The phenomenon of copper tolerance by brown rot fungal strains has been known for a long period but the complete mechanism of copper tolerance by these fungi is not understood yet. Copper tolerance has previously been linked to oxalic acid excreted by copper tolerant brown rot fungal strains. This acid reacts with copper in the wood to form an insoluble and therefore less toxic copper oxalate. There has been a suggestion that copper tolerance had more to do with lowering of the pH of the substrate rather than the low solubility of copper oxalate. In order to elucidate this presumption CCB treated wood samples were acidified with organic (oxalic, acetic, lactic, formic) and inorganic (sulphuric) acids and afterwards exposed to copper tolerant (Antrodia vaillantii, Leucogyrophana pinastri) and copper sensitive (Poria monticola, Gloeophyllum trabeum) brown rot fungal strains according to the mini block procedure. After eight weeks of exposure, the samples were isolated and their mass losses were determined. In addition, electron paramagnetic resonance (EPR) measurements on the exposed samples were performed. The EPR spectra of the samples decayed by A. vaillantii were very similar to those of the samples acidified with oxalic acid. Furthermore, acidification of the CCB impregnated samples made them significantly more susceptible to copper tolerant and copper sensitive brown rot fungi what can be clearly seen from weight losses.

Download document (462 kb)
free for the members of IRG. Available if purchased.

Purchase this document