Soil-borne wheat mosaic virus
M. K. Brakke
Agricultural Research Service, US Department of Agriculture, Plant Pathology Department, University of Nebraska, Lincoln, Nebraska 68503 USA
- Marmor tritici
- Wheat viruses 1 and 3
An RNA-containing virus with stiff rod-shaped particles of two lengths, 110-160
and 300 nm, which appear hollow when negatively stained. It has a narrow host range,
is transmitted by the fungus, Polymyxa graminis, and by inoculation of sap
and causes mosaic diseases in winter wheat and barley.
Causes mosaic diseases in winter wheat
and barley, the severity of
symptoms depending on variety, strain of virus, and weather. Mosaic may be light
green to yellow. Roots are usually stunted. Some varieties of wheat, e.g.
those related to Harvest Queen, show rosetting, with extreme stunting of tops and
roots and excessive tillering. Symptoms normally appear on new growth of winter
wheat in the spring, but have been seen in occasional years in the autumn. However,
virus can be detected in the autumn in the roots of young plants not showing leaf
(Brakke, Estes & Schuster, 1965
Affected areas of the field appear
yellow or light green from a distance. The disease tends to be more severe in
low-lying areas of a field, but is not confined to these areas. Symptoms become
milder and tend to disappear as the weather becomes warmer and the wheat plants
(Koehler, Bever & Bonnett, 1952
Winter wheat-growing areas of USA, Japan and Italy.
Host Range and Symptomatology
The host range of US strains is limited to several Triticum
species, Hordeum vulgare
(barley), Secale cereale
commutatus, B. tectorum
and some Chenopodium
Rao & Brakke, 1969
Agropyron repens, Bromus inermis, Avena
(oats), A. byzantina, Zea mays
(maize), Nicotiana tabacum,
Lycopersicon esculentum, Cucumis sativus,
and Phaseolus vulgaris
- Triticum aestivum (wheat). The virus is manually transmissible to wheat,
producing symptoms in 2 weeks or more at 20°C or less, but few or no symptoms
above 20°C. The optimum temperature for symptoms in the greenhouse, or in growth
chambers, is about 16°C, with an optimum day length of about 8 hr. Infected
plants show a green or yellow mosaic and stunting. It is difficult to infect all
the inoculated plants by leaf-rubbing. Inocula prepared by grinding infected leaves
in 0.1 M K2HPO4 are usually more infectious than those
prepared by grinding leaves in water. Air-brush inoculation gives a higher percentage
infection than leaf-rubbing
(Pring & Gumpf, 1970).
The virus is translocated
slowly in the plant. Seedlings with two leaves or more, inoculated either by
leaf-rubbing, or through the roots by the vector, seldom show mosaic symptoms; the
virus apparently remains localized in roots or crown. The percentage of inoculated
plants showing symptoms is increased when the plants are placed in the dark for
4-5 days starting a few days after inoculation, or when the leaves are cut off
after a month and new growth observed
(Rao & Brakke, 1970).
- Wheat (cv. Michigan Amber and many others).
- Systemic assays on wheat (cv. Michigan Amber or others) and local lesions on
Chenopodium quinoa and C. amaranticolor.
Green and yellow mosaic strains and a rosetting strain were selected by
The degree of relationship between apparently similar viruses
from the USA and Italy has not been determined. Isolates from Japan (the soil-borne
green mosaic of wheat and barley) and USA are serologically related but those from
Japan can infect tobacco and Zea mays
(Tsuchizaki, Hibino & Saito, 1970
Transmission by VectorsMcKinney, Paden & Koehler (1957)
suggested that a vector transmitted this
virus in soils because (i) some chemical treatments eradicated the virus from soils,
and (ii) steamed soil in which manually inoculated wheat plants grew did not become
infective whereas soil mixed with washed, naturally infected roots did
Similar results were reported by
Saito et al. (1964c
Linford & McKinney (1954)
suggested that the fungus, Polymyxa graminis
found in roots of plants infected through the soil, might be a
Estes & Brakke (1966)
established correlations between transmission of
the virus and the presence of P. graminis.
