Antifungal effect and mechanism of magnolol against the Alternaria tenuissima causing leaf blight on Schisandra chinensis

Leaf blight on Schisandra chinensis caused by Alternaria tenuissima severely impacts its yield and quality. Plant-derived bioactive compounds serve as a key component of biological control systems, offering promising solutions for environmentally friendly disease management through their natural and sustainable properties. This study systematically investigated the antifungal activity of magnolol, a key bioactive compound from Magnoliae Officinalis Cortex (“Houpo” in Chinese), against A. tenuissima and elucidated its underlying mechanisms. In vitro assays demonstrated that magnolol dose-dependently inhibited mycelial growth, achieving a 93.4% inhibition rate at 100 µg/mL. The field experiments showed that after treatment with magnolol for 14 days, the control effect of the leaf blight on S. chinensis was 76.8%. Magnolol compromised the cell membrane integrity of A. tenuissima and induced dynamic changes in antioxidant enzyme (CAT, POD, SOD) activities, characterized by an initial increase followed by suppression. Transcriptome analysis revealed that magnolol induced a total of 4,767 differentially expressed genes (DEGs) of the A. tenuissima , of which 2,510 were upregulated and 2,257 were downregulated. Notably, DEGs involved in toxin biosynthesis, ATP synthesis and ergosterol biosynthesis exhibited an overall downregulation trend in the magnolol treatment group. Meanwhile, reactive oxygen species (ROS) metabolism-related genes were markedly disrupted. Overall, magnolol exerts its antifungal effects by disrupting cell membrane integrity, inhibiting key pathways of toxin and energy metabolism, while also disrupting the homeostasis of ROS metabolism. This study provides a theoretical foundation for developing new plant-derived pesticides based on magnolol.