The role of extractive depletion in the fungal colonization of Western redcedar (Thuja plicata Donn)

Western redcedar (Thujaplicata Donn) (WRC) is a naturally durable softwood species native to British Columbia, Canada, as well as Washington, Oregon and California in the USA. WRC wood products are valued for their durability conferred by anti-microbial extractive compounds. However, such products are still susceptible to fungal colonization that can result in decay and discoloration. The main objective of this thesis was to provide information on the relationship between durability, the change in extractives, and micro-organisms on WRC products in-service in order to help the industry to develop strategies to improve product service life. We first developed protocols to extract, separate and quantifl extractives by ultra-sonication and reverse phase high performance liquid chromatography. We developed techniques to screen a range of fungi commonly isolated from WRC in service products for extractive-tolerance in vitro. Results indicated that the Basidiomycete Pachnocybe ferruginea exhibited the highest extractive-tolerance of the range of fungi tested. The next section of this thesis focuses on black stain of WRC siding by Aureobasidiurn pullulans and the role of weathering. We characterized the effect of weathering on extractives at the surface and correlated this with ability of A. pullulans to colonize. UV plus water spray treatments substantially reduced extractives but did not promote fungal colonization. In contrast, UV-only treatments reduced extractive contents less but stimulated fungal colonization. A. pullulans exhibited high tolerance to the tropolone Pthujaplicin in vitro; thus loss of tropolone content may not be required for colonization. In the final part of this thesis we investigated the relationship between extractive depletion caused by leaching and how this influenced decay. Leaching resulted in an 80% reduction of extractives, which generally resulted in a greater degree of decay by six commonly isolated fungal species. Fungi which exhibited low tolerance to WRC leachate in vitro were able to decay leached WRC blocks more readily than non-leached WRC blocks. Extractive-tolerant species did not require leaching of extractives for decay to occur. The Basidiomycetes P. ferruginea, and to a lesser extent Acanthophysium lividocaeruleum and Heterobasidion annosum consistently exhibited high extractive tolerance and could decay non-leached WRC to a similar extent as leached. Such species are candidate ’pioneer’ species that may detoxify extractives in wood products, paving the way for decay by less specialized fungi to occur.Forestry, Faculty ofGraduat