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Mutations in Potato virus Y Genome-Linked Protein Determine Virulence Toward Recessive Resistances in Capsicum annuum and Lycopersicon hirsutum

¹Station de Pathologie Végétale, Institut National de la Recherche Agronomique, F-84143 Montfavet cedex, France; ²Danish Institute of Agricultural Sciences, Biotechnology Group, Thorvaldsensvej 40, opg 8. 2. sal, DK-1871 Frederiksberg C, Denmark; ³Unité de Génétique et d'Amélioration des Fruits et Légumes, Institut National de la Recherche Agronomique, F-84143 Montfavet cedex, France

The recessive resistance genes pot-1 and pvr2 in Lycopersicon hirsutum and Capsicum annuum, respectively, control Potato virus Y (PVY) accumulation in the inoculated leaves. Infectious cDNA molecules from two PVY isolates differing in their virulence toward these resistances were obtained using two different strategies. Chimeras constructed with these cDNA clones showed that a single nucleotide change corresponding to an amino acid substitution (Arg119His) in the central part of the viral protein genome-linked (VPg) was involved in virulence toward the pot-1 resistance. On the other hand, 15 nucleotide changes corresponding to five putative amino acid differences in the same region of the VPg affected virulence toward the pvr2¹ and pvr2² resistances. Substitution models identified six and five codons within the central and C terminal parts of the VPg for PVY and for the related potyvirus Potato virus A, respectively, which undergo positive selection. This suggests that the role of the VPg-encoding region is determined by the protein and not by the viral RNA apart from its protein-encoding capacity.