Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 20, 1998
Publication Date: N/A
Technical Abstract: In terms of its abundance and diversity, Fusarium oxysporum Schlecht. is one of the most successful plant pathogens as reflected in the 150 host specific formae speciales described for this vascular wilt pathogen. Each forma specialis is distinguished by a unique host range and may consist of one or more vegetative compatibility groups (VCGs) and pathogenic races. Numerous studies have documented considerable genetic diversity within pathogenic and putatively nonpathogenic strains of F. oxysporum. In taxonomic practice, most researchers use Snyder and Hansen's emendation of F. oxysporum which includes all of the species recognized in the infra- generic group called Section Elegans. In this molecular phylogenetic study, DNA sequences from the mitochondrial small subunit ribosomal DNA and translation elongation factor EF-1 alpha introns and exons were used to infer phylogenetic relationships, using different tree building methods and measures of clade stability. A clade containing the F. oxysporum and Gibberella fujikuroi complexes and an Asian grass-associated clade formed an unresolved trichotomy in the molecular phylogeny. Four clades within the F. oxysporum complex were resolved comprising the 332 ingroup strains sequenced. This complex is strongly supported as monophyletic; however, several F. oxysporum like strains representing phylogenetically distinct species were nested outside of this complex. Approx. 80% of the formae speciales with two or more VCGs appear to be either para- or poly-phyletic. Isolates from humans have multiple evolutionary origins; however, 19 of the 41 clinical strains sequenced formed a single clade. Ongoing studies are directed at extending this database to every forma specialis and VCG and towards developing a robust phylogeographic hypothesis.