Potato virus Y (PVY) is one of the most important pathogens affecting tobacco. Some cultivars, such as VAM and Wiślica, carry va type of resistance which can be broken by more virulent strains of PVY. Here, we compare effects of inoculation of resistant (VAM, Wiślica) and susceptible (Samsun H, Burley 21) cultivars using three PVY isolates differing with their virulence. We recorded symptoms of PVY infection two, three and four weeks after inoculation and confirmed the presence of the virus in the leaves using DAS-ELISA tests done four weeks after inoculation. We observed one-week delay in the development of the first disease symptoms on resistant cultivars compared to susceptible ones. However, four weeks after inoculation, DAS-ELISA tests confirmed the presence of the virus in the tissues with visible symptoms. At this time, disease symptoms were observed on all tested cultivars inoculated with two isolates (named IUNG 16 and IUNG 13). The least virulent isolate (IUNG 5) broke the resistance of Wiślica but not VAM, what contradicts results of previous inoculations tests using this isolate. Previously, IUNG 5 was unable to break the resistance of Wiślica. The observed change of virulence of isolate IUNG 5 was confirmed in subsequent inoculation tests: PVY from the infected Wiślica broke resistance of VAM.

Keywords: Potato virus Y, PVY resistance, Nicotiana tabacum