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Genetic Diversity of Potato virus Y Infecting Tobacco Crops in China

First, third, fourth, fifth, and sixth authors: Laboratory of Plant Virology, Department of Plant Pathology, Shandong Agricultural University, Tai'an, Shandong 271018, P. R. China; second author: College of Plant Sciences, Jilin University, Changchun, Jilin 130062, P. R. China; first and eighth authors: Department of Plant Biology and Forest Genetics, Genetics Center, Swedish University of Agricultural Sciences, PO Box 7080, SE-75007, Uppsala, Sweden, and Department of Agricultural Sciences, PO Box 27, FIN-00014, University of Helsinki, Finland; seventh author: Heilongjiang Tobacco Institute, Mudanjiang, Heilongjiang 157011, P. R. China.

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 PVY^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.