Rhodonia (Oligoporus) placenta is known as a relative aggressive basidiomycete fungus against thermally modified timber. In durability lab tests, this often results in a lower durability class, compared to other test fungi. In the reported work, the virulence of three different strains of Rhodonia placenta for untreated and thermally modified timber was determined and compared. Therefore, two lab strains and an isolate (sourcing from a field sample) were used for durability tests according to CEN/TS 15083-1. Complementary, Coniophora puteana and Trametes versicolor were used as test fungi. The tests were performed with untreated and thermally modified wood (180 °C, 190 °C and 200 °C) from Scots pine sapwood (Pinus sylvestris L.) and European beech (Fagus sylvatica L.). To verify the identity of the fungi species, the strains were specified by both morphological and molecular analysis, the last one based on sequencing the internal transcribed spacer (ITS) of the nuclear ribosomal DNA (nrDNA). As expected, the durability of beech and pine sapwood was considerably increased by thermal modification. Distinct differences were found between the virulence of the R. placenta strains. Generally, at all 8 material variants the isolate of R. placenta showed a higher degradation capability than the lab strains. At thermally modified pine sapwood, the isolate of R. placenta led to higher mass losses and resulted in lower durability classes than the standard test strains required by CEN/TS 15083 1. The highest mass loss at pine and beech wood, untreated or modified at 180 °C or 190 °C, was caused by C. puteana. From 190 °C to 200 °C treatment level, the durability class of thermally modified beech changed remarkably from 3-4 to 1-2, referring to all fungal strains. In contrast to the durability tests, the R. placenta isolate, as the strain with the highest virulence, showed the least cellulolytic enzyme activities, which were determined in rapid tests.

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