Slow-growing fungi belonging to the unnamed lineage in Chaetothyriomycetidae form hyphal coils in vital ericaceous rhizodermal cells in vitro.

The diversity and functionality of ericoid mycorrhizal (ErM) fungi are still being understudied. Members of Chaetothyriomycetidae evolved a specific lifestyle of inhabiting extreme, poor, or toxic environments. Some taxa in this subclass, especially in Chaetothyriales, are also putative ErM taxa, but their mycorrhizal ability is mostly unknown because the members are generally hard to isolate from roots. This study herein focused on eight root isolates and provided their phylogeny and morphology of root colonization. Phylogenetic analysis based on rRNA sequences clarified that the isolated strains were not classified into Chaetothyriales, but in an unnamed lineage in Chaetothyriomycetidae. This lineage also contains rock isolates, bryosymbionts, and a resinicolous species as well as various environmental sequences obtained from soil/root samples. All strains grew extremely slow by mycelia on cornmeal or malt extract agar (2.9-8.5 mm/month) and formed hyphal coils in vital rhizodermal cells of sterile blueberry seedlings in vitro. This study illustrated the presence of a novel putative ErM lineage in Chaetothyriomycetidae.