The susceptibility of some acetylated hardwood species to mould fungi attack - An attempt to objectify the assessment

The resistance of natural and treated with preservative wood to filamentous (mould) fungi (Ascomycota, Fungi Imperfecti) and the efficacy of fungicides in terms of control of discolourations and disfigurements caused by the fungi growing on the wood surface over a very short time is determined by several, mainly descriptive, laboratory methods, very often using a subjective visual grading base. The aim of the research was to evaluate the growth of filamentous fungi on wood samples by comparing a descriptive method and instrumental methods, to attempt to quantify and objectify the assessment of wood susceptibility to mould fungi using as both an example and a model wood acetylated with acetic anhydride and control wood samples of the same species. For 4 weeks samples of beech (Fagus sylvatica), birch (Betula pendula) and poplar (Populus nigra) wood were exposed to a mixture of pure cultures of: Aspergillus niger, Penicillium funiculosum, Paecilomyces variotii, Trichoderma viride and Alternaria alternata fungi or only to Chaetomium globosum fungus. The growth of fungi on the surface of the test samples was evaluated using descriptive (4-grade accepted scale) and instrumental (total colour changes and ergosterol content measurements) methods. The mean descriptive grade of fungal growth was from 2.3 to 3.0 and the instrumental evaluation of the growth was between 8.1 and 31.0 in terms of total colour change and from 152.3 to 437.5 μg 10 cm−2 of ergosterol content. Measurements of the colour changes of the wood surface and ergosterol content show a greater differentiation of wood infestation grades than the evaluation based on descriptive methods.