Abstract
Citrus B viroid (CBV), differing from the citrus exocortis viroid in host range, symptom expression, and reaction with viroid-specific molecular probes, has been identified in many commercial citrus trees in Sicily. Citrus B viroid replicates in cucumber (Cucumis sativus L. ''Suyo'') plants and produces symptoms similar to those induced in cucumber by the hop stunt viroid (HSV). Molecular hybridization with HSV-specific RNA probes has demonstrated that the nucleotide sequence of CBV is closely homologous to that of HSV, indicating hat the viroid is a strain of HSV. Citrus B viroid, alone or in conjunction with other viroids, may be responsible for inducing the citrus cachexia (xyloporosis) disease.