In vitro studies were undertaken to evaluate the synergy between chitosan and selected GRAS (Generally Recognised As Safe) compounds against two sapstain fungi Sphaeropsis sapinea and Leptographium procerum. Bioassays performed on nutrient medium suggested that some of the GRAS compounds tested including sodium benzoate, potassium sorbate and ascorbic acid had a synergistic effect when combined with chitosan against both test fungi. However the degree of activity varied depending on concentration used and species tested. Synergy between chitosan and sodium benzoate/or potassium sorbate was also apparent when bioassays were performed on sterile wood discs. After 3 weeks of incubation, discs dip-treated with either 1.5% chitosan or 0.5% sodium benzoate/or potassium sorbate had 60%-100% coverage by the test fungi. This was reduced to 5-10% fungal coverage on discs treated with the combination of chitosan and sodium benzoate and virtually no growth was observed on discs dip-treated with chitosan and potassium sorbate at the concentrations tested. Furthermore, fungicidal activity against S. sapinea was confirmed after re-culturing wood pieces taken from these discs on fresh malt-agar medium.

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