cultures of P. graminis
transmitted the soil-borne wheat mosaic virus in
Italy. Virus transmission was not prevented by treating zoospores of P. graminis
with antiserum to the virus, nor by treating resting spores of the fungus with
0.1 N NaOH or 0.1 N HCl. Zoospores could not be freed of virus by washing by repeated
centrifugation. Zoospores did not acquire virus in vitro,
acquired virus when grown in plants infected with virus by manual
(Rao & Brakke, 1969
The infectivity in soil survived air-drying
Transmission through Seed
The virus is very immunogenic in rabbits; injection of purified virus results
in antisera with precipitation end-points of 1/1000 or more. The end-point in
precipitin reactions depends on the virus preparation, being higher in preparations
where the virus has partly aggregated before addition of antisera. Reactions have
also been obtained in agar diffusion tests
(Saito, Takanashi & Iwata, 1964b
Rao & Brakke, 1969
The virus is morphologically similar to other tubular viruses, in particular
barley stripe mosaic
viruses. It appears to be
unrelated to some other soil-borne viruses in cereals, such as
wheat spindle streak mosaic
oat mosaic viruses
occurring in USA and UK,
and to the
yellow mosaic viruses of barley
and wheat in Japan
of which reportedly have flexuous filamentous particles.
Stability in Sap
The thermal inactivation point in wheat sap is 60-65°C (10 min) and
dilution end-point is 10-2
. The virus survived more
than 11 years in dried leaves
(McKinney, Silber & Greeley, 1965
The main difficulty in purifying the virus is its tendency to aggregate.
It has been purified by differential centrifugation after clarifying the plant
extracts with chloroform
(Saito et al., 1964a
or chloroform and
It has also been purified by differential
centrifugation followed by treatment with detergent to disperse chloroplast fragments
and other impurities
(Rao & Brakke, 1969
The virus appears to be extracted
better with 0.5 M sodium orthoborate, pH 9.0, than with extractants of lower pH
and salt concentration. The yield is up to 150 mg per kg of tissue
Properties of Particles
The following properties were determined for the Nebraska isolate
Sedimentation coefficient, (s20,w): 172 S (160 nm rods);
211 S (300 nm rods).
A260 for 1 mg/ml, 1 cm light path: 3.1 (not corrected for light scattering).
A260/A280: 1.20 (not corrected for light scattering).
Particles are stiff rods
appearing hollow, like those of
when negatively stained. The diameter is about
20 nm. The most frequent length is 150-160 nm
(Tsuchizaki et al. (1970)
reported 110-120 nm for some Japanese isolates), but many are about 300 nm long
(Brakke et al., 1965
Brandes, Phillipe & Thornberry, 1964
the particles in preparations of the 300 nm rods appear to be dimers of the 160
nm rods. Such preparations are infective, but preparations of 160 nm rods are
Particle CompositionNucleic acid:
The Nebraska isolate contains two classes of single-stranded
RNA, with sedimentation coefficients (s20,w
) of 24.3 and
33.4 S in 0.15 M NaCl, 0.015 M sodium citrate, pH 7.0. Their respective
M. Wts are 1.0 x 106
and 2.0 x 106
, based on their
sedimentation rate after formaldehyde treatment. The 160 nm rods contain only
the 24.3 S RNA. Preparations of the 300 nm rods have both classes of RNA,
the 24.3 S RNA coming from dimers of 160 nm rods and the 33.4 S RNA
from true 300 nm rods. There is always more of the 24.3 S RNA than of the
33.4 S, but the ratio is variable. After one centrifugation through sucrose
gradients, which may be insufficient for complete separation, the 33.4 S
RNA is infective, hut the 23.4 S RNA is not
ratio suggests that the particles have about 5% RNA.
Protein: No information.
Relations with Cells and Tissues
The virus infects both roots and leaves.
