The pathogenicity of basidiospores of Phellinus noxius which causes brown root rot disease in Taiwan

The role of basidiospores of Phellinus noxius in nature has not been clearly elucidated since brown root rot disease was discovered. Previously, it was reported that P. noxius rarely produces basidiocarps in nature, while a total of 33 new tree host species bearing basidiocarps were recently found in Taiwan. The more-abundant basidiospores were collected for germination and infection studies in this paper. Fresh basidiospores were collected from live basidiocarps growing on a small-leafed banyan (Ficus microcarpa), and the basidiospores were rinsed out. The germination experiment revealed that they could germinate in all kinds of liquids including rainwater, with germination rates usually exceeding 50%. The direct inoculation of basidiospore suspensions at concentration of 105~106 spores/mL on four tree species was consistently unsuccessful. The same spore suspension was used to inoculate wood chips from Taiwan zelkova (Zelkova serrata) sapwood. After 2 months, some of the wood chips had been colonized by basidiospores, showing dark-brown line or network symptoms. Using these colonized wood chips, we successfully inoculated wounded roots of Taiwan zelkova seedlings within 3 months, proving the virulence and role of basidiospores in nature. Since 2007, 13 cases of twig or stem infection by P. noxius were found in the field, confirming transmission by basidiospores. In Taiwan, due to the high frequency of typhoon damage to trees, abundant stem wounds should act as important sites for basidiospore deposition and infection. This could facilitate the long-distance dispersal of this disease in nature