Sulfur dioxide enhances the resistance of postharvest grape berries to gray mold through hydrogen peroxide signaling

Abstract

Gray mold, caused by Botrytis cinerea, presents a serious problem to the table grape industry. Sulfur dioxide (SO₂) can protect berries from pathogenic fungal infections by exerting biological functions, but the underlying mechanisms remain largely unknown. To investigate the mechanism by which SO₂ enhances postharvest grape disease resistance through reactive oxygen species (ROS) pathway, grapes were fumigated with SO₂ (500 μL L⁻¹) and then inoculated with B. cinerea. The results showed that SO₂ effectively inhibited the expansion of B. cinerea on postharvest grapes. SO₂ promoted the transient production of superoxide anions and hydrogen peroxide (H₂O₂) during the initial stage (in the first 9 h) by rapidly increasing the enzyme activities and gene expression of respiratory burst oxidase homologs and superoxide dismutase. From 1–7 d, the ROS and malondialdehyde levels were significantly reduced by SO₂. Further analysis showed that SO₂ can boost the antioxidant capacity of berries (total antioxidant capacity, and ABTS and DPPH scavenging capacities) by promoting ROS scavenging enzyme activities and the ascorbate-glutathione (AsA-GSH) cycle. In addition, the expression of ROS scavenging-related, AsA-GSH cycle-related genes, and VvPRs was effectively upregulated by SO₂. Together with correlation analysis results, we propose that the initial H₂O₂ signal contributes to improved antioxidant capacity and upregulation of VvPRs, which plays a crucial role in strengthening the long-term resistance of postharvest grapes to B. cinerea. In conclusion, SO₂ can enhance postharvest grape resistance to gray mold by leveraging the H₂O₂ signaling pathway, highlighting its pivotal role in activating the defense mechanisms of plants.