(2016). Phylogeny of Fomitopsis pinicola: a species complex. Mycologia: Vol. 108, No. 5, pp. 925-938.

Two new species, Fomitopsis mounceae and F. schrenkii (Polyporales, Basidiomycota) in the F. pinicola species complex in North America, are described and illustrated. Previous molecular phylogenetic analyses identified three well-delimited lineages that represent F. mounceae and F. ochracea from Canada, the Appalachian Mountains, and the northern United States and F. schrenkii from western and southwestern regions of the United States. Fomitopsis pinicola sensu stricto is restricted to Eurasia and does not occur in North America. Morphological descriptions of basidiocarps and cultures for F. mounceae, F. schrenkii, and F. ochracea are presented. The three species are readily differentiated by nuc rDNA internal transcribed spacer (ITS1-5.8S-ITS2 = ITS) sequence, geographic distribution, and basidiospore size. Polyporus ponderosus H. Schrenk is an earlier illegitimate synonym of F. schrenkii. Both F. mounceae and F. schrenkii have a heterothallic multiallelic incompatibility system.

Magnetic resonance imaging (MRI) was used to evaluate free water content and distribution in wood–plastic composite (WPC) materials decayed during exterior exposure because moisture is an essential factor for the progression of the decay process. Two segments of the same board were selected from six commercial decking boards that showed signs of decay (from a total of 27 boards that were exposed near Hilo, Hawaii). The decay process was indicated by the presence of fungal fruiting bodies. One of the two board segments was exposed in sun, the other in shadow. Whole board segments were imaged using a clinical MRI unit, and then selected areas were examined using scanning electron microscopy (SEM). Samples were cut from the cross section of the board to determine material density as an indicator of the degree of decay advancement. The presence of free water detected by MRI was correlated to the mechanism of decay in the WPC board segments and to the water distribution measured in the boards. Both board segments showed a significant amount of decay, where SEM images showed the presence of fungal hyphae inside the boards, particularly the segment exposed in shadow. MRI showed that the expected pattern of free water distribution—a moisture gradient from greatest on the outside of the board to least inside—was not evident in the decayed board evaluated in this study. On the contrary, a reverse moisture gradient was observed in some areas where there appeared to be a relatively high concentration of free water in the center of the board. This could be explained by moisture transfer of fungal mycelia into the core of the board and the generation of water as decay fungi metabolize wood.

Fungal species with a broad distribution may exhibit considerable genetic variation over their geographic ranges. Variation may develop among populations based on geographic isolation, lack of migration, and genetic drift, though this genetic variation may not always be evident when examining phenotypic characters. Fomitopsis pinicola is an abundant saprotrophic fungus found on decaying logs throughout temperate regions of the Northern Hemisphere. Phylogenetic studies have addressed the relationship of F. pinicola to other wood-rotting fungi, but pan-continental variation within F. pinicola has not been addressed using molecular data. While forms found growing on hardwood and softwood hosts exhibit variation in habit and appearance, it is unknown if these forms are genetically distinct. In this study, we generated DNA sequences of the nuc rDNA internal transcribed spacers (ITS), the TEF1 gene encoding translation elongation factor 1-α, and the RPB2 gene encoding the second largest subunit of RNA polymerase II for collections across all major geographic regions where this fungus occurs, with a primary focus on North America. We used Bayesian and maximum likelihood analyses and evaluated the gene trees within the species tree using coalescent methods to elucidate evolutionarily independent lineages. We find that F. pinicola sensu lato encompasses four well-supported, congruent clades: a European clade, southwestern US clade, and two sympatric northern North American clades. Each clade represents distinct species according to phylogenetic and population-genetic species concepts. Morphological data currently available for F. pinicola do not delimit these species, and three of the species are not specific to either hardwood or softwood trees. Originally described from Europe, F. pinicola appears to be restricted to Eurasia. Based on DNA data obtained from an isotype, one well-defined and widespread clade found only in North America represents the recently described Fomitopsis ochracea The remaining two North American clades represent previously undescribed species.

Since nitrogen is in short supply in wood yet relatively plentiful in the bodies of nematodes, wood-decay fungi have been thought to be nematophagous. In an earlier study, we confirmed the nematophagy of two species of wood-decay fungi (Pleurotus ostreatus and P. pulmonarius), although we also found nematode species that could turn the tables and consume Pleurotus. In this study, we tested interactions between nematode species and Fomitopsis, another genus of common wood-decay fungi. Four geographically distinct isolates, or provenances, within each of four species (i.e., the European F. pinicola and three North American species: F. ochracea, F. schrenkii, and F. mounceae) were confronted with a total of twenty nematode species (twenty-four strains) in four experiments. Nematophagy was observed much less frequently in Fomitopsis than in Pleurotus: only 31 of the 516 interactions (6%), overall, resulted in nematophagy by a Fomitopsis isolate, whereas with Pleurotus, the result was 16 of 28 (57%). In contrast, all 20 species of nematode here were capable of mycophagy and dominated interactions with all isolates of Fomitopsis overall. Clearly, not all wood-decay fungi are as strongly nematophagous as the Pleurotus species. Perhaps arboreal nematodes even tend towards mycophagy, given the limiting nitrogen in wood.