Submitted to: Fungal Genetics Newsletter
Publication Type: Abstract Only
Publication Acceptance Date: March 23, 1997
Publication Date: N/A
Technical Abstract: As part of a phylogenetically-based revision of Fusarium, we investigated the evolutionary history of the phytopathogenic Gibberella fujikuroi species complex by parsimony analysis of DNA sequences from multiple loci. Gene phylogenies inferred from five loci were generally concordant, providing strong support for a fully resolved phylogeny of most species. The biogeographic hypothesis proposed from the phylogenetic evidence is based primarily on the formation of natural barriers associated with the fragmentation of the ancient super- continent Gondwanaland over the last 100 million years. Discordance of the nuclear rDNA internal transcribed spacer 2 (ITS2) gene tree with trees from the other loci is due to nonorthologous ITS2 sequences. The molecular evidence suggests that two highly divergent ITS2 types were combined by an ancient interspecies hybridization or gene duplication that occurred early in the evolutionary radiation of the Gibberella lineage of Fusarium. Only one of the two ITS2 types is discernible within each species when conserved ITS primers were used; however, the second ITS2 type was recovered from every strain tested with ITS2 type- specific PCR primers. Distribution of the major ITS2 type within the species lineages obscures true phylogenetic relationships because the major ITS2 type switched between a type I and type II sequence at least twice during the evolution of the G. fujikuroi complex. Remarkably, the two intragenomic ITS2 types have escaped concerted evolution within this lineage of Fusarium.