Alfalfa latent virus
Department of Plant Pathology, University of Missouri, Columbia, Missouri 65211, USA
- Described by Veerisetty & Brakke (1977a).
- An RNA-containing virus with straight to slightly flexuous particles about 635
nm long. Manually transmissible to a few species, mostly in the Leguminosae. Aphids
transmit the virus in the non-persistent manner readily to pea and broad bean but
with difficulty to alfalfa. Found in the USA.
Occurs symptomlessly in alfalfa (Medicago sativa
Recorded in the USA. Prevalent in Nebraska and Wisconsin.
Host Range and Symptomatology
Host range is very limited. Experimentally transmitted mainly to legumes.
Alfalfa and hairy vetch (Vicia villosa)
become infected without producing
symptoms at 20 or 26°C. Pea (Pisum sativum
cv. Lincoln) shows obvious
symptoms only at 13°C.
- Diagnostic species
- Vicia faba (broad bean). Very few dark reddish-brown necrotic local
lesions appear on inoculated leaves followed by dark reddish-brown necrosis on
top leaves. Wilting and abscission of the leaves with occasional dark reddish-brown
necrosis on stems leading to the death of plants (Fig.1).
- Pisum sativum (pea) cv. Lincoln. Symptomless systemic infection at 20
or 26°C but at 13°C the plants show vein clearing, chlorosis of young leaves
and, more than 2 months after inoculation, necrosis of old leaves (Veerisetty &
- Cassia occidentalis. The Wisconsin isolate induces small local lesions
in inoculated leaves (Khan et al., 1977).
- Propagation species
- Pisum sativum. Dwarf pea varieties (Lincoln and Little Marvel) are better
than tall varieties (Tall Telephone and Alaska). Systemically infected Lincoln pea
plants are a good source of virus for purification (Veerisetty & Brakke, 1978).
- Assay species
- V. faba is not a good assay host, though it reacts with local lesions;
C. occidentalis may prove better (numerous local lesions are produced
after inoculation with the Wisconsin isolate).
No critical tests were made to establish differences between Nebraska and
Transmission by Vectors
Pea aphids (Acyrthosiphon pisum),
starved for 30 min and then allowed
an acquisition access period of 5 to 10 min, transmitted the virus efficiently
to pea and broad bean, regardless of virus source. When pea served as the virus
source plant, the virus was consistently transmitted to alfalfa, but with low
efficiency (Veerisetty & Brakke, 1977a
Transmission through Seed
Not seed-transmitted in pea (Veerisetty & Brakke, 1977a
The virus is moderately immunogenic. Antiserum with a precipitin titre of 1/512
was prepared by injecting rabbits (twice intramuscularly and once intravenously)
with partially purified virus (10 mg total virus). The antiserum reacted with
homologous antigen in microprecipitin tests, or in immunodiffusion tests in the
presence of 0.05% sodium dodecyl sulphate.
An isolate from Wisconsin is serologically related to the original isolate
from Nebraska (Khan et al., 1977
). Properties in vitro
morphology suggest that the virus should be placed in the carlavirus group
no serological relationship was detected to pea streak virus
or red clover vein
(Veerisetty & Brakke, 1977a
Stability in Sap
In crude sap of Vicia faba,
infectivity was lost after 4-6 days at
25°C, 10 min at 65-70°C, and the dilution end-point was between
(Veerisetty & Brakke, 1977a
The following procedure consistently gives yields of about 0.7 to 1.0 mg
virus/g tissue (Veerisetty & Brakke, 1978
). Harvest pea cv. Lincoln tissue
(whole plant excluding roots) 3 weeks after inoculation. Blend frozen tissue
with two parts (w/v) of 0.165 M disodium phosphate + 0.018 M trisodium citrate
buffer, pH 9.0, containing 0.1% diethyldithiocarbamate (DIECA) and 0.5%
mercaptoethanol (ME) and centrifuge at low speed. Clarify the supernatant fluid
by adding 0.05 vol. 0.2 M Na2
and 0.01 vol. 1.0 M
, stirring for 15-20 min and then centrifuging at low speed.
Precipitate the virus from the supernatant fraction by dissolving polyethylene
glycol (PEG, M. Wt 6000) to 6% (w/v) and centrifuging at low speed. Resuspend
in 16 mM disodium phosphate + 2 mM trisodium citrate buffer, pH 9.0, containing
1% Triton X-100. Purify further by centrifuging the virus once each through 20
and 30% sucrose cushions.
