Impact of Cluster Thinning on Quality of “Malbec” Grapes in Encruzilhada do Sul-RS

The cultivar Malbec has been present’s good performance and quality in the South Half of Rio Grande do Sul (RS). In this context, we aimed to evaluate the quality of “Malbec” grapes in relation to the phytotechnical, physicochemical parameters and bioactive compounds under different intensities of cluster thinning in Encruzilhada do Sul-RS. The experiment was carried out in a commercial vineyard in the 2015/16 with the cultivar Malbec (Vitis vinifera L.) under rootstock “1103 Paulsen”, with spacing of 2.2 m between rows and 1.1 m between plants. The experimental design was of randomized complete blocks with five replications. The treatment factor tested was the cluster thinning, with four levels (0%, 10%, 30% and 50%), performed in veraison. The evaluated phytotechnical variables were cluster length, cluster fresh weight, berries fresh weight, number of berries, rachis fresh weight. Also what were determined are the number of clusters, production and Ravaz index. The physicochemical variables verified were pH, soluble solids (SS), titratable acidity (TA) and SS/TA ratio. The bioactive compounds were total polyphenols index and total anthocyanins. The appropriate balance between source and sink, by the Ravaz index, occurs to zero and 10% of cluster thinning. The “Malbec” grapes present an increase of the maturation index (SS/TA) at 50% of cluster thinning, due to the low titratable acidity at this level. The total polyphenols index has a larger increment when the plants are submitted to the cluster thinning of 10%, providing a larger quality to the fruits. At all the levels of cluster thinning tested, when compared to the control, there was a greater contribution of total anthocyanins in the berries.