Clone identification and population genetic analysis of Phellinus noxius collected from Taiwan

Since 1990s, brown root rot caused by Phellinus noxius has become a major tree disease in Taiwan. This fungal pathogen has a very wide host range, including Cinnamomum camphora、Ficus microcarpa、Koelreuteria henryi and Delonix regia. When infecting the trees, it can not only destroy bark and wood structure, but also seriously impair nutrient transportation and water uptake. In the early stage of infection, the infected trees may not show any obvious symptom, but as the disease develops, the tree may decline and eventually fall down or die within few months, thereby resulting in considerable economic loss and causing public danger. In order to investigate the disease dissemination pathway and epidemic dynamics of P. noxius, we have developed genotyping methods which were based on ISSR (inter-simple sequence repeat) or SSR (simple sequence repeat). These methods are useful not only for the distinction of basidiospores from different fruiting bodies, but also detection of genetic recombination in the process of sexual reproduction. The SSR prof n the process of sexual reproduction iles also verified the haploid nature of the basidiospore. Furthermore, single-arthrospore isolation might cause certain degree of genetic segregation. In the field survey, P. noxius isolates were obtained from 28 infected trees in two campuses (c.a. 4 hectares) of Taipei, and analyzed for their genotypes. The results revealed the presence of 11 clonal lineages, each occupying a distinct infection zone. As revealed by SSR profiles, mycelia of the field isolates were heterokaryon in most cases. Furthermore, for fungal isolates collected from infected trees nearby each other, most of them tend to display similar genotypes, indicating that root contact may serve as an important way for pathogen dissemination. However, to address important questions regarding epidemiology of P. noxius, including its major reproductive way and possible existence of a predominant virulent strain in the field, it is necessary to analyze more fungal isolates.