Effects of cluster thinning on grape composition: preliminary experiences on Sangiovese grapevines

Effects of cluster thinning on grape and wine quality has been widely explored in relations to several factors (cultivar, time of application, environmental conditions). Results have shown that yield reduction and quality improvement are not always strictly related, especially when unthinned vines are characterized by a balanced vegetative/productive ratio. The trial was conducted over a two-year period (2003-2004) on cv Sangiovese, spur-pruned cordon trained (1 m x 2.8 m spaced) in a hillside vineyard near Bologna. In the first year the vines were adjusted to 15 clusters per plant after fruit set and at veraison the plants were randomly divided in three groups: a) T1, thinned at 10 clusters per vine; b) T2, thinned at 5 clusters per vines and c) CK, unthinned vines. The same treatments were applied in the second year of experiments. The two years average data as concern the ratio between total leaf area and production at harvest was 2.0, 3.5 and 1.3 m2/kg in T1, T2 and CK respectively, while sugar content of grapes (°Brix) was 22.7 in T1, 23.1 in T2 and 21.8 in CK. Berry skin analysis showed a tendency to a decreasing in trisubstituited anthocyanins (delphinidin-3-glucoside, petunidin-3-glucoside and malvidin-3-glucoside) and an increasing of disubstituited anthocyanins (peonidin-3-glucoside and cyanidin-3-glucoside) in thinned vines, as compared to control, especially in 2004. In the same year total anthocyanins were 1685 mg/kg, 1680 mg/kg and 1243 mg /kg in T1, T2 and CK respectively. Sensorial analysis of wine obtained from microvinification in 2003 showed no significative differences between the treatments. Microvinifications of musts and evaluations of 2004 wines are actually in progress.