Potato virus Y (PVY) is one of the most damaging virus in potato industries and it can cause crop loss up to 80%. Several strains of PVY have been identified that differ by the symptoms they cause. PVY^O, the common strain causes mosaic symptoms; PVY^C that causes stipple streak; PVY^N, the necrotic strain that causes mild foliage symptoms, but necrosis in tobacco plants. Mixed infections of common and necrotic strains are frequent, and genomes can mix, producing recombinant strains. Over the last years, several reports (Davie et al. 2017, Gray et al. 2010, Karasev et al. 2013, MacKenzie et al. 2018, Elwan et al. 2017, Chikh Ali et al. 2013) from all over the world are declaring that recombinant strains are becoming dominant. Those recombinant strains, mostly PVY^N-Wi (PVY^N:O) and PVY^NTN (main cause of tuber necrosis) are of increasing importance in European seed stocks. Symptoms on plants alone cannot distinguish these virus strains. Diagnosis between the different PVY strains can be difficult, as the widely used serological method (ELISA) is only able to distinguish PVY strain between O- and N-serotype but is unable to distinguish recombinant strains from non-recombinant. Recent emergence of genetically recombinant and serologically different strains of PVY has led to the development of several diagnostic protocols to determine strain identity and to detect mixed strain infections including simplex and multiplex PCR assays. Other approaches include a combination of immunological and molecular methods, though no common method for the detection of PVY and its strains has been adopted by the pathogen detection laboratories within Europe.

The main aim of the project was to develop and validate a protocol for the detection and identification of Potato virus Y and its associated strains. During the project different PVY strain identification tests described in published scientific articles were considered and data on these tests were provided by project partners in order to select those that allowed PVY wide range strain identification; an interlaboratory comparison was organized and a validated protocol was agreed and is presented in Annex 1.