New phylogenetic insights into Saprolegniales (Oomycota, Straminipila) based upon studies of specimens isolated from Brazil and Argentina

Abstract

Saprolegniales is a complex and monophyletic order of oomycetes. Their members inhabit terrestrial, freshwater, and marine ecosystems and have a worldwide distribution. In these ecosystems, they are found as saprobes, parasites, or even pathogens of animals and plants of economic importance. In this study, a concatenate phylogeny of the partial LSU and complete ITS rDNA regions is presented, including isolates from Brazil and Argentina, which were sequenced after a detailed morphological analysis. Among the sequenced species, Achlya orion, Leptolegnia eccentrica, Phragmosporangium uniseriatum, and Pythiopsis irregularis are included for the first time in a phylogeny. Our results are in agreement with the recent informal proposals outlined in taxonomic overviews of the Oomycota of G.W. Beakes and collaborators, who placed the family Verrucalvaceae into the Saprolegniales and introduced the family Achlyaceae to group Achlya s.s., Brevilegnia, Dictyuchus, and Thraustotheca. These results also support the transference of Achlya androgyna to Newbya. Leptolegnia appears as paraphyletic, with the separation of L. eccentrica from the other species of this genus. In addition, Phragmosporangium, which is herein sequenced for the first time, clustered as sister to some species of Aphanomyces, including the type species, A. stellatus.