Potato spindle tuber and citrus exocortis viroids undergo no major sequence changes during replication in two different hosts.

Potato spindle tuber viroid and citrus exocortis viroid, each purified from tomato (Lycopersicon esculentum) and from Gynura aurantiaca, were iodinated in vitro with (125)I, digested with ribonuclease T1, and subjected to two-dimensional RNA fingerprinting analysis. With the exception of minor variations, each viroid retained its distinctive fingerprint pattern irrespective of the host species from which it was isolated. We conclude that the nucleotide sequences of these viroids are principally determined by the infecting viroid and not by the host.