The work reported here investigated the fungal community inhabiting western redcedar fence material with a focus on species colonizing wood below the surface, of which little is known. From seven pieces of fence material, twenty-three different fungal species were isolated and characterized using both traditional morphology and molecular identification methods. The species identified included thirteen ascomycetous and ten basidiomycetous fungi. Isolates were tested for their resistance to beta-thujaplicin - one of the principle fungicidal agents of western redcedar heartwood extractives. Generally, ascomycetous fungi exhibited greater resistance to beta-thujaplicin than basidiomycetous fungi. Interestingly, three ascomycetous and two basidiomycetous species frequently isolated had high tolerance to this compound. These species could be candidate 'pioneer' species that invade and detoxify western redcedar extractives, paving the way for colonization by decay fungi.
Western red cedar (Thuja plicata Donn) is a naturally durable softwood species native to British Columbia in Canada, and Washington, Oregon and California in the USA. Untreated T. plicata products are usually durable because of the presence of extractives with anti-microbial activity. However, there are extractive tolerant fungi that can attack T. plicata. To screen for extractive-tolerant species we developed a T. plicata feeder strip assay. When the feeder strips were placed on malt extract agar, extractives from the wood accumulated in the media and strongly inhibited growth of non-tolerant fungal strains. Extractives remaining in feeder strips following incubation on media were characterized. Of the many compounds leached out, g-and b-thujaplicin, b-thujaplicinol, plicatic acid and thujic acid were quantified. The growth of selected fungal strains was not affected by plicatic acid; however, it was inhibited to different degrees by band g-thujaplicin. Pachnocybe ferruginea was extractivetolerant and may play an important role in the initial stages of degradation of T. plicata products.
We tested the effect of leaching on the concentration of western red cedar (WRC; Thuja plicata Donn ex D. Don) heartwood extractives that are known to exhibit antimicrobial activity and correlated this with fungal growth and decay. We assessed the extractive tolerance of the following fungal species: Acanthophysium lividocaeruleum, Coniophora puteana, Heterobasidion annosum, Pachnocybe ferruginea, Phellinus sulphurascens, and Phellinus weirii by measuring their growth rate (mm/day) on media with or without WRC leachate. These data were correlated with the ability of the fungal species to grow on and decay leached versus nonleached WRC. We used an ergosterol assay to estimate growth and a standard soil-block test to assess decay. We estimated that leaching reduced the concentration of 5 major extractives: (-)-plicatic acid, beta-thujaplicin, gamma-thujaplicin, beta-thujaplicinol, and thujic acid by approximately 80%. Phellinus sulphurascens exhibited the lowest extractive-tolerance in vitro, grew poorly on and caused minimal decay in nonleached WRC, but it grew well on and decayed pine and leached WRC. Coniophora puteana, H. annosum, and P. weirii displayed moderate to high tolerance to leachate, grew on and caused decay in nonleached as well as leached WRC, but their growth and decay were always greatest on leached WRC and pine, suggesting that leaching enhances decay by these fungi. Acanthophysium lividocaeruleum and Pachnocybe ferruginea exhibited high extractive-tolerance. Whereas A. lividocaeruleum clearly caused decay on all types of wood, no decay was observed with Pachnocybe ferruginea, which grew very slowly in the different wood species, and it may or may not be able to decay wood.
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