ABSTRACT This study aimed to assess the effect of rootstocks (IAC 572 and IAC 766) and potassium fertilization at different concentrations (0, 75, 150 and 300 kg·ha-1 K2O) on the phenology and thermal demand of the Niagara Rosada grapevine, and to evaluate the development of chemical traits during maturation stage. The length of the main phenological stages was recorded within two production seasons. Total thermal demand was calculated using the degree-day concept. The berries’ titratable acidity and soluble solids contents were determined during maturation. Results indicated that IAC 572 and IAC 766 rootstocks along with potassium fertilization had no influence on the phenological cycle or thermal demand of the Niagara Rosada grapevine. The production cycle lasted 144 to 148 days with thermal demands ranging from 1,465.2 to 1,615.1 degree-days. For better grape quality, i.e., with a balance between soluble solids and acidity levels, it is estimated that the grape harvest is carried out around 21 to 24 days after the veraison.

ABSTRACT This study aimed to evaluate the productive performance and physicochemical traits of wine grape cultivars (Cabernet Sauvignon, Syrah, Cabernet Franc, Merlot, and Sauvignon Blanc) grafted on two different rootstocks (IAC 766 Campinas, and 106-8 Mgt) under subtropical conditions. The productive components (number of bunches, production per vine, yield, number of berries per bunch, fresh mass, length, and width of berries) and the grape must physicochemical composition (pH, titratable acidity, soluble solids, and maturation index) were determined after four consecutive harvest seasons. Results from analysis of variance and principal component analysis showed that Cabernet Franc and Syrah were generally more productive than the other ones. In addition to that, Cabernet Sauvignon presented the lowest production and the smallest grape berries of all. With regards to rootstocks, IAC 766 induced higher scions yield than 106-8 Mgt; besides that, IAC 766 had greater affinity with Cabernet Franc and Merlot, which was observed by the increase in the number of bunches per vine, larger and heavier bunches, as well as higher soluble solids content and pH value than the ones in 106-8 Mgt. Furthermore, IAC 766 also induced higher soluble solids content and pH value for Cabernet Sauvignon. Results showed similar effects for Syrah and Sauvignon Blanc, regardless of the rootstocks.