INDIAN BUNCHY TOP DISEASE OF TOMATO PLANTS IS CAUSED BY A DISTINCT STRAIN OF CITRUS EXOCORTIS VIROID

A viroid has been isolated from tomato plants affected by Indian bunchy top disease of tomato (Lycopersicon esculentum Mill.). In dot blot hybridization assays with P-32-labelled cRNA probes specific for the detection of various viroids, the Indian viriod was shown to be most closely related to the citrus exocortis viroid (CEVd). Sequence determination showed that the viroid consists of 372 nucleotides and confirmed its close relationship with CEVd. The viroid, for which we propose the acronym CEVd-t, differs from the Australian CEVd strains A and B by 36 and 47 nucleotides, respectively, and from the Spanish grapevine isolate by 52 changes. A phylogenetic analysis confirmed the closest relationship with CEVd in all structural domains, except the pathogenicity and left-terminal domains, which are closely related to the corresponding domains of the potato spindle tuber and tomato apical stunt viroids, respectively.