Family: Pospiviroidae

Genus: Coleviroid

Distinguishing features

Circular ssRNA genomes between 248 and 364 nt depending on species and sequence variants. The most stable secondary structure is a rod-like conformation with a central conserved region (CCR) different from those of members of other viroid genera and a terminal conserved region (TCR) in the two members of the genus with the largest genome (Figure 3. Pospiviroidae). Replication most probably occurs through an asymmetric rolling-circle model by analogy with potato spindle tuber viroid (PSTVd) (Figure 1.Viroids). 

Biology

The host range of viroids in the genus Coleviroid (coleviroids) is confined to the plants in the genus Coleus. Coleviroids have been found in Brazil, Canada, China, Germany, India and Korea. Seed transmission of Coleus blumei viroid 1 (CbVd-1) [and presumably Coleus blumei viroid 2 (CbVd-2) and Coleus blumei viroid 3 (CbVd-3)] is particularly efficient (Nie and Singh 2017). Coleviroids have high propensity to recombine, as shown by CbVd-2 that likely evolved from a recombination event between CbVd-1 and CbVd-3.

Species demarcation criteria

Viroids with a rod-like conformation, a CCR identical to that of members of the type species of the genus (Coleus blumei viroid 1), the TCR, in the ones with the largest genome, less than 90% sequence identity and distinct biological properties with respect to the other members of the genus are classified in different species (Di Serio et al., 2014). A terminal conserved hairpin (TCH) can be present instead of a TCR in the viroids with the smallest genome. 

Related, unclassified viroid-like RNAs

Virus names and virus abbreviations are not official ICTV designations.