Potato leafroll virus
B. D. Harrison
Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK
- Infectious nature of potato leafroll disease described by Quanjer,
Van der Lek & Oortwijn Botjes (1916), virus particles purified
by Peters (1967).
- Potato phloem necrosis virus (Quanjer, 1913)
- A virus with RNA-containing isometric particles c. 24 nm
in diameter. Host range limited. Apparently confined to phloem tissue
and not transmissible by inoculation with sap. Transmitted by several
aphid species in the persistent manner. Occurs in most places where
potatoes are grown.
Causes an economically very important disease in potato
) in many countries.
Symptoms of primary infection consist typically of pallor, and in
some cultivars reddening, of the tip leaves, which may become rolled
and assume an erect habit. Secondary symptoms, in plants grown from
infected tubers, are stunting of the shoots and upward rolling of
leaflets, especially those on lower leaves (Fig.1
), which break
easily when crushed and may develop marginal necrosis. Upper
leaves are slightly chlorotic. Carbohydrates accumulate in affected
leaves because phloem transport is impaired. The virus is
transmitted through a variable proportion of tubers on plants
with primary infection and through all tubers on plants with
secondary infection. In some cultivars (e.g. Golden Wonder and
Russet Burbank), tubers on plants with either primary or secondary
infection may develop internal net necrosis (Fig.5
In some cultivars of S. tuberosum ssp. andigena
grown in S. America, leaf rolling is not a typical symptom of
secondary infection, but the plants are stunted and their tip
leaves develop marginal yellowing (enanismo amarillo;
Fig.2; Rodriguez & Jones, 1978).
In tomato, tomato yellow top strains cause stunting of plants,
marginal yellowing and curling of leaflets (Fig.3), and death of
flower buds (Braithwaite & Blake, 1961).
Occurs in potato in most places where the crop is grown.
Tomato yellow top diseases are reported from N. America (Altstatt
& Ivanoff, 1945
), S. America (Costa, 1949
) and Australasia
), but not all are known to be caused by strains of
potato leafroll virus.
Host Range and Symptomatology
The virus is not transmitted by manual inoculation with sap but
is transmissible by vector aphids and by grafting. Most known hosts
(about 20 species) are in the Solanaceae. Non-solanaceous hosts
include Amaranthus caudatus, Celosia argentea
(Amaranthaceae), Nolana lanceolata
(Nolanaceae) (Natti, Kirkpatrick & Ross, 1953
(Cruciferae; Thomas, 1984
(Portulacaceae; Tamada, Harrison &
- Diagnostic species
- Datura stramonium. Systemically infected leaves develop
- Physalis floridana. Plants become more or less stunted,
and systemically infected leaves develop mild interveinal chlorosis
(Fig.4). Older leaves may become slightly rolled.
- Solanum tuberosum ssp. tuberosum (potato). Plants
inoculated by aphids or by grafting develop the symptoms described
under Main Diseases.
- Brassica pekinensis (Chinese cabbage), Raphanus
sativus (radish) and Vicia faba (broad bean) are thought
to be non-hosts.
- Propagation species
- Virus cultures are readily maintained in potato clones; dormant
infected tubers can be stored at 4°C for more than a year.
Systemically infected leaves of P. floridana or potato are
suitable sources of virus for purification.
- Assay species
- P. floridana can be used as a test plant in aphid
transmission experiments in which the aphids acquire the virus by
feeding on plants, or by feeding through membranes on virus
preparations, or by injection. Infectivity can also be measured by
inoculating purified virus to mesophyll protoplasts obtained from
tobacco (Takanami & Kubo, 1979a) or potato (Barker &
Harrison, 1982), incubating the protoplasts for about 2 days and
then determining the percentage that can be stained by fluorescent
Strains from potato have been distinguished by the severity of
symptoms induced in potato, P. floridana
Larson & Walker, 1951
) or Montia perfoliata
, or by
their ease of transmission by Myzus persicae
et al., 1984
). These strains did not, however, differ
antigenically (Tamada et al., 1984
), and avirulent strains
protected P. floridana
plants from virulent strains (Webb,
Larson & Walker, 1952
; Harrison, 1958a
Tomato yellow top strains (Thomas, 1984) differ from potato
strains in causing yellow edge symptoms in tomato leaves (Fig.3)
and little or no symptom in potato, and in being readily
transmitted by the aphid Macrosiphum euphorbiae
(Braithwaite & Blake, 1961). Potato leafroll and tomato yellow
top isolates from Australia were antigenically indistinguishable
(Thomas, 1984) and they cross-protected in P. floridana
plants (J. E. Thomas, unpublished results).
