ACTIVITY OF CHITOSAN WITH DIFFERENT MOLECULAR WEIGHTS ON ALTERNARIA SOLANI

ABSTRACT Chitosan has shown significant antifungal activity against several plant pathogens. The aim of this study was to evaluate the antifungal effect of chitosans on Alternaria solani, the causal agent of early blight in tomato. Three chitosans were used: a commercial one (Qcom), found in food supplement stores; one of low molecular weight (Qbpm; 50 - 190 KDa) and one of medium molecular weight (Qmpm; 190 - 310 KDa), the latter two obtained from Sigma Aldrich. The chitosan were deposited on slides, to assess the conidial germination and germ tube elongation, or incorporated into the BDA medium, to evaluate the mycelial growth of A. solani. The results showed an antifungal activity of these polysaccharides on A. solani, with inhibition of spore germination and mycelial growth of 85% and 50%, respectively, when used at concentrations of 0.125 mg/mL and 0.5 mg/mL. The molecular weight has not influenced the in vitro activity of chitosan.