379
May 2001
Family: Pospiviroidae
Genus: Coleviroid
Species: Coleus blumei viroid 1
Acronym: CbVd-1


Coleus blumei viroid 1

D J Robinson
Scottish Crop Research Institute, Invergowrie, Dundee, UK

Contents

Introduction
Main Diseases
Geographical Distribution
Host Range and Symptomatology
Strains
Transmission by Vectors
Transmission through Seed
Transmission by Grafting
Transmission by Dodder
Serology
Nucleic Acid Hybridization
Relationships
Stability in Sap
Purification
Properties of Particles
Particle Structure
Particle Composition
Properties of Infective Nucleic Acid
Molecular Structure
Genome Properties
Satellites
Relations with Cells and Tissues
Ecology and Control
Notes
References
Acknowledgements
Figures

Introduction

First described by Fonseca et al. (1989); type isolate described by Spieker et al. (1990).

Synonyms:
Yellow coleus viroid (Fonseca et al., 1989)
Coleus yellow viroid (Fonseca et al., 1994)

A viroid comprising 248 - 251 bases of non-coding single-stranded RNA, depending on the isolate, with a stable secondary structure. No nucleoprotein particles. Transmissible by mechanical inoculation of sap to a very narrow host range.

Main Diseases

Causes slight chlorosis or purple pigmentation in leaves of some Coleus blumei cultivars, but is symptomless in others (Fonseca et al., 1989). Infected plants may be dwarfed (Spieker, 1996a).

Geographical Distribution

Reported from Brazil (Fonseca et al., 1989), Germany (Spieker et al., 1990), Canada (Singh et al., 1991) and Japan (Ishiguro et al., 1996). Probably occurs more widely, including in the USA and Costa Rica (Singh et al., 1991).

Host Range and Symptomatology

Found naturally in only certain cultivars of C. blumei. Transmissible by mechanical or graft inoculation to uninfected plants of some C. blumei cultivars (Fonseca et al., 1989) and to a few species in the family Labiatae (Singh et al., 1991; Ishiguro et al., 1996). None of these plants produce diagnostic symptoms.

Propagation species: susceptible cultivars of C. blumei.

Strains

Isolates from different C. blumei cultivars often differ slightly in size or nucleotide sequence from the type isolate, which was obtained from cv. "Bienvenue" (Spieker, 1991). The original Coleus yellow viroid differs from the type isolate at three nucleotide positions (Fonseca et al., 1994).

Transmission through Seed

Transmitted through seed from infected C. blumei at frequencies of 10 - 70 % (Singh et al., 1991; Spieker, 1996a). Not transmitted through seed of Ocimum sanctum (Singh et al., 1991).

Relationships

Isolates differ in nucleotide sequence from the type isolate. The most divergent is an isolate from C. blumei cv. "Rainbow Gold", which is 3 nucleotides longer than the type isolate and 93.1% similar to it in sequence (Spieker, 1996a).

CbVd-1 is 56.8% similar in sequence to Coleus blumei viroid 3, and has 51.7% or less similarity with viroids in other genera (Spieker, 1991). Coleus blumei viroid 2 is a recombinant molecule, consisting of the right half of CbVd-1 and the left half of CbVd-3 (Spieker, 1996b).

Purification

CbVd-1 can be purified from infected Coleus leaves by extracting tissue with the aid of phenol, and partially purifying the nucleic acids using chromatography on cellulose CF-11 (Fonseca et al., 1989). Viroid circular molecules are obtained by bidirectional ("return") polyacrylamide gel electrophoresis (Schumacher et al., 1983).

Genome Properties

The circular single-stranded non-coding RNA genome comprises 248 - 251 nt, depending on the isolate. Sequence database accession numbers are X52960, X95291, X95366 and X69293.

Secondary structure models are presented by Spieker et al. (1990), Spieker (1991), Fonseca et al. (1994), Ishiguro et al. (1996) and Spieker (1996a, 1996b). They show a rod-like structure of minimum free energy, with five domains and a central conserved region typical of viroids in the family Pospiviroidae (Fig.1).

The isolated RNA is infective (Fonseca et al., 1989).

Relations with Cells and Tissues

In C. blumei, the viroid is found throughout the vegetative and floral parts, and in the seed endosperm but not in the seed coat (Singh et al., 1991).

Ecology and Control

The viroid is readily spread in C. blumei by vegetative propagation and through seed. All plants of a vegetatively propagated cultivar in Brazil were reported to be infected (Fonseca et al., 1989), and infection of commercial seed lots in North America was common (Singh et al., 1991). Control could be through selection of healthy plants for propagation (Singh et al., 1991).

References

  1. Fonseca, Boiteux, Singh & Kitajima, Fitopatologia Brasileira 14: 94, 1989.
  2. Fonseca, Marcellino, Kitajima & Boiteux, Journal of General Virology 75: 1447, 1994.
  3. Ishiguro, Sano & Harada, Annals of the Phytopathological Society of Japan 62: 84, 1996.
  4. Schumacher, Randles & Reisner, Analytical Biochemistry 135: 288, 1983.
  5. Singh, Boucher & Singh, Plant Disease 75: 184, 1991.
  6. Spieker, Karlsruher Beiträge zur Pflanzenphysiologie 22: 1, 1991.
  7. Spieker, Archives of Virology 141: 2153, 1996a.
  8. Spieker, Journal of General Virology 77: 2839, 1996b.
  9. Spieker, Haas, Charng, Freimüller & Sänger, Nucleic Acids Research 18: 3998, 1990.


Figure 1

Predicted secondary structure of the type isolate of CbVd-1. The box encloses the central conserved region (CCR), and the approximate locations of the five domains are indicated: LT, left terminal; P, pathogenic; C, central; V, variable; RT, right terminal. Adapted from Spieker et al. (1990).