Studies on the diversity and phylogeny of Heterobasidion species
The genus Heterobasidion include several species that are aggressive pathogens of managed coniferous forests in Europe (H. abietinum, H. annosum sensu stricto, H. parviporum) and North America (H. irregulare (EPPO A2 List) and H. occidentale). In addition, other species have been described in Asia (H. amyloideopsis, H. amyloideum, H. australe, H. ecrustosum, H. insulare, H. linzhiense, H. orientale, H. tibeticum) and in Australia (H. araucariae). Based on mating studies, it is now considered that both H. annosum and H. insulare are species complexes.
Phylogenetic studies have been carried out on a set of Heterobasidion samples from Asia, Europe, North America, and Oceania. During these studies, the following three new Heterobasidion species from East Asia (China) have been described:
- Heterobasidion armandii sp. nov. (found on a Pinus armandii stump in Yunnan);
- Heterobasidion subinsulare sp. nov. (found on a Pinus sp. stump in Yunnan);
- Heterobasidion subparviporum sp. nov. (found on a fallen trunk of Larix sp. in Hebei; as well as on a fallen trunk of Picea sp and a living tree of Abies sp. in Jilin, and on a stump of Picea sp. in Xizang (Tibet)).
A fourth species, Heterobasidion sp. found in California (US) on Pinus ponderosa is probably another distinct species but it could not be further studied.
The present phylogenetic studies also concluded that Heterobasidion consists of three lineages:
- lineage associated to pines, firs and spruces (H. amyloideopsis, H. amyloideum, H. araucariae, H. armandii, H. australe, H. insulare, H. linzhiense, H. orientale, H. subinsulare, and H. tibeticum);
- lineage mainly associated to pines (H. annosum s.s., H. sp. and H. irregulare);
- lineage associated to firs and spruces (H. abietinum, H. occidentale, H. parviporum, and H. subparviporum).
The authors noted that as most Asian species (8 out of 10) have been found in the Himalayas this could confirm the hypothesis of an Asian origin for Heterobasidion. Considering the pathogenicity of European and North American species and the fact that Asian taxa are saprotrophs, they suggested that Asian countries should consider the European and North American species as quarantine fungi. Parallelly, they propose that European countries should consider the American H. occidentale and H. irregulare as quarantine fungi, while North America should treat H. abietinum, H. annosum s.s., and H. parviporum as quarantine fungi.
Sources
Yuan Y, Chen J-J, Korhonen K, Martin F, Dai Y-C (2021) An updated global species diversity and phylogeny in the forest pathogenic genus Heterobasidion (Basidiomycota, Russulales). Frontiers in Microbiology 11, 596393. https://doi.org/10.3389/fmicb.2020.596393