Transmission by Vectors
Several aphid species are reported to transmit the virus (Kennedy,
Day & Eastop, 1962
). Myzus persicae
is the most efficient
and important vector; Macrosiphum euphorbiae
strains less efficiently but is a good vector of Australian tomato
yellow top isolates. The minimum access times needed by M.
to acquire and to inoculate the virus are each about
1 h. There is a latent period and the minimum total time for
transmission is about 12 h (Sugawara, Kojima & Murayama, 1974
however, transmission frequency increases with increase in the access
periods up to 2 days or more. Larval and adult aphids can transmit
the virus. Aphids remain infective after moulting and can retain
infective virus for life. The virus can be detected in aphid
haemolymph, and virus-free M. persicae
become infective after
virus containing preparations are injected into their haemocoeles
; Day, 1955
The virus content of aphids decreases when they are kept on
immune plants (Harrison, 1958b). However, Stegwee &
Ponsen (1958) reported that the virus could be transferred many
times by serial injection of aphids kept on virus-immune plants,
although this was not confirmed by Sugawara, Kojima & Murayama
(1973) or Eskandari, Sylvester & Richardson (1979). Serological
assay of aphid extracts indicates that the virus content of aphids
increases with increase in acquisition access period up to about 7 days,
but decreases in a temperature dependent manner after the aphids are
removed from the virus source, at first more rapidly and later very
slowly (Tamada & Harrison, 1981). Despite this evidence, the
possibility of limited virus replication in aphids cannot be excluded.
Indeed, Weidemann (1982) found that virus particle antigen accumulated
in the nuclei of cells of the midgut and principal salivary gland of
M. persicae 1-2 days after the beginning of virus acquisition
and suggested that the virus multiplied in these cells. Gildow (1982)
detected virus-like particles in cells of the accessory salivary
glands of M. persicae, on their probable path from the
haemolymph to saliva.
Transmission through Seed
The virus particles are very immunogenic. Antisera with titres
of 1/1000 in gel diffusion precipitin tests can be prepared; a
single reaction line is obtained. Mouse monoclonal antibodies have
been prepared to a Canadian isolate of the virus (Martin &
). Intracellular virus antigen can be detected
with fluorescein-conjugated antibody (Kubo & Takanami, 1979
Because of the low concentration of virus antigen in tissues,
sensitive serological techniques have proved especially valuable.
ELISA can detect the virus reliably in potato leaves (Casper, 1977
Maat & de Bokx, 1978; Mehrad, Lapierre & Maury, 1978
; Tamada & Harrison, 1980a
), potato tubers
and virus-carrying aphids (Clarke, Converse & Kojima, 1980
; Tamada & Harrison, 1980b
Immunosorbent electron microscopy has been similarly successful
(Kojima, Chou & Shikata, 1978
; Roberts & Harrison, 1979
Van Balen, 1982
In its particle properties, tissue tropism and symptoms, and its
transmission in the persistent manner by aphids, potato leafroll
virus is a typical luteovirus
. Relationships to several members of
this group have been detected by gel-diffusion serological tests
(Kubo & Takanami, 1978
; T. Tamada, unpublished results),
immunoelectron microscopy (Roberts, Tamada & Harrison, 1980
and/or by density gradient zone-depletion serological tests
(Waterhouse & Murant, 1981
). The closest relationships are to
tobacco necrotic dwarf
(SDI = 1), beet western yellows
yellowing (SDI = 2-4) and bean leaf roll
viruses: however, antisera
to potato leafroll virus react more strongly with particles of the
beet viruses than do antisera to the beet viruses with particles of
potato leafroll virus (Kubo & Takanami, 1978
et al., 1980
; Kubo, 1981
; Tamada et al., 1984
T. Tamada, unpublished results). Strains of beet western yellows
virus differ in the extent of their serological relationship to
tomato yellow top isolates of potato leafroll virus occurring in
Australia (Thomas, 1984
There is no evidence of antigenic variation among potato
isolates of potato leafroll virus (Kojima, 1981; Tamada
et al., 1984), but Thomas (1984) obtained results
suggesting that luteovirus isolates from tomato plants with yellow
top diseases in different countries may differ antigenically.
