ANTIFUNGAL ACTIVITY OF CHITOSAN ON POSTHARVEST PATHOGENS - INDUCTION OF MORPHOLOGICAL AND CYTOLOGICAL ALTERATIONS IN RHIZOPUS-STOLONIFER

The effect of chitosan preparations with different levels of deacetylation and other polyanions on the growth of post-harvest pathogens was investigated. Chitosan markedly reduced the radial growth of all the fungi tested, with a greater effect at higher concentration. Chitosan was more effective than N,O-carboxymethylchitosan, polygalacturonate or D-glucosamine, and its inhibitory activity appeared to increase with the level of deacetylation. In addition to inducing cellular leakage of amino acids and proteins in Botrytis cinerea and Rhizopus stolonifer, chitosan also caused morphological changes in R. stolonifer. The ultrastructural study showed that chitosan caused deep erosion of the cell wall as well as increasing the cell-wall thickness. Although chitosan treatment did not affect chitin distribution in R. stolonifer wall, it stimulated the activities of chitin deacetylase, an enzyme involved in the biosynthesis of chitosan. This may well upset the balance between biosynthesis turnover of chitin, thereby rendering the cell wall more viscoelastic.