Field studies have revealed that when timber is irradiated (i.e. killed) it is more susceptible to colonisation by mould fungi than sapstain fungi. By comparison, freshly sawn timber shows very little mould colonisation, tending to be colonised by sapstain fungi. It appears, therefore that the physiological state of the wood may influence the pattern of colonisation. A laboratory trial was undertaken to investigate in more detail the observations recorded in the field studies. A spore suspension of the mould Trichoderma was used to inoculate one set of living and one set of gamma irradiated (dead) wood blocks; similar sets of blocks were inoculated with a spore suspension of the sapstain fungus Ophiostoma piceae and a final treatment consisted of inoculating further sets of blocks with a mixed spore suspension of both fungi. Results clearly indicated that Trichoderma rapidly colonised and discoloured the irradiated blocks whereas there was very little defacement on the living blocks. The dead wood blocks inoculated with the mixed spore suspension were also rapidly colonised by the mould Trichoderma and 0. piceae was clearly out competed. However the living wood blocks were predominantly colonised by 0. piceae when they were inoculated either alone or in combination with Trichoderma. The factors controlling these patterns of colonisation are being investigated.

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