The emerging BritishVerticillium longisporumpopulation consists of aggressiveBrassicapathogens

ABSTRACT The impact of diseases depends on the dynamic interplay between host, pathogen and the environment. Newly emerging diseases may be the consequence of novel pathogen introductions that are typically associated with unpredictable outcomes, as their interaction with the host in a novel environment is unprecedented. Alternatively, new diseases may emerge from latent, previously established, pathogen populations that are triggered by changes in environmental factors like weather, agricultural practices and ecosystem management. Verticillium stem striping recently emerged in British oilseed rape ( Brassica napus ) production from a latent Verticillium longisporum population. V. longisporum is a hybrid fungal pathogen consisting of three lineages, each representing a separate hybridization event. Despite its prevalence, little is known of the pathogenicity of the British V. longisporum population. In this study, the pathogenicity of British isolates was tested on four different cultivars of three different Brassica crop species as well as on the model plant Arabidopsis thaliana and compared with previously characterized V. longisporum strains from other regions of the world, including representatives of all three hybrid lineages. Intriguingly, the British isolates appeared to be amongst the most pathogenic strains on Brassica crops. In conclusion, Verticillium stem striping poses a genuine threat to oilseed rape production as the British V. longisporum population consists of aggressive pathogens that have the potential to significantly impact Brassica crops.