Potato virus X
Biologische Bundesanstalt für Land und Forstwirtschaft, Braunschweig, Germany
- Potato latent virus (Rev. appl. Mycol. 11: 595)
- Potato mild mosaic virus (Rev. appl. Mycol. 22: 367)
- Solanum virus 1 (Rev. appl. Mycol. 17: 52)
An RNA-containing virus with elongated particles, normal length c.
515 nm. Most known host plants are in the Solanaceae. Transmission mainly by contact.
Very readily transmitted by inoculation of sap. Widely distributed in potato growing
Causes mild mosaic of potato
mosaic and slight stunting of tomato, and
mottle or necrotic ring spotting of tobacco.
World-wide in potato growing areas.
Host Range and Symptomatology
Very readily transmissible by inoculation of sap. The host range is mostly limited
to the Solanaceae, although some plants in other families, e.g. in the Amaranthaceae and
Chenopodiaceae, are susceptible. Strains differ greatly in the symptoms they cause. In
potato, the symptoms range from complete latency to severe necrotic streak.
- Datura stramonium is very susceptible. Most strains give chlorotic rings which
later form a mosaic mottle
- In Nicotiana tabacum (tobacco) and other species of Nicotiana, many
strains cause ringspot symptoms
others cause mottle. Some strains cause no
symptoms at high temperatures in glasshouses in the summer.
- Nicotiana tabacum varieties and other Nicotiana spp.
- Gomphrena globosa is a useful local lesion host
The middle leaves of
plants with 8-10 leaves on the main shoot are the most suitable.
Many minor variants can be distinguished, mainly by the symptoms they give in tobacco.
Strains fall into 4 groups on the basis of serology
into 4 other groups
on the basis of their infectivity for different potato varieties
Cockerham & Davidson, 1963
and into a further 3 groups on the basis of thermal inactivation
Strains that were originally isolated from potato may lose ability to infect this host
after passages on tobacco
Transmission by Vectors
Transmission occurs mainly by contact. Transmission is reported by the grasshoppers
and Tettigonia viridissima
The virus is probably transmitted mechanically on the insects
mouthparts. Transmission has also been reported by the fungus Synchytrium
(Nienhaus & Stille, 1965
Transmission through Seed
Transmission by Dodder
Transmission results inconclusive; the virus infects some dodder species
The virus is strongly immunogenic. It normally reaches high concentrations in host
plants and can readily be detected serologically by using the slide precipitin test in
which the precipitates are flocculent (flagellar). Agar gel-diffusion tests can be
done with virus fragments
(Tomlinson & Walkey, 1967
Serologically the strains of potato virus X fall into 4 groups
plant protection tests, strains may protect against the effects of one another completely,
partially or not at all.
There is a distant serological relationship with the following viruses of the same or
similar normal lengths:
white clover mosaic,
cactus X and
clover yellow mosaic.
Because these viruses also possess other common properties they can be
grouped together to form the potato virus X group
(Brandes & Bercks, 1965).
Stability in Sap
In tobacco sap, the thermal inactivation point (10 min) is between 68 and 76°C
depending on the strain, the dilution end-point is between 10-5
and infectivity is retained at 20°C for several weeks and in the presence of glycerol
for more than 1 year.
Several methods seem satisfactory. The virus has a tendency to aggregate. To avoid
aggregation the following procedure is recommended by
Francki & McLean (1968)
plant sap is clarified by adsorption with charcoal and DEAE-cellulose and then filtered
through Celite, the virus concentrated by ultracentrifugation, and the pellet resuspended
in distilled water. The suspension is emulsified with chloroform, and the virus precipitated
from the aqueous phase by ultracentrifugation. Chloroform treatment and ultracentrifugation
are repeated and the virus is suspended in distilled water. In other published methods,
which disregard the possibility of aggregation, the plant sap is often clarified with
organic solvents; for example
Pfankuch & Kausche (1938)
diluted the sap with an equal
volume of water and stirred it for 20 min with 1/7 volume of chloroform. For investigating
the properties of the particles, clarification procedures should be done rapidly because
prolonged contact with crude plant sap causes degradation of the protein subunits
(Koenig et al., 1970
Properties of Particles
Sedimentation coefficient (s20,w
) at infinite dilution: 117.7 S.
Molecular weight (daltons): 35 x 106
Isoelectric point: pH 4.4.
Partial specific volume: 0.73 cm3/g.
