Impact of trellis systems and rootstocks on global phenolic composition and antioxidant activity of Isabel precoce grapes produced during rainy seasons in semi-arid region of Brazil.

Crop components, such as trellis systems, might affect solar radiation uptake by grapevines while others, such as rootstocks, influence the vigor of the scion. Proper management provides a suitable reproductive and vegetative balance that could influence the chemical composition of grapes. This study aimed to characterize the global phenolic composition and antioxidant activity of ?Isabel Precoce? grapes raised for juice, growing under different trellis systems and rootstocks, in rainy seasons, in semi-Arid conditions in Brazil. With a randomized block experimental design and split-split plots over time, the overhead trellis, lyre, and vertical shoot positioning systems and two rootstocks (?IAC 572? and ?IAC 766?) in the harvest seasons of January-May, 2017 and January-May, 2018 were studied. Trellis systems, rootstocks, harvest seasons and their interactions affected the characteristics of the grapes. The treatments with equivalent responses in the seasons defined the specific characteristics of the grapes. The rootstock 'IAC 766' provided greater bunch weight and lower acidity to the ?Isabel Precoce? grapes, while 'IAC 572' induced higher soluble solids contents. In both seasons, there was lower variation in berry resistance to compression and polyphenol and anthocyanin contents in grapes from grapevines grown on an overhead trellis. In turn, the use of lyre provided high antioxidant activity by the ABTS?+ method in 2018. The highest antioxidant activity by the DPPH? method was due to the association of overhead trellis and 'IAC 766?. With the use of the overhead trellis, equivalent phenolic compounds and antioxidant activity during the seasons resulted in a uniform quality