Turnip Yellows Virus Resistances Differ in Effectiveness Against Three Diverse Isolates

Turnip yellows virus (TuYV; species Turnip yellows virus, genus Polerovirus, family Solemoviridae) is one of the most economically important pathogens of canola (syn. oilseed rape, Brassica napus L.) worldwide. Despite this, there are few cultivars with TuYV resistance available to canola growers. Several sources of quantitative resistance have been identified in Europe and Australia in varieties of B. napus and its progenitor species B. oleracea and B. rapa. These resistances were identified and examined in studies using only a single isolate of TuYV, which is a highly diverse virus. In this study, we evaluated the resistance responses of eight such varieties when challenged with three genetically diverse TuYV isolates under greenhouse conditions. Plants were inoculated with TuYV using its vector, Myzus persicae, and the infection response was measured by comparing enzyme-linked immunosorbent assay absorbance values with those of a susceptible control variety. The resistance response of each variety differed from highly resistant to highly susceptible primarily depending on the TuYV isolate but also the experiment and time after inoculation. A spectrum of resistance specificity was observed, with some varieties being moderately to highly resistant against all three isolates and other varieties being resistant to one isolate and susceptible to the other two. This demonstrates that previous approaches to resistance phenotyping using a single TuYV isolate can result in the development of strain-specific resistance that is ineffective when deployed against the broader virus population. Resistance screening programs should challenge lines against a range of locally common virus strains to increase the likelihood of identifying durable resistance.