Genetic Diversity of Potato virus Y Infecting Tobacco Crops in China

Tian, Y. P., Liu, J. L., Zhang, C. L., Liu, Y. Y., Wang, B., Li, X.-D., Guo, Z. K., and Valkonen, J. P. T. 2011. Genetic diversity of Potato virus Y infecting tobacco crops in China. Phytopathology 101:377-387.Genetic variability of Potato virus Y (PVY) isolates infecting potato has been characterized but little is known about genetic diversity of PVY isolates infecting tobacco crops. In this study, PVY isolates were collected from major tobacco-growing areas in China and single-lesion isolates were produced by serial inoculation on Chenopodium amaranticolor. Most isolates (88%) caused systemic veinal necrosis symptoms in tobacco. Of these, 16 isolates contained a PVY(O)-like coat protein (CP) and PVY(N)-like helper component proteinase (HC-pro) and, in this respect, were similar to the PVY(N-wi), PVY(N:O), and PVY-HN2 isolates characterized from potato in Europe, the United States, and China, respectively; two isolates contained a PVV(O)-like HC-pro and a PVY(N)-like CP; another two isolates had recombination junctions in the CP-encoding region. Both the HC-pro and CP of PVY were under negative selection as a whole; however, seven amino acids in HC-pro and six amino acids in CP were under positive selection. Selection pressures differed between the subpopulations of PVY distinguished by phylogenetic analysis of HC-pro and CP sequences. When PVY isolates from potato were included, no host-specific clustering of the PVY isolates was observed in phylogenetic and nucleotide diversity analyses, suggesting frequent spread of PVY isolates between potato and tobacco crops in the field.