Biological control of wood decay in ground contact timbers

• Main Author: Brown, Heather
• Published: Abertay University 2002
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760043

Wood placed in ground contact situations is susceptible to attack by a wide range of soil micro-organisms which degrade the wood structure, causing significant deterioration of the mechanical properties of the timber such as strength and elasticity. Chemical preservatives such as CCA (copper-chrome-arsenic) and CCB (copper-chrome-boron) are currently used to prevent the decay of wood exposed to biodeteriogens. However, increasing concerns regarding the long-term environmental effects of the toxic chemicals applied to ground contact timbers has resulted in the investigation and development of a number of alternatives to chemical preservation. This project examined the use of biological control as a means of protecting ground contact timbers from fungal decay. <i>Trichoderma </i>spp. are soil-inhabiting fungi with broad-spectrum antagonistic properties, and have been extensively investigated as potential biocontrol agents in agriculture and forestry. A small-scale wood-based screening system was developed for the rapid assessment of biocontrol potential. The screening system used non-sterile soil as a test medium to provide a natural environment for the evaluation of potential biocontrolagents. A number of <i>Trichoderma </i>isolates were tested using the developed system, andone <i>Trichoderma viride</i> isolate, (T60) demonstrated an initial protective effect against non-sterile soil. This isolate has previously been shown to be totally effective against basidiomycete decay fungi. The isolate was therefore selected as a potential biocontrol agent for ground contact timber, and a field trial was designed to assess the isolate on a larger scale. Development of the field trial included the formulation of an appropriate delivery system. The biocontrol agent was applied to wood as a fungal spore suspension prepared in water. Wood was pressure impregnated with spores using a pilot preservation plant, integrating biological control strategies with current industry processes. Spore viability was retained, as indicated by the germination of <i>Trichoderma </i>spores on the wood surface. Field trial and fungal cellar testing of the biocontrol agent on ground contact was based on European Standard test methods for chemical wood preservatives. T60-treated stakes, CCA-treated stakes and untreated control stakes of 2 softwood species were uplifted after 9 and 18 months exposure to soil. Recommended subjective assessmentswere supplemented with biological examinations of decay. Results indicated partial protection of T60-treated wood. However, the study highlighted the influence of test system and wood species on the activity and behaviour of the applied biocontrol agent. To assess the distribution of the biocontrol agent in wood following the novel application procedure, a molecular-based method for the specific detection and quantification of T60 in treated wood was investigated. DNA was extracted from wood and amplified using the polymerase chain reaction (PCR). A random primer was used to detect T60 DNA in extracted material, and image analysis software was utilised to assess the relative abundance of amplified DNA indicating a non-uniform distribution of detected spores. In summary, results from the field and fungal cellar testing of a selected biocontrol isolate showed a variation in the degree and constancy of protection against wood decay fungi. Standard testing guidelines were used as a basis for a field trial, with modifications designed to provide a more comprehensive assessment of biological control in ground contact timbers. The research presented in this thesis highlights the importance of field testing with regard to the biological control of wood decay, and indicates the influence of environmental factors on the overall performance of fungal biocontrol agents.