Isolates of citrus exocortis viroid (CEV) from a single sweet orange citrus source have been selected by sequential passage through the alternative hosts citron, Gynura aurantiaca, a hybrid tomato Lycopersicon esculentum x L. peruvianum, and from disorganized callus culture of the hybrid tomato. The distinctions in symptom expression, titre and electrophoretic mobility among the CEV isolates, o...

Citrus Bent Leaf Viroid (CBLVd) and Dwarfing (CDVd), from genus Apscaviroid, are two of the widely distributed citrus viroids among eight reported to date. They have been found induce reduction in canopy volume fruit production trees on trifoliate orange hybrids rootstocks. Moreover, infected only with CBLVd or combinations Exocortis (CEVd), Hop Stunt (HSVd) CDVd associated a poor development r...

Viroids are autonomously replicating, small singlestranded circular RNA molecules that do not code for proteins and may cause disease in infected, susceptible plants. Viroids have the ability to induce both RNA-mediated transcriptional gene silencing (TGS) and posttranscriptional gene silencing (PTGS) in infected plants. Viroid PTGS has also been demonstrated in a wheat germ extract system. A p...

The mutation rates of viroids, plant pathogens with minimal non-protein-coding RNA genomes, are unknown. Their replication is mediated by host RNA polymerases and, in some cases, by hammerhead ribozymes, small self-cleaving motifs embedded in the viroid. By using the principle that the population frequency of nonviable genotypes equals the mutation rate, we screened for changes that inactivated...

gummy bark disease of sweet orange (citrus sinensis) trees has been reported from a few citrus growing regions of the world. the disease symptoms consist of mild to severe stem pitting and brown gummy flecks in the bark of sweet orange trees on sour orange ( c. aurantium) rootstock, being conspicuous several centimeter above the bud :union: on the trunk. the pits were usually impregnated with b...