Certain wood decay fungi exhibit tolerance to one or more wood preservatives. Copper tolerance of brown-rot fungi has been studied in our laboratory for the past six years. We have observed some degree of tolerance to N’N-naphthaloylhydroxamine (NHA), a recently patented termite bait, by the brown-rot fungus Tyromyces palustris TYP-6137. In an effort to try and confirm this tolerance in other isolates of T. palustris and to dissect the mechanism of tolerance, an additional ten isolates of T. palustris were tested in soil-block bottles for 12 weeks against southern yellow pine wood blocks vacuum treated with 0.5 % NHA. Of the isolates tested, only TYP-6137 showed complete tolerance to NHA. The other 10 isolates showed varying degrees of tolerance, but at a lower NHA retention than TYP-6137. This shows that although preservative tolerance is directly related to the mechanisms of decay, caution should be used when making generalizations based on the metabolism of a single isolate (Clausen et al., 2000). Wood blocks exposed to T. palustris were tested for oxalic acid production at week 12. Two isolates produced more oxalic acid on NHA treated blocks than untreated SYP blocks, but we did not find any direct relationship between the amount of oxalic acid produced and the NHA tolerance of T. palustris. A separate test on malt agar plates with 0.1% NHA confirmed the notion of tolerance in two T. palustris strains, 6137 and TYP-L-15755, by solubilizing the NHA and migrating across the agar plate. Other fungi tested, G. trabeum 617, Trametes versicolor 697, Postia placenta 698, Serpula lacrymans 12C and Antrodia vaillantii TFFH, were not able to colonize malt agar supplemented with NHA. Thus, we conclude that NHA tolerance observed in T. palustris is apparently not mediated solely by overproduction of oxalic acid and that the apparent variation among strains in NHA tolerance is comparable to copper tolerance previously reported in Wolfiporia coccos.

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