McKinney, Eckerson & Webb (1923)
observed vesicular, amorphous inclusions by
light microscopy, whereas three types of inclusion have been observed by electron
microscopy. Crystalline inclusions, apparently composed of virus particles, were
frequently found in the vacuole. The other two types of inclusion were found in
the cytoplasm. One of these was apparently crystalline and had a smaller lattice
spacing than would be expected if it contained virus; it was surrounded by virus
particles. The other type of inclusion was amorphous and contained convoluted
tubules and scattered virus particles
The particles of this virus vary in length with the strain
(Tsuchizaki et al., 1970
as happens with
tobacco rattle virus
The wide range of lengths
reported for soil-borne wheat mosaic virus (see
Brandes et al., 1964
for references) could also indicate this, but it is not certain that all these
reports refer to strains of the same virus. Lengths of rods, and the size and
function of the RNA components of different strains should be compared. Perhaps
the best way to recognize this virus is by symptoms, together with the pattern of
infected areas in the field, and the numerous rods found by electron microscopy
of leaf-dip preparations.
Barley stripe mosaic virus
is the only other virus with
a similar morphology found in wheat; it differs in having a shorter incubation
period after manual transmission to wheat and in giving good symptoms at 20-25°C.
- Brakke, Estes & Schuster, Phytopathology 55: 79, 1965.
- Brandes, Phillipe & Thornberry, Phytopath. Z. 50: 181, 1964.
- Canova, Phytopath. Mediterranea 5: 53, 1966.
- Estes & Brakke, Virology 28: 772, 1966.
- Gumpf, Ph.D. Thesis, University of Nebraska, Lincoln, 1970.
- Gumpf, Virology 43: 588, 1971.
- Inouye, Ber. Ohara Inst. landw. Biol. 15: A7, 1969.
- Koehler, Bever & Bonnett, Bull. Ill. agric. Exp. Stn 556: 567, 1952.
- Linford & McKinney, Pl. Dis. Reptr 38: 711, 1954.
- McKinney, J. agric. Res. 23: 771, 1923.
- McKinney, Science, N.Y. 73: 650, 1931.
- McKinney, Circ. U.S. Dep. Agric. 442, 22 pp., 1937.
- McKinney, J. Wash. Acad. Sci, 34: 322, 1944.
- McKinney, Phytopathology 38: 1003, 1948.
- McKinney, Eckerson & Webb, J. agric. Res. 26: 605, 1923.
- McKinney, Paden & Koehler, Pl. Dis. Reptr 41: 256, 1957.
- McKinney, Silber & Greeley, Phytopathology 55: 1043, 1965.
- Paulsen, Phytopathology 60: 1307, 1970.
- Peterson, Virology 42: 304, 1970.
- Pring & Gumpf, Pl. Dis. Reptr 54: 550, 1970.
- Rao, Phytopathology 58: 1516, 1968.
- Rao & Brakke, Phytopathology 59: 581, 1969.
- Rao & Brakke, Phytopathology 60: 714, 1970.
- Saito, Takanashi, Iwata & Okamoto, Bull. natn. Inst. agric. Sci., Tokyo Ser. C 17: 1, 1964a.
- Saito, Takanashi & Iwata, Bull. natn. Inst. agric. Sci., Tokyo Ser. C 17: 23, 1964b.
- Saito, Takanashi, Iwata & Okamoto, Bull. natn. Inst. agric. Sci., Tokyo Ser. C 17: 41, 1964c.
- Saito, Takanashi, Iwata & Okamoto, Bull. natn. Inst. agric. Sci., Tokyo Ser. C 17: 61, 1964d.
- Slykhuis, Phytopathology 60: 319, 1970.
- Tsuchizaki, Hibino & Saito, Ann. phytopath. Soc. Japan 36 : 187, 1970.
Soil-borne wheat mosaic virus in leaf-dip preparation mounted in a 3:1
mixture of 2% potassium phosphotungstate: 1% ammonium vanadatomolybdate. Bar
represents 200 nm.
Polymyxa graminis sporangium with exit tube reaching host cell
wall. Bar represents 12 µm. Inset is a biflagellate zoospore of P.
graminis at 2.5 x the magnification of the sporangium. (From Rao, 1968.)
Wheat leaves; (left) a leaf showing non-parasitic mottling;
(centre) three leaves showing soil-borne mosaic; (right) a healthy
leaf. (From Koehler et al., 1952.)
P. graminis resting spores in a wheat root, unstained. Bar
represents 20 µm. (Photograph by Jean Peterson.)