DNA fingerprinting and vegetative compatibility analysis indicate multiple origins for Verticillium dahliae race 2 tomato isolates from Ontario, Canada

RFLP, DNA fingerprinting and VCG methods were used to characterize fourteen Verticillium dahliae isolates collected from southwestern Ontario, Canada. The isolates were typed as not pathogenic to tomato (NP), race 1 (avirulent on cvs carrying the Ve resistance gene) or race 2 (virulent on Ve cvs). On the basis of RFLPs, RAPDs, and DNA fingerprints detected by hybridization to a dispersed, repetitive genomic DNA probe, the isolates were classified into five DNA types. Type I included two NP isolates. Type II included four race 2, and three NP isolates. Types III and V were represented by single race 2 and race 1 isolates, respectively. Type IV included one race 2, and two race 1 isolates. Vegetative compatibility was determined for selected NP, race 1, and race 2 isolates of each race type/DNA type combination. Isolates of the same DNA type were compatible, as were type II and III isolates (VCG 4B), and type IV (VCG 2A) and V isolates (VCG 2B). These data show a level of genetic diversity not previously identified in the V. dahliae tomato pathogen population, and suggest multiple origins for the Ontario race 2 pathotype.