Resistance of Potato Cultivars as a Determinant Factor of Potato virus Y (PVY) Epidemiology

Potato virus Y (PVY) is considered the most economically damaging virus for seed-potato production. PVY isolates are usually divided into three historical PVY strains, namely PVYC, PVYO and PVYN. More recently, recombinant strains named PVYNTN and PVYN-Wi appeared in Europe and North America, rapidly spread into seed-potato production and gradually replaced historical strains. This progression can be explained by several factors, including the differential susceptibility of cultivars to PVY strains. This article presents the results of a Swiss survey of PVY strains conducted in 2012 in which the progressive increase of the prevalence of PVYN-Wi was observed. The occurrence of PVY strains in the two main potato cultivars grown in Switzerland, cv. Agria and cv. Charlotte, is described through the 2012 survey and one additional PVY strain survey conducted in 2014. Both surveys were completed with a mechanical-inoculation assay. The inoculation assay showed that cv. Agria is more susceptible to PVYN-Wi than to PVYNTN, whereas cv. Charlotte is susceptible to both strains. The inoculation assay also showed that the expression of symptoms on cultivars is strain-dependent. These results stress the major role of the resistance profile of cultivars to explain the balance of the PVY strains in potato crops.