Assessment of decay risk of airborne wood-decay fungi
I Momohara, Y Ota, K Sotome, T Nishimura
The decay risk of airborne wood-decay fungi was investigated by using an air sampler. Japanese cedar disks measuring about 8 cm in diameter and 3 mm in thickness with moisture content at about 100 % were placed in a “BIOSAMP” air sampler and exposed to 1000 liters of air. Air sampling was carried out from June to September at the same sampling site in Tsukuba, Japan. The exposed disks were then incubated for 16-week in a damp container kept at 26 ± 2°C. During the incubation period, wood mass loss ranged from -15 mg to 807 mg with a mean mass loss of 244 mg. Factors affecting mass loss were explored. Wood moisture content and ratio of heartwood area proved to be significant factors. In addition, five weather factors were found to influence mean mass loss. Disks that were sampled on a cloudy day showed significantly higher mean mass loss compared to those sampled on a shiny day.
Filamentous fungi grown on the disks during 16-week incubation were subcultured to investigate the relationship between the taxa of airborne fungi and the decay risk. The subcultured fungi were isolated and DNA extracted from each isolate was amplified with the primers ITS4/ITS5. The DNA sequences of the amplified products were determined and compared to the sequence data of GenBank to determine the species or genus according to a BLAST search. This search revealed that the isolate consisted of 5 major taxa, namely Bjerkandera sp., Phanerochaete sp. (A), Phanerochaete sp. (B), Polyporales sp. Polyporus arcularius, and 6 minor ones. Statistical analysis revealed that the disks attached by Phanerochaete spp. or Polyporales sp. showed higher mean mass loss. It is concluded that, under these experimental conditions, related species of P. sordida play an important role in increasing the decay risk caused by airborne wood-decay fungi.