Zinc oxide nanoparticles inhibit Penicillium italicum growth and activate defense response of postharvest ‘Shatang’ mandarin fruit

Postharvest disease caused by Penicillium italicum ( P. italicum ) is a major factor limiting the marketability of ‘Shatang’ mandarin fruit. In this study, the antifungal activity of zinc oxide nanoparticles (ZnO NPs) against P. italicum in relation to postharvest disease control of ‘Shatang’ mandarin fruit were investigated. ZnO NPs significantly inhibited mycelial growth and spore germination of P. italicum , with a minimum inhibitory concentration (MIC) of 1.00 mg mL⁻¹ . Microscopic and physiological analyses showed that application of ZnO NPs disrupted membrane integrity, induced excessive accumulation of reactive oxygen species (ROS), increased lipid peroxidation, and reduced intracellular ATP levels, resulting in cell damage of P. italicum . Application of ZnO NPs effectively suppressed blue mold development by reducing lesion diameter and decay incidence in ‘Shatang’ mandarin fruit. Furthermore, ZnO NPs treatment enhanced antioxidant capacity by increasing superoxide dismutase (SOD) and catalase (CAT) activities, reduced H₂O₂ content and malondialdehyde (MDA) accumulation, and increased the activities of phenylalanine ammonia-lyase (PAL) and β-1,3-glucanase (GLU) of ‘Shatang’ mandarin fruit during storage at ambient temperature. In addition, ZnO NPs treatment maintained high vitamin C content and reduced free amino acid accumulation of ‘Shatang’ mandarin fruit during storage. Overall, ZnO NPs exhibited dual functions of direct antifungal activity and induced host resistance, highlighting the potential as an environmentally friendly alternative for postharvest disease management of ‘Shatang’ mandarin fruit during storage.