| Phylogenetic relationships among isolates of Cercospora species pathogenic to waterhyacinth, collected from several geographic regions of the weed, were examined by using partial DNA sequences from three protein-coding genes, elongation factor-1alpha, beta-tubulin, and histone 3. Each gene included at least one intron area. In cladograms from individual, as well as from combined datasets for 14 isolates, with the maximum parsimony, maximum likelihood, and neighbor-joining methods, two statistically well-supported clades were found: a major clade-grouping of isolates from Brazil, Venezuela, Mexico, Florida (United States), South Africa, and Zambia; and a minor clade-grouping of isolates from Texas (United States). In the grouping pattern of the phylogenetic trees, most of the isolates have spread together with the plant host, from its center of origin in South America. The isolates grouped together by DNA analysis had distinctive differences in colony color, pigmentation color, and intensity, growth rate, cercosporin production, and virulence. In addition, the rDNA region containing ITS1, ITS2, and the 5.8S gene were invariant even when compared with C. beticola as the outgroup. In the discriminant analysis, the fatty acids methyl ester (FAME) profiles had reduced resolution for differentiating populations and species among isolates of C. piaropi/C. rodmanii and the level of resolution was influenced by the age of the colonies. The grouping defined by discriminant analysis of FAME profiles had no relation to the grouping defined by DNA analysis. Shape and dimensions of conidia were unreliable criteria for taxonomic differentiation of isolates that composed the two clade-groupings. In addition, the isolate that typified C. rodmanii did not show differences in DNA sequence in relation to the other isolates grouped in the major clade, including some that had conidial size and morphology typical of C. piaropi. Therefore, the separation of these species, besides of not having strong phenotypic support, did not also have support from the phylogenetic analysis. Consequently, the description of the species C. piaropi is emended herein to include C. rodmanii as a synonym. |
