|
Type Species |
(PSTVd) |
A circular ssRNA between 356 and 359-360 bases depending on isolates and sequence variants. The most stable secondary structure is a rod-like or quasi-rod-like conformation with five domains, a central conserved region (CCR) similar to that of hostu- and cocadviroids, and a terminal conserved region (TCR) (Fig. 2 and 5). Replication occurs through an asymmetric rolling-circle model since longer-than-unit minus strands have been found in infected tissue (Fig. 3). PSTVd replicates and accumulates in the nucleus. It is naturally found in potato, pepino (Solanum muricatum) and avocado and can be transmitted experimentally to many other hosts, most of them solanaceous species, in which no symptoms develop. The viroid, when encapsidated by potato leafroll virus particles, can also be transmitted by aphids. PSTVd strains differing in symptom expression from symptomless to almost lethal in tomato, the preferred experimental host, have been isolated and sequenced. Reported in North and South America, the former USSR and widespread in China.
List of Species Demarcation Criteria in the Genus
An arbitrary level of less than 90% sequence similarity and distinct biological properties, particularly host range, currently separates species within genera.
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:
|
Chrysanthemum stunt viroid |
[V01107] |
{354, 356} |
(CSVd) |
|
Citrus exocortis viroid (226)† (Indian tomato bunchy top viroid) |
[M34917] |
{370-375, 463} |
(CEVd) |
|
Columnea latent viroid‡ |
[X15663] |
{370, 372} |
(CLVd) |
|
Iresine viroid 1 |
[X95734] |
{370} |
(IrVd-1) |
|
Mexican papita viroid |
[L78454] |
{359-360} |
(MPVd) |
|
Potato spindle tuber viroid (66) |
[V01465] |
{356, 359-360} |
(PSTVd) |
|
Tomato apical stunt viroid§ |
[K00818] |
{360, 363} |
(TASVd) |
|
Tomato planta macho viroid |
[K00817] |
{360} |
(TPMVd) |
† Agent also isolated from grapevine, broad bean, eggplant, carrot and turnip.
‡ Isolated also from Nematanthus wettsteinii and Brunfelsia undulata.
§ Isolated also from Solanum pseudocapsicum.
Tentative Species in the Genus
None reported.
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