White clover mosaic virus
Biologische Bundesanstalt für Land- und Forstwirtschaft, Braunschweig, Germany
- Described by
- Clover mosaic virus (Rev. appl. Mycol. 39: 232)
- Trifolium virus 1 (Rev. appl. Mycol. 19: 210)
- White clover virus 1 (Rev. appl. Mycol. 15: 418)
An RNA-containing virus with elongated particles 480 x 13 nm. It has a fairly narrow
host range, and is readily transmitted by inoculation of sap, but normally not by vectors.
Causes mosaic and mottle of different degrees of severity in various clover species,
and vein-clearing, light green mottle and sometimes small light yellow spots in pea.
North America, Europe and New Zealand.
Host Range and Symptomatology
Most of the known hosts are legumes; many legumes are susceptible. A strain from Indiana,
USA, infected plants from four other families
(Bancroft, Tuite & Hissong, 1960
- Trifolium spp. (clovers). A weak and diffuse, sometimes irregular mosaic
occasionally latent, sometimes giving necrotic flecks.
- Phaseolus vulgaris (French bean). Chlorotic spots in the inoculated leaves, often
forming necrotic patches in leaf veins
Chlorotic discolorations of the veins of
systemically infected leaves.
- Vicia faba (broad bean). Diffuse ring-like or necrotic local lesions; mild systemic
mosaic, sometimes accompanied by necrosis.
- Vigna sinensis (cowpea). Small necrotic lesions or chlorotic spots or rings in
inoculated primary leaves. Systemic mosaic, sometimes with vein-banding.
- Pisum sativum (pea). Wilting of the inoculated leaves; occasionally develops local
lesions. Systemically infected leaves show vein-clearing initially, then diffuse mottling
sometimes with mild necrotic flecks. If the wilt progresses upwards
(Bos, Delevic & van der Want, 1959).
- Cucumis sativus (cucumber). Inoculated cotyledons develop yellow-green spots or
indistinct white local lesions; diffuse yellow spots appear in systemically infected leaves
- Phaseolus vulgaris is suitable both for maintaining cultures and as a source of virus
- Vigna sinensis is a good local lesion host; some varieties of Phaseolus vulgaris
give lesions with some strains.
Minor variants can be distinguished on the basis of symptom differences in various hosts.
A Californian isolate causes local lesions in Gomphrena globosa
; Dutch isolates produce
systemic mosaic in cowpea. An isolate from Indiana produces local lesions in Ipomoea purpurea,
Datura inoxia, D. stramonium,
and an exceptionally severe local lesion reaction in
inoculated leaves of bean and cowpea
(Bancroft et al., 1960
Transmission by VectorsGoth (1962)
reported a low percentage of transmission of one virus strain by
Acyrthosiphon pisum (Macrosiphum pisi
) to a clonal line of Ladino clover (Trifolium
). However, other authors have failed to transmit the virus using various insects,
including A. pisum.
Transmission through Seed
Recorded (6%) in Trifolium pratense
Transmission by Dodder
Dodder can become infected and transmit the virus
(Bos et al., 1959
transmit has also been reported
(Bancroft et al., 1960
The virus is moderately to strongly immunogenic. It reacts with antiserum to form specific
flocculent precipitates in liquid media. It is most simply assayed by the slide-precipitin test.
It gives specific precipitates in agar gel-diffusion tests with virus fragments but such tests
are much less sensitive than precipitation tests with intact virus particles
Only minor serological differences, if any, exist between different strains. There is
partial or complete protection between strains in plant protection tests. The virus is distantly
related serologically to
clover yellow mosaic
all of which have particles with the same or similar normal lengths. These viruses form the
potato virus X group
(Brandes & Bercks, 1965
Stability in Sap
The thermal inactivation point is about 60°C (for a strain from Indiana 75-80°C),
dilution end-point usually 10-5
, longevity in vitro
temperature 10-99 days.
