LATE WINTER PRUNING AS A TOOL TO CONTROL VINE YIELD AND ACCUMULATION OF SOLUBLE SOLIDS IN SANGIOVESE GRAPEVINES

The aim of this research was to verify the possibility of limiting vine yield and delaying soluble solid (SS) accumulation by delaying winter pruning (beginning of April and May and June). In a spur-pruned vineyard of Sangiovese located in Italy, winter pruning was carried out on : a) February 1 st (BBCH0); b) March 1st (BBCH0); c) April 2nd (BBCH1); d) May 2nd (BBCH55); e) June 1 st (BBCH64); 80 vines were pruned in each date. Progression of phenological stages as well as bud fertility, vine yield and grape composition were not affected by shifting from a standard timing of pruning (BBCH0) to the pruning performed at BBCH1. By contrast, pruning at BBCH55 (inflorescences swelling and flowers closely pressed together) decreased the number of inflorescences bore on the 2 basal shoots originated from spurs retained with the pruning and determined also a significant reduction of fruit-set and berry and cluster weight. No inflorescences were instead retained on vines pruned at BBCH64 (40% flowerhoods fallen). Vines pruned in early May had a sharp slowdown in ripening and the SS was 1 °Brix lower than the other treatments, while the acidity was higher by about 1.8 g/l. These preliminary results suggest that when a source limitation is induced through a very late winter pruning the floral primordia already initiated during late spring and summer of the previous year partially or totally lose their ability to differentiate into full flowers. At the single bud level, this process is likely accentuated by the strong competition between shoot growth and flower differentiation. If these results will be confirmed also in the next years, this management technique could be applied in all situations where a constraint of vine yield and/or a delayed technological ripeness of the grapes is desirable.