Alfalfa mosaic virus
Institute for Phytopathological Research, Wageningen, Netherlands
E. M. J. Jaspars
Biochemical Dept, State University, Leiden, Netherlands
- Lucerne mosaic virus (Rev. appl. Mycol. 24: 513)
- Alfalfa virus 1 and 2 (Rev. appl. Mycol. 13: 488)
- Medicago virus 2
- Marmor medicaginis (Rev. appl. Mycol. 28: 514)
An RNA-containing virus with bacilliform particles of three different lengths,
the longest c.
60 nm. Readily transmissible by sap inoculation and in the non-persistent manner
by aphids to a
very wide range of host plants. Common in most countries.
Causes mosaic in lucerne
calico and tuber necrosis in potato
and garden lupin, mosaic in chilli pepper, severe necrosis in tomato, mosaic
in Malva parviflora, Daphne
and Viburnum opulus,
yellow fleck in
white mottle in Philadelphus
sp., and is one of the causes of mosaic
in red and white
clover, mosaic or calico in celery and lettuce, and necrotic streak in pea;
occurs naturally in many
other herbaceous and some woody species (46 spp. in 12 families).
Host Range and Symptomatology
Infects over 305 spp. in 47 dicotyledonous families
Sap transmission is easy between
most hosts but may be difficult from lucerne. Symptoms greatly depend on virus strain,
host variety and
environmental conditions, and may be masked; recovery frequent. In many species mottle
or mosaic is bright
yellow (calico); severe necrosis may also occur. In lucerne and clover, yield is
often reduced and
predisposition to drought and winter injury increased.
- Phaseolus vulgaris (French bean). Strains most commonly found in lucerne
sometimes spreading, lesions in most varieties; other strains produce chlorotic
local lesions or none
at all but give systemic mild mottle, vein necrosis and leaf distortion.
- Vigna sinensis (cowpea). The commonest strains produce necrotic local
lesions; others infect
- Vicia faba (broad bean). Most strains give black necrotic local lesions,
by a mild mottle, but more often by stem necrosis and plant death.
- Pisum sativum (pea). In most varieties, necrotic local lesions and/or
wilting of inoculated
leaves with necrotic stem streaking and death of the plant.
- Chenopodium amaranticolor and C. quinoa. Local lesions;
chlorotic and necrotic flecking, which distinguishes alfalfa mosaic virus from most strains of
cucumber mosaic virus.
- Nicotiana tabacum (tobacco). Necrotic or chlorotic local lesions
give no local reaction. Systemic symptoms are mild mottle, bright chlorotic vein-banding,
and, rarely, deformation
Enations occur with certain strains. Plants
- Nicotiana tabacum and N. glutinosa are suitable for maintaining cultures.
tabacum, especially cultivars hypersensitive to
tobacco mosaic virus,
e.g. Samsun NN,
are good sources of virus for purification.
- Phaseolus vulgaris (most cultivars) and Vigna sinensis for strains that
lesions; Chenopodium amaranticolor and C. quinoa.
Numerous strains or variants with minor differences have been described.
and Vigna sinensis
are mostly used for differentiation. Some more important
Alfalfa yellow spot mosaic strain of
AMV425 strain of Hagedorn
& Hanson (1963) (severe symptoms in red clover and Melilotus alba);
mosaic strain of
Potato calico strain of
tuber necrosis strain of
AMV15/64 strain of Hull (1969).
Transmission by Vectors
Transmitted by at least 13 aphid spp.
