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Type Species |
(ASBVd) |
A circular ssRNA between 246 and 250 bases depending on isolates and sequence variants. It is unique in having a base composition rich in A+U (62%) in contrast to the other viroids which are rich in G+C (53-60%). The most stable secondary structure is a rod-like or quasi-rod-like conformation in which neither five domains nor a central conserved region (CCR) can be distinguished. It is soluble in 2 M LiCl as are typical viroids like Potato spindle tuber viroid (PSTVd), Apple scar skin viroid (ASSVd) and Coleus blumei viroid 1 (CbVd-1) having also rod-like or quasi-rod-like most stable secondary structures. Plus and minus strands of Avocado sunblotch viroid (ASBVd) can form hammerhead structures. Because both single hammerhead structures of ASBVd are thermodynamically unstable, double hammerhead structures have been proposed to operate in the self-cleavage reactions, specially in that of the plus polarity (Fig. 3). Replication occurs through a symmetric rolling-circle model since the minus circular monomer has been found in infected tissue (Fig. 3). ASBVd accumulates, and probably replicates, in the chloroplast. Found naturally only in avocado but it can be experimentally transmitted into other members of the Lauraceae family. Reported in USA, Australia, Israel, Spain, South Africa and South America.
List of Species Demarcation Criteria in the Genus
Not applicable.
Official viroid species names are in italics. Tentative names, alternative names ( ), or strains are not italicized. Viroid names, CMI/AAB description numbers ( ), genomic accession numbers of typical sequence variants [ ], sizes {b}, and assigned abbreviations ( ) are:
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Avocado sunblotch viroid (254) |
[J02020] |
{246-250} |
(ASBVd) |
Tentative Species in the Genus
None reported.
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