DESCRIPTION OF VIRUSES

Subviral Agents: Viroids

Genus Apscaviroid

Genus Apscaviroid

Type Species

Apple scar skin viroid

(ASSVd)

Distinguishing Features

A circular ssRNA of a size of 329-330 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) and a terminal conserved region (TCR) (Fig. 2). Replication most probably occurs through an asymmetric rolling-circle model by analogy with PSTVd (Fig. 3). Known hosts are confined to Malus and Pyrus genera. Widespread in Japan and China, and reported in USA, Canada and France.

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.

List of Species in the Genus

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:

Species in the Genus

Apple dimple fruit viroid

[X99487]

{306-307}

(ADFVd)

Apple scar skin viroid (349)

[M36646]

{329-330}

(ASSVd)

(Dapple apple viroid)

(Pear rusty skin viroid)

(Japanese pear fruit dimple viroid)

Australian grapevine viroid

[X17101]

{369}

(AGVd)

Citrus III viroid

[S76454]

{294, 297}

(CVd-III)

Citrus bent leaf viroid

[M74065]

{318}

(CBLVd)

Grapevine yellow speckle viroid 1

[X06904]

{366-368}

(GYSVd-1)

Grapevine yellow speckle viroid 2

[J04348]

{363}

(GYSVd-2)

Pear blister canker viroid (365)

[S46812]

{315-316}

(PBCVd)

Tentative Species in the Genus

None reported.


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