Abstract

Viroids are smallest, single-stranded, circular, highly structured plant pathogenic RNAs that do not code for any protein. Viroids belong to two families, the Avsunviroidae and the Pospiviroidae. Members of the Pospiviroidae family adopt a rod-like secondary structure. In this study the most stable secondary structures of citrus viroid variants that reported from Fars province were drawn. The most stable secondary structures of these viroid variants were a classical rod-like structure and adopted cruciform structure including various additional small hairpins. Comparison of secondary structures of these viroid variants with other viroid variants indicates their highly similarities in the rod-like structures, number of loops and free energies and it’s obvious to result these closest variants of the Pospiviroidae family. HSVd-cit1 and CVd-III-1 differed from under study variants in the stability and number of secondary structure branches. Because of relationship between secondary structure and pathogenicity of viroids, it is supposed that these two variants possibly will have high risk for citrus cultivations.