(Kennedy, Day & Eastop, 1962
no period of latency,
transmission increased by starving the aphids before acquisition
can acquire the virus from purified preparations through Parafilm membranes
Transmission through Seed
Reported (up to 6%) in certain alfalfa varieties
and (1-5%) in chilli pepper
Transmission by Dodder
Occurs in at least five Cuscuta
Moderately immunogenic, giving antibody titres of 1/1024
(Bancroft et al., 1960
antisera contain three groups of antibodies, one specific for antigenic sites on the
the second specific for antigenic sites on the disaggregated virus protein
and the third specific
(Moed & Veldstra, 1968
The variously sized intact particles of the virus are
No serological relationships to other viruses have been found. The bacilliform particles
those of a mushroom virus, and
cacao swollen shoot
cacao mottle leaf viruses.
widely in pathogenicity and geographical origin were closely related serologically
(Bancroft et al., 1960
Most strains, when tested in Phaseolus vulgaris, Nicotiana tabacum
cross protect against one another; however, lucerne isolates do not
protect against infection with isolates from Viburnum
when tested in
Stability in Sap
The thermal inactivation point is usually between 60 and 65°C, but may range between 50
and 75°C, dilution end-point is around 10-3
but may approach 10-5
longevity in vitro
is usually 2-4 days. Infectivity seems best retained at
pH 7.0-7.5 and
when phosphate buffers (0.01 M to 0.5 M) are used for leaf extraction.
Modifications of Steeres butanol/chloroform method are mostly used
(Gillaspie & Bancroft, 1965
and yield up to 1.5 g virus per kg leaf tissue. Preparations sometimes contain ribosomal
material. Alternatively, the virus may be precipitated with polyethylene glycol,
M. Wt 20,000, in
0.2 M NaCl
The virus components are separated by differential precipitation in 0.03 M
sucrose gradient centrifugation
(Van Vloten-Doting, Kruseman & Jaspars, 1968),
or by differential
solubilization of a polyethylene glycol precipitate
Biological activity of purified
components often decreases rapidly, but can be stabilized by
ethylenediamino-tetraacetate (0.001 M).
Infective preparations of the RNA are best prepared by phenol extraction of the virus in
phosphate buffer containing 1% sodium dodecyl sulphate or 2% sodium pyrophosphate.
isolated RNA, assayed on Phaseolus vulgaris, is about 1% of that of intact virus.
way to isolate the protein is to dissociate the virus in 0.5 M MgCl2;
the RNA precipitates,
and the supernatant fluid, after dialysing against 0.05 M acetate buffer, pH 5.5,
protein in dimer form.
Properties of Particles
Analytical ultracentrifugation of purified preparations reveals up to six components
(Bancroft & Kaesberg, 1958
consisting of bacilliform particles of different lengths
(Gibbs, Nixon & Woods, 1963
The three larger, obviously bacilliform, components
for infection and, in order of decreasing size, are named bottom (B), middle (M), and
(Tb). The two or three spheroidal accessory top components (Ta, To, and Tz) are not
singly or together, and cannot replace the function of any of the three larger components
(Van Vloten-Doting, Dingjan-Versteegh & Jaspars, 1970
by a mixture of the functional components of two different virus strains give hybrid
properties of both parents. The relative amount of the different components depends on the
strain and growing conditions.
Sedimentation coefficients (svedbergs) at infinite dilution: c. 99 (B), 89 (M), 75
68 (Ta), 60 (To) and 53 (Tz).
Molecular weights: c. 7.3 x 106 (B), 3.7 x 106 (Ta).
Electrophoretic mobility: -6.6 x 10-3 cm2sec-1
at pH 7 and 0.1 ionic strength. The virus migrates as a single component. The RNA
the surface charge
(Bol & Veldstra, 1969).
The virus is precipitated below pH 6. Above pH 4,
precipitates retain infectivity for at least a few hours at 4°C.
A260/280: 1.7-1.8 (B, Ta and probably also M and Tb).
Absorbance at 260 nm (1 mg/ml, 1 cm light path): 5.2; may be lower for accessory components.
Buoyant density in CsCl after fixation with formaldehyde: 1.385 (B) and 1.382 (Ta).
The virus is sensitive to pancreatic ribonuclease
ribonuclease, particles lose RNA fragments and ultimately degrade to smaller structures
(Bol & Veldstra, 1969).
At high ionic strength (e.g. 1.5 M NaCl, pH 5.5) a partially reversible
(Bol & Kruseman, 1969).
