Rhizoglomus melanum, a new arbuscular mycorrhizal fungal species associated with submerged plants in freshwater lake Avsjøen in Norway

A new species of arbuscular mycorrhizal (AM) fungi (Glomeromycota) was isolated from the rhizosphere of isoetid vegetation, namely of Littorella uniflora and Isoetes lacustris, in the freshwater lake Avsjoen (Central Norway), and propagated on bait cultures on Zea mays and L. uniflora, respectively. The fungus is distinguished by chestnut brown to dark brown, triple-layered spores, (137–)165–226(−285) μm in diameter, and 1–2 concolorous subtending hyphae that regularly form multiple septae within 100–600 μm from the spore base, each approximately 10–25 μm apart, while the pore directly at the spore base is open. It can easily be differentiated from all other species in the Glomeraceae by the combination of spore size, spore color, and the characteristics of the subtending hyphae. Phylogenetic analyses of the partial SSU, ITS, and partial LSU nrDNA sequences placed the fungus in the genus Rhizoglomus, well separated from all other species in the genus. The fungus described here as Rhizoglomus melanum was hitherto only found in lake sediments which might suggest its specificity for aquatic environment. It is the first new AM fungus ever, isolated and propagated from submerged, aquatic vegetation.