The following method is satisfactory. Add ascorbic acid (to 0.2%) and sodium sulphite (to
0.2%) to sap of infected Phaseolus vulgaris,
shake with an equal volume of ether,
centrifuge at low speed and discard the ether phase, shake the aqueous phase for 5 min with an
equal volume of carbon tetrachloride, centrifuge at low speed and discard the carbon
tetrachloride phase; repeat the treatment with carbon tetrachloride, and store the clarified
sap at 4°C overnight. Sediment and clarify by two cycles of high and low speed
centrifugation, resuspending the pellets obtained at high speed in 0.01 M phosphate buffer,
An alternative method is to mince frozen infected pea plants, express the sap after
thawing, extract the fibre with 0.1 M K2HPO4 and mix the extract
with the sap. Clarify and sediment by three cycles of low and high speed centrifugation,
resuspending the pellet obtained at high speed in distilled water. Further purify the
preparation by precipitating the virus with a half volume of saturated ammonium sulphate
or by adjusting to pH 4.5 with 1 N acetic acid
(Fry, Grogan & Lyttleton, 1960).
Properties of Particles
The virus sediments as a single component in the analytical ultracentrifuge.
Sedimentation coefficient at infinite dilution (s20,w
): 119 S
(Varma, Gibbs & Woods, 1970
Isoelectric point: about pH 4.5.
Electrophoretic mobility: -7 x l0-5 cm2 sec-1
volt-1 in phosphate buffer pH 7.5, ionic strength 0.1.
Absorbance at 260 nm (1 mg/ml, 1 cm light path): about 3.6
(Fry et al., 1960).
Particles are flexuous helically constructed filaments
normal length about
480 nm, diameter about 13 nm
axial canal about 3.5 nm in diameter, pitch
of helix 3.4 nm, perhaps 11 subunits per turn
(Varma et al., 1968
probably single stranded. M. Wt 2.4 x 106
Molar percentages of nucleotides: G 15.5; A 31.8; C 26.9; U 25.7. RNA is about 6% of particle
(Varma et al., 1970
Miki & Knight (1967)
found the protein subunit to have a molecular
weight of 1.4 x 104, whereas
Koenig et al. (1970)
report a value of 2.0 x
104. The amino acid composition of the protein (moles percent) is: ala 14.4; arg
4.0; asx 9.3; cys 1.3; glx 6.9; gly 5.5; his 1.6; ile 6.1; leu 7.5; lys 5.8; met 1.5; phe
4.2; pro 6.1; ser 7.6; thr 8.4; trp 1.6; tyr 1.9; val 5.4 (calculated from
Miki & Knight, 1967).
Relations with Cells and Tissues
- Bancroft, Tuite & Hissong, Phytopathology 50: 711, 1960.
- Bos, Delevic & van der Want, Tijdschr. PlZiekt. 65: 89, 1959.
- Brandes, Mitt. biol. BundAnst. Ld- u. Forstw. 110, 130 pp., 1964.
- Brandes & Bercks, Adv. Virus Res. 11: 1, 1965.
- Fry, Grogan & Lyttleton, Phytopathology 50: 175, 1960.
- Goth, Phytopathology 52: 1228, 1962.
- Hampton, Phytopathology 53: 1139, 1963.
- Koenig, Phytopath. Z. 65: 379, 1969.
- Koenig, J. gen. Virol. 10: 111, 1971.
- Koenig, Stegemann, Francksen & Paul, Biochim. biophys. Acta 207: 184, 1970.
- Miki & Knight, Virology 31: 55, 1967.
- Pierce, J. agric. Res. 51: 1017, 1935.
- Varma, Gibbs & Woods, J. gen. Virol. 8: 21, 1970.
- Varma, Gibbs, Woods & Finch, J. gen. Virol. 2: 107, 1968.
- Wetter, Arch. Mikrobiol. 37: 278, 1960.
Photographs except Fig.4: courtesy of Dr L. Bos, Wageningen.
Primary leaf of Phaseolus vulgaris cv. Beka, 5 days after inoculation.
Primary leaf of Phaseolus vulgaris cv. Beka, 14 days after inoculation.
Systemic diffuse yellow spots in Cucumis sativus.
Shadowcast virus particles from a purified preparation. Bar represents 250 nm.
Wilting in Pisum sativum cv. Eroica.
Diffuse mottle in Pisum sativum cv. Fertilas.
Mosaic symptoms in leaves of Trifolium pratense.