Stability in Sap
In Physalis floridana
sap, the thermal inactivation point
(10 min) was between 70° and 80°C, dilution end-point about
, and longevity at 2°C between 5 and 10 days,
when infectivity was assayed by the aphid injection method (Murayama
& Kojima, 1965
). Infectivity was retained for at least a year in
leaf tissue stored at -70°C (T. Tamada & B. D. Harrison,
(Based on Takanami & Kubo, 1979a
). Freeze infected
or potato leaves for a week or more at
-70°C (-20°C may be adequate). Grind leaves (500 g) at
room temperature with 1 litre 0.1 M sodium citrate buffer,
pH 6.0, containing 0.5% 2-mercaptoethanol and 1% Driselase,
then incubate at 25°C for 2-3 h with shaking. Adjust extract
to pH 7.0 by adding 0.2 M Na2
with 0.67 vol. chloroform/butanol mixture (1:1, v/v) and
centrifuge at 5000 rev./min for 15 min. To the aqueous phase,
add polyethylene glycol, M. Wt 6000, to 8% (w/v) and NaCl to
0.2 M. Stir for 1 h at 4°C, incubate at room temperature for
1-2 h, then centrifuge at 15,000 rev./min for 15 min. Resuspend
precipitates in 100 ml 0.02 M sodium phosphate buffer, pH 7.5,
containing 1% Triton X-100, and centrifuge at 10,000 rev./min
for 15 min. Further purify by two cycles of high-speed (using
cushions of 20% sucrose) and low-speed centrifugation,
resuspending the final high-speed sediments in 2 ml phosphate
buffer. Further purification may be achieved by centrifugation
in 10-40% sucrose gradients. Purified virus particles can be stored
frozen but precipitate reversibly at about 4°C. All
centrifugation is therefore done at 15°C. Virus yields are about
0.7 mg/kg potato leaf and 1 mg/kg P. floridana
Properties of Particles
Purified preparations contain one sedimenting component.
Sedimentation coefficient (s20,w): 115 S
(Takanami & Kubo, 1979a).
A260/A240: 1.43 (Takanami
& Kubo, 1979a).
A(0.1%;1 cm) at 260 nm: 8.6 (Takanami & Kubo, 1979a).
Buoyant density in CsCl: 1.39 g/cm3 (Rowhani &
Buoyant density in Cs2SO4: 1.34 g/cm3
Particles are isometric, c
. 24 nm in diameter (Peters,
; Takanami & Kubo, 1979a
). Some particles seem to
have small projections at the vertices (Fig.6
; I. M. Roberts &
B. D. Harrison, unpublished results).
Particle CompositionNucleic acid:
RNA, single-stranded, c
. 30% of particle
weight. M. Wt c
. 2.0 x 106
, estimated by
polyacrylamide gel electrophoresis under non-denaturing conditions.
Sedimentation coefficient in 0.15 M sodium chloride,
0.015 M sodium citrate, pH 7.0 = 34.5 S (Rowhani &
; Takanami & Kubo, 1979b
reports (Sarkar, 1976
) that the virus nucleic acid is DNA were not
confirmed in more recent work. The virus RNA is covalently bonded to
a genome-linked protein of M. Wt c
. 7000 and contains no
substantial polyadenylate sequence (Mayo et al., 1982
Protein: c. 70% of particle weight. One main protein
species of M. Wt c. 26,000, estimated by SDS/polyacrylamide
gel electrophoresis (Rowhani & Stace-Smith, 1979).
Virus particle RNA is infective, even after treatment with
proteinase K, and is translated in rabbit reticulocyte lysates to
give polypeptides of M. Wt c
. 125,000 and 71,000, but not
particle protein (Mayo et al., 1982
). An additional
translation product of M. Wt c
. 29,000 is found with the
wheat germ system but likewise does not react with antiserum to
virus particles (Mayo & Barker, 1984
). Nucleic acid extracts
from potato leaves contain a subgenomic RNA species of M. Wt
. 1 x 106
in addition to molecules of
M. Wt 2 x 106
(Barker, Mayo & Robinson, 1984
Relations with Cells and Tissues
The virus is apparently confined to the phloem tissue of intact
plants. In ultrastructural studies, the greatest numbers of virus
particles are found in the cytoplasm of phloem parenchyma and
companion cells, where they may form unstructured aggregates.
