| Summary: | In this thesis I hypothesized that the graying of wood exposed outdoors is due to the presence of melanized fungi that are relatively resistant to UV-light. To test this hypothesis I examined the color and chemical changes at wood surfaces exposed to the weather and filtered solar radiation, isolated and identified fungi colonizing wood samples by DNA analysis and microscopy and examined the survival, growth and melanin production of staining fungi under UV, visible or no light. The ability of isolated fungi to decay wood was also tested by evaluating changes in the microstructure, mechanical, viscoelastic and chemical properties of spruce and lime wood incubated with fungi. Finally, I tested a novel non-biocidal approach to reduce the staining of wood by fungi, which employed melanin biosynthesis inhibitors (MBIs). My results support the general hypothesis (above) and reveal that weathered wood surfaces are grayed by the interactive effects of solar radiation and fungal colonization. UV-radiation increased the production of melanin by the fungus most frequently isolated from weathered wood (Aureobasidium pullulans), which leads to darker weathered wood surfaces. Decay tests showed that species of Cladosporium, Coniochaeta, Epicoccum, Lewia, Mollisia and Phialocephala, were able to degrade wood tissues. In artificial media, MBIs in combination with UV-radiation blocked the growth of staining fungi, but at wood surfaces MBIs reduced fungal staining irrespective of the type of light that samples were exposed to. I conclude that UV-radiation and melanized fungi interact to influence the color of weathered wood surfaces. Degradation of wood by surface fungi is possible, but the extent of damage probably depends on the presence of conditions that favor microbial decay. Finally, the use of MBIs is a promising approach to control graying of weathered wood surfaces, but further research is required to optimize the treatments and test them outdoors. === Forestry, Faculty of === Graduate
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