Genus: Apscaviroid

Genus: Apscaviroid

Distinguishing features

Circular ssRNAs between 293 and 369 nt depending on species 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) identical to that of the reference variant of the type species of the genus (apple scar skin viroid, ASSVd) and the terminal conserved region (TCR) (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

Members of the genus Apscaviroid (apscaviroids) are reported to occur worldwide, particularly those affecting genera Citrus and Vitis. Several of them may cause severe losses to economic relevant fruit crops, while others do not induce visible symptoms. The most common pathway of apscaviroid spread is provided by the use of infected plants for grafting or propagation. Seed transmission has been reported for ASSVd (Hadidi et al., 1991) and grapevine yellow speckle viroid 1 (GYSVd-1) (Wan Chow Wah and Symons 1999), while it has been experimentally excluded for apple dimple fruit viroid (ADFVd) and pear blister canker viroid (PBCVd) (Di Serio et al., 2017). ASSVd has been reported to be transmitted to herbaceous hosts in the greenhouse by the whitefly Trialeurodes vaporariorum (Walia et al., 2015), but the epidemiological relevance of this finding is unclear. No role for natural vectors has been shown in the natural transmission of other apscaviroids (Tessitori 2017, Habili 2017).

Species demarcation criteria

Viroids with rod-like or quasi rod-like conformation, with the TCR, a CCR identical to that of members of the type species of the genus, less than 90% sequence identity and distinct biological properties with respect to the members of the genus, are classified in different species (Di Serio et al., 2014).

Member species

Exemplar isolate of the species
SpeciesVirus nameIsolateAccession numberRefSeq numberAvailable sequenceVirus Abbrev.
Apple dimple fruit viroidapple dimple fruit viroidDi SerioX99487NC_003463Complete genomeADFVd
Apple scar skin viroidapple scar skin viroidChinaX17696NC_001340Complete genomeASSVd
Australian grapevine viroidAustralian grapevine viroidRezaianX17101NC_003553Complete genomeAGVd
Citrus bent leaf viroidcitrus bent leaf viroid225U21125NC_001651Complete genomeCBLVd
Citrus dwarfing viroidcitrus dwarfing viroidE21aAF447788NC_003264Complete genomeCDVd
Citrus viroid Vcitrus viroid VSpainEF617306NC_010165Complete genomeCVdV
Citrus viroid VIcitrus viroid VIJCVd 1AB019508NC_004359Complete genomeCVdVI
Grapevine yellow speckle viroid 1grapevine yellow speckle viroid 1type3AF059712NC_001920Complete genomeGYSVd1
Grapevine yellow speckle viroid 2grapevine yellow speckle viroid 2KoltunowJ04348NC_003612Complete genomeGYSVd2
Pear blister canker viroidpear blister canker viroidHernandezD12823NC_001830Complete genomePBCVd

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.

Related, unclassified viroid-like RNAs

Name

Accession number

Abbreviation

apple chlorotic fruit spot viroid*

MF521431

ACFSVd

apple fruit crinkle viroid

E29032

AFCVd

citrus viroid VII

KX013549

CVd-VII

Dendrobium viroid

MT013216

DVd

grapevine latent viroid

KR605505

GlVd

grapevine yellow speckle viroid 3

DQ371462

GYSVd-3

lychee viroid-like RNA*

MF156698

LVd

persimmon latent viroid*

AB366022

PVd

persimmon viroid 2*

AB817729

PVd-2

Virus names and virus abbreviations are not official ICTV designations.
* Autonomous replication has not been conclusively shown