Multi-pathway antifungal mechanism of isobavachalcone against Epicoccum sorghinum unlocks new green strategies for tea.

Fungal drug resistance and pesticide residue in tea plantations have become urgent problems, driving the development of eco-friendly antifungal agents. Isobavachalcone (IBC), a natural chalcone flavonoid, exhibits broad-spectrum antifungal activity, yet its precise mode of action against tea pathogens remains elusive. This study evaluated the antifungal potential of IBC against four major tea pathogenic fungi and elucidated its mechanism against the most sensitive species, Epicoccum sorghinum. IBC significantly inhibited mycelial growth with an EC50 of 16.95 mg/L and showed a 53.98% curative effect in detached leaf assays at 300 mg/L. Microscopy revealed severe hyphal shrinkage, cell wall/membrane damage, and mitochondrial swelling with cristae dissolution. Physiological analyses confirmed that IBC compromised cell envelope integrity, evidenced by increased electrical conductivity, nucleic acid leakage, elevated extracellular alkaline phosphatase activity, and enhanced lipid peroxidation. Furthermore, IBC treatment collapsed mitochondrial membrane potential and triggered excessive reactive oxygen species (ROS) accumulation. Integrated transcriptomic and metabolomic analyses, including correlation network analysis, revealed a multi-pathway antifungal mechanism: IBC disrupts mitochondrial redox homeostasis, leading to the collapse of energy metabolism (TCA cycle and oxidative phosphorylation), which in turn triggers a lethal systemic cascade involving cell wall and membrane damage. Specifically, this cascade involves the inhibition of ergosterol biosynthesis, depletion of key TCA cycle intermediates, and accumulation of L-palmitoylcarnitine, indicating blocked fatty acid β-oxidation. RT-qPCR validation confirmed the reliability of transcriptome data. Collectively, IBC exerts fungicidal activity through a multi-site mode involving cell envelope disruption, mitochondrial dysfunction, and global metabolic collapse. These findings provide novel insights into chalcone antifungal mechanisms and support IBC as a promising green fungicide for sustainable tea disease management.