Molecular and Virulence Polymorphism in Clonal Lineages of the Wheat Leaf Rust Fungus, Puccinia triticina, in Canada

Isolates (69) of the wheat leaf rust fungus Puccinia triticina from the eastern (Ontario and Quebec), prairie (Manitoba and Saskatchewan), and Pacific (Alberta and British Columbia) regions of Canada were tested for virulence to 22 near- isogenic Thatcher wheat lines, and for amplified fragment length polymorphism (AFLP) using 10 specific amplification primer pairs. There were 37 distinct virulence phenotypes, and 69 molecular phenotypes with 164 AFLP markers. Both virulence and AFLP markers distinguished four major groups of isolates which could also be grouped according to geographic region or in broadly defined virulence groups. The weighted average virulence distance (simple distance coefficient) within groups was 0.21, and between groups was 0.36. The weighted average AFLP variation (1- Dice coefficient) within groups was 0.24, and between groups was 0.38. Isolates from the prairies with virulence to resistance gene Lr17 were in a distinct AFLP group while prairie isolates that were avirulent to Lr17 were in a different group. Isolates from eastern Canada avirulent to Lr2a and virulent to Lr2c, and isolates avirulent to Lr22b were also in distinct AFLP groups. There was a 0.53 correlation between the virulence polymorphism and AFLP variation generated by all 10 selective primer pairs. Asexual reproduction prevents genetic exchange between clonal groups of P. triticina, thus preserving their distinctiveness.