Crystalline aggregates of virus particles are found in the vacuoles
of some cells (Arai et al., 1969
; Kojima et al., 1969
Vesicles occur in the cytoplasm and some of them seem to enter nuclei
after fusing with the nuclear envelope (Shepardson, Esau &
). Virus particle antigen can be detected in phloem cells
by staining with fluorescent antibody (Weidemann & Casper, 1982
and variable amounts of necrosis develop in phloem tissue. Walls of
primary phloem cells in stems and petioles become thickened. Callose
accumulates in some sieve tubes of tubers and its presence is the basis
of various staining tests (e.g. with 1% resorcin blue) used, before
serological methods were developed, to assess the incidence of infection
in stocks of seed tubers (De Bokx, 1967
). Although mesophyll cells
of intact leaves seem not to become infected, isolated mesophyll
protoplasts of tobacco and potato can be infected by inoculation
with purified virus in the presence of poly-L-ornithine
(Kubo & Takanami, 1979
; Barker & Harrison, 1982
Virus multiplication can be inhibited by adding actinomycin D to
protoplast suspensions within 3 h after inoculation (Mayo &
Ecology and Control
In much of Western Europe, the virus seems essentially to be
confined to potato, and infection is perpetuated in seed tubers,
which give rise to infected plants. The virus is spread from these
sources by winged and wingless aphids, principally Myzus
, to other potato plants, which are especially
susceptible to infection when young. In some other countries,
notably in S. America, Australia and, probably, in N. America,
other solanaceous hosts occur and are likely to play a role as
Control of the virus in potato crops relies mainly on:
1. Selecting tubers from symptom-free clones of mother plants.
2. Eliminating virus from individual tubers by heat treatment
(e.g. 10-20 days in air at 37.5°C; Kassanis,
3. Growing seed-potato crops in areas where vector aphids are
few or arrive late in the growing season, and
weather conditions are less favourable for aphid activity.
4. Roguing (removing) plants with symptoms of secondary infection
when the crop is young and before
vector aphids reach it.
5. Applying insecticides to crops to minimise aphid activity.
6. Harvesting the crop or destroying the haulms before recently
inoculated virus has passed from the shoots
to the tubers.
7. Isolating healthy seed-potato crops spatially from infected
8. Planting cultivars that are resistant to infection in field
9. Assessing the health of tuber stocks by serological tests
(especially ELISA) after harvest.
Potato leafroll virus differs from most other viruses occurring
in potato in possessing isometric particles c
. 24 nm in
diameter and in being transmissible in the persistent manner by
but not by inoculation with sap. It may not
be easily distinguished from some other luteoviruses
potato or tomato: indeed beet western yellows virus
is reported to
occur in leafroll-affected potato plants in the USA
) and Tasmania
(Duffus & Johnstone, 1982
Beet western yellows virus includes a range of strains, many of which
(unlike potato leafroll virus) can infect Brassica
, and/or cause obvious leaf yellowing in sugar beet.
Some isolates of beet western yellows virus are serologically
related to, though distinguishable from, isolates of potato
leafroll virus; further work is needed with a large range of
isolates to ascertain whether these two viruses can be reliably
differentiated by serological tests. The degree of relationship
between potato leafroll virus and luteovirus isolates obtained
from tomato plants in the states of Florida (Zitter & Tsai,
) and Washington (Hassan & Thomas, 1981
), USA, is not clear.
- Altstatt & Ivanoff, Pl. Dis. Reptr 29: 29, 1945.
- Arai, Doi, Yora & Asuyama, Ann. phytopath. Soc. Japan 35: 10, 1969.
- Barker & Harrison, Plant Cell Reports 1: 247, 1982.
- Barker, Mayo & Robinson, Rep. Scott. Crop Res. Inst., 1983: 194, 1984.
- Braithwaite & Blake, Aust. J. agric. Res. 12: 1100, 1961.
- Casper, Phytopath. Z. 90: 364, 1977.
- Clarke, Converse & Kojima, Pl. Dis. 64: 43, 1980.
- Costa, Biologico 15: 79, 1949.
- Day, Aust. J. biol. Sci. 8: 498, 1955.
- De Bokx, Eur. Potato J. 10: 221, 1967.
- Duffus, Phytopathology 71: 193, 1981a.
- Duffus, Pl. Dis. 65: 819, 1981b.
- Duffus & Johnstone, Aust. J. exp. Agric. Anim. Husb. 22: 353, 1982.
- Eskandari, Sylvester & Richardson, Phytopathology 69: 45, 1979.
- Gildow, Phytopathology 72: 1289, 1982.
- Gugerli, Phytopath. Z. 96: 97, 1979.
- Gugerli, Potato Res. 23: 137, 1980.
- Harrison, Virology 6: 278, 1958a.
- Harrison, Virology 6: 265, 1958b.
- Hassan & Thomas, Phytopathology 71: 1004, 1981.
- Heinze, Phytopath. Z. 25: 103, 1955.
- Kassanis, Nature, Lond. 164: 881, 1949.
- Kennedy, Day & Eastop, A Conspectus of Aphids as Vectors of Plant Viruses, London, Commonwealth Institute of Entomology, 1962.
