Co-inoculation of C2 W2B , C1 and T3 onto N. glutinosa plants followed by multiple passages at 1-2 weekly intervals showed that C1C2 W2B T3 induced symptoms as severe as those induced by C1C2 T2B T3, which were much more severe than those induced by either of the parental viruses (21) . Northern blot hybridization showed that RNA 3 derived from C1C2 W2B T3 also had recombined with a CMV sequence in the passage plants, but not in the inoculated plants ( Figure 2C and D, compare lanes 27 and 34, and lanes 29 and 36). This was supported by RT-PCR analysis (data not shown). These data strongly indicate that the 2b protein was required for recombination and/or selection or the recombinant RNA 3s, and that this process was not TAV 2b protein-specific.