Taxonomic and phylogenetic analysis of Saprolegniaceae (Oomycetes) inferred from LSU rDNA and ITS sequence comparisons

The aim of this study was to improve our knowledge about the taxonomy and p hylogeny of the family Saprolegniaceae, a group of water molds including se veral pathogens of plants, fish and crustacea. ITS and LSU rDNA were sequen ced for representatives of forty species corresponding to ten genera (Achly a, Aphanomyces, Brevilegnia, Dictyuchus, Leptolegenia, Plectospira, Pythiop sis, 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 clos ely related to the eccentric species of the genus Achlya. The genus Achlya appears polyphyletic, corroborating more or less the three known subgroups, defined by their sexual spore type (eccentric, centric and subcentric). Th e achlyoid type of spore dehiscence, shared by Aphanomyces and Achlya gener a, is shown to be an ancestral character. The saprolegnioid, dictyoid and t hraustothecoid types of spore dehiscence are derived characters but their r elative evolutionary positions are not resolved.