Natural infections of tomato by Citrus exocortis viroid, Columnea latent viroid, Potato spindle tuber viroid and Tomato chlorotic dwarf viroid

Since 1988, viroids have been occasionally detected in samples of tomato ( Lycopersicon esculentum) originating both in the Netherlands and other countries. Infected plants showed chlorosis, bronzing, leaf distortion and growth reduction. Initial diagnosis of these viroids was by return-polyacrylamide gel electrophoresis, which did not allow a further identification. This paper reports the identification of these viroids by reverse transcription-polymerase chain reaction and sequence analysis. Three known viroids of tomato, i.e. Citrus exocortis viroid; Potato spindle tuber viroid and Tomato chlorotic dwarf viroid were identified. In addition, six isolates were identified as Columnea latent viroid, a viroid so far only detected in some ornamental species. Like the isolates previously isolated from ornamental species, the isolates from tomato share genetic characteristics of both the genera Hostuviroid and Pospiviroid. The biological characteristics of all four viroids, especially their potential effects on both potato ( Solanum tuberosum) and tomato, stress the need for reconsideration of their phytosanitary risks.