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In Situ Observations on the Influence of Wood Moisture Content and Temperature on Spore Germination and Wood Colonization by Poria carbonica. P. R. Przybylowicz, Former graduate research assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, Present address: Northwest Mycological Consultants, 702 NW 4th St., Corvallis, OR 97330; M. E. Corden, professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, Present address: Forest Products Department, Oregon State University, Corvallis 97331. Phytopathology 76:212-214. Accepted for publication 10 September 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-212.

A method for observing germinating fungal spores on wood was developed in which temperature and wood moisture content could be easily controlled and subsequent wood colonization could be determined. Thin radial sections of Douglas-fir (Pseudotsuga menziesii) heartwood (8 mm x 8 mm x 60 μm) were inoculated with a fungal spore suspension and a similar wood section was placed over the inoculated section forming a 'spore sandwich.' The 'spore sandwiches' were incubated between larger blocks of Douglas-fir heartwood to maintain control of the wood moisture content during incubation in controlled temperature-humidity chambers. Spore germination was observed by opening the 'spore sandwiches' and staining the spores in situ for microscopic observation. Wood colonization was determined by isolations from the surrounding wood blocks. The 'spore sandwich' method was used to study the influences of temperature and wood moisture content on spore germination of Poria carbonica. Basidiospores and asexual spores germinated and colonized wood at and above the fiber saturation point (about 30% moisture content), but not below. Both spore types germinated and colonized wood at 22 and 30 C, but basidiospores failed to germinate at 5 and 35 C, whereas asexual spores germinated at 5 and 35 C, but were unable to colonize the wood. The 'spore sandwich' method provides a means for assessing spore germination and wood colonization by wood-decaying fungi under conditions simulating those occurring naturally in wood in service.