Properties of Particles
Purified preparations contain a single infective nucleoprotein component
when centrifuged in rate zonal sucrose or equilibrium CsCl density gradients.
Sedimentation coefficient (s20,w
): 161 ± 1.5 S
(Veerisetty & Brakke, 1978
Amax(260)/Amin(244): 1.12 (both without correction for
M. Wt (obtained by calculation from M. Wt of RNA and protein subunits and
percentage RNA composition) is c. 4.7 x 107
(Veerisetty & Brakke, 1977b).
Particles are straight to slightly flexuous filaments (Fig.2
), of helical
construction. Modal lengths of c.
635 nm and 653 nm, respectively, were
obtained with diffraction grating replica (22,835 lines/cm) and tobacco mosaic
(300 nm) as standards (Veerisetty & Brakke, 1977a
1635 identical protein subunits packed in a helix (c.
8.2 subunits/turn). There are 5 nucleotides per subunit and the RNA is
located at a radius of c.
3.3 nm from the centre of the particle (Veerisetty,
; Veerisetty & Brakke, 1977b
Particle CompositionNucleic acid:
RNA, single-stranded, infective. Single component,
M. Wt = 2.45 x 106
(estimated by sucrose density gradient
sedimentation and by gel electrophoresis); s20,w
= 38 S,
probably 5.4% of particle weight as in other carlaviruses
(Veerisetty & Brakke,
Protein: A single type of protein is found by electrophoresis in
polyacrylamide/SDS gels, with M. Wt c. 2.7 x 104
(Veerisetty & Brakke, 1977b).
Relations with Cells and Tissues
No inclusion bodies were found by light microscopy in epidermal strips of
leaves, petioles and stems of infected pea and broad bean (Veerisetty &
Although particle morphology places alfalfa latent virus in the carlavirus
, it differs in host range and symptomatology from three other carlaviruses
occurring naturally in legumes, namely cowpea mild mottle virus
, pea streak
, and red clover vein mosaic virus
. Cowpea mild mottle virus does not
infect Lincoln pea whereas alfalfa latent virus gives symptomless systemic
infection; pea streak virus produces chlorosis and necrosis of the leaves and
extensive stem necrosis, resulting in death of the plants; and red clover vein
mosaic virus produces vein-clearing and chlorosis, curling, and downward
rolling of the young leaves leading to terminal rosetting, stunting, and death
of the plants. Alfalfa latent virus does not infect Trifolium pratense, T.
or T. hybridum,
which are hosts of red clover vein mosaic and
pea streak viruses (Hagedorn & Hanson, 1951
; Hagedorn & Walker, 1949
Veerisetty & Brakke, 1977a
). Cowpea mild mottle virus does not
infect Vicia faba
but is easily transmitted to Vigna unguiculata
and Glycine max
whereas the reverse is true of alfalfa latent virus.
Also cowpea mild mottle virus differs in not being transmitted by the pea aphid
(Brunt & Kenten, 1973
; Veerisetty & Brakke, 1977a
Alfalfa latent virus is serologically unrelated to red clover vein mosaic and
pea streak viruses, and it also differs from all other legume carlaviruses in
coat protein M. Wt (Veerisetty & Brakke, 1977b). Alfalfa latent
virus should not be confused with lucerne latent virus (Taylor & Smith,
1971; Blackstock, 1978) which is a member of the nepovirus group, and has
been renamed lucerne Australian latent virus (Jones, Forster & Mohamed, 1979).
- Blackstock, Aust. J. agric. Res. 29: 291, 1978.
- Brunt & Kenten, Ann, appl. Biol. 74: 67, 1973.
- Hagedorn & Hanson, Phytopathology 41: 813, 1951.
- Hagedorn & Walker, Phytopathology 39: 837, 1949.
- Khan, Maxwell, Palmer & Hanson, Proc. Am. Phytopath. Soc. 4: 122, 1977.
- Jones, Forster & Mohamed, Ann. appl. Biol. 92: 49, 1979.
- Taylor & Smith, Rep. Vict. Pl. Res. Inst. 5: 17, 1971.
- Veerisetty, Virology 84: 523, 1978.
- Veerisetty & Brakke, Phytopathology 67: 1202, 1977a.
- Veerisetty & Brakke, Virology 83: 226, 1977b.
- Veerisetty & Brakke, Phytopathology 68: 59, 1978.
Dark reddish-brown stem necrosis in Vicia faba.
Particles in a leaf dip preparation stained with 1.5% potassium
phosphotungstate, 0.25% ammonium vanadatomolybdate, pH 6.5. Bar represents