Ginkgo biloba sarcotesta extract suppresses Alternaria alternata via membrane disruption and oxidative damage: a dual-mode antifungal mechanism.

Alternaria alternata is a major postharvest pathogen of apples, capable of producing multiple mycotoxins that pose significant health and safety risks. This study evaluated the antifungal activity and underlying mechanisms of Ginkgo biloba sarcotesta extract (GFSE) against A. alternata in vitro and in vivo. Among three types of tested extracts, GFSE exhibited the strongest inhibitory effect on mycelial growth, with a calculated IC50 of approximately 477 mg/L. Mechanistic assays revealed that GFSE disrupted cell membrane integrity, as evidenced by increased electrolyte leakage and enhanced efflux of intracellular proteins and nucleic acids. GFSE also induced oxidative stress, indicated by elevated levels of hydrogen peroxide and malondialdehyde, along with a transient upregulation of antioxidant enzymes (SOD, CAT, POD). However, higher GFSE concentrations overwhelmed the antioxidant defense system, leading to redox imbalance. In parallel, the activities of pathogenicity-related enzymes, polyphenol oxidase (PPO), polygalacturonase (PG), and pectin lyase (PL), were significantly reduced in a concentration-dependent manner, suggesting impaired fungal virulence. In vivo validation on artificially inoculated apples demonstrated that GFSE effectively suppressed lesion expansion and disease incidence. Furthermore, GFSE treatment enhanced the activities of defense-related enzymes in apple tissues, including POD, CAT, PAL, and GLU, supporting the induction of host resistance. GFSE exerts a dual antifungal action by disrupting membrane integrity and inducing oxidative stress, which overwhelms the fungal antioxidant defenses and inhibits the activity of virulence-associated enzymes in A. alternata. It also enhances host resistance by upregulating defense-related enzymes in apple tissues. These findings uncover a novel antifungal mechanism that integrates oxidative disruption with anti-virulence interference, highlighting the potential of GFSE as a bio-based alternative for postharvest disease control.