Characterization of a Novel Resistance-Breaking Isolate of Potato Virus Y in Nicotiana Tabacum

Potato virus Y (PVY) was identified from a PVY-resistance flue-cured tobacco variety KF120 showing vein necrosis at Buron province, Korea. Biological properties of the isolate named PVY-ToBR1 was characterized using various host plants with another isolate PVY-ToJC37. The isolated PVY-ToBR1 induced systemic vein necrosis symptoms on a PVY-resistant tobacco cultivar (VAM) harboring potyvirus resistant va gene, though tissue printing showed the systemic movement of virus was slightly delayed. By contrast, the isolate PVY-ToJC37 failed to infect VAM plants and the virus was not detected on inoculated leaf and systemic leaves in VAM plants. Similarly, the isolated PVY-ToBR1 induced distinctly systemic vein necrosis symptoms on PVY-resistant tobacco cultivars (V.SCR, PBD6, TN86, TN90, Virgin A Mutant, NC744, and Wislica) that have the recessive potyvirus resistance gene va, but PVY-ToJC37 did not infect systemically infect these tobacco cultivars, suggesting that PVY-ToBR1 is a novel resistance-breaking isolate in tobacco. The coat protein (CP) genes of PVY-ToBR1 and PVY-ToJC37 were amplified using RT-PCR assays with specific primers for PVY isolates and nucleotide sequences of the CP genes were determined. The isolate PVY-ToBR1 showed 88.4% - 99.4% and 86.6% - 99.4% CP identities to the 46 different PVY isolates at the nucleotide and amino acid, respectively. Phylogenetic relationship from CP comparisons showed that PVY-ToBR1 isolate clustered with PVYNTN isolates and PVY-ToBR1 isolate more closely related to the isolates from European than from North American PVY NTN.