Tobacco etch virus
R. J. Shepherd
Department of Plant Pathology, University of California, Davis, California, USA
D. E. Purcifull
Plant Pathology Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida, USA
Described by Johnson (1930).
- Marmor erodens (Rev. appl. Mycol. 28: 514)
- Tobacco virus 13 (Rev. appl. Mycol. 17: 52)
- Tomato etch virus (Rev. appl. Mycol. 20: 85)
- Nicotiana virus 7 (Rev. appl. Mycol. 17: 52)
An RNA-containing virus of the potato virus Y group
with flexuous filamentous particles c.
730 nm in length. It is found mainly in solanaceous plants, is transmitted in the
manner by aphids and is readily transmissible by inoculation of sap.
Causes necrotic and/or chlorotic mottle diseases of tobacco, pepper, tomato and
Common in North and South America.
Host Range and Symptomatology
Species in about 15 dicotyledonous families are susceptible to infection
Usually confined to solanaceous plants in nature. Mechanically transmissible to
- Nicotiana tabacum (tobacco). Inoculated leaves usually develop
indefinite chlorotic spots or
necrotic rings or arcs. Systemic symptoms are vein-clearing and necrotic etching
chlorotic mottle; virulent strains cause necrotic spots and distortion.
Some strains produce mild
interveinal mottle with green vein-banding.
- Capsicum annuum (pepper). Systemic chlorotic mottle with distortion in
many varieties. Most
strains cause root necrosis, wilt and death of C. frutescens cv.
- Datura stramonium. Mottle, vein-banding, and leaf distortion
- Lycopersicon esculentum (tomato). Mild distortion, inconspicuous mottle.
- N. glutinosa or varieties of N. tabacum hypersensitive to
tobacco mosaic virus are
suitable for maintaining cultures and are good sources of virus for purification.
- The virus causes local lesions in Chenopodium album, C. amaranticolor
quinoa and Physalis peruviana. N. tabacum is preferable as an assay host
when using aphid
Variants differing in virulence towards tobacco and other hosts are common.
Variants called severe
etch induce more prominent stunting, chlorosis, and necrosis than mild etch
variants (Johnson, 1930
Bawden & Kassanis, 1941
Transmission by Vectors
Transmissible in the non-persistent manner by more than 10 species of aphids
(Kennedy, Day & Eastop, 1962
Laird & Dickson, 1963
notably Myzus persicae.
All instars can transmit.
Acquisition and inoculation can occur in 1-2 min. No latent period.
Virus is retained for only 1-4 h
by feeding aphids. No transmission to progeny aphids
Transmission through Seed
Transmission by Dodder
Transmitted by Cuscuta californica
but not by two other species of Cuscuta
The virus is strongly immunogenic. Tube or micro-precipitin tests with clarified
sap or partially
purified virus preparations are the most useful because the virus does not diffuse
well in agar gels.
Preparations containing intact virus particles give flagellar type precipitates
in tests in liquid.
Immunodiffusion tests have been used for diagnosis and for tests for relationship
with other viruses,
using alkali-treated (pH 10.5) virus as antigen
(Purcifull & Shepherd, 1964
Purcifull & Gooding, 1970
The virus has also been diagnosed serologically in crude extracts using agar gels
containing sodium dodecyl sulphate
(Gooding & Bing, 1970
Particle length and other biological and physical properties place
tobacco etch virus in the
potato virus Y
group of viruses and it is probably distantly serologically related to other viruses in this
Colombian datura viruses
Kahn & Bartels, 1968
Purcifull & Gooding, 1970
Pokeweed mosaic virus
may be serologically related
(Shepherd, Fulton & Wakeman, 1969
In plant-protection tests, strains protect against the
effects of one another and may or may not protect against the effects of those viruses
distantly serologically related
(Bawden & Kassanis, 1945
Schmelzer, Bartels & Klinkowski, 1960
Stability in Sap
In tobacco sap, the thermal inactivation point (10 min) is about 55°C,
. Infectivity of sap survives for 5-10 days at 20°C.
Of the various methods described, the following two are probably best for
and insolubility of virus. Systemically infected tobacco may yield 30-60 mg virus
per litre of sap.
1. Purcifull (1966).
Homogenize tissue in 0.5 M phosphate buffer (pH 7.5) containing 1% sodium
sulphite. Filter and incubate extract at 4°C for 8-16 h. Clarify extract by
(1 ml per 10 ml extract) and centrifuge at low speed. Sediment virus from the
clarified extract by
centrifuging at high speed, and resuspending the pellets in 0.02 M borate buffer,
pH 8.2. Precipitate
virus by adding NaCl to 0.5% (w/v) and adjusting to pH 4.8. Remove virus by
low speed centrifugation
and resuspend in 0.02 M borate; further purify by two cycles of differential centrifugation.
2. Damirdagh & Shepherd (1970a).
Homogenize in 0.5 M phosphate buffer (pH 7.1, containing
1% 2-mercaptoethanol) using 120 ml buffer per 100 g tissue. Clarify by adding
1/10th volume n-butanol
and centrifuge at low speed. Precipitate virus from clarified extract by adding
4 g polyethylene
glycol (6000-7000 M. Wt) per 100 ml extract and centrifuge at low speed.
