Construction of novel viroid chimeras containing portions of tomato apical stunt and citrus exocortis viroids.

Several novel tomato apical stunt viroid (TASV) recombinants were isolated after inoculation of tomato seedlings with monomeric viroid cDNAs. Two intraspecific recombinants were constructed by exchanging the left and right sides of the closely related Ivory Coast and Indonesian strains of TASV, and a third, interspecific, recombinant was constructed by similar manipulations involving TASV and citrus exocortis viroid (CEV) cDNAs. Characterization of these TASV recombinants by RNA protection assays and nucleotide sequence analysis of polymerase chain reaction-amplified cDNAs revealed no evidence for sequence instability. The symptoms induced by replication of the CEV-TASV chimera in tomato were milder than those induced by either TASV or the TASV chimeras and resembled those induced by the CEV isolate which provided its pathogenicity domain.