Specificity of satellite activation by tobacco necrosis virus correlates with nucleic acid hybridization pattern between helper virus isolates.

Tobacco necrosis virus (TNV) comprises over 20 different isolates which are usually classified on the basis of serological cross-reactivity of their virus particles or specific activation of satellite virus strains (STNV-1, -2, and -C). We have studied the relationships between five TNV isolates, TNV-A, -G, -CN, -D, and -AC36 which exhibit considerable differences in symptom formation on Phaseolus vulgaris. It is shown that, like TNV-A, TNV-G and -CN support the multiplication of STNV-1 and -2. The ability to activate STNV-1 and -2 is not completely correlated with the virulence of the TNV isolates on Phaseolus as TNV-CN infects Phaseolus very inefficiently. The RNAs of all STNV-1 and -2 supporting TNV isolates were detectable by Northern blot analysis using RNA probes derived from TNV-A, whereas the RNAs of the STNV-C activating isolates (TNV-D and -AC36) were only detected with a TNV-D-derived RNA probe. This indicates that the classification of the TNV isolates on the basis of satellite activation is representative of the evolutionary relationships between the isolates.