Pseudorecombinant viruses formed between RNAs 1 and 2 of CMV and RNA 3 of TAV have been shown gradually to yield stable, recombinant viruses after multiple passage (30, 31, 38) . However, the effects of the various viral genes on the selection of these recombinant viruses have not been examined. Previously, using interspecies hybrid viruses, we examined the roles of different 2b genes on virulence and virus accumulation and showed that while the nature of the 2b gene influenced virulence, the RNA 3 (and therefore the two genes encoded by RNA 3; the 3a movement protein and the capsid protein) did not (21, 47) . Therefore, the hybrid viruses generated previously, C1C2 T2B C3 and C1C2 T2B T3, where C indicates Q-CMV, T indicates TAV, 1, 2 and 3 indicate RNAs 1, 2 and 3, and the subscript T2B indicates that the 2b gene of Q-CMV was replaced precisely with that of TAV ( Figure 1 ), were subjected to long-term, multiple passages in N. glutinosa to determine whether the 2b gene had any effect on the selection of recombinant viruses. The progeny viral RNAs were examined by northern blot hybridization, with probes specific to the 3 0 terminal NTR sequences of either the three Q-CMV RNAs or the three TAV RNAs (Figure 1 ). This analysis indicated that in the multiple passage plants TAV RNA 3 derived from C1C2 T2B T3 had recombined with CMV RNA, as the progeny RNA 3 was detected by both the Q-CMV-specific and TAV-specific probes (Figure 2A and B, compare lanes 9 and 20). By contrast, RNA 3 derived from the same virus maintained for several weeks in the plasmidinoculated plants was not a recombinant RNA, as it was only detected by the TAV-specific probe, but not by the Q-CMV-specific probe (Figure 2A and B, compare lanes 5 and 16). The specificity of the CMV-specific and TAV-specific probes was demonstrated in that both probes only detected their own specific viral RNAs ( Figure 2A and B, compare lanes 2 and 3, and lanes 13 and 14) . The other RNAs of C1C2 T2B T3 were still detected by their specific probes in both the inoculated plants and the multiple passage plants (Figure 2A and B) .