (Vitis vinifera L.) from 2006 to 2008 and compared with non-defoliated (ND) controls. Over a three-year period, defoliation induced a 34% average reduction in berry number as compared to ND, which led to a notable decrease in fruit-set (-7.6 %), cluster mass (-34%) and yield per shoot (-30%). The berry mass showed a significant relationship with the year factor, as berry size in D shoots was larger, similar and smaller than ND in 2006, 2007 and 2008, respectively. In both treatments, skin mass was closely correlated with berry mass and, within each season and berry mass category, D had relative skin mass values higher than ND. Although the effects were milder in 2007, D induced a significant increase in soluble solids, anthocyanins and phenolics, whereas total acidity was unaffected. Conclusion: These results indicate that, regardless of final berry size, a pre-flowering defoliation favors skin development, which results in higher relative skin mass than ND vines. This effect appears to predominate over variations due to specific weather and cultural conditions along the season and leads to a marked improvement in final grape composition. Significance and impact of study: Repeatability of results implies a strong physiological regulation of this technique and encourages extension of its use in areas where the occurrence of high cropping and large clusters with a high degree of compactness does exist. In a global warming scenario, it is also relevant that the yield decrease and the improvement in overall grape composition are not obtained at the expense of a further reduction in berry acidity.