106
October 1972
Family: Bromoviridae
Genus: Ilarvirus
Species: Tobacco streak virus
Acronym: TSV

Black raspberry latent virus is now known to be a distinct strain of tobacco streak virus
(Jones & Mayo, Ann. appl. Biol. 79: 297, 1975.)

Black raspberry latent virus

R. M. Lister
Dept. of Botany and Plant Pathology, Purdue University, Lafayette, lndiana, USA

R. H. Converse
USDA ARS Plant Science Research Division, Dept. Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, USA

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 Converse & Lister (1969, 1970).

Synonym

New Logan-64 virus (Rev. appl. Mycol. 46: 3311n)

A virus with isometric particles about 26 nm in diameter, which occurs with no apparent symptoms in black raspberry (Rubus occidentalis L.) cultivars in the eastern USA, and is transmissible by sap-inoculation to a fairly wide range of herbaceous hosts. It has no known vectors, but in black raspberry is transmitted by pollen to pollinated plants and through seed.

Main Diseases

The virus may be obtained from symptomless black raspberry plants, and is not associated with any specific disease syndrome in raspberry. It has not been reintroduced into healthy raspberry plants for observation of growth or yield effects.

Geographical Distribution

In the eastern USA the virus is probably common in cultivated black raspberry though rare in red raspberry. It was obtained from Thornless Youngberry (a Rubus hybrid) collected in western Canada (R. M. Lister, unpublished), but is not reported elsewhere.

Host Range and Symptomatology

Experimental host range is fairly wide; about 30 species in 8 dicotyledonous families have been infected by sap-inoculation. Many hosts produce only mild symptoms or none.

Diagnostic species

Chenopodium quinoa. Local vein chlorosis in inoculated leaves after 2-3 days, followed by irregularly-shaped spreading necrotic and chlorotic lesions, and severe systemic chlorosis, necrosis and distortion of shoot tips (Fig.1). Symptomless infected leaves may be produced later.

Nicotiana tabacum cvs. White Burley and Turkish. Local chlorotic and necrotic ringspots and line patterns (Fig.2); virus is recoverable from symptomless new leaves.

Cucumis sativus cv. National Pickling. Chlorotic lesions in inoculated cotyledons, with severe systemic mottling, distortion and dwarfing (Fig.3).

Phaseolus vulgaris cvs. The Prince and Bountiful. No symptoms in inoculated leaves. Irregular systemic red-brown veinal necrosis, especially visible on the underside of leaves; also browning and reddening of nodes.

Gomphrena globosa. Occasional small red rings and spots.

Propagation species

Chenopodium quinoa is the best source plant for bulk propagation; Cucumis sativus, though unproductive, is useful as a source of inoculum. Gomphrena globosa is suitable for maintaining cultures.

Assay species

No reliable local lesion hosts are known. Some Chenopodium spp. give lesions sporadically:

C. quinoa is the best systemic assay species.

Strains

No major variants have been distinguished. The isolate described in detail by Converse & Lister (1969) was from black raspberry, Rubus occidentalis, cv. New Logan, collected in the eastern USA (Converse, Lister & Cadman, 1966; Converse, 1967).

Transmission by Vectors

No aerial or soil-living vector is known. Not transmitted experimentally by Amphorophora agathonica under conditions in which this vector transmitted raspberry mosaic viruses. In black raspberry the virus is transmitted by pollen to pollinated plants.

Transmission through Seed

Experimentally seed-transmitted through about 10% of open-pollinated seed of black raspberry cultivars New Logan and Cumberland. Seed-transmission not tested in other hosts.

Transmission by Dodder

Not reported.

Serology

The virus is poorly immunogenic. Antisera obtained from rabbits given various schedules of intramuscular and intravenous injections of untreated or aldehyde-fixed virus reacted specifically only at dilutions less than 1/8.

Relationships

Lacking good antisera, testing for possible relationships between this virus and others has been based on one-way serological tests, and cross-protection tests (Converse & Lister, 1969). Serologically, the virus is unrelated to the following viruses: almond calico, arabis mosaic, cherry rugose mosaic, cucumber mosaic, prune dwarf, raspberry ringspot, sowbane mosaic, strawberry latent ringspot, sweet cherry narrow leaf, tobacco necrosis, tobacco ringspot, tomato black ring, tomato ringspot and tobacco streak. Barnett & Murant (1970) found no serological relationship to raspberry bushy dwarf virus. Cross-protection tests suggest no relationship to prunus necrotic ringspot or tobacco streak viruses.

