A study of soft-rot in hardwoods

The main aims of this study were to examine the wood substrate degrading capacities of microorganisms isolated from soft-rotted CCA-treated Eucalyptus sp. power transmission poles in ground contact, and to evaluate techniques for assessment of the degree of wood degradation caused by microbial attack. The performances of various wood preservatives, including remedial and ground-line maintenance treatment systems for poles, were assessed. The predominant organism isolated from Tasmanian woods in this study, the Hyphomycete Phialophora mutabiIis, had demonstrable celIuIase, hemicelIulase, amylase and pectic enzyme activities as well as a measurable wood-degrading capacity. Trichoderma viride was a highly cellulolytic fungus in pure culture, and a dominant early coloniser of untreated E. obIiqua wood in ground contact. However, it produced minimal wood degradation in this examination. A small ( < 10 4 cel I s/g wood sawdust) bacterial microflora was found in untreated and preservative-treated hardwoods. Bacterial isolates possessed a number of wood-degrading enzymes: A strain of Bacillus megaterium (S9NC) isolated in this study, showed cel I ulase, xy I anase, amylase and pectic enzyme activities, whilst CelIulomonas sp. 8N produced at least one celIuIase, xyIanase, pectic enzyme and Iaccase. However, no definite degradation of intact E. obIiqua sapwood cell walls by pure cultures of bacteria was observed by light microscopy and scanning electron microscopy. Fungi (including Basidiomycetes) and bacteria were earl y colonizers of untreated E. obliqua stakes in the ground. A mutual istic relationship, albeit not a close one, was demonstrated between propagule counts of fungi and bacteria, isolated from CCA-treated Eucalyptus sp. sawdusts. Two techniques for estimating microbial activity in wood samples were developed in this study, and compared with other methods for estimating the degree of wood degradation. The methods were: i . a Cx-celIuIase assay i i . a modified and improved chitin assay for estimation of fungal biomass in wood. Appropriate parameters for both assay methods were determined. The Cx-celIuIase and chi tin assays were relatively quick and sensitive methods for assessing the degree of microbial attack of woods. These assay procedures, plus impaction determinations using the Pilodyne(R) instrument, and to a much lesser extent the fungal propaguIe count, were largely objective procedures. Visual and microscopic estimates of wood degradation were found to be highly subjective in this study. Several field trials of wood preservatives were used to compare the newly developed assay methods with fungal propagule counts, Pilodyne(R ) impaction determinations, and visual and microscopic estimates of wood degradation. The trial s examined were remedial treatments of transmission poles at Warrane, Tasmania, and bandage treatments of poles at Grafton, N .S.W . and Coff 's Harbour, N.S.W. In addition, an E. obliqua preservative-treated sapwood stake trial was emplaced at Grove, Tasmania. In this study, the best performed remedial preservative systems were the Wolman CFB bandage and the CSIRO-developed Busan 30 and Blue 7 (Mark IV) bandages. These bandage systems show promise as agents for treatment of soft-rot attack in Australian power transmission poles