- Kojima, Bull. Fac. Agric. Niigata Univ. 33: 73, 1981.
- Kojima, Shikata, Sugawara & Murayama, Virology 39: 162, 1969.
- Kojima, Chou & Shikata, Ann. phytopath. Soc. Japan 44: 585, 1978.
- Kubo, CMI/AAB Descr. Pl. Viruses 234, 4 pp., 1981.
- Kubo & Takanami, Ann. phytopath. Soc. Japan 44: 398, 1978.
- Kubo & Takanami, J. gen. Virol. 42: 387, 1979.
- Maat & de Bokx, Neth. J. Pl. Path. 84: 149, 1978.
- Martin & Stace-Smith, Can. J. Pl. Path. 6: 206, 1984.
- Mayo & Barker, J. gen. Virol. 64: 1775, 1983.
- Mayo & Barker, Rep. Scott. Crop Res. Inst., 1983: 186, 1984.
- Mayo, Barker, Robinson, Tamada & Harrison, J. gen. Virol. 59: 163, 1982.
- Mehrad, Lapierre & Maury, C. r. hebd. Seanc. Acad. Sci., Paris D 286: 1179, 1978.
- Murayama & Kojima, Ann. phytopath. Soc. Japan 30: 209, 1965.
- Natti, Kirkpatrick & Ross, Am. Potato J. 30: 55, 1953.
- Peters, Virology 31: 46, 1967.
- Quanjer, Meded. LandbHoogesch. Wageningen 6: 41, 1913.
- Quanjer, Van der Lek & Oortwijn Botjes, Meded. LandbHoogesch. Wageningen 10: 1, 1916.
- Roberts & Harrison, Ann. appl. Biol. 93: 289, 1979.
- Roberts, Tamada & Harrison, J. gen. Virol. 47: 209, 1980.
- Rodriguez & Jones, Phytopathology 68: 39, 1978.
- Rowhani & Stace-Smith, Virology 98: 45, 1979.
- Sarkar, Virology 70: 265, 1976.
- Shepardson, Esau & McCrum, Virology 105: 379, 1980.
- Stegwee & Ponsen, Entomologia exp. appl. 1: 291, 1958.
- Sugawara, Kojima & Murayama, Ann. phytopath. Soc. Japan 39: 410, 1973.
- Sugawara, Kojima & Murayama, Ann. phytopath. Soc. Japan 40: 39, 1974.
- Sutton, Agric. Gaz. N.S.W. 66: 655, 1955.
- Takanami & Kubo, J. gen. Virol. 44: 153, 1979a.
- Takanami & Kubo, J. gen. Virol. 44: 853, 1979b.
- Tamada & Harrison, Ann. appl. Biol. 95: 209, 1980a.
- Tamada & Harrison, Ann. appl. Biol. 96: 67, 1980b.
- Tamada & Harrison, Ann. appl. Biol. 98: 261, 1981.
- Tamada, Harrison & Roberts, Ann. appl. Biol. 104: 107, 1984.
- Thomas, Ann. appl. Biol. 104: 79, 1984.
- Van Balen, Neth. J. Pl. Path. 88: 33, 1982.
- Waterhouse & Murant, Ann. appl. Biol. 97: 191, 1981.
- Webb, Larson & Walker, Am. Potato J. 28: 667, 1951.
- Webb, Larson & Walker, Res. Bull. Wis. agric. Exp. Stn 178, 1952.
- Weidemann, Z. angew. Ent. 94: 321, 1982.
- Weidemann & Casper, Potato Res. 25: 99, 1982.
- Zitter & Tsai, Pl. Dis. 65: 787, 1981.
Potato (Solanum tuberosum ssp. tuberosum) cv.
Up-to-Date plant with symptoms of secondary infection. (Courtesy
J. A. T. Woodford).
Foliage of a Solanum tuberosum ssp.
andigena clone, showing enanismo amarillo symptoms.
(Courtesy R. A. C. Jones).
Experimentally infected plant of tomato cv. Grosse Lisse
with yellow top disease. (Courtesy J. F. Thomas).
Physalis floridana plants infected with virulent
(upper left), intermediate (upper right) and avirulent
(lower left) virus strains. Uninfected plant
(lower right). (Courtesy T. Tamada and B. D. Harrison).
Infected potato tuber with internal net necrosis.
(Courtesy Department of Agriculture and Fisheries for Scotland).
Purified virus particles (Scottish isolate) stained
with uranyl acetate. Bar represents 100 nm. (Courtesy I. M. Roberts)