Grapevine Response to Pyroligneous Acid: Antifungal, Physiological, and Biochemical Impacts

Botrytis cinerea is a major fungal pathogen causing significant economic losses in grapevines worldwide. To address the environmental concerns associated with overreliance on synthetic fungicides, this study investigated the antifungal efficacy of varying concentrations of pyroligneous acid (PA) (0, 2, and 4%) compared to a commercial fungicide (Switch^®) against B. cinerea in grapevines (Vitis vinifera ‘Himrod’), as well as its physiological and biochemical responses. Our preliminary in vitro assays using the poisoned food method showed that PA significantly (p < 0.05) inhibited B. cinerea mycelial growth by approximately 0.70-, and 1-fold, respectively, compared to the 0% PA during the three weeks of observation. The results also demonstrated that the 2% PA and 4% PA treatments, as well as the Switch^® application, significantly (p < 0.05) reduced average lesion length by 0.19-, 0.52-, and 0.85-fold, respectively, compared to the untreated plants with Botrytis alone. Both the 4% PA and Switch^® significantly (p < 0.05) increased the maximum quantum efficiency of photosystems II (F_v/F_m) and potential photosynthetic capacity (F_v/F_o) by approximately 0.02-fold and 0.1-fold, respectively, compared to the untreated plants with Botrytis alone. The 2 and 4% PA treatments also increased total carotenoids and flavonoids. Further molecular studies are recommended to elucidate the mechanisms underlying the observed physiological and biochemical changes.