Host-directed processing of Citrus exocortis viroid.

Prolonged infection of tomato hybrid (Lycopersicon esculentum x Lycopersicon peruvianum) by Citrus exocortis viroid (CEVd) resulted in viroid-like enlarged structures, detected by gel electrophoresis. This population included two new enlarged variants or D-variants, D-87 and D-76, and three transient species or D-forms, D-38, D-40 and D-43. Sequence analyses exposed a locus near the terminal repeat region where major changes appeared consistently. In transmission tests to CEVd hosts, a variety of progeny populations were recovered, including progeny enlargements of and reversions to CEVd, as well as sequence fidelity to the inoculum. Transmission tests to citrus hosts of the genera Citrus, Poncirus or Fortunella were unsuccessful. The importance of host specificity to the recovery and processing of the various CEVd-related structures, as well as the temporal variability of progeny populations, was demonstrated.