To lengthen the service life of wood coated with transparent and semi-transparent finishes, better methods of preventing colonization by black stain fungi are needed. These fungi generally lack the ability to metabolize lignocellulose, but are capable of growing on a wide range of carbon sources, including lignin breakdown products formed by photodegradation. This project is investigating whether using heartwood with low nutrient content and preventing the accumulation of photodegradation products, which black stain fungi use as a carbon source, could limit colonization by these fungi.
In the present work, spruce heartwood, unexposed and exposed to intense UV and visible light, was extracted with water or ethanol. Larger amounts of extractive were obtained from samples exposed to UV and visible light. HPLC analysis revealed both qualitative and quantitative differences between unexposed and exposed extracts. These extracts were then added as carbon sources to fungal growth media. Growth rates were similar on extracts from both unexposed and UV and visible light exposed wood, and in some extracts similar to growth rates on control media with no added carbon. However, mycelia were much denser on media containing spruce heartwood extracts than on control media. There were no clear differences between the colony morphology of black stain fungi growing on media containing unexposed extracts and UV and visible light exposed extracts. This suggests that effective light protection alone will not be enough to prevent colonization by black stain fungi on spruce heartwood.