Cluster thinning in cv. Verdejo rainfed grown: Physiologic, agronomic and qualitative effects, in the D.O. Rueda (Spain)

Abstract

The control of grape yield can be a critical aspect for grape quality of white varieties, moreover in the conditions of high water limitation that occurs in most Spanish growing regions. In the case of Verdejo variety, it is necessary to know its response to the reduction of the number of clusters per vine in order to regulate the production and improve the grape quality. During the period 2012–2014, the application of cluster thinning has been studied, by means of a treatment (A) of removing 27% of clusters, in comparison with a reference treatment (T) without thinning. The trial has been developed with vines of cv. Verdejo on 110R rootstock, planted in 2006 and trellised on bilateral Royat cordon. Vine distances were 2.60 m × 1.25 m (3077 plants/ ha). Vineyard growing was developed under rainfed conditions in Medina del Campo (Valladolid, Spain), within the D.O. Rueda. The water and physiological response of vines subjected to thinning has been similar to that of the reference vines. The vegetative growth has not shown significant differences between treatments. However, as expected, the cluster thinning resulted in a substantial reduction of grape yield as a direct consequence of the removal of clusters, although the cluster weight was slightly favored by cluster thinning. The quality of grapes has been modified by cluster thinning, in such a way that the sugar concentration has benefited, while the titratable acidity and tartaric acid have been reduced. However, the malic acid and the pH have hardly been affected by cluster thinning, whereas the potassium concentration has clearly increased as a result of cluster thinning.