Arracacha virus A
R. A. C. Jones
Ministry of Agriculture, Fisheries and Food, Harpenden Laboratory, Hatching Green, Harpenden, Herts
R. H. Kenten
Rothamsted Experimental Station, Harpenden, Herts
Contents
Introduction
Described by
Jones & Kenten (1978).
A virus with isometric particles c. 26 nm in diameter which
sediment as three components. It is readily transmissible by inoculation
of sap and has a wide host range but has been found so far only in arracacha
(Arracacia xanthorrhiza; Umbelliferae) in the Andean region of Peru.
Main Diseases
The virus was consistently isolated from arracacha plants showing a
distinct yellow mosaic on young leaves, but was not detected in plants with
a normal appearance. Attempts to return it to healthy arracacha plants by
mechanical inoculation were unsuccessful (
Jones & Kenten, 1978).
Geographical Distribution
Peru.
Host Range and Symptomatology
A wide experimental host range, infecting species in at least 10
dicotyledonous families (
Jones & Kenten, 1978). Readily transmissible
by inoculation of sap.
- Diagnostic species
- Chenopodium quinoa: Chlorotic local lesions; systemic chlorotic
mottle and twisting of young leaves followed by systemic necrosis (Fig.1).
Plants inoculated when young are sometimes killed.
- C. murale: Local chlorotic or necrotic spots or rings; systemic
symptoms are chlorotic mottle and twisting of young leaves followed by necrosis.
- Tetragonia expansa: Few local necrotic rings, severe systemic
chlorotic mottle followed by necrosis, plants severely stunted (Fig.3).
- Nicotiana clevelandii: Local necrotic ringspots or rings (Fig.2);
systemic chlorotic mottling or mosaic with occasional necrotic flecks and
line patterns. Leaves produced later contain virus but may appear normal.
- Propagation species:
- Chenopodium quinoa and Nicotiana clevelandii are suitable
species for maintaining cultures. N. clevelandii is a good source
for virus purification.
- Assay species:
- Chenopodium quinoa is a satisfactory local lesion host.
Strains
None reported.
Transmission by Vectors
The virus was not transmitted by
Myzus persicae (
Jones &
Kenten, 1978). A nematode vector is suspected because the virus has
similarities to
nepoviruses (see Relationships).
Transmission through Seed
The virus was readily transmitted through seed of
N. clevelandii
(R. A. C. Jones, unpublished results).
Serology
An antiserum with a titre of 1/1024 was readily obtained (
Jones &
Kenten, 1978). The virus produces a single band of precipitate in double
diffusion tests in agar gel.
Relationships
The virus has biological and physico-chemical characteristics typical
of
nepoviruses. However, in gel diffusion tests (
Jones & Kenten, 1978),
purified virus failed to precipitate with antisera to 33 other morphologically
similar viruses including the following members of the nepovirus group: Andean
potato calico (=
potato black ringspot),
arabis mosaic,
artichoke Italian
latent,
