216
September 1980
Family: Secoviridae
Genus: Nepovirus
Species: Arracacha virus A
Acronym: AVA


Arracacha virus A

R. A. C. Jones
Ministry of Agriculture, Fisheries and Food, Harpenden Laboratory, Hatching Green, Harpenden, Herts

R. H. Kenten
Rothamsted Experimental Station, Harpenden, Herts

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

Described by Jones & Kenten (1978).

A virus with isometric particles c. 26 nm in diameter which sediment as three components. It is readily transmissible by inoculation of sap and has a wide host range but has been found so far only in arracacha (Arracacia xanthorrhiza; Umbelliferae) in the Andean region of Peru.

Main Diseases

The virus was consistently isolated from arracacha plants showing a distinct yellow mosaic on young leaves, but was not detected in plants with a normal appearance. Attempts to return it to healthy arracacha plants by mechanical inoculation were unsuccessful (Jones & Kenten, 1978).

Geographical Distribution

Peru.

Host Range and Symptomatology

A wide experimental host range, infecting species in at least 10 dicotyledonous families (Jones & Kenten, 1978). Readily transmissible by inoculation of sap.

Diagnostic species
Chenopodium quinoa: Chlorotic local lesions; systemic chlorotic mottle and twisting of young leaves followed by systemic necrosis (Fig.1). Plants inoculated when young are sometimes killed.

C. murale: Local chlorotic or necrotic spots or rings; systemic symptoms are chlorotic mottle and twisting of young leaves followed by necrosis.

Tetragonia expansa: Few local necrotic rings, severe systemic chlorotic mottle followed by necrosis, plants severely stunted (Fig.3).

Nicotiana clevelandii: Local necrotic ringspots or rings (Fig.2); systemic chlorotic mottling or mosaic with occasional necrotic flecks and line patterns. Leaves produced later contain virus but may appear normal.

Propagation species:
Chenopodium quinoa and Nicotiana clevelandii are suitable species for maintaining cultures. N. clevelandii is a good source for virus purification.

Assay species:
Chenopodium quinoa is a satisfactory local lesion host.

Strains

None reported.

Transmission by Vectors

The virus was not transmitted by Myzus persicae (Jones & Kenten, 1978). A nematode vector is suspected because the virus has similarities to nepoviruses (see Relationships).

Transmission through Seed

The virus was readily transmitted through seed of N. clevelandii (R. A. C. Jones, unpublished results).

Serology

An antiserum with a titre of 1/1024 was readily obtained (Jones & Kenten, 1978). The virus produces a single band of precipitate in double diffusion tests in agar gel.

Relationships

The virus has biological and physico-chemical characteristics typical of nepoviruses. However, in gel diffusion tests (Jones & Kenten, 1978), purified virus failed to precipitate with antisera to 33 other morphologically similar viruses including the following members of the nepovirus group: Andean potato calico (= potato black ringspot), arabis mosaic, artichoke Italian latent, cherry leaf roll, cocoa necrosis, grapevine Bulgarian latent, grapevine chrome mosaic, grapevine fanleaf, mulberry ringspot, myrobalan latent ringspot, peach rosette mosaic, raspberry ringspot, strawberry latent ringspot, tobacco ringspot (eucharis mottle strain), tomato black ring (Scottish and English strains) and tomato ringspot. In further tests (R.A.C. Jones, unpublished data; A. F. Murant, unpublished data), antiserum to arracacha virus A failed to react with Andean potato calico virus (=potato black ringspot virus) or tobacco ringspot virus (type strain).

Stability in Sap

In sap from infected C. quinoa leaves, infectivity is lost after dilution to 10-5 or heating for 10 min at 65-70°C but is retained for at least 15 days at 20°C (Jones & Kenten, 1978).

Purification

Extract infected N. clevelandii leaves in 0.05 M phosphate buffer at pH 7.5 containing 0.05 M ethylene diamine tetra-acetate, and clarify with chloroform, followed by differential precipitation with ammonium sulphate and three cycles of differential centrifugation. Up to 200 A1cm,260 units of purified virus can be obtained per 1 kg of infected leaf by this procedure (Jones & Kenten, 1978).

Properties of Particles

In sucrose density gradients, purified virus preparations separate into three components, apparently empty protein shells (T) and two kinds of nucleoprotein with different amounts of nucleic acid (M and B). In equilibrium sedimentation in CsCl at 2°C, B component is not resolved into more than one class of particle (R. H. Kenten, unpublished results).

Sedimentation coefficients (s°20,w) (svedbergs): 50 (T), 92 (M) and 125 (B) (Fig.5).

A260/A280: 0.65 (T), 1.50 (M) and 1.85 (B).

Buoyant density in CsCl (g/cm3): 1.32 (T), 1.45 (M) and 1.52 (B).

Particle Structure

Particles are isometric, c. 26 nm in diameter with a hexagonal profile. Electron micrographs show particles, some completely, some partially and some not penetrated by negative stain (Fig.4). Detailed structure of the particles is not known.

Particle Composition

Nucleic acid: RNA, single-stranded. There are two species, with M. Wt 2.5 x 106 and 1.4 x 106 (R. J. Barton, unpublished results). From the sedimentation coefficients and buoyant densities, the nucleic acid contents of the M and B particles were estimated at 30-35% and 43-44% respectively. Although equilibrium sedimentation in CsCl detected only one class of particle in B component, it is still possible that there are two classes, one containing a single 2.5 x 106 dalton molecule and the other containing two 1.4 x 106 dalton molecules.

Protein: The coat protein has a M. Wt of c. 53 000 daltons estimated by electrophoresis in polyacrylamide gels containing sodium dodecyl sulphate.

Relations with Cells and Tissues

No information.

Notes

Arracacha virus A and the type strain of arracacha virus B have similar particle size, shape and properties in sap, and both infect arracacha crops in Peru, sometimes occurring together in the same plant. However, they can be readily distinguished by differences in host range and symptomatology in indicator hosts; arracacha virus A causes the more severe symptoms in hosts such as C. quinoa, T. expansa and N. clevelandii but fails to infect Vigna unguiculata. Moreover, the two viruses are serologically unrelated (Jones & Kenten, 1978; Kenten & Jones, 1979).

References

  1. Jones & Kenten, Ann. appl. Biol. 90: 85, 1978.
  2. Kenten & Jones, Ann. appl. Biol. 93: 31, 1979.


Figure 1

Local lesions and systemic necrosis in Chenopodium quinoa.

Figure 2

Ringspots (above) and rings (below) in inoculated leaves of Nicotiana clevelandii.

Figure 3

Necrosis and stunting in Tetragonia expansa; healthy plant on right.

Figure 4

Particles in neutral phosphotungatate. Bar represents 50 nm.

Figure 5

Schlieren pattern produced after centrifuging for 16 min at 29500 rev/min. Schlieren angle 40°; sedimentation from left to right.