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Abstract
Purified preparations of the two sedimenting nucleoprotein components (M and B) of tomato ringspot virus (TomRSV) and of strains of cherry leaf roll virus (CLRV) from elderberry (G) and from rhubarb (R) had little infectivity alone whereas mixtures of homologous components were very infective. However, whereas heterologous mixtures of the components of CLRV strains G and R were also very infective, heterologous mixtures of the components of CLRV-R and TomRSV were not. These results and serological evidence indicate that CLRV and TomRSV are not closely related to each other or to other nepoviruses with similar properties.
Pseudo-recombinants produced by exchanging the nucleoprotein components of CLRV strains R and G were less stable than the parent isolates on storage in sap at 18 °C. Component M determined serological specificity whereas component B determined ability to infect Gomphrena globosa, and the lesion type and severity of systemic symptoms in Chenopodium and Nicotiana spp. Virulence also depended on the compatibility of M and B components and neither pseudo-recombinant was as virulent as the parent donating component B. Systemic infection and symptom production in Petunia hybrida required M and B components from strain R. In plant protection tests, the parent strains of CLRV protected tobacco plants against either parent and against the two pseudo-recombinants, whereas the pseudo-recombinants protected plants against either pseudo-recombinant but not against the parent strains. This suggests that determinants in both nucleoprotein components of either the protecting or challenging virus are involved.
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