Use of DNA sequence data to identify wood-decay fungi likely associated with stem failure caused by windthrow in urban trees during a typhoon

Abstract

Molecular biology methods identified wood-decay fungi in wind-thrown trees. The stem failure height was in accordance with the colonization strategies of each fungal species. The dominant fungus was Polyporus squamosus. Decay reduces wood strength and can lead to the collapse of urban and roadside trees, which can occasionally cause extensive property damage or injury to people. For managing trees in urban green areas, it is essential to assess the risk of stem failure by detecting fungal species that act as decay agents. Wood decay was found in the stems of many trees broken by a windthrow during a typhoon in an urban green area dominated by Japanese elm. We measured the height of failure in the sampled trees to compare the fungal infection and point on the stems and the strategies of colonization of each fungal species. No fruit bodies of fungi were found on the stems of broken tress in the damaged area for species identification based on morphological characteristics. Therefore, we used rDNA-ITS sequence data to identify species of wood-decay fungi at the point of stem failure caused by windthrow. The stem failure height was in accordance with the localization of each fungal species, i.e., above or below the ground level. In the Japanese elm, the dominant fungus was Polyporus squamosus, which was detected in large trees with diameter breast height ranging from 89 to 230 cm. P. squamosus infection is considered particularly hazardous as it increases the risk of large tree falling. The mean stem failure height of the trees infected with P. squamosus infection was 6.4 m. We speculated that this fungus had penetrated the tree via stem wounds, thereby causing stem failure.