The yeast Debaryomyces hansenii as a short-term biological control agent against fungal spoilage of sawn Pinus sylvestris timber

Previous work has found isolates of the yeast genus Debaryomyces to be successful biological control agents against molding of fruits. An isolate of Debaryomyces hansenii was tested for its ability to protect sapwood of Pinus sylvestris timber against visual degrade by surface growth of molds and staining fungi. Successful protection of presterilized wood blocks inoculated with a mixture of common wood molding fungi was achieved when yeast was applied at a rate of 6 X 10(8) CFU/cm(2). Yeast cells were sprayed onto wood blocks at the same time as spoilage fungi and blocks were incubated under conditions favorable to fungal development for 15 and 25 days before assessment using a visual scale. Protection of presterilized blocks against blue staining by Ophiostomatoid fungi was achieved when yeast cells were applied at a rate of 2 X 10(6)-6 X 10(8) CFU/cm(2). Significant reduction in disfigurement of nonsterile wood was demonstrated at a yeast application rate of 9 X 10(6)-9 X 10(8) CFU/cm(2). Survival and reproduction of D. hansenii on sterilized P. sylvestris sapwood blocks were also determined across a range of relative humidities and temperatures previously found to support development, of wood molding and staining fungi. Following 4 months incubation at 8-25 degreesC and 93-100% relative humidity, between 46 and 473% of the number of colony-forming units applied to the wood were recovered. Maximum increase in viable yeast count on wood blocks occurred at 100% relative humidity and 15 degreesC. (C) 2001 Academic Press.