Blue and Transparent Protective Covers Improve Yield, Quality, and Peel Antioxidant Profiles of Vitis vinifera L. ‘Flame Seedless’ Grapes

Uncovered grape cultivation in subtropical regions is constrained by unpredictable premonsoon rainfall, causing strong seasonal variability in yield and fruit quality. This study evaluated the effects of colored protective covers (yellow, blue, and transparent) on yield attributes and fruit quality of ‘Flame Seedless’ grapes, with uncovered vines as control, over two consecutive seasons. Blue cover significantly increased marketable yield (kg/plant) compared with control and yellow covering, while remaining statistically similar to transparent cover. Relative to control, blue cover increased berry weight (28.7%, 6.9%), berry length (12.9%, 4.9%), berry diameter (11.5%, 4.9%), and total soluble sugars (6.9%, 11.0%) in 2021 and 2022, respectively; these increases were smaller in 2022. Titratable acidity increased under all protective coverings, with no differences among cover colors. Across both seasons, total anthocyanin content was highest in control and statistically similar to blue cover, whereas yellow cover reduced anthocyanins (25.4%, 30.8%); total flavonoid and phenolic contents increased under transparent cover (24.8%, 22.7%, and 9.7%, 3.9%, respectively), but were similar to blue cover and control. Blue and transparent covers reduced hydrogen peroxide accumulation compared to yellow cover. Overall, blue and transparent covers improved yield stability and maintained fruit quality important for commercial grape production in subtropical regions.