Black Stain of Western Red Cedar ( Thuja Plicata Donn) By Aureobasidium Pullulans: The Role of Weathering

Western red cedar ( Thuja plicata Donn) is valued for its natural durability conferred by fungicidal extractive chemicals. However, weathered surfaces of T. plicata products are susceptible to black stain caused by fungi such as Aureobasidium pullulans. The effect of weathering on extractive concentrations at the wood surface was characterized and correlated with the ability of this fungal species to colonize weathered surfaces. UV plus water spray treatments substantially reduced extractives but did not promote fungal colonization. In contrast, UV-only treatments reduced extractive contents less than the other treatments but stimulated fungal colonization. A. pullulans exhibited high tolerance to the tropolone β-thujaplicin in vitro; thus loss in tropolone content may not be required for colonization. Water spray most likely washed away products of lignin photo-degradation, which resulted in decreased fungal colonization.