Antifungal Efficacy of Strawberry Leaf Extract and Its Effects on Conidia Cell Integrity of Postharvest Citrus Pathogens

Postharvest diseases caused by fungal pathogens lead to significant economic losses in citrus production. The intensive use of synthetic fungicides has triggered the emergence of resistant strains and environmental contamination, emphasizing the need to search for sustainable alternatives. This study evaluated the antifungal efficacy of a strawberry leaf aqueous extract (SLE) against local isolates of citrus phytopathogens such as Penicillium digitatum and P. italicum (both fungicide−sensitive and fungicide−resistant) and Geotrichum citri-aurantii. In vitro assays showed complete inhibition of mycelial growth for all pathogens on potato dextrose agar plates supplemented with 0.05 g·mL−1 SLE after 5 days at 24 °C. Furthermore, total inhibition of conidial germination and loss of viability were achieved at 0.1 g·mL−1 following an 8 or 24 h exposure period respectively. To elucidate the underlying mode of action, membrane integrity and cellular ultrastructure were examined. SYTOX™ Green staining revealed increased membrane permeability, and transmission electron microscopy showed marked intracellular disorganization in SLE-treated conidia from all phytopathogens. These findings were further validated through in vivo assays using artificially inoculated lemons where a significant reduction in green mold incidence was demonstrated. Overall, SLE exhibited broad-spectrum efficacy against major citrus postharvest pathogens, effectively overcoming established fungicide resistance. Our results could position SLE as a promising biocontrol agent for sustainable fruit preservation.