Stability in Sap

In Chenopodium quinoa sap (1:1 w/v, in 0.1 M phosphate buffer at pH 7), thermal inactivation point is 46-49°C, dilution end-point is up to 10-4 and longevity in vitro is a few hours at 20°C or 3-5 days at 4°C. Extracts made at pH 5 have lower infectivity than those made at pH 8, but it persists longer - up to 23 days at 4°C. Freezing infected leaves or sap drastically lowers infectivity. Reducing agents only slightly increase retention of infectivity; therefore oxidation seems to be only a minor factor in affecting longevity.

Purification

The best method involves clarifying C. quinoa extracts by acidification. Extraction at pH 6 gives higher yields than extraction at pH 5 or 7, but yields are low at best (up to 0.5 mg/100 g leaf). Component ratios (see below) are influenced by the pH of extraction.

Blend infected leaves (1:1.5 w/v) with acetate (0.2 M) or phosphate (0.1 M) buffer at pH 6, containing 0.1 M sodium diethyldithiocarbamate and 0.2 M sodium thioglycollate. Squeeze through cheesecloth and adjust pH to 5 with acetic acid. Readjust to pH 6 after 1 hr and leave overnight. Centrifuge at low speed, and then subject the straw-coloured supernatant fluid to 2 cycles of differential centrifugation, resuspending the high-speed pellets in 0.1 M pH 5 acetate buffer. Concentration by precipitation with 10% polyethylene glycol (av. M. Wt 6000-7500) can be substituted for the first cycle of differential centrifugation. Further purification can be obtained by sucrose rate-zonal density gradient ultracentrifugation.

Do all steps at 4°C. Purified virus is degraded by brisk agitation.

Properties of Particles

Three nucleoprotein components occur (top, middle and bottom) with respective s20, w values of 81, 89 and 98 S at pH 5, or 78, 88 and 93 S at pH 7 (not extrapolated to infinite dilution). Only the bottom component particles appear to be infective, and the role of the others is unknown.

A260/A280: 1.6.

Particle Structure

Stained in phosphotungstate at pH 5, or after pretreatment at pH 7 with 1% glutaraldehyde (Lister & Cathro, 1967), the particles are roughly isometric, about 26 nm in diameter. Size and shape is rather variable, possibly because of distortion (Fig.4).

Particle Composition

Details unknown.

Relations with Cells and Tissues

Details unknown: exposure of infected black raspberry plants to a constant temperature of 37°C for 16 days failed to eliminate the virus.

Notes

In the absence of good antisera and definitive symptoms in its natural host, the routine differential diagnosis of the virus is unsatisfactory. Production of systemic necrosis in C. quinoa by a virus from raspberry is not presumptive evidence for infection by black raspberry latent virus because a strain of tobacco streak virus is common in some Rubus cultivars (R. H. Converse, in press). Serological tests are needed to distinguish black raspberry latent virus from other viruses with similar herbaceous host ranges and symptomatology.

References

  1. Barnett & Murant, Ann. appl. Biol. 65: 435, 1970.
  2. Converse, Lister & Cadman, Rep. Scott. hort. Res. Inst. 1965: 51, 1966.
  3. Converse, Phytopathology 57: 97, 1967.
  4. Lister & Cathro, Rep. Scott. hort. Res. Inst. 1966: 63, 1967.
  5. Converse & Lister, Phytopathology 59: 325, 1969.
  6. Converse & Lister, in Virus diseases of small fruits and grapevines, Univ. Calif Div. Agr. Sci., Berkeley: 151, 1970.


Figure 1

Chenopodium quinoa, showing systemic necrosis.

Figure 2

Nicotiana tabacum cv. Turkish with ringspots on inoculated leaves.

Figure 3

Cucumis sativus cv. National Pickling with mottling on a systemically infected leaf.

Figure 4

A selected field from an unfractionated virus preparation, negatively stained with phosphotungstate (pH 7) after pretreatment with glutaraldehyde. Note variations in apparent particle shape, presumably due to distortion. Some particles appear to be disintegrating. Bar represents 100 nm (photo by C. E. Bracker).