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Poster: Epidemiology: Systematics/Evolution


Phylogenomic analysis supports polyphyly in Pythium sensu lato
E. GOSS (1), M. Ascunce (2), J. Huguet-Tapia (2), E. Braun (2), A. Ortiz-Urquiza (2), N. Keyhani (2) (1) University of Florida, U.S.A.; (2) University of Florida, U.S.A.

Pythium is a large and morphologically diverse genus that includes economically costly root pathogens. Molecular phylogenies support the morphological clustering of Pythium into three monophyletic groups: Clades A-D are characterized by filamentous sporangia, clades E-J by globose sporangia, and clade K has been reassigned to the new genus Phytopythium. However, different markers have supported different relationships among these clades and to the genus Phytophthora. The absence of a robust phylogeny has prevented advances in Pythium systematics and evolutionary genomics. In the last six years, whole genome sequences have been generated for seven Pythium species and ten other oomycetes. We conducted a phylogenomic analysis using the nucleotide sequences of 277 orthologous genes found in the 17 analyzed oomycete genomes to examine the evolutionary relationships among the major clades of Pythium. Our results supported the position of Phytopythium vexans as a sister clade to Phytophthora. As expected, the remaining Pythium taxa formed two monophyletic groups. One group was composed of three taxa that correspond to Pythium clades A, B and C, and the other group contained taxa representing clades F, G and I, which was consistent with previous Pythium phylogenies. However, the group containing Pythium clades F, G and I formed a sister group to the Phytophthora-Phytopythium clade and thus Pythium clades F-J are not monophyletic.