Variable impact of Verticillium longisporum on oilseed rape yield in field trials in the United Kingdom

The Verticillium genus comprises economically important plant pathogens that collectively affect a broad range of annual and perennial crops. Verticillium longisporum mainly infects brassicaceous hosts, including oilseed rape. The most conspicuous symptom of V. longisporum infection on oilseed rape is black stem striping that appears towards the end of the cropping season. Thus far, the impact of V. longisporum infection on oilseed yield remains unclear. Verticillium stem striping recently emerged as a new disease in UK and currently displays a widespread occurrence in England. In this study, we assessed the impact of Verticillium stem striping on British oilseed rape production. To this end, four cultivars (Incentive, Vision, Harper and Quartz) were grown in field plots with different levels of V. longisporum disease pressure at different locations over two consecutive years. Whereas Incentive and Vision developed relatively few stem striping symptoms, Harper and especially Quartz showed severe symptoms during these field experiments. Furthermore, higher inoculum levels induced more severe symptoms in these cultivars. Intriguingly, significant yield reductions upon V. longisporum infection only occurred in a single field trial on all tested oilseed rape cultivars. Thus we conclude that Verticillium stem striping does not consistently impact oilseed rape yield, despite the occurrence of abundant disease symptoms.