Electrophoretic mobility: -4 x 10-6/cm2 sec-1
volt-1 in 0.06 M phosphate buffer at pH 7.0
(Bawden & Kleczkowski, 1959).
Absorbance at 260 nm (1 mg/ml, 1 cm light path): 2.97
Particles are flexuous filaments
substructure of normal length c
. 515 nm, diameter c.
with cross banding and a central hole of diameter c.
3.4 nm. Pitch of helix 3.4 nm
(Varma et al., 1968
about 10 subunits per turn
(Wilson & Tollin, 1969
Molecular weight 2.1 x 106
, single stranded. Molar percentages of
nucleotides: G22; A32; C24; U22. RNA is about 6% of particle weight
Protein: Subunits in rapidly purified preparations have a molecular weight of
c. 3.0 x 104; after prolonged contact with crude sap, values of 2.2-2.4
x 104 have been found
(Koenig et al., 1970;
Miki & Knight, 1968).
The amino acid composition of the protein has been reported for different strains by
Shaw & Larson (1962),
Shaw, Reichmann & Hatt (1962) and
Miki & Knight (1968).
the ringspot strain it is (moles percent): ala 13.4; arg 6.3; asx 11.3; glx 9.4; his 1.2;
ile 5.5; leu 5.1; lys 6.4; met 4.2; phe 7.3; pro 7.2; ser 6.4; thr 13.8; tyr 1.4; val 6.2
(Shaw, Reichmann & Hatt, 1962).
Relations with Cells and Tissues
During the early phases of infection the virus is found mainly in the palisade cells,
less frequently in the epidermis, of Datura stramonium
and potato. Particles are
distributed diffusely or in densely packed aggregates or in X-bodies. The aggregates may
fill the greater part of the cells. Virus particles and spherical inclusion bodies occur
in the plastids. The X-bodies, which occur mainly near the nucleus, also contain cellular
components, chiefly ribosome like particles, either free or in linear groups from 500 to
1600 nm in length; mitochondria, dictyosomes and areas of endoplasmic reticulum are also
(Kozar & Sheludko, 1969
- Bawden & Kleczkowski, Virology 7: 375, 1959.
- Bercks, Phytopath. Z. 20: 113, 1953.
- Brandes, Mitt. biol. BundAnst. Ld- u. Forstw. 110, 130 pp., 1964.
- Brandes & Bercks, Adv. Virus Res. 11: 1, 1965.
- Cockerham, Proc. 2nd Conf. Potato Diseases, Lisse-Wageningen, 1954: 89, 1955.
- Cockerham & Davidson, Rep. Scott. Pl. Breed. Stn 1963: 26, 1963.
- Francki & McLean, Aust. J. biol. Sci. 21: 1311, 1968.
- Knight, Protoplasmatologia 4(2): 177 pp., 1963.
- Koenig, Stegemann, Francksen & Paul, Biochim., biophys. Acta 207: 184, 1970.
- Köhler, Phytopath. Z. 44: 189, 1962.
- Kozar & Sheludko, Virology 38: 220, 1969.
- Matthews, Ann. appl. Biol. 36: 460, 1949.
- Miki & Knight, Virology 36: 168, 1968.
- Nienhaus & Stille, Phytopath. Z. 54: 335, 1965.
- Paul, Arch. Mikrobiol. 32: 416, 1959.
- Pfankuch & Kausche, Biochem. Z. 299: 334, 1938.
- Reichmann, Can. J. Chem. 37: 384, 1959.
- Schmelzer, Phytopath. Z. 28: 1, 1956.
- Schmutterer, J. angew. Ent. 47: 277, 1961.
- Shaw & Larson, Phytopathology 52: 170, 1962.
- Shaw, Reichmann & Hatt, Virology 18: 79, 1962.
- Smith, Proc. R. Soc., B 109: 251, 1931.
- Tomlinson & Walkey, Virology 32: 267, 1967.
- Varma, Gibbs, Woods & Finch, J. gen. Virol. 2: 107, 1968.
- Walters, Phytopathology 42: 355, 1952.
- Wilson & Tollin, J. gen. Virol. 5: 151, 1969.
Nicotiana tabacum cv. Samsun infected with a ringspot strain of the
Shadowcast virus particles from a purified preparation. Bar represents 250
Local lesions in Gomphrena globosa.
Mosaic and vein clearing in Datura stramonium.
Systemically infected plant of Solanum tuberosum, showing mosaic.