Repeated multiple passages of virus generated from the plasmids comprising C1C2 T2B T3 in 10 N. glutinosa plants or 10 N. clevelandii plants resulted in the appearance of the same recombinant RNA 3s with the same border sequences among the sequenced clones. These recombinant RNAs were not detected by northern blot hybridization in the inoculated parental plants, even if the plasmid-inoculum was increased 5-fold (50 mg/10 ml) or decreased 20-fold (0.5 mg/10 ml), although the same recombinant RNAs were detected again in the multiple passage plants, when the initial inoculum concentration was changed (data not shown).