Antifungal effect of chito-oligosaccharides with different degrees of polymerization

Chitosan, obtained from chitin by partial N-deacetylation, shows little or no toxicity towards mammalian cells, is biodegradable, and non-allergenic. It is known that chitosan may have antifungal properties, but the effect of defined chitosan or chito-oligosaccharides (CHOS) with different degree of polymerization is not well known. The objective of this study was to produce CHOS with different DPn (average degree of polymerization) and determine the most effective DPn of chitosan and CHOS against Botrytris cinerea Pers. Ex Fr. and Mucor piriformis Fischer. In vitro testing showed that CHOS of DPn 23 and 40 had the highest germination inhibition against the tested pathogens. The original chitosan (DPn 206) and a collection of short CHOS (degree of polymerization of 3-10) were significantly (P < 0.01) less effective than CHOS of DPn 23 and 40. M. piriformis M119J showed the most abnormal swelling in presence of CHOS DPn 40, but all abnormally swollen conidia showed further germ tube elongation. In vivo testing showed that CHOS DPn 23 was the most effective in reducing flower infection by two isolates of B. cinerea. Our results show that CHOS inhibit fungal germination and growth and that the effect depends highly on the level of polymerization of the oligomers.