Discovery of Rhizopogon associated with Larix from northeastern Siberia: Insights into host shift of ectomycorrhizal fungi

Rhizopogon (Boletales) is an ectomycorrhizal fungal genus that exhibits a strong specificity to Pinaceae. This strict association occurs almost exclusively with Pinus and Pseudotsuga, while associations with other genera in Pinaceae are inconclusive. Here, we describe Rhizopogon laricinus sp. nov. associated with Larix cajanderi distributed in northeastern Siberia, where forest fires are frequent. We confirmed the host identity by comparing rDNA internal transcribed spacer (ITS) sequences obtained from basidiomata and ectomycorrhizal root tips collected at the same sites. Morphological characteristics and molecular identification revealed that R. laricinus is a new species associated with Larix unequivocally. The molecular phylogeny based on ITS sequences placed this species sister to the subgenus Roseoli, which is specific to Pinus, and not to the Pseudotsuga-specific subgenus Villosuli. Thus, R. laricinus evolution does not correspond to host phylogeny as Larix and Pseudotsuga form a monophyletic clade. Instead, ecological traits of Rhizopogon for adapting to disturbed habitats may have driven the host shift to Larix under high-frequency fire ecosystems.