Submitted to: Fungal Genetics Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 1/20/2003
Publication Date: 3/19/2003
Citation: Goodwin, S.B., Levy, M., Cavaletto, J.R., Tian, Y. 2003. Multi-gene phylogenies reveal taxonomic confusion in the genus magnaporthe (abstract). Fungal Genetics Newsletter. 50(S):146.
Technical Abstract: The species of Magnaporthe which causes blast of rice formerly was called M. grisea. However, rice-infecting isolates were separated recently into the new species, M. oryzae. To determine in more detail the phylogenetic relationships of M. grisea, the internal transcribed spacer region of isolates from diverse hosts was sequenced. Sequences from related species, primarily Magnaporthe and Gaeumannomyces, were downloaded from GenBank, along with sequences representing the Diaporthales as an outgroup. Neighbor-joining analysis revealed that the genus Magnaporthe was polyphyletic; M. poae, M. rhizophila and the type species for the genus, M. salvinii, all clustered within Gaeumannomyces rather than with M. grisea and M. oryzae. The species M. grisea comprised a monophyletic group of several genetically distinct taxa that are mostly host delimited. In addition to M. oryzae, clusters with high bootstrap support that may represent separate species include: most isolates from Cenchrus/Pennisetum; isolates from Pennisetum typhoideum; isolates from Digitaria spp. (including the type for M. grisea); and some isolates from Eleusine hosts. These conclusions were confirmed by analysis of beta-tubulin and calmodulin sequences which gave the same results but with varying levels of resolution. The only exception was translation elongation factor alpha which did not resolve the Gaeumannomyces group from M. oryzae. The evolutionary diversification of M. grisea appears to be recent and rapid, and the multi-continental distribution of several forms likely reflects human-aided dispersal of infested seed. Clustering of the type species for the genus, M. salvinii, with Gaeumannomyces rather than with M. oryzae and M. grisea increases the taxonomic confusion surrounding this genus.