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 hy brid tomato (Lycopersicon esculentum Mill. x L. peruvianum). The 92 nu cleotide larger variant, CEV D-92, which displayed the characteristic circular and linear viroid structural forms, contained two repeated se quences spanning the V and T2 domains. A dramatic moderation of sympto m expression in Gynura accompanied the incorporation of these repeated sequences. A comparison of the sequence and structure of CEV D-92 wit h coconut cadang-cadang viroid revealed similarities in the regions ge nerating the naturally occurring terminal repeats suggesting a possibl e preferred site for RNA recombination between viroids.