RT Journal Article SR Electronic T1 A previously established divergent lineage of the hybrid fungal pathogen Verticillium longisporum emerges as stem striping pathogen in British oilseed rape JF bioRxiv FD Cold Spring Harbor Laboratory SP 102541 DO 10.1101/102541 A1 Jasper R. L. Depotter A1 Michael F. Seidl A1 Grardy C. M. van den Berg A1 Bart P.H.J. Thomma A1 Thomas A. Wood YR 2017 UL http://biorxiv.org/content/early/2017/01/23/102541.abstract AB Population genetic structures illustrate evolutionary trajectories of organisms adapting to differential environmental conditions. Pathogen populations are typically shaped by co-evolution with their hosts through genetic co-structuring. Verticillium stem striping was mainly observed in continental Europe, but has recently emerged in other countries including the United Kingdom. The disease is caused by the hybrid fungal species Verticilliumlongisporum that originates from at least three separate hybridization events, yet strains from the hybridization event between Verticillium progenitor species A1 and D1 are mainly responsible for Verticillium stem striping. By using multi-locus genotype analysis, we reveal a hitherto un-described dichotomy within V. longisporum lineage A1/D1 that correlates with the geographic distribution of the isolates with an “A1/D1 West” and an “A1/D1 East” cluster according to their relative location in Europe. Genome comparison between representatives of the A1/D1 West and East clusters confirmed mutual common origin, excluding distinctiveness through separate hybridization events. The A1/D1 West population is responsible for the sudden emergence of Verticillium stem striping in the UK. Remarkably, this emergence is caused by a British V. longisporum population that is genetically more diverse than the entire A1/D1 East cluster. Conceivably, V. longisporum has previously established in the UK, but remained latent or undiagnosed as an oilseed rape pathogen until recently. This finding illustrates that a recent introduction is not a prerequisite for a pathogen to emerge, as environmental factors and cultural practices can also play a pivotal role in outbreaks of novel diseases.