A molecular phylogeny of Phytophthora and related oomycetes

Phylogenetic relationships among 50 Phytophthora species and between Phytop hthora and other oomycetes were examined on the basis of the ITS sequences of genomic rDNA. Phytophthora grouped with Pythium, Peronospora, and Haloph ytophthora, distant from genera in the Saprolegniales. Albugo was intermedi ate between these two groups, Unlike Pythium, Phytophthora was essentially monophyletic, all but three species forming a cluster of eight clades, Two clades contained only species with nonpapillate sporangia, The other six cl ades included either papillate and semipapillate, or semipapillate and nonp apillate types, transcending traditional morphological groupings, which are evidently not natural assemblages, Peronospora was related to P, megakarya and P, palmivora and appears to be derived from a Phytophthora that has bo th lost the ability to produce zoospores and become an obligate biotroph, T hree other Phytophthoras located some distance from the main Phytophthora-P eronospora cluster probably represent one or more additional genera, (C) 20 00 Academic Press.