Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2002
Publication Date: 10/1/2003
Citation: MARTIN, F.N., TOOLEY, P.W. PHYLOGENETIC RELATIONSHIPS AMONG PHYTOPHTHORA SPECIES INFERRED FROM SEQUENCE ANALYSIS OF THE MITOCHONDRIALLY-ENCODED CYTOCHROME OXIDASE I AND II GENES. MYCOLOGIA. 95:269-284. 2003. Interpretive Summary: We analyzed the relationships among 27 species of Phytophthora, a fungal group that includes many plant pathogens of importance to global agriculture. The group includes species that attack many important agricultural crops including potatoes, alfalfa, soybeans, and many others. We used sequences of DNA of a specific gene to compare species in the Phytophthora group and compared our results with results based on other genes, as well as on characters such as spore size and shape, type of fungal reproduction, and optimal temperature for growth. We found, as have past DNA workers, that species groupings observed based on the DNA sequence information did not always correlate with those based on observable characters such as spore size and shape. For the most part, the groupings of species we found based on the gene analyzed agreed with groupings based on another widely used gene, but there were some notable exceptions. The results will help other scientists better understand the relationships among the pathogen species in this large and important group, and the DNA sequence obtained may be used to develop identification and detection methods for some of these pathogens.
Technical Abstract: The relationships of 51 isolates representing 27 species of Phytophthora were assessed by aligning DNA sequences of the mitochondrially-encoded cytochrome oxidase IT gene and cytochrome oxidase 2 gene. The cox II gene analyses revealed 18 species grouping into 7 Glades and 9 species unaffiliated with a specific Glade. The relationships among species observed on cox XI gene trees did not exhibit consistent similarities in groupings for morphology, pathogenicity, and host range or temperature optima. The cox I: gene trees constructed using maximum parsimony for a bootstrap 50% majority-rule consensus tree for 13 species revealed 10 species grouping into 3 Glades and 3 species unaffiliated with a specific Glade. The groupings in general agreed with what was observed in the cox II tree. Phytophthora species relationships observed for the cox II gene tree were in general agreement with those based on the widely used internal transcribed spacer (ITS), regions of the ribosomal RNA gene cluster, with some notable exceptions. Analysis of combined data sets of ITS and cox III generated a tree that did not differ substantially from analysis of ITS data alone. The results help clarify species relationships in the important plant pathogen genus Phytophthora and will assist in the taxonomic placement of new species.