Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/31/2005
Publication Date: 8/1/2004
Citation: Ordonez, M.E., Szabo, L.J., Groth, J.V. 2004. Evolutionary relationship between sympatric microcyclic forms of Tranzschelia spp. Phytopathology. 94:S79.
Technical Abstract: Speculations have been made regarding the position of microcyclic life cycles in the evolution of rust fungi. It is believed that the change from a macrocyclic to a microcyclic form is unidirectional and permanent, serving as a basis for speciation. To test this we compared the microcyclic autoecious Tranzschelia fusca and the macrocyclic T. arthurii. Paired collections of the two rusts occurring in close proximity in the Northern forests of Minnesota were made on Anemone quinquefolia, as well as telial collections of T. arthurii from Prunus spp. Phylogenetic analysis of DNA sequence data from the nuclear rDNA ITS region revealed the separation of the two species into three well supported groups, rather than two: two macrocyclic and one microcyclic. However, there were few exceptions. Physical proximity of pairs did not correlate with DNA sequence type. These results indicate that the primary separation of the macrocyclic T. arthurii and microcyclic T. fusca occurred long ago and suggests that switching between microcyclic and macrocyclic life cycles may occur occasionally.