The antifungal activity of chitosan on a common fungal phytopathogen, Sclerotinia sclerotiorum, and the control effect on
sclerotinia rot of carrot were investigated. Mycelial growth and fungal biomass were strongly inhibited by chitosan. Using
propidium iodide stain combined with fluorescent microscopy, the plasma membrane of chitosan-treated S. sclerotiorum
mycelia was observed to be markedly damaged. Concomitantly, protein leakage and lipid peroxidation was also found
to be significantly higher in chitosan-treated mycelia compared to the control. Chitosan provided an effective control of
sclerotinia rot of carrot, with induction of activity of defense-related enzymes including polyphenoloxidase and peroxidase.
These data suggest that the effects of chitosan on sclerotinia rot of carrot may be associated with the direct damage to the
plasma membrane and lipid peroxidation of S. sclerotiorum, and the elicitation of defense response in carrot.