Antifungal properties of chitosan salts in laboratory media

Some aliphatic carboxylic acids were used to produce chitosan (CS) salts by reaction with CS, and their antifungal activity against three kinds of phytopathogens was estimated by hypha measurement in vitro. The fungicidal assessment showed that all of the CS salts had excellent activity against the tested fungi. Their inhibitory indices were 41.15–64.15, 56.25–76.56, and 35.94–68.75% for Cladosporium cucumerinum (Ell.) et Arthur, Monilinia fructicola (Wint.) Honey, and Fusarium oxysporum sp. Cucumis sativus L., respectively, at 1000 μg/mL; these indices were higher than that of CS. It was confirmed that the amino groups' protonation was important for the antifungal activity of CS derivatives. The substituted groups with stronger electronegativity drew more electrons from the nitrogen atoms in the derivative molecules, which relatively strengthened the polycationic character of the CS derivatives. Therefore, the antifungal activity of the CS salts was improved.