The virus has been partially reconstituted from
isolated RNA and protein by
Lebeurier, Wurtz & Hirth (1969)
The components represent a series of six-sided elongated particles of different lengths,
cylindrical part of the particles consisting of an hexagonal lattice net
(angle of prominent lattice
vector with particle axis: 0°; lattice spacing: 4.8 nm. At either end is a half
structure bisected at right angles to a threefold axis. The subunits are possibly
grouped in hexamer
clusters in the cylindrical part and in 6 pentamer clusters at the ends. The particles
Tz are probably icosahedral (by optical diffraction of electron micrographs)
(Gibbs et al., 1963
Hull, Hills & Markham, 1969a
The lengths of the components (nm) in purified preparations
(mounted in potassium phosphotungstate after fixation with formaldehyde) are about
58 (B), 49 (M),
38 (Tb), 29 (Ta) and 19 (Tz). In crude preparations particles over 1 µm in length
observed. Diameter of all particles is about 18 nm. With uranyl acetate as
negative stain, fixation
Single-stranded. About 18% of the weight of each of the three
Approximate M. Wt of
RNA: 1.3 x 106
(B), 1.1 x 106
(M), 0.9 x 106
contains two RNA molecules of M. Wt c.
0.3 x 106
. M. Wt of RNAs from
To and Tz
(Hull, Rees & Short, 1969b
Hull et al., 1969a
Sedimentation coefficients (svedbergs) at infinite dilution
(solvent: 0.01 M Tris, 0.1 M KCl, pH 7):
26 (B) and 13 (Ta). Molar percentages of nucleotides:
G23; A27; C21; U30 for B; and G24;
A25; C23; U28 for Ta
(Rauws, Jaspars & Veldstra, 1964
Nicolaieff, Pinck & Hirth (1969)
isolated double-stranded RNA molecules 0.5 and 0.9 µm long directly from
Protein: All components have the same coat protein.
Hull et al. (1969b)
reported that the protein subunit has a M. Wt of 32,600 (strain 15/64),
but others have failed
to confirm this. From hydrodynamic data and amino acid analyses a M. Wt of 24,500 has
for strain 425 whereas electrophoresis of the protein in sodium dodecyl
gels suggests that it is about 27,500 (eight strains, including 425 and 15/64;
Kruseman et al., 1971;
J. M. Carpenter, pers. comm.). Amino acid compositions have been reported by
Kelley & Kaesberg (1962),
Hull et al. (1969b),
Tremaine & Stace-Smith (1969) and
Kruseman et. al. (1971).
Relations with Cells and Tissues
Transient, amorphous, granular inclusion bodies are seen by light microscopy in tobacco
Electron microscopy of thin sections shows whorled aggregates and
rafts of particles hexagonally packed side by side in the vacuoles and cytoplasm
In host range, symptoms, vector relationships and many other properties alfalfa mosaic virus
cucumber mosaic virus
The latter, however, has spherical particles, produces local
lesions in Phaseolus vulgaris
only in winter, and most strains do not infect
or C. quinoa
systemically; moreover not all strains of
alfalfa mosaic virus
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Lucerne with mosaic symptoms (after Zaumeyer & Wade, 1935).
Electron micrograph of purified virus preparation, fixed with formaldehyde
in phosphotungstate. B, bottom component; M, middle component; Tb, top component
particles are the top components Ta, To or Tz. Bar represents 100 nm.
(Courtesy Dr M. Verhoyen &
Mr S. Henstra.)
Potato cv. Eersteling (Duke of York), with calico symptoms after
inoculation with an
isolate from white clover. (Photo I. P. O., Wageningen.)
Phaseolus vulgaris cv. Bataaf, with local lesions of strain
AMV 425. (Photo I.P.O.,
Lesions of strain AMY 425 in inoculated leaf of Nicotiana tabacum, cv.
Burley. (Photo I.P.O., Wageningen.)
Systemic symptoms of strain AMY 425 in N. tabacum cv.
White Burley. (Photo I.P.O.,
N. tabacum, cv. White Burley, infected with the yellow spot
mosaic strain. (Photo
Biochem. Dept. State Univ., Leiden.)