Phylogeny of the Peronosporomycetes (Oomycota) based on partial sequences of the large ribosomal subunit (LSU rDNA)

The phylogeny of the nuclear large ribosomal subunit (LSU) rDNA from Perono sporomycetes (Oomycota) was studied. Five orders Rhipidiales, Leptomitales, Saprolegniales, Pythiales and Peronosporales were included in the study in order to reveal phylogenetic relationships within the group. Based on maxi mum parsimony, neighbour-joining and maximum-likelihood the Peronosporomyce tes seem to have evolved as two major lineages. One lineage includes member s of the Rhipidiales, Leptomitales and Saprolegniales and the other include s the members of Pythiales and Peronosporales. However, the inclusion of Rh ipidiales in Saprolegniomycetidae was not well supported. Leptomitales were placed basal to the Saprolegniales in the LSU rDNA based tree. In the Sapr olegniaceae sensu Into the primary zoospore seems to have been lost several times in the evolution of this family. Species of Aphanomyces were placed on the most basal branch in this family. The obligate parasite, Albugo, was placed on the most basal branch within the Peronosporomycetidae. Phytophth ora showed a closer relationship to Peronospora and Peronophythora than to Pythium suggesting that this genus should be removed from Pythiales to Pero nosporales.