Phenological Development, Thermal Requirement, and Quality of ‘BRS Núbia’ (Vitis vinifera L. x Vitis labrusca L.) Grapes on Different Rootstocks

The cultivation of table grapes in Brazil is economically significant, with production influenced by edaphoclimatic factors and rootstock selection. The cultivar ‘BRS Núbia’ (Vitis vinifera L. x Vitis labrusca L.) is a promising alternative; however, its phenological behavior, thermal requirements, and compatibility with different rootstocks under subtropical conditions require further evaluation. This study aimed to assess the duration of phenological stages, thermal requirement, and ripening dynamics of ‘BRS Núbia’ grapevines grafted onto the rootstocks ‘IAC 572 Jales’, ‘IAC 766 Campinas’, and ‘Paulsen 1103’. The experiment was conducted in São Manuel, São Paulo, Brazil during the 2021 and 2022 production cycles using a split-plot experimental design (3 × 2). Evaluations included the duration of phenological stages from pruning to budburst, flowering, fruit set, onset of ripening, and harvest, as well as the ripening curve and thermal accumulation from pruning to harvest. Rootstocks did not significantly affect (p > 0.05) the duration of phenological stages; however, differences were observed between production cycles. The 2022 cycle was longer (167.7 days) compared to 2021 (142.6 days), with greater thermal accumulation (1871.7 GDDs vs. 1743.4 GDDs). The analysis of phenological stages revealed that, across both production cycles evaluated, the ‘BRS Núbia’ cultivar required an average accumulation of 1807.5 growing degree days from pruning to harvest. Soluble solids content ranged from 17.43 to 18.50°Brix, and titratable acidity decreased throughout maturation. The maturation index was highest in vines grafted onto ‘Paulsen 1103’, indicating its positive influence on fruit quality. The ‘BRS Núbia’ grapevine exhibited a mean thermal requirement of 1807.5 growing degree days (GDDs) to complete its phenological cycle, which lasted approximately 150 days under subtropical conditions.