Potato virus A
Biologische Bundesanstalt für Land- und Forstwirtschaft, Braunschweig, Germany
- Described by Murphy & McKay (1932).
- Selected synonyms
- Marmor solani (Rev. appl. Mycol. 18: 607)
- Potato mild mosaic virus (Rev. appl. Mycol. 18: 607)
- Potato virus P (Rev. appl. Mycol. 15: 391)
- Solanum virus 3 (Rev. appl. Mycol. 17: 52)
- An RNA-containing virus with filamentous particles, normal length c.
730 nm. Only hosts known are in the Solanaceae. Transmitted by aphids in
the non-persistent manner and by inoculation of sap. Widely distributed in
Leaves of infected potatoes may show a mild mosaic, roughness of the surface,
waviness of the leaf margin (Fig.1
), or no symptoms at all depending on the
variety and on the weather. Some hypersensitive varieties develop top necrosis.
Potatoes infected with potato virus A in combination with potato virus X
or potato virus Y
show crinkle symptoms. Potato virus A decreases yield of infected potatoes by up
Widespread in most potato-growing countries.
Host Range and Symptomatology
Known hosts are limited to the Solanaceae. Sap-transmission without abrasive
is usually difficult because of low virus concentration.
- Diagnostic species
- Nicotiana tabacum (tobacco) cv. Samsun. Vein-clearing and diffuse mottle
depending on strain and conditions of culture (Fig.3).
- N. tabacum (tobacco) cv. White Burley. Vein-clearing and dark green
vein-banding depending on strain and conditions of culture (Fig.4).
- Nicandra physalodes. Slight vein-clearing and mottle to severe necrosis,
rugosity and stunting, depending on virus strain.
- Lycopersicon pimpinellifolium. Systemic necrosis; plant usually dies
(MacLachlan, Larson & Walker, 1953).
- Solanum demissum x S. tuberosum cv. Aquila (=A6 hybrid) and S.
demissum SdA. Numerous local lesions (Fig.2).
- Propagation species
- Nicotiana tabacum cv. Samsun is a good source for purification. The
maximum virus concentration in this host plant depends on the conditions of
culture (Bartels, 1954).
- Assay species
- Aquila (A-6) hybrid is a useful local lesion host. Detached inoculated leaves
kept in a humid
chamber at 24°C and illuminated by fluorescent lamps (1000 lux) give small
dots with regular or star-shaped borders or intense black necrotic flecks (Fig.2)
1953; Bartels, 1970).
Solanum demissum SdA gives necrotic local lesions
- For aphid transmission tests Nicandra physalodes is useful, being very
susceptible to infection by Myzus persicae.
Strains differing in virulence towards potato and Nicandra physalodes
may be classed into four groups: very mild, mild, moderately severe, severe
). Their virulence is correlated with their physical properties
such as dilution end-point, thermal inactivation point and longevity in vitro
(MacLachlan et al., 1953
) and also with their behaviour in Nicotiana
Transmission by Vectors
Transmissible by at least 7 species of aphids in the
non-persistent manner, notably Aphis frangulae, A. nasturtii
Virus can be acquired by Myzus persicae
in 20 sec, inoculated
in 20 sec (MacLachlan et al., 1953
), and retained for 20 min (Sylvester,
). No latent period. Myzus persicae
can transmit potato aucuba mosaic
when the source plants also contain potato virus A
(Clinch, Loughnane &
Transmission through Seed
Transmission by Dodder
Moderately immunogenic. Antisera with titres of 1/512 are usually obtained;
maximum 1/4096 (Bartels, unpublished). With the slide-precipitin test virus can
readily be detected in sap of infected tobacco, but not in sap from infected
potato plants. The precipitates are flocculent (flagellar). No agar gel-diffusion
tests are reported.
Serologically related to potato Y
(common and tobacco veinal necrosis strains),
and tobacco etch
viruses, although the degree of relationship among
these four viruses is difficult to assess, because reciprocal heterologous tests
do not give the same results (Bartels, 1964
; Fribourg & de Zoeten, 1970
These serological relationships, together with its particle morphology and other
properties show that potato virus A is a member of the potato virus Y group
viruses (Brandes, 1964
Stability in Sap
In Nicandra physalodes
sap, different strains of virus lose
infectivity after heating 10 min at 44-52°C, dilution 1/10 to 1/40, or storage
for 12-18 hr at 18°C (MacLachlan et al., 1953
). The virus did not
survive lyophilization (Hollings & Stone, 1970
Differential centrifugation of infective sap gives poor results and little or
no virus is obtained. The following method, however, is successful, if done in
the cold. Leaves are homogenized along with 0.2%(w/v) ascorbic acid and 0.2%(w/v)
sodium sulphite, n-
butanol is added dropwise to 8%(v/v) and the mixture
centrifuged at low speed. The supernatant fluid is homogenized once or twice
with an equal volume of CCl4
and the virus purified by differential
centrifugation (Bartels, unpublished). Another way of stabilizing the virus is
to grind each 100 g infected tissue in 100 ml phosphate buffer (pH 7.0)
containing 10 g Al2
(Fribourg & de Zoeten, 1970
Properties of Particles
Particles are flexuous filaments (Fig.5
) with normal length
730 nm, diameter c.
15 nm (Brandes & Paul, 1957
Relations with Cells and Tissues
No intracellular inclusions found in infected potato plants (Bawden &
Potato virus A and potato virus Y
both infect potato, have particles indistinguishable
by electron microscopy, and are difficult to distinguish by the symptoms they
produce in many test plants. However, they may be distinguished serologically
and only potato virus A produces local lesions in Solanum demissum
- Bartels, Phytopath. Z. 21: 395, 1954.
- Bartels, Phytopath. Z. 49: 257, 1964.
- Bartels, Potato Res. 13: 119, 1970.
- Bawden & Sheffield, Ann. appl. Biol. 31: 33, 1944.
- Brandes, Mitt. biol. BundAnst. Ld- u. Forstw. 110, 130 pp., 1964.
- Brandes & Paul, Arch. Mikrobiol. 26: 358, 1957.
- Calvert, Pl. Path. 9: 144, 1960.
- Clinch, Loughnane & Murphy, Scient. Proc. R. Dubl. Soc. 21: 431, 1936.
- Cockerham, Proc. 3rd Conf. Potato Virus Diseases, Lisse-Wageningen, 1957: 199, 1958.
- Fribourg & de Zoeten, Phytopathology 60: 1415, 1970.
- Hollings & Stone, Ann. appl. Biol. 65: 411, 1970.
- Köhler, Züchter 23: 173, 1953.
- MacLachlan, Larson & Walker, Res. Bull. agric. Exp. Stn Univ. Wis. 180, 36pp., 1953.
- Murphy & McKay, Scient. Proc. R. Dubl. Soc. 20: 347, 1932.
- Schmelzer, Naturwissenschaften 46: 83, 1959.
- Sylvester, Hilgardia 23: 53, 1954.
Naturally infected plant of Solanum tuberosum (potato) cv.
Servena, showing rough mosaic and waviness of the margin of leaflets. (Photo
courtesy O. Bode.)
Necrotic lesions in inoculated leaf of Solanum demissum x
S. tuberosum cv. Aquila (A6).
Systemically infected leaf of Nicotiana tabacum cv. Samsun,
showing diffuse chlorotic mottling.
Systemically infected leaf of N. tabacum cv. White Burley showing
Virus particles from leaf-dip preparations mounted in phosphotungstate.
Bar represents 500 nm. (Photo courtesy D. Lesemann.)