Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2000
Publication Date: N/A
Interpretive Summary: Two fungi that cause similar disease on the invasive aquatic weed waterhyacinth were examined to determine their relationship. Both fungi are capable of controlling the spread of the weed if sprayed in large quantities in weed-infested areas. This study demonstrates that the two fungal species in fact are almost certainly a single species so that independent registration of these organisms is unnecessary. This study will directly benefit the waterways of the Southern United States and those that use them because the fungi may eliminate or reduce the use of herbicides for weed control. By doing so, the procedure may help protect water quality and reduce human exposure to synthetic chemicals.
Technical Abstract: Phylogenetic relationships among isolates of Cercospora species pathogenic to waterhyacinth, collected from several geographic regions of the world, were examined by using partial DNA sequences from three protein-coding genes, elongation factor-1a, beta-tubulin, and histone H3. In cladograms from individual, as well as from combined datasets for 14 isolates, two statistically well-supported clades were found: a major grouping of isolates from Brazil, Venezuela, Mexico, Florida (United States), South Africa, and Zambia; and a minor grouping of isolates from Texas (United States). 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 the species 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 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.