New bio-protector for combating heat and light stress across different grape cultivars and environments

Direct sunlight on berries during ripening enhances flavonoid accumulation in the skin, acting as a defence against UV damage and lipid peroxidation. However, these flavonoids, particularly quercetins, influence bitterness, astringency, and deposit formation in wines. This study evaluated the effectiveness of a new bio-protector (NBP), composed of β-carotene and α-pinene, in reducing flavonol levels in grape skins across cultivars and locations, applied by spraying the basal part of the canopy, completely wetting all leaves and grapes. In 2023, trials were conducted in non-irrigated vineyards with Sangiovese and Trebbiano Toscano in Umbria, and Grillo and Carricante in Sicily. In 2024, Merlot and Grenache in South Australia were included. Thirty vines per vineyard were treated with NBP (2 % in water) at veraison (BBCH 81), while 30 control vines received water. In two vineyards, basal leaf removal was performed a day before NBP application. Gas exchange measurements, yield components, grape composition, and berry phenolic and carotenoid profiles were recorded. NBP-treated leaves showed reduced photosynthesis, transpiration, and stomatal conductance but no impact on yield, cluster weight, or berry weight. NBP delayed technological ripening, reducing sugar accumulation and increasing acidity. Flavonol profiles revealed quercetin-3-O-glucoside (60–74 %) and quercetin-3-O-glucuronide (28–38 %) as dominant, with Sicilian cultivars showing 10 times lower flavonol levels than central Italian cultivars. Basal leaf removal increased quercetin and kaempferol by three–four times. NBP significantly reduced flavonol accumulation in berry skins across cultivars and sites, delaying ripening without causing dehydration or sunburn damage. This could reduce wine bitterness and astringency and allow later harvests, especially in red cultivars. Exogenous β-carotene application did not increase berry skin carotenoids, but the correlation between flavonol accumulation and irradiance was confirmed. NBP’s potential to mitigate the impact of rising temperatures on grape and wine quality is promising.