Resuspend virus in 0.025
M phosphate (pH 7.4) containing 0.5-1.0 M urea and 0.1% 2-mercaptoethanol and subject
to 2 cycles of
differential centrifugation, resuspending the virus in this solution at each step.
To each 3.2 ml of
virus solution add 1.8 ml of saturated CsCl (at 4°C) in 0.025 M phosphate, pH 7.4,
for 24 h at high speed in an angle or swinging-bucket rotor. Remove the virus,
which bands in about
the centre of these equilibrium density gradients, and dialyse against
0.005 M glycylglycine buffer,
Properties of Particles
Sedimentation coefficient (s20, w
) at infinite dilution: 154 S. No
accessory components are found by analytical ultracentrifugation.
Absorbance at 260 nm (1 mg/ml, 1 cm light path): 2.4 when virus is mostly unaggregated.
A260/A280: about 1.27-1.30.
Buoyant density: 1.33 (in CsCl).
Particles are flexuous filaments
of diameter 12-13 nm and length 730 nm
(Brandes & Wetter, 1959
Single-stranded. Molar percentages of nucleotides: G23; A30; C20; U27.
RNA is 5% of
(Damirdagh & Shepherd, 1970b
Protein: 95% of particle weight
(Damirdagh & Shepherd, 1970b).
Relations with Cells and Tissues
The virus induces nuclear crystals and cytoplasmic inclusions
which are readily observed by light microscopy
especially when stained in epidermal
consisting of striated lamellae are found in
the cytoplasm of tissues infected with tobacco etch virus, as with other viruses of the
potato virus Y
Edwardson, Purcifull & Christie, 1968
These proteinaceous inclusions
are structurally and serologically distinct from virus particles
(Hiebert et al., 1971
lamellae of tobacco etch virus-induced pinwheel inclusions are characteristically
seen as striated
in negatively stained leaf extracts
(Purcifull, Edwardson & Christie, 1970
Several members of the
group of viruses, e.g.
potato Y and
occur in solanaceous plants and are easily confused with tobacco etch virus.
induced in tobacco and pepper varieties, susceptibility of Datura stramonium,
intra-nuclear inclusions, presence of triangular striated lamellae in leaf extracts,
tests are helpful in diagnosis of the virus.
- Bartels, Phytopath. Z. 49: 257, 1964.
- Bawden & Kassanis, Ann. appl. Biol. 28: 107, 1941.
- Bawden & Kassanis, Ann. appl. Biol. 32: 52, 1945.
- Bennett, Phytopathology 34: 905, 1944.
- Brandes & Wetter, Virology 8: 99, 1959.
- Christie, Virology 31: 268, 1967.
- Damirdagh & Shepherd, Phytopathology 60: 132, 1970a.
- Damirdagh & Shepherd, Virology 40: 84, 1970b.
- Edwardson, Am. J. Bot. 53: 359, 1966.
- Edwardson, Purcifull & Christie, Virology 34: 250, 1968.
- Gooding & Bing, Phytopathology 60: 1293, 1970.
- Greenleaf, Phytopathology 43: 564, 1953.
- Hiebert, Purcifull, R. Christie & S. Christie, Virology 43: 688, 1971.
- Holmes, Phytopathology 36: 643, 1946.
- Johnson, Bull. Ky agric. Exp. Stn 306: 289, 1930.
- Kahn & Bartels, Phytopathology 58: 587, 1968.
- Kassanis, Ann. appl. Biol. 26: 705, 1939.
- Kassanis, Ann. appl. Biol. 28: 238, 1941.
- Kennedy, Day & Eastop, A conspectus of aphids as vectors of plant viruses, London, Commonwealth Institute of Entomology, 1962.
- Laird & Dickson, Phytopathology 53: 48, 1963.
- Purcifull, Virology 29: 8, 1966.
- Purcifull & Gooding, Phytopathology 60: 1036, 1970.
- Purcifull & Shepherd, Phytopathology 54: 1102, 1964.
- Purcifull, Edwardson & Christie, Phytopathology 60: 779, 1970.
- Schmelzer, Phytopath. Z. 60: 301, 1967.
- Schmelzer, Bartels & Klinkowski, Phytopath. Z. 40: 52, 1960.
- Sheffield, Jl R. microsc. Soc. 61: 30, 1941.
- Shepherd, Fulton & Wakeman, Phytopathology 59: 219, 1969.
Necrotic etching in tobacco leaf (Nicotiana tabacum cv. Havana 425).
(Left) virus-induced wilting of Tabasco pepper; (right) healthy plant.
Leaf distortion in Datura stramonium. (Photograph courtesy of T. A. Zitter).
Local lesions in Chenopodium amaranticolor.
Filamentous particles mounted in phosphotungstate. Bar represents 500 nm.
Electron micrograph of pinwheel inclusion in thin section of
tobacco leaf, vacuum-dehydrated
prior to fixation. Bar represents 100 nm.
Photomicrograph of nuclear crystals and cytoplasmic inclusions in epidermal cell of tobacco
Triangular inclusion in leaf extract prepared in phosphotungstate.
Bar represents 500 nm.
Insert is an enlargement of a portion of a triangle showing its striated nature
(periodicity 5 nm).