Potato aucuba mosaic virus
B. Kassanis
Rothamsted Experimental Station, Harpenden, Hertfordshire, England
D. A. Govier
Rothamsted Experimental Station, Harpenden, Hertfordshire, England
Contents
Introduction
- Described by
Quanjer (1921)
and
Clinch, Loughnane & Murphy (1936).
-
Selected synonyms
- Potato virus G (Rev. appl. Mycol. 16: 117)
- Potato calico virus (Rev. appl. Mycol. 14: 786)
- Potato virus F (= tuber blotch virus) (Rev. appl. Mycol. 16: 117)
-
An RNA-containing virus with filamentous particles about 580 nm long. It is transmitted
by aphids in the non-persistent manner only when aided by certain ‘helper’
viruses, and
is readily transmitted by mechanical inoculation.
Main Diseases
Causes yellow spotting or necrosis of potato leaves and necrosis in potato tubers,
but is rare and consequently of little economic importance.
Geographical Distribution
World-wide but uncommon. The virus was prevalent in a few potato cultivars no longer
grown commercially.
Host Range and Symptomatology
The type and intensity of the symptoms in potato plants depend on the strain of virus
and the cultivar of potato. The two main types of symptom are: (1) bright yellow spots on
the lower leaves, later coalescing to form large yellow or whitish patches
(
Fig.1);
(2)
necrotic spots, often leading to systemic or top necrosis
(
Fig.2)
(
Clinch, 1941).
Some
infected plants do not show foliage symptoms, especially during the second and subsequent
years of infection and when growing under glass. During storage the tubers of many cultivars
develop necrosis in the cortex and pith
(
Fig.4)
visible on the surface as irregularly
shaped, brown patches or sunken dry brown areas
(
Fig.3).
Virulent virus strains may
kill the tuber eyes.
-
Diagnostic species
- Capsicum annuum and C. frutescens (pepper). Necrotic local lesions
(Fig.5)
followed by epinasty, systemic necrosis
(Fig.6)
or severe mosaic; plants
infected when young are killed.
- Nicotiana glutinosa. Light green mottle with dark green vein-banding
(Fig.7).
- Lycopersicon esculentum (tomato). Some strains produce small round yellow
spots on lower leaves.
- Nicotiana tabacum cvs. White Burley and Xanthi-nc, Datura stramonium
and Petunia sp. may be infected systemically but are usually symptomless.
-
Propagation species
- N. tabacum cv. Xanthi-nc is a good plant for maintaining the virus and a good
source of virus for purification. Maximum virus concentration is found in inoculated
leaves 10 days after inoculation using carborundum.
-
Assay species
- Capsicum annuum cv. Long Red and C. frutescens cv. Early Calwonder,
and other cultivars.
Strains
Potato virus F, syn. tuber blotch virus
(
Clinch et al., 1936)
is a minor
variant causing mild leaf symptoms but typical tuber necrosis.
Transmission by Vectors
Transmitted by
Myzus persicae in the non-persistent manner but only when
aided by certain ‘helper’ viruses of the
potato virus Y group,
of which
potato virus A
and
potato virus Y are the most efficient. Aphids transmit it from plants also infected with the
‘helper’ virus, or after feeding first on a source of ‘helper’
virus and then on a
source of potato aucuba mosaic virus
(
Kassanis & Govier, 1971a;
1971b).
In these conditions aphids can acquire the virus in 1 min. Starving aphids lose
infectivity in a few hours.
Transmission through Seed
Not known; it is transmitted through the tubers produced by infected potato plants.
Transmission by Dodder
Not known.
Serology
The virus is strongly immunogenic and antisera with titres in excess of 1/10,000
are readily obtained. The virus gives flocculent precipitates in tube-precipitation tests.
Relationships
Strains of the virus are closely related to one another serologically and an avirulent
strain protects potato plants from infection with a virulent strain. No serological
relationship with other viruses has been demonstrated but potato aucuba mosaic virus
resembles viruses of the
potato virus X group morphologically.
Stability in Sap
In tobacco sap, the thermal inactivation point (10 min) of most strains is between
65 and 70°C, the dilution end-point between 10
-5 and 10
-6, and
some infectivity remains after 1 to 2 months at 18 to 20°C in sap diluted 1/10, when
inoculated using carborundum
(
Kollmer & Larson, 1960).
