SYSTEMIC INFECTION OF TOBACCO BY PEPPER VENOUS MOTTLE POTYVIRUS (PVMV) DEPENDS ON THE PRESENCE OF POTATO VIRUS-Y (PVY)

In single inoculations, both PVY and PVMV replicated in inoculated leaves of Nicotiana tabacum cv. 'Xanthi nc' plants, but only PVY infected the tobacco plants systemically, whereas PVMV caused localized infection. A mixed infection b the PVY-To72 and PVMV-type strains was experimentally realized in 'Xanthi nc' plants. in the presence of PVY, PVMV migrated systemically into the upper leaves of the tobacco plant, as was proved by back inoculation. It would appear that in tobacco, PVY acts as a ''helper'' virus, providing PVMV with the necessary component factor for migration. In extracts from the co-infected leaves, Immune Electron Microscopy (IEM) revealed phenotypic mixed particles which contained a mixture of coat proteins of PVY and PVMV. The role of the structural and functional interactions between the two viruses, which enable PVMV to migrate systemically in tobacco plants, is discussed.