Isolation of velvet tobacco mottle virus capable of replication with and without a viroid-like RNA.

Field isolates of velvet tobacco mottle virus (VTMoV) induce severe symptoms in Nicotiana clevelandii and encapsidate viroid-like RNA reported to be essential for virus infection. An isolate of the virus producing only mild symptoms on N. clevelandii and devoid of viroid-like RNA has now been isolated from a plant inoculated by a single viruliferous Cyrtopeltis nicotianae, the mirid vector. However, after adding viroid-like RNA isolated from normal VTMoV to the inoculum, the new isolate was shown to support the synthesis of, and encapsidated the viroid-like RNA, thereby reverting to virulence characteristic of the normal isolate. This indicates that the viroid-like RNA can behave as a satellite RNA of VTMoV. The data are discussed in relation to previously published conclusions that viroid-like RNA is essential for the infectivity of VTMoV.