Correlation between oxalic acid production and tolerance of Tyromyces palustris strain TYP-6137 to N′,N-naphthaloylhydroxamine

Eleven strains of T. palustris were evaluated for mass loss and production of phosphate buffer soluble oxalic acid on pine wood blocks treated with 0.5% N′,N-naphthaloylhydroxamine (NHA) in a soil-block test. After 12 weeks higher percentage mass loss was observed in control groups for 10 strains, while TYP-6137 was shown to be tolerant with no difference between the untreated controls and 0.5% NHA-treated blocks. Strain TYP-6137 was evaluated at 6, 8, and 10 weeks for mass loss and production of oxalic acid in a colorimetric assay with increasing levels of NHA treatment (0.5–1%). Tyromyces palustris TYP-6137 was shown to be successful in degrading NHA-treated wood in the 0.5–0.8% treatment range, but was inhibited in the 0.9–1% treated groups. Although there is no simple linear correlation between mass loss and production of oxalic acid, there was an inverse relationship at the 6-week time period. Thus, it was concluded that production of oxalic acid in T. palustris TYP-6137 at 6 weeks may facilitate mass loss at 8–10 weeks in the 0.5–0.8% NHA-treated blocks. In the 0.9–1% treatment groups this response was not seen. The broad variation seen in oxalic acid production among the 11 T. palustris strains suggests that high oxalic acid production alone is not the sole mechanism of NHA tolerance. Oxalic acid appears to be non-specifically produced in response to the preservative treatment, yet its association with mass loss could not be clearly defined.