MOKUZAI HOZON (Wood Protection)

White rot fungi produce lignolytic enzymes to depolymerize lignin when they degrade wood. Among them, heme peroxidases such as manganese peroxidase (MnP) and lignin peroxidase (LiP) have been considered to play an important role in lignin degradation. In the present study, the technique that permits a specific amplification of the genes encoding MnP and LiP by polymerase-chain reaction (PCR) was developed to detect the white rot fungi having these genes. As a result, the genes encoding MnP and LiP from white rot fungi including Trametes versicolor, Pycnoporus cinnabarinus, Pycnoporus coccineus, and Irpex lacteus were detected using newly-designed primers (MnP_F1 and MnP_R1). Moreover, various peroxidase genes were also detected when DNAs prepared from decayed woods were used as a template. The genes encoding MnP and LiP were remarkably separated when PCR products were applied for denaturing gradient gel electrophoresis analysis. The results clearly indicate that the technique is useful when naturally-occurring decayed wood containing various gene resources encoding MnP and LiP was used as a subject of research.

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Sugi heartwood specimens finished with 10 kinds of wood preservative semi-transparent coatings were exposed to the weather at 45° inclination facing south in Yamagata city in Japan for 24 months. Changes in color difference (Δ E^*_ab) and water repellency index (WR) of finished surfaces were monitored. Changes in arithmetic mean deviation of the roughness profile (Ra) were also measured to estimate the extent of surface erosion by using a non-contact three-dimensional measuring equipment with a laser beam probe. For all the coatings, Δ E^*_ab gradually increased from the start of exposure. On the other hand, WR indices were maintained about 100% for the first 6 months and they began to decrease after 9 months. Ra values showed a similar tendency in which they were kept less than 10μm for the first 6 months and starting to increase after 9 months. It was also found that, after 24 months, there were a strong negative correlation between Ra and WR, and a moderate positive correlation between Ra and Δ E^*_ab. Based on these results, relationships of surface degradation of finished wood to Ra , Δ E^*_ab and WR were discussed.

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