Cowpea mosaic virus
A. van Kammen
Laboratorium voor Virologie, Wageningen, The Netherlands
Smith (1924) and
- Cowpea yellow mosaic virus (Rev. appl. Mycol. 39: 204)
An RNA-containing virus with isometric particles about 28 nm in diameter. It
has a limited host range, is transmitted by beetles and readily by inoculation
of sap. Infected plants contain two kinds of nucleoprotein particles similar in
size, but differing in RNA content; both are necessary for virus infectivity.
Particles containing no RNA are also produced.
Causes mosaic of Vigna
spp. In Nigeria it greatly decreases the leaf
area, flower production and yield of infected plants
recorded natural infection of soya beans (Glycine max
), mungo beans
and P. aureus
) and sunn hemp (Crotalaria
), but only when growing near to infected cowpeas.
Reported from Nigeria, Trinidad, Surinam and USA.
Host Range and Symptomatology
Host range rather limited. Only dicotyledons have been described as hosts,
but monocotyledons have not been tested systematically
symptoms caused by the yellow and the severe strains (see Strains) differ
greatly. Readily transmitted by inoculation of sap.
- Vigna unguiculata (cowpea). The yellow strain produces chlorotic lesions
in the inoculated primary leaves, bright yellow mosaic and vein-yellowing in
systemically infected trifoliate leaves
and dark green spots and mosaic
on the pods. The severe strain produces chlorotic and some necrotic spots in
inoculated primary leaves and severe mosaic with vein-clearing, leaf distortion
and necrosis in the trifoliate leaves. Necrosis of the stem just below the primary
leaves and in the veins results in collapse of the plants
- Phaseolus vulgaris cv. Beka (French bean). The yellow strain produces
yellow spots in inoculated leaves and mild systemic symptoms, some puckering of
the trifoliate leaves and local vein necrosis. The severe strain produces severe
systemic necrosis and leaf distortion, and plants usually collapse
- Chenopodium amaranticolor. The yellow strain produces, in inoculated
leaves, yellow local lesions (0.5-1 mm), later becoming necrotic, and in the upper
leaves severe systemic mosaic, chlorotic spots, distortion and puckering
The severe strain produces only local lesions and no systemic reaction
- Vigna unguiculata or V. sinensis are good sources of virus for
purification and for maintaining cultures.
- Phaseolus vulgaris (cvs. Pinto and Scotia) and Chenopodium amaranticolor
are suitable local lesion hosts.
Among isolates of the virus from Surinam, Trinidad and Nigeria,
distinguished yellow and severe strains by the type of
symptoms they caused in
V. unguiculata, C. amaranticolor
and P. vulgaris
Little work has been done on the prevalence of different strains in nature.
isolated a naturally occurring mutant of the yellow strain, which differs
from the parent strain in the relative amount of RNA-free particles it produces.
De Jager & Van Kammen (1970)
treated the yellow strain with nitrous acid and
obtained a mutant which gave no systemic reaction in Beka beans and produced a
relatively large proportion of RNA-free particles.
Transmission by Vectors
Transmitted by various leaf beetles: Ceratoma ruficornis
In Surinam the yellow strain was transmitted
by Ceratoma variegata,
but not by Diphaulaca
sp. (probably D.
), whereas the severe strain was transmitted by Diphaulaca
sp. (probably D. laeta
(Van Hoof, 1963
remained viruliferous for 14 days
Van Hoof (1963)
reported that C. variegata
for only 4 days, but in his experiments the beetles soon died.
found that 30% of the beetles collected in the field were viruliferous and
Van Hoof (1963)
found 50% of the beetles used in an experiment able to transmit.
Outbreaks of mosaic disease in cowpea crops are influenced by seasonal and
climatic factors which determine the prevalence of vector beetles (Van Hoof,
Transmission through Seed
An isolate from Trinidad was seed-transmitted in Vigna unguiculata,
but not in Vigna sinensis
This virus is probably a
representative of the severe strain
The virus is strongly immunogenic. Standard methods give antisera with
titres of 1/1024 in the Ouchterlony double diffusion test, but higher titres
may be obtained. Virus preparations tested by the Ouchterlony method give a
single band of precipitate, even though they contain more than one centrifugal
or electrophoretic component.
The yellow and severe strains are distantly serologically related: antiserum
to each strain has a titre to homologous antigen at least sixteen times higher
than that to heterologous antigen and absorption with heterologous antigen
leaves the titre to homologous antigen virtually unchanged (Van Kammen,
reported isolates from Arkansas and Trinidad to
be related but not identical. Cross-absorption tests have not been reported,
but cowpea mosaic virus is distantly related to
bean pod mottle
red clover mottle
pea green mottle
(Valenta & Gressnerova, 1966
broad bean stain
(Gibbs, Giussani-Belli & Smith, 1968
These viruses form the
cowpea mosaic virus group.
Stability in Sap
The thermal inactivation point (10 min) of the virus in Vigna
65°-75°C. The dilution end-point is 10-4
sap diluted 1/10 in 0.01 M phosphate buffer pH 7.0 and stored at room temperature,
infectivity survived 3-5 days in vitro.
found crude sap
remained infective over 20 days at room temperature.
