Correlation between oxalic acid production and copper tolerance in Wolfiporia cocos

The increased interest in copper-based wood preservatives has hastened the need for understanding why some fungi are able to attack copper-treated woo d. Due in part to accumulation of oxalic acid by brown-rot fungi and visual ization of copper oxalate crystals in wood decayed by known copper-tolerant decay fungi, oxalic acid has been implicated in copper tolerance by the fo rmation of copper oxalate crystals. Nineteen isolates of the brown-rot fung us Wolfiporia cocos were evaluated for oxalic acid production and weight lo ss on wood treated with 1.2% copper citrate. Twelve of 19 isolates that cau sed moderate to high weight losses in copper citrate-treated wood produced low oxalic acid in liquid culture, whereas isolates with high oxalic acid p roduction had low weight losses in treated wood. Seven W. cocos isolates de monstrated enhanced weight loss in Cu-treated wood. Wood weight loss was un affected by the presence of copper citrate for two W. cocos isolates and we ight loss was lower for 10 isolates compared to weight losses in untreated wood. Citrate did not significantly influence oxalic acid production in liq uid culture. Previous hypotheses linking oxalic acid and copper tolerance w ere based upon observations of single isolates of Postia and Tyromyces . Al though most isolates produced more oxalic acid in copper citrate-treated wo od than in untreated wood, we found no statistical relationship between the amount of oxalic acid production in liquid culture or wood and copper tole rance in W. cocos. Production of oxalic acid does not seem to be the factor controlling copper tolerance in W. cocos. The diversity seen within W. coc os demonstrates that caution should be used when reporting results, so that generalizations are not based on the behavior of a single isolate. Publish ed by Elsevier Science Ltd.