Chitosan and salicylic acid enhance postharvest resistance in grapes via integrated modulation of antioxidant, antifungal, and anti-senescence pathways

The limited postharvest life of grapes poses a significant challenge to their commercial value. This study employed an integrated approach, combining in vitro and in vivo antifungal assays, storage experiments at two temperatures (4 and 26 °C), and physiological and molecular analyses, to elucidate the effects and underlying mechanisms of chitosan (CTS), and salicylic acid (SA) on preserving the quality of 'Shine Muscat' grapes. The results demonstrated significant antifungal activity of both CTS and SA against Aspergillus niger, with 2% CTS inducing hyphal deformities, and 1.0 mmol/L SA strongly inhibiting conidiation. Under storage conditions, 2.0% CTS at 4 °C most effectively reduced decay, fruit drop, and weight loss, while enhancing antioxidant enzyme activities (SOD, CAT) and minimizing malondialdehyde accumulation. Conversely, at 26 °C, 1.0 mmol/L SA was superior in alleviating quality deterioration by activating the antioxidant system and delaying acid degradation. Quantitative analysis revealed that the optimal treatments (2.0% CTS and 1.0 mmol/L SA) upregulated genes related to phenylpropanoid metabolism (VvPAL), antioxidant defense (VvCAT, VvAPX, VvGR), and defense responses (VvBGLU, VvGST), while downregulating senescence- and browning-related genes (VvPPO, VvPOD, VvLOX). Mechanistically, CTS primarily formed a protective semipermeable coating to reduce water loss and pathogen contact, whereas SA enhanced membrane stability and systemic antioxidant capacity. These findings elucidate the distinct mechanisms of CTS and SA and provide a theoretical basis for developing targeted, eco-efficient preservation strategies based on storage temperature.