Continuous replication of potato spindle tuber viroid (PSTV) in permanent cell cultures of potato and tomato.

The continuous replication of potato spindle tuber viroid (PSTV) in callus cultures from PSTV-infected wild-type potato (Solanum demissum L.) and tomato (Lycopersicon peruvianum L. Mill) plants and in cell suspensions derived from potato protoplasts (Solanum tuberosum L.) inoculated in vitro is described. The persistence of PSTV replication in these cell lines through at least 14 subculture passages, which corresponds to a continuous replication over a period of more than one year, was demonstrated by infectivity assay and by polyacrylamide-gel electrophoresis of isolated nucleic acids. This continuous synthesis de novo of PSTV was substantiated by the incorporation of [3H]uridine and of [32P]orthophosphate into viroid RNA.