Taxonomic and phylogenetic analysis of Saprolegniaceae (Oomycetes) inferred from LSU rDNA and ITS sequence comparisons.
The taxonomy and phylogeny of the family Saprolegniaceae, a group of water moulds including several pathogens of plants, fish and crustacea, were studied. ITS and LSU rDNA were sequenced for representatives of 40 species corresponding to 10 genera (Achlya, Aphanomyces, Brevilegnia, Dictyuchus, Leptolegnia, Plectospira, Pythiopsis, Saprolegnia, Thraustotheca). Phenetic and cladistic analyses were then carried out. The species Brevilegnia bispora does not appear to belong to the family Saprolegniaceae. Plectospira myrianda clusters with Aphanomyces spp. and they constitute an ancestral group. Thraustotheca clavata is closely related to the eccentric species of the genus Achlya. The genus Achlya appears polyphyletic, corroborating more or less the 3 known subgroups, defined by their sexual spore type (eccentric, centric and subcentric). The achlyoid type of spore dehiscence, shared by Aphanomyces and Achlya genera, is shown to be an ancestral character. The saprolegnioid, dictyoid and thraustothecoid types of spore dehiscence are derived characters but their relative evolutionary positions are not resolved.