The effect of solubilised, low molecular weight chitosan on established mycelial growth of a range of decay fungi, moulds and staining fungi was investigated using nutrient medium amended with different concentrations of chitosan that ranged from 0.1 to 0.4% weight per volume (%w/v). Also, spore germination of Trichoderma harzianum and Leptographium procerum was examined on chitosan amended nutrient medium using visual and microscopic assessment. The results showed that chitosan affected mycelial growth of a wide range of test fungi which generally showed lower growth rates as the chitosan concentration increased. However, the degree of inhibition exhibited by chitosan varied with fungal species. Under the present test conditions, chitosan was fungistatic, but not fungitoxic, against established mycelium of the staining fungi tested and also two moulds, Botrytis cinera and Cladosporium herbarum, but not against any of the decay fungi tested. Spores of T. harzianum germinated on chitosan amended nutrient medium at all chitosan concentrations tested, except for the highest level (0.2%w/v) used, while L. procerum failed to germinate on 0.15 and 0.2%. Also, T. harzianum and L. procerum spores incubated on 0.15% and 0.2% chitosan failed to germinate when placed onto fresh malt extract agar suggesting fungitoxic activity of chitosan at these higher concentration levels.

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