Evaluation of resistance levels to verticillium wilt in UK oilseed rape varieties and relevance to productivity

Abstract

This project aimed to determine whether consistent and reproducible differences in the levels of verticillium wilt infection occur between oilseed rape varieties on the AHDB Recommended List (RL). Inoculated or naturally occurring infection tests were used to determine the relevance of infection to oilseed rape production, in terms of the yield loss incurred. Such information could be potentially be used to devise disease resistance ratings or rankings on the RL.

Over the three years of testing, highly consistent differences between varieties, in terms of the level of symptom expression, were observed. These occurred regardless of whether trials were inoculated with fungal microsclerotia or established on land associated with high levels of infection. Objective scoring methodology was devised that would be appropriate for use in variety evaluation systems.

Clear and significant differences in disease levels were observed between varieties and, though none was found to be completely resistant, several showed consistently low infection levels. This differentiation allowed the selection of three varieties with high levels of partial resistance and three more susceptible varieties for inclusion in four trials to investigate the effects of verticillium on yield. Inoculation of blocks of land was used to create differentiation in disease pressure on the resistant and susceptible varieties. Though yield effects were variable, losses were larger in the trials with clear differences in disease levels between inoculated and non-inoculated blocks. Susceptible varieties showed significantly greater yield depression in one trial, and resistant varieties showed little or no effect throughout all trials. The project has shown that variety reactions to verticillium infection are significantly and consistently different, and that the differences are great enough to enable a rating system to be introduced. Selecting resistant varieties on land with known high levels of infection is highly likely to mitigate against yield loss. Visible production of microsclerotia was also less on more resistant varieties, and this factor could also contribute towards disease management, by reducing the return of disease to the soil.