Species recognition, geographic distribution and host-pathogen relationships: a case study in a group of lignicolous basidiomycetes, Phellinus s.l.

Morphological, phylogenetic (sequencing of the ribosomal ITS region) and, if applicable, biological (pairings of single-spore testers) species recognition have been used to resolve relationships among 69 collections belonging to the Hymenochaetales genera Phellinus s.str. and Fomitiporia. The isolates originate from a variety of host plants in Europe, North America and Asia. Separate application of recognition modes led to differing results concerning the number of species, geographic distribution and host range. Sole application of morphological criteria was of limited value, especially in taxa exhibiting a wide distribution, both in terms of geographic origin and ecological niche. Relationships of putatively con-specific collections originating from different continents preferably should be resolved by using an integrative approach. In this study, application of a strict morphological approach led to the recognition of seven species. When using molecular and pairing test data, at least 12 species were detectable. Two of them, F. hesleri and F. polymorpha, are described as new. The number of Phellinus s.str. and Fomitiporia species supposed to have Northern Hemispheric or cosmopolitan distribution, when morphological characters are applied for species recognition, has been reduced significantly. As firm tendencies within morphological species, genetic divergence was more distinct in uniparental than in biparental taxa. In the latter, a strong correlation was observed between phylogenetic and biological species recognition. Overall length of the ribosomal ITS region clearly separated Phellinus s.str. and Fomitiporia but was of limited value as a diagnostic tool at species level. The level of innerspecific morphological plasticity of fruit bodies differs widely between even closely related species, suggesting that morphological transitions occur quite frequently in this fungal group. Considerable instability of the reproduction mode was evident in strains belonging to Phellinus tremulae and among closely related species of Fomitiporia.