Details of DPV and References

DPV NO: 357 September 1998

Family: Secoviridae

Genus: Nepovirus

Species: Cassava American latent virus | Acronym: CsALV

Cassava American latent virus

B. Walter INRA, 28 rue de Herrlisheim, F 68021 Colmar, France

Contents

Introduction

First described by Walter et al. (1989) from Manihot esculenta cultivars originating from Brazil and Guayana.

A virus with isometric particles c. 28 nm in diameter sedimenting as three components. The genome comprises two RNA species of M_r c. 2.54 x 10⁶ (RNA-1) and 1.44 x 10⁶ (RNA-2). Host range limited to species in the families Chenopodiaceae, Euphorbiaceae and Solanaceae.

Main Diseases

Cassava American latent virus (CsALV) was detected during a survey of cassava (Manihot esculenta) cultivars originating from South America (Walter et al., 1989). It was found in plants that were also infected by the potexvirus cassava common mosaic virus and showed symptoms of mild mosaic. Preparations of purified CsALV back inoculated on to cassava seedlings induced no visible symptoms, though the virus was detected in systemically infected leaves by ELISA 9 weeks after inoculation.

Geographical Distribution

Reported only from Brazil and Guyana. No further information.

Host Range and Symptomatology

The virus is mechanically transmissible to species of Chenopodiaceae, Euphorbiaceae and Solanaceae (Walter et al., 1989).

Diagnostic species

Chenopodium album and C. amaranticolor: local chlorotic lesions becoming necrotic (Fig. 1).

Nicotiana benthamiana: diffuse chlorotic areas both on inoculated and on systemically infected leaves followed by discrete flecking on the whole plant (Fig. 2).

Tetragonia expansa (Aizoaceae), Gomphrena globosa (Amaranthaceae), Euphorbia prunifolia (Euphorbiaceae) and Nicotiana tabacum (Solanaceae) are useful non-host species.

Assay species

C. amaranticolor.

Propagation species

Nicotiana benthamiana and N. clevelandii.

Strains

No information.

Transmission by Vectors

No information.

Transmission through Seed

No information.

Serology

Strongly immunogenic. Rabbit polyclonal antiserum has been used in gel double-diffusion (titre 1/2048), ELISA and ISEM. The virus was detectable by double antibody sandwich (DAS)-ELISA in high dilutions (10^-3 to 10^-4) in cassava and N. benthamiana leaf extracts (Walter et al., 1989).

Relationships

On the basis of its particle properties, the virus is placed in the genus Nepovirus (Mayo & Robinson, 1996). No serological relationship was detected to another nepovirus from cassava, cassava green mottle virus, nor to seven other nepoviruses: arabis mosaic, grapevine chrome mosaic, grapevine fanleaf, raspberry ringspot (serotypes E and S), strawberry latent ringspot, tomato black ring (serotypes G and S) and tomato ringspot (Walter et al., 1989).

Stability in Sap

In sap of N. benthamiana the thermal inactivation point (10 min) is between 70 and 72°C and the dilution end-point is between 10^-3 and 10^-4 (Walter et al., 1989).

Purification

Virus purification is possible from leaves of N. benthamiana or N. clevelandii ground in 0.05 M KH₂PO₄-Na₂HPO₄ buffer, pH 7.5 (2 ml/1 g leaves). After clarification with butan-1-ol, precipitation with 10% polyethylene glycol (PEG) and differential centrifugation, centrifuge the virus through a 20% (w/v) sucrose cushion and fractionate in a 10-50% sucrose gradient (Walter et al., 1989).

To purify the virus directly from cassava, grind leaves in phosphate buffer containing 2% polyvinylpyrrolidone (2 ml/1 g leaves). After addition of 2% Triton X-100 and emulsifying with 1/10 volume chloroform, process the aqueous phase as above (PEG, sucrose cushion and sucrose gradient).

Properties of Particles

B component particles have a buoyant density of 1.5 g cm^-3 in CsCl.

Particle Structure

Three virus-associated peaks (T, M and B components) are observed in sucrose gradients. When observed in electron microscopy, M and B fractions contain only isometric particles c. 28 nm in diameter appearing mostly unpenetrated by negative stain (Fig. 3); the T fraction contains particles of the same size penetrated by the stain.

Particle Composition

Nucleic acid: Two RNA molecules of M_r 2.54 x 10⁶ (RNA-1) and 1.44 x 10⁶ (RNA-2). B component particles contain both RNA molecules, whereas M component particles contain only RNA-2; T component particles contain no RNA.

Protein: A single protein, of M_r 57,000 (Walter et al., 1989).

Genome Properties

No information.

Notes

Many of the properties of CsALV are typical of nepoviruses. It may belong to those nepoviruses having a single major coat protein and a heterogeneous B component with either one molecule of RNA-1 or two molecules of RNA-2, and an RNA-2 of M_r 1.3-1.5 x 10⁶ (Mayo & Robinson, 1996).

Figures

References list for DPV: Cassava American latent virus (357)

1. Mayo & Robinson, in The Plant Viruses, Vol. 5, p. 139, ed. B.D. Harrison & A.F. Murant, 362 pp., New York: Plenum Press, 1996.
2. Walter, Ladeveze, Etienne & Fuchs, Ann. appl. Biol. 115: 279, 1989.