The virus concentration is
greater in the inoculated leaves of tobacco than in systemically infected ones, reaching
a serological titre of 1/512 about 10 days after inoculation.
Purification
We find that the method described by
Juo & Rich (1969)
gives very aggregated
preparations. The following method (D. A. Govier & B. Kassanis, unpublished) gives
infective, largely unaggregated, preparations with yields of about 100 mg virus from 1
kg of leaves. Homogenize leaves in a cooled blender with 0.1 M ethylenediaminetetra-acetate
pH 7.6 containing 0.01 M Na-diethyldithiocarbamate (DIECA), 2 ml/g tissue. Squeeze the sap
through muslin, clarify by centrifuging for 30 min at 15,000
g, dialyse for
18-24 h against 10 volumes of 0.005 M DIECA, and reclarify. Shake the supernatant fluid
for 5-10 min with 1/4 volume of chloroform, centrifuge, and subject the aqueous phase to
2 cycles of differential centrifugation (50 min at 100,000
g and 10 min at
15,000
g), resuspending the virus pellets in 0.01 M borate pH 7.5. Aggregation
is largely prevented by leaving pellets covered with buffer overnight at 5°C before
resuspending, by concentrating only slightly when resuspending the first high-speed pellets
and, when a large weight of leaves is used, by infiltrating the leaves with extracting
solution under vacuum before homogenizing them.
Properties of Particles
Sedimentation coefficient (
s20,w) at infinite dilution: about
130 S.
Electrophoretic mobility: -0.7 x 10-5 cm2/sec-1/
volt-1 at pH 7 in 0.067 M phosphate buffer.
Absorbance at 260 nm (1 mg/ml, 1 cm light path): 2.6.
A260/A280: 1.1.
Particle Structure
Particles are filamentous, about 580 nm long and 11 nm wide
(
Fig.8).
They often
aggregate end-to-end and side-to-side.
Particle Composition
RNA: About 5% of particle weight. Molar percentages of nucleotides: G25; A30;
C24; U21 (J. M. Carpenter, unpublished).
Protein: Subunits have molecular weight of about 2.6 x 104 (J. M.
Carpenter, unpublished).
Relations with Cells and Tissues
Thin sections of infected tobacco leaves show virus particles in the cytoplasm,
sometimes in dense aggregates. No other inclusions known (R. H. Turner, unpublished).
Notes
The yellowing of potato leaves resembles that caused by
potato mop-top virus.
Both viruses also cause necroses on the tuber surface, but those caused by potato
aucuba mosaic virus are usually less clearly patterned than the raised necrotic rings
caused by first-year infection with potato mop-top virus; however, sometimes potato
aucuba mosaic virus causes necrotic rings. By contrast with potato aucuba mosaic virus,
potato mop-top virus does not infect
Capsicum annuum systemically, and has
straight tubular particles about 20 nm in diameter
(
Harrison & Jones, 1970).
References
- Clinch, Scient. Proc. R. Dubl. Soc. N.S. 22: 435, 1941.
- Clinch, Loughnane & Murphy, Scient. Proc. R. Dubl. Soc. N.S. 21: 431, 1936.
- Harrison & Jones, Ann. appl. Biol. 65: 393, 1970:.
- Juo & Rich, Phytopathology 59: 1816, 1969.
- Kassanis & Govier, J. gen. Virol. 10: 99, 1971a.
- Kassanis & Govier, J. gen. Virol. 13: 221, 1971b.
- Kollmer & Larson, Res. Bull. agric. Exp. Stn Univ. Wis. 223, 40 pp., 1960.
- Quanjer, R. hort. Soc., Lond. Rep. int. Potato Conf. pp. 127-145, 1921.
Systemically infected leaf of potato cv. Ninetyfold. (Courtesy Scottish
Horticultural Research Institute.)
Potato cv. Majestic, systemically infected.
Infected potato tuber cv. Majestic.
Cut tuber of infected potato cv. Majestic.
Inoculated leaf of Capsicum annuum cv. Long Red.
Systemically infected Capsicum annuum cv. Long Red.
Systemically infected leaf of Nicotiana glutinosa.
Virus particles from a purified preparation. Bar represents 200 nm.
