Inhibitory activity and mechanisms of chitosan against Fusarium avenaceum, a pathogen causing Angelica root rot disease.

The polysaccharide chitosan possesses broad-spectrum antimicrobial properties and has proven effective in controlling various postharvest diseases in fruits. Nevertheless, the fundamental mechanisms underlying its action remain unclear. In this study, the antifungal effects of chitosan with different molecular weights against Fusarium avenaceum, a pathogen causing root rot in Angelica sinensis, were evaluated. Additionally, the potential mechanisms of these effects were explored at the microstructural and transcriptomic levels. Notably, low-molecular-weight chitosan (20 kDa) exhibited superior antifungal activity when compared to high-molecular-weight chitosan (500 kDa and 1000 kDa). The half-maximal inhibitory concentration (IC₅₀) of 20, 500, and 1000 kDa chitosan were 0.2103, 0.2183, and 0.2707 g/L, respectively. Morphological and physiological experiments demonstrated that chitosan can inhibit the growth of F. avenaceum by decreasing spore germination, destroying mycelial morphology and microstructure, and promoting the release of intracellular electrolytes. RNA sequencing revealed considerable changes in the transcriptomic profile of F. avenaceum after chitosan treatment, with 2030 genes being differentially expressed. Subsequent KEGG pathway analysis demonstrated that genes associated with translation, human diseases, and transcription were upregulated in F. avenaceum after chitosan treatment. In contrast, genes associated with carbohydrate and amino acid metabolism, cellular processes, exogenous substance degradation and metabolism, and the metabolism of cofactors and vitamins were downregulated. Collectively, these results indicated that chitosan may influence the growth of F. avenaceum by disrupting protein biosynthesis and key metabolic pathways. These findings highlight the substantial potential of chitosan as an alternative agent for the management of fungal diseases in plants used in Chinese herbal medicine.