Wood Science and Technology 28 (1994) 199-~o8 9 Springer-Verlag 1994 Diffuse cavity formation in soft rot of S. E. Anagnost, J. J. Worrall, C. J. K. Wang pine Summary A new type of soft rot of southern pine longitudinal tracheids is described. In this type, soft-rot cavities form by diffuse degradation of the $2 cell wall layer by hyphae growing within the cell wall. Cavity formation is diffuse and irregular as opposed to the restricted, peri- odic cavity formation typical of type i soft rot. Proboscis hyphae are small (diameter 0.6 to 0.9 gm) and rapidly autolyse. These proboscis hyphae are not easily recognizable with light mi- croscopy, especially at later stages of decay, but require transmission electron microscopy to confirm their presence. This may be an alternative interpretation of the type 2 soft rot of soft- woods described previously as being caused by lumenal hyphae through an intact $3. Chemical analysis of pine test blocks revealed a greater loss of glucose and an increase of galactose with diffuse type i species compared to typical type 1 soft rot species. The term "diffuse type 1" is suggested to describe this soft rot. Introduction Soft rot was first defined anatomically as the spiralling growth of hyphae within the $2 cell wall resulting in chains of cavities with conical ends caused by some Ascomycetes and Fungi Imper- fecti (Savory 1954). Courtois (1963) first described the erosion of the cell wall from the lumen surface as different than typical soft rot and later (1965) Corbett used the terms type i and type 2 to describe the two types of decay by microfungi. According to Corbett (1965) type I was cavity formation as described by Savory (1954) and was observed in the hardwood, birch and in the softwood, Scots pine. Type 2 consisted of a dissolution of the wall ($3 and $2) beneath hy- phae in the cell lumen resulting in erosion troughs and V-shaped notches. Type 2 was found in birch but not in Scots pine. Later, Nilsson (1973) in his study of wood-degrading ability of many microfungi, observed erosion of the $2 in pine and spruce by hyphae in the lumen with the intervening $3 layer remaining intact. He expanded the definition of type 2 soft rot to include any degradation by microfungi of the cell wall by hyphae lying in the lumen. As part of a study to test the soft-rot capabilities of microfungi isolated from fumigated utility poles, light microscopy of pine (Pinus taeda L.) and birch (Betula alleghaniensis Britton) 199 Received25 August 1992 Facultyof Environmentaland Forest Biology SUNY Collegeof EnvironmentalScienceand Forestry,Syracuse,New York13210 The authors thank the ElectricPower ResearchInstitute (EPRI) and the USDA CompetitiveResearchGrants Program for financial support, Kathy M. Anderson for technicalassistance and The N.C. Brown Center for Ultrastructure Studies at the SUNY Collegeof EnvironmentalScienceand Forestry for use of their facil- ities.