Taxonomy and phylogeny of Aphanomycopsis bacillariacearum, a holocarpic oomycete parasitoid of the freshwater diatom genus Pinnularia

Abstract Investigations into simple holocarpic oomycetes are challenging, because of the obligate biotrophic nature many lineages and periodic presence in their hosts. Thus, despite recent efforts, still, majority species described remains to be investigated for phylogenetic relationships. One these is Aphanomycopsis bacillariacearum , type genus . Species endobiotic parasites diverse hosts (e.g., diatoms, desmids, dinoflagellates). All classified this were assigned it based on branching hyphae formation two generations zoospores, which first one not motile. Originally, with its species, A. had been Saprolegniaceae However, has undergone multiple taxonomic reassignments (to Ectrogellaceae Lagenidiaceae Leptolegniellaceae ) past. To settle taxonomy investigate placement efforts undertaken isolate from original host, Pinnularia viridis infer nrSSU (18S) sequences. By targeted isolation, diatom parasitoid was rediscovered Heiðarvatn lake, Höskuldsstaðir, Iceland. Phylogenetic reconstruction shows that embedded within Saprolegniales largely unrelated both diatom-infecting Leptomitales ( Ectrogella Lagenisma those placed early-diverging Miracula Diatomophthora Oomycota