Fungistatic activity of modified chitosans against Saprolegnia parasitica.

Five chemically modified chitosans were tested for their antifungal activities against Saprolegnia parasitica by the radial growth assay in chitosan-bearing agar, and the fungal growth assay in chitosan-bearing broth. Results indicated that methylpyrrolidinone chitosan, N-carboxymethyl chitosan and N-phosphonomethyl chitosan exerted effective fungistatic action against S. parasitica: in fact the radial growth was nil for 50 h at 20 degrees C, and the fungus was precipitated when the Bacto YM broth contained one of these chitosans. Electron microscopy observations (TEM and SEM) provided evidence of ultrastructural alterations, damaged fungal structures, uptake of modified chitosans, and hyphal distortion and retraction.