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Different Mutations in the Genome-Linked Protein VPg of Potato virus Y Confer Virulence on the pvr2³ Resistance in Pepper

¹I.N.R.A., Unité de Pathologie Végétale, BP94, F-84143 Montfavet Cedex, France; ²I.N.R.A., Unité de Génétique et Amélioration des Fruits et Légumes, BP 94, F-84143 Montfavet Cedex, France; ³I.N.R.A., Unité de Biométrie, Site Agroparc, F-84914 Avignon Cedex 9, France

Five different amino acid substitutions in the VPg of Potato virus Y were shown to be independently responsible for virulence toward pvr2³ resistance gene of pepper. A consequence of these multiple mutations toward virulence involving single nucleotide substitutions is a particularly high frequency of resistance breaking (37% of inoculated plants from the first inoculation) and suggests a potentially low durability of pvr2³ resistance. These five mutants were observed with significantly different frequencies, one of them being overrepresented. Genetic drift alone could not explain the observed distribution of virulent mutants. More plausible scenarios were obtained by taking into account either the relative substitution rates, the relative fitness of the mutants in pvr2³ pepper plants, or both.

Additional keyword: positive selection.