262
July 1983
Family: Betaflexiviridae
Genus: Carlavirus
Species: American hop latent virus
Acronym: AHLV


American hop latent virus

D. J. Barbara
East Malling Research Station, Maidstone, Kent, England

A. N. Adams
East Malling Research Station, Maidstone, Kent, England

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 recorded by Probasco & Skotland (1976) and described by Adams & Barbara (1982a).

A virus with filamentous RNA-containing particles, c. 15 x 680 nm, frequently occurring in hop (Humulus lupulus) in North America. Transmitted by mechanical inoculation of sap and in the non-persistent manner by aphids.

Main Diseases

Natural infection has been reported only from hop (Humulus lupulus) but is not associated with any disease. The virus induced no symptoms in experimentally inoculated British cultivars (Adams & Barbara, 1982a) but caused a faint ring-and-line pattern in an American seedling clone (Probasco & Skotland, 1976).

Geographical Distribution

Common in USA (E. G. Probasco & C. B. Skotland, personal communication) otherwise reported only in plant breeders’ introductions from USA to England (Adams, 1980) and West Germany (A. Eppler, personal communication).

Host Range and Symptomatology

Experimentally the virus infected 17 of 41 species in 7 of 13 families (Adams & Barbara, 1982a). Symptoms were indistinct or absent in most hosts.

Diagnostic species
Chenopodium quinoa. Chlorotic spots appear within c. 10 days in inoculated leaves (Fig.1) followed by a faint systemic veinbanding and chlorotic mottle in some of the first leaves to be invaded systemically. Systemic symptoms intensify with age (Fig.2).

Datura stramonium. Small necrotic lesions which often develop into necrotic ringspots (Fig.3) appear within c. 14 days in the inoculated leaves; no systemic infection.

Propagation species
Chenopodium quinoa is suitable for maintaining cultures and as a source of virus for purification.

Assay species
Datura stramonium can be used for local lesion assay.

Strains

None reported.

Transmission by Vectors

In a single experiment the aphid Phorodon humuli transmitted the virus from hop to hop in the non-persistent manner (Adams & Barbara, 1982a).

Transmission through Seed

No reports.

Serology

Antisera with tube precipitin titres of up to 1/800 were obtained by injecting rabbits intramuscularly and/or subcutaneously with preparations of intact particles. Extracts from infected hop and Chenopodium quinoa react at dilutions well in excess of 10-3 in direct ELISA (Adams & Barbara, 1982a) and no cross-reactions occur with the other two carlaviruses common in hop, hop mosaic and hop latent . Antibody coating of virus particles is useful for quick identification by electron microscopy particularly in mixed infections (Fig.5).

Relationships

The properties of American hop latent virus place it in the carlavirus group. No serological relationship to any of 15 carlaviruses was found in tube precipitin tests or by direct ELISA, but F(ab')2-based indirect ELISA revealed a distant relationship to nerine latent virus and very distant relationships to chrysanthemum B, hop latent and hop mosaic viruses; no relationship was found to carnation latent, helenium S, lily symptomless, narcissus latent, poplar mosaic, potato M, potato S, shallot latent or red clover vein mosaic viruses (Adams & Barbara, 1982a, 1982b).

Stability in Sap

No information.

Purification

Up to 30 mg virus/kg of inoculated C. quinoa leaves can be obtained by the following procedure. Use 0.05 M Tris-HCl buffer, pH 7.5, throughout. Harvest inoculated leaves after c. 3 weeks and extract in buffer (4 ml/g leaf) containing 0.016 M sodium sulphite. Clarify the extract by addition of 1/5 vol of chloroform, then precipitate the virus by adding polyethylene glycol (M. Wt 6000) to 6% and sodium chloride to 0.6%. The virus in the resuspended pellets may be further purified by differential centrifugation and sucrose density gradient centrifugation (Adams & Barbara, 1982a).

Properties of Particles

Purified preparations show one component in sucrose density gradient centrifugation.

A260/A280: 1.21 (corrected for light-scattering; Adams & Barbara 1982a).

Particle Structure

Particles are straight or slightly flexuous filaments c. 15 x 680 nm.

Particle Composition

Nucleic acid: RNA, single-stranded, c. 5-7% of the particle weight (estimated from the A260/A280 ratio). M. Wt c. 3.0 x 106, estimated by polyacrylamide gel electrophoresis under non-denaturing conditions (Adams & Barbara, 1982a).

Protein: c. 93-95% of the particle weight (estimated from the A260/A280 ratio). A single polypeptide species, M. Wt c. 32,700, estimated by SDS/polyacrylamide gel electrophoresis (Adams & Barbara, 1982a).

Relations with Cells and Tissues

No information.

Notes

American hop latent virus is distinct from the two other carlaviruses known to occur in hop, hop mosaic and hop latent; it is only very distantly related to them serologically, has a wider host range, and differs from them in causing obvious symptoms in several species, notably Datura stramonium and Chenopodium quinoa, both of which are immune to hop latent virus and sustain only symptomless local infection by hop mosaic virus. Symptoms caused by the latter two viruses in herbaceous hosts are too mild for diagnosis, and identification of all three viruses, which can occur together in hop, is best done by serology.


Outside North America, American hop latent virus has been found only in recent introductions to W. Germany and England, indicating that it may be a relatively new pathogen of North American hop plants.

References

  1. Adams, Rep. E. Malling Res. Stn for 1979: 103, 1980.
  2. Adams & Barbara, Ann. appl. Biol. 101: 483, 1982a.
  3. Adams & Barbara, Ann, appl. Biol. 101: 495, 1982b.
  4. Probasco & Skotland, Proc. Am. Phytopath. Soc. 3: 319, 1976.


Figure 1

Chenopodium quinoa leaf c. 12 days after inoculation.

Figure 2

Systemic infection in C. quinoa c. 6 weeks after inoculation.

Figure 3

Necrotic ringspots in Datura stramonium c. 30 days after inoculation.

Figure 4

Particle negatively stained with 2% ammonium molybdate. Bar represents 200 nm.

Figure 5

Leaf extract from hop infected with American hop latent, hop latent and hop mosaic viruses incubated with antiserum to American hop latent virus and negatively stained with 2% sodium phosphotungstate, pH 6.5. Only particles of American hop latent virus are coated with antibody. Bar represents 200 nm.