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Potato cultivar Exploits and breeding clone F87084 have been considered resistant to Potato virus Y (PVY). To further explore the degree of resistance and whether the resistance is strain specific, these materials, together with cultivar Rochdale Gold-Dorée and breeding line F02010, were investigated for their response to different PVY strains including PVY, PVY, PVY and PVY. Both F02010 and Rochdale Gold-Dorée were readily infected with all tested PVY strains after either mechanical or graft inoculation, indicating susceptibility of the materials to PVY. F87084 was unable to be infected by any of the tested PVY strains as no ELISA-detectable level of PVY were found in plants after either mechanical or graft inoculation, demonstrating extreme resistance in F87084 to all strains of PVY tested. Exploits was infected with PVY/PVY/PVY after either mechanical or graft inoculation, indicating susceptibility of the cultivar to these PVY strains. The cultivar was also infected readily with PVY after graft inoculation. However, despite induction of local lesions on the inoculated leaves, mechanical inoculation with PVY may or may not lead to systemic symptoms and ELISA-detectable level of PVY, depending on temperature. At low temperature (e.g., 22 °C), no visible systemic symptoms or ELISA-detectable level of PVY was found in the plants; whereas at high temperature (e.g., 30 °C), systemic symptoms and high level of PVY were detected in the plants. These results demonstrate that Exploits possesses temperature-dependent hypersensitive resistance to PVY. Analysis of a segregating population of F87084 × F02010 revealed that the ER in F87084 is controlled by a dominant resistance gene. [ABSTRACT FROM AUTHOR]

A field isolate of Potato virus Y (PVY) was collected in New Brunswick, Canada in 2007 due to unusual symptoms observed on different potato cultivars. To unveil the PVY strain identity, tobacco and potato bioassays, PVY O and PVY N -specific antibody-based enzyme-linked immunosorbent assays, and reverse-transcription polymerase chain reaction (PCR)-based genotyping were carried out. All the assays demonstrated that the isolate, designated as PVY O -FL in this study, belonged to the PVY O strain group. Greenhouse tests with the potato cvs. FL 1533 and Jemseg confirmed the severe nature of infection by PVY O -FL. The complete genome sequences of PVY O -FL and PVY O -RB, the latter a mild PVY O isolate, were determined. BLAST analysis revealed that the two isolates shared 97 and 98% sequence identities at the nucleotide and polyprotein levels, respectively. Further BLAST analysis unveiled that PVY O -FL shared 99.7% nucleotide sequence identity with PVY O -Oz, an isolate reported in New York, United States, whereas the PVY O -RB isolate shared 99.2% sequence identity with PVY O -139, a PVY O isolate reported in New Brunswick, Canada. A phylogenetic tree of available, full-length sequences of PVY isolates demonstrated two subgroups within the PVY O branch, one clustered with PVY O -RB and the other with PVY O -FL. Group-specific sense primers for differentiation of the two subgroups were developed and evaluated. A limited survey of potato tubers collected from a field plot at the Potato Research Centre, Agriculture and Agri-Food Canada, using the newly developed PCR primers, indicated that 65.3 and 2.4% of the PVY O -positive tubers were infected with PVY O isolates belonging to the PVY O -FL and PVY O -RB subgroups, respectively. Assessment of the pathogenicity of three representative isolates from each subgroup on the potato cv. Jemseg demonstrated that severe and mild symptoms were induced by the PVY O -FL-like and PVY O -RB-like isolates, respectively.