A stable 463 nucleotide variant of citrus exocortis viroid produced by terminal repeats

An unusual variant of citrus exocortis viroid (CEV) was detected when an inoculum source from Gynura aurantiaca D.C. was used to infect a hybrid tomato (Lycopersicon esculentum Mill. x L. peruvianum). The 92 nucleotide larger variant, CEV D-92, which displayed the characteristic circular and linear viroid structural forms, contained two repeated sequences spanning the V and T2 domains. A dramatic moderation of symptom expression in Gynura accompanied the incorporation of these repeated sequences. A comparison of the sequence and structure of CEV D-92 with coconut cadang-cadang viroid revealed similarities in the regions generating the naturally occurring terminal repeats suggesting a possible preferred site for RNA recombination between viroids.