Short-Term Host Selection Pressure Has Little Effect on the Evolution of a Monoclonal Population of Verticillium dahliae Race 1

Understanding pathogen evolution over time is vital for plant breedingand deployment of host resistance. In the context of a soilborne pathogen, the potential of host- directed evolutionof a Verticillium dahliaerace 1 isolate and genotypic variation of V. dahliaeassociated with two major hosts (lettuce and tomato) were determined. In total, 427 isolates were recovered over 6 years from a resistance screening nursery infested with a single V. dahliaerace 1 isolate. In a separate study, an additional 206 isolates representing 163 and 43 isolates from commercial lettuce and tomato fields, respectively, were collected. Analyses of isolates recovered from the screening nursery over 6 years revealed no changes in the race and mating typecomposition but did uncover seven simple sequence repeat (SSR) variant genotypes. No significant genotypic variation in V. dahliaewas observed between or within fields of either lettuce or tomato but pathogen populations were significantly differentiated between these two ...