Yields of virus may reach 2 g/kg leaf tissue from Vigna
at 30°C in a growth chamber. In the chloroform-butanol method
Bruening & Agrawal, 1967
the frozen leaves are crushed and blended in twice
their weight of buffer (0.02 M potassium acetate, 0.002 M EDTA, pH 5.8) at about
4°C. The mixture is filtered through gauze, mixed with an equal volume of a
mixture (1:1) of chloroform and n
-butanol, and stirred for 20 min. The
phases are separated by centrifugation and the aqueous phase recovered. In an
alternative method using polyethylene glycol (PEG) and NaCl
Van Kammen, 1967
the frozen leaves are homogenized in 0.1 M phosphate buffer pH 7.0
(1 ml/g leaf). The homogenate is filtered and the extract centrifuged at 10,000
for 15 min. To the supernatant fluid, PEG is added to a final
concentration of 4% (w/v) and NaCl to give a concentration of 0.2 M. The mixture
is stirred at room temperature to dissolve the PEG and NaCl and, after one hour,
centrifuged at 10,000 g
for 15 min; the pellets are resuspended in
0.01 M phosphate buffer, pH 7.0. The preparations obtained by these methods may
then be further purified by differential centrifugation.
Properties of Particles
Purified preparations of the virus contain three centrifugal components, empty
protein shells without RNA (T), and two nucleoprotein components (M and B)
containing 24% and 33% RNA respectively. The separated nucleoprotein components
are not infectious
(Van Kammen, 1968
but mixtures of the M and B components are.
The infectivity of a mixture depends upon the proportions of the two components
and the concentration of the component present in the lowest amount. Mixtures of
the M or B components of the yellow strain with the B or M components of mutants
of the yellow strain are infectious but similar heterologous mixtures of components
of the yellow and severe strains are not
De Jager & Van Kammen, 1970
This again indicates that the yellow and severe strains differ considerably.
Sedimentation coefficients (s20,w) at infinite dilution
(svedbergs): 58 (T), 95 (M), 115 (B). For the yellow strain the proportion of M:B
is about 2:1, for the severe strain 10:1.
Molecular weight: about 6 x 106 (M) and 7.7 x 106 (B).
Isoelectric point: between pH 3.4 and 4.5.
Absorbances at 260 nm (1 mg/ml, 1 cm light path): 6.2 (M), 10.0 (B).
A260/A280: 0.69 (T), 1.57 (M), 1.67 (B).
Buoyant density in CsCl (g/ml): 1.30 (T), 1.41 (M); component B gives two bands
of density 1.43 and 1.47. The two bands have the same sedimentation coefficient
Van Kammen & Van Griensven, 1970).
Purified preparations of the virus contain two electrophoretic components, each
of which contains all three centrifugal components
mobility (yellow strain): -4.0-4.25 x 10-5 and -2.6-2.8 x 10-5
cm2 sec-1 volt-1 in 0.1 M phosphate buffer pH 7.0.
The mobilities are somewhat lower for the severe strain. The slower migrating form
predominates in early infection and the faster one in late infection. The slower
migrating form is reported to be converted into the faster migrating form in
vivo. The conversion of the slower form into the faster form can be simulated
in vitro by treating the preparation with a mixture of carboxypeptidases A
and B or with chymotrypsin. This conversion is accompanied by an increase of about
85% in specific infectivity
(Niblett & Semancik, 1969).
Particles are isometric, c.
28 nm in diameter. The particles may be
seen most clearly when negatively stained with phosphotungstate, but it is difficult
to deduce their substructure from such pictures
The single RNA strands in components M and B have sedimentation
) of 26 S and 34 S and molecular
weights of about 1.45 x 106
and 2.55 x 106
the yellow strain their respective base compositions (molar percentages of
nucleotides) are G 20.7; A 28.4; C 19.3; U 31.6 and G 22.9; A 28.5; C 17.2; U 31.4
(Van Kammen & Van Griensven, 1970
Protein: Probably one type of protein with 159-165 amino acid residues.
That of the faster electrophoretic form contains three amino acid residues (arg,
glu, ile) fewer than that of the slower form
(Niblett & Semancik, 1969).
Relations with Cells and Tissues
The virus particles occur scattered and in clusters throughout the cytoplasm.
They do not form crystalline arrays
Amorphous inclusion bodies frequently
occur around or close to the nucleus in epidermal cells of infected Vigna
The yellow and severe strains of cowpea mosaic virus were both first isolated
spp.; however, they seem no more closely related to each other
than to other members of the cowpea mosaic virus group (e.g.
bean pod mottle virus
red clover mottle virus
Therefore it would perhaps be better to regard
them not as strains but as separate members of the cowpea mosaic virus group.
Many other viruses have been isolated from Vigna spp. showing mosaic
symptoms; the most notable of these are:
cowpea aphid-borne mosaic virus
(Lovisolo & Conti, 1966),
a strain of
bean southern mosaic virus
(Shepherd & Fulton, 1962),
cowpea chlorotic mottle virus
and a legume-infecting
tobacco mosaic virus
(Lister & Thresh, 1955).
Cowpea mosaic virus may be distinguished from these and other viruses of cowpea by
the morphology of its particles and their behaviour in the ultracentrifuge, but
serological tests seem to be the only sure way of identifying the virus.
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Symptoms in Vigna unguiculata cv. Blackeye Early
Ramshorn: yellow strain.
Symptoms in Vigna unguiculata cv. Blackeye Early
Ramshorn: severe strain.
Symptoms in Chenopodium amaranticolor: yellow strain.
Symptoms in Chenopodium amaranticolor: severe strain.
Virus particles from a purified preparation in phosphotungstate.
Bar represents 100 nm.
Symptoms in Phaseolus vulgaris cv. Beka, (left) yellow
strain, (right) severe strain.
Ultra-thin section of systemically infected V. unguiculata leaf,
fixed in 3% glutaraldehyde and stained with 1% uranyl acetate, showing a cluster
of virus particles as well as particles scattered singly through the cytoplasm.
Bar represents 500 nm.