3‐Methyl‐1‐Butanol Enhances Postharvest Resistance of Red Grapes to <i>Botrytis cinerea</i> by Activating Phenylpropanoid Metabolism and Antioxidant Defences

Grey mould, caused by Botrytis cinerea, is a significant postharvest disease leading to substantial economic losses in the grape industry. This study investigated the regulatory mechanism of 3-methyl-1-butanol (3M1B), a yeast volatile substance, on B. cinerea resistance in red grapes (Vitis vinifera L.). Our findings demonstrate that 3M1B induces resistance by modulating phenylpropane and reactive oxygen species (ROS) metabolism. Specifically, treatment with 50 μL mL^-1 3M1B effectively inhibited B. cinerea lesion development on red grape surfaces and delayed fruit quality deterioration. Further analysis revealed that 3M1B enhanced the activity and gene expression of key enzymes in the phenylpropane pathway, including phenylalanine aminase, cinnamic acid-4-hydroxylase and 4-coumaric acid coenzyme A ligase, promoting the accumulation of related secondary metabolites. Furthermore, ROS metabolic analysis showed that 3M1B treatment reduced hydrogen peroxide and superoxide anion accumulation. This treatment also stimulated the activity and transcriptional levels of antioxidant enzymes involved in ROS clearance, and synergistically improved oxidative stress through the glutathione-ascorbic acid cycle. These results indicate that 3M1B maintains postharvest quality of red grapes by enhancing phenylpropane and ROS metabolism.