An investigation was undertaken to compare the antifungal effects caused by chitosan against two selected wood degrading fungi Sphaeropsis sapinea and Trichoderma harzianum on their growth, morphological and ultra-structural characteristics, using differential interference microscopy, epifluorescence microscopy and transmission electron microscopy. The effect of chitosan on fungal morphology was pronounced against both test fungi but was more severe on S. sapinea compared to T. harzianum. Increasing concentrations of chitosan induced excessive branching, vacuolation and a reduction in hyphal diameter. Transmission electron microscopy (TEM), which provided information on cell ultrastructure showed more sever changes in S. sapinea hyphae from chitosan treatment as compared to T. harzianum. The information provided suggests that growth inhibitory effect of chitosan is related to significant alterations in the organisation of vital cell components, and indicated that plasma membrane may be the primary target of chitosan action, and that the two fungi differ in the extent to which they are affected. Fluorescence microscopy provided further indication that the effect of chitosan on fungal hyphae is mediated through alterations in the plasma membrane properties.

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