Quality and antioxidant activity of Isabel Precoce grapes installed on different training systems and rootstocks in warmer seasons in a tropical semi-arid region.

Production system and environmental factors might cause changes in grapevine physiology, affecting grape yield, quality, phenolic composition, and antioxidant potential. The aim of this study was to characterize the quality and antioxidant potential of 'Isabel Precoce' grapes on different training systems and rootstocks in warmer seasons, in tropical conditions. Experimental design was in randomized blocks, in sub-subplots through time and four replicates. Three training systems (overhead trellis, lyre and vertical shoot positioning - VSP) and two rootstocks (‘IAC 572’ and ‘IAC 766’) were studied in the production cycles from July to October, 2017 and from July to October, 2018 in the Submedium of São Francisco Valley. Berry weight; cluster weight; color attributes; berry resistance to compression (COMP); titratable acidity; soluble solids; total soluble sugars (TSS); yellow flavonoids; total anthocyanins; total extractable polyphenols and antioxidant activity by ABTS●+ and DPPH● free radical capture methods were analyzed. Lyre and VSP resulted on increases of 6% and 17% in berry weight and COMP, respectively. Moreover, differences between production cycles were more intense for both variables. In production cycle from July to October 2017, lyre and VSP systems provided increases of 2 g 100 g-1 of TSS and higher anthocyanin and yellow flavonoid contents, while grapes trained in VSP had higher antioxidant activity. Mean values of anthocyanins reached 529.34 mg 100 g-1 in grapes harvested in October 2017. Some grape quality and chemical components showed high variation in warmer seasons of sucessive years, according to training system or rootstock and their combinations