Biocontrol effect and mechanism of endophytic fungus Alternaria alternata against root rot of Lycium barbarum

• YBG8 fermentation filtrate exhibits antagonistic activity against Fusarium solani . • AME, altenusin, and altenuene are the primary antifungal components of YBG8. • YBG8 fermentation filtrate had good control effect on Lycium barbarum root rot. Root rot caused by Fusarium solani is a severe soil-borne disease affecting Lycium barbarum (goji berry), which has long been managed through chemical control. However, prolonged reliance on chemical agents can lead to pathogen resistance and environmental risks. Initially isolated from healthy L. barbarum , the strain YBG8 exhibited antagonistic properties against F. solani and was identified as Alternaria alternata . However, the precise antifungal mechanism of YBG8 remained unclear. This study aimed to elucidate the antifungal mechanism and biocontrol effect of the fermentation filtrate of the antagonistic strain YBG8. The findings indicated that the YBG8 fermentation filtrate treatment significantly impeded the radial growth of F. solani , altered its spore surface morphology, and triggered an upsurge in alkaline phosphatase activity. Additionally, YBG8 fermentation filtrate treatment also resulted in heightened levels of malondialdehyde (MDA), increased electrical conductivity, and notable leakage of intracellular proteins and nucleic acids. Assessment with propidium iodide staining validated the disruption of cell membrane integrity. Liquid chromatography-mass spectrometry (LC-MS) analysis of the YBG8 fermentation filtrate unveiled 252 metabolites, encompassing coumarins, carboxylic acid derivatives, purine nucleosides, and others, with 15 constituents exhibiting concentrations exceeding 10 μg/mL. Subsequent analysis identified alternariol methyl ether as the predominant polyketide compound, with a concentration of 130.086 μg/mL. Additionally, altenusin, a diphenyl ether derivative, and altenuene, a cell wall synthesis inhibitor, were also detected at concentrations of 26.664 μg/mL and 18.291 μg/mL, respectively. These findings collectively suggest that the YBG8 fermentation filtrate inhibits the growth of F. solani through multiple pathways, such as cell wall disruption, oxidative stress induction, and membrane function interference. Alternariol methyl ether, altenusin, and altenuene are presumed to be the primary antimicrobial agents in the fermentation filtrate. This investigation illustrates that the YBG8 fermentation filtrate exerts potent antimicrobial effects through a dual-targeting strategy that disrupts both cell wall and membrane systems. These findings establish a theoretical framework and material basis for the development of environmentally friendly biopesticides.