Molecular and biological characterization of natural variants of Citrus dwarfing viroid.

Citrus dwarfing viroid has been proposed as an agent to control tree size in high-density plantations. Thirty-three field isolates have been characterized, and the most frequent sequence/s have been identified. Five distinct variants were selected for biological characterization. Symptom expression analysis demonstrated a good correlation between leaf/stem symptoms and plant growth. The discriminating nucleotide sequence differences included two deletions and an insertion resulting in a reorganization of the base pairing of the terminal left loop, two (G42 --> A and C52 --> U) changes found in one of the variants, and as many as thirteen changes located in the right and left regions flanking the CCR.