Potato (Solanum tuberosum L.) is a staple food in the world. Potato virus Y (PVY; Potyvirus: Potyviridae ) is an important virus that affects yield and quality of potatoes. PVY exists as biologically distinct strains: PVY-N induces systemic veinal necrosis in tobacco, PVY-O causes hypersensitive response (HR) in potato cultivars carrying the Ny gene and PVY-NTN produces necrotic rings on the tubers of sensitive potato cultivars. The vsiRNA profiles of three distinct PVY strains, ordinary (PVY-O), tobacco-veinal necrotic (PVY-N) and tuber-necrotic (PVY-NTN) strains were determined in potato cv. Russet Burbank. The frequency and distribution of vsiRNAs varied among different strains. PVY-NTN infected plants accumulated the highest population of PVY-vsiRNAs in comparison to plants infected with PVY-O and PVY-N. In PVY-infected plants, the 21 nt class was predominant whereas in healthy potato plants 24 nt class had the maximum population. VsiRNAs were derived from every nucleotide position of the PVY genome and certain hotspots were identified which produced relatively more vsiRNAs. Additionally, six novel microRNAs were found in PVY-infected plants. Potato virus S (PVS; Carlavirus: Betaflexiviridae) is another important potato virus distributed worldwide. The outcome of mixed infection of PVS and PVY was studied under controlled conditions in three potato cultivars, Defender, Desiree and Russet Burbank. Results showed that PVS has an antagonistic effect on PVY replication in mixed infection. The antagonistic effect was associated with less severe symptoms in dual infections as well as reduced PVY multiplication. Symptoms of PVS were not visible in Desiree and Russet Burbank plants except Defender which showed bronzing spots on the leaves. PVY symptoms included mosaic, mottling and leaf drop. It was found that the antagonistic effect of PVS on the replication of PVY is independent of host genetic background as the same pattern was found in all three potato cultivars. Potato cultivars such as Desiree carrying the Ny gene show HR to infection with the ordinary strain of PVY. In comparison to Russet Burbank, PVY levels in Desiree decreased with increasing number of days post-inoculation. The HR was found to be specific to PVY-O and was not elicited by infection by PVY-N or PVY-NTN.

Potato virus Y (PVY) infects a wide host range mainly within the Solanaceae and is distributed worldwide. PVY is transmitted by more than 40 aphid species in a non persistent manner. Isolates of the PVY species are highly variable at biological, serological and molecular levels. Epidemiological studies have highlighted the emergence of distinct potato PVY variants able to induce necroses on potato tubers. Due to the lack of efficient resistance to PVY isolates inducing necrotic symptoms in cultivated varieties and the plant-to-plant transmission of isolates through the daughter tubers, PVY has become the most economically important virus for the potato industry. The review offers an overview of several decades of research on PVY but also focuses on the latest data obtained by expert on PVY worldwide on the biological characteristics of PVY, interactions between aphids-hosts, its evolution and management. Identified knowledge gaps to understand further PVY biology will be discussed.

Potato (Solanum tuberosum) is one of the most important crops grown in Washington State. In 2011, Washington growers raised 160,000 acres of potatoes with an average yield of 615 CWT per acre, 98 CWT total, with a farm gate value of over $734 million. Late blight, caused by Phytophthora infestans, is an extremely devastating disease of potato worldwide. Defender is the only cultivar with foliar and tuber resistance to this disease in the U.S. However, under field conditions this cultivar exhibits high susceptibility to infection by Potato virus S (PVS, family Betaflexiviridae, genus Carlavirus).

Characterization and identification of potato viruses and viroids; Viruses, viroids, mycoplasmas and diseases with a virus-like; Viruses and potatoes.

Potato viruses cause significant potato yield loss world wide. It is important to understand the nature of the potato virus populations present in a geographical region in order to develop appropriate control strategies. A wide-ranging survey of potato viruses in potatoes being grown in the northeastern USA had never been done. A survey of six potato viruses, Potato virus A (PVA), Potato virus M (PVM), Potato virus S (PVS), Potato virus X (PVX), Potato virus Y (PVY), and Potato leafroll virus (PLRV), was conducted in New York and Maine during 2002 and 2003. Leaf samples were tested by ELISA and PVY-positive samples were further tested to determine if a necrotic strain of PVY (PVYN, PVYN:O, or PVYNTN) was present. In both years, PVY and PVS were identified in a majority of the samples, and mixed infections predominated in 83% of the symptomatic leaves in 2002. Of the total 394 PVY-positive samples, three reacted with monoclonal antibody (MAb) 1F5 and caused veinal necrosis (VN) in tobacco. Two of these isolates caused tuber necrosis in the potato cv. Yukon Gold. Three PVY isolates reacted with MAb 1F5 but did not cause VN in tobacco, and two caused VN but did not react with MAb 1F5. Two of the necrotic PVY isolates collected, along with a PVYO isolate, were used to conduct multi-year experiments to determine the impact of PVY strain, potato cultivar, and time of infection on marketable yield and tuber infection efficiency. It was found that final disease incidence in the field could not be used to predict tuber infection, as inoculated plants testing negative in the field produced infected tubers. PVY infection decreased marketable yield, but yield was dependent on the potato cultivar and inoculation time. PVY infected between 25 and 100% of the marketable tubers. Our results suggest that, compared with other isolates, necrotic strains of PVY might be less effectively removed in seed potato production systems and this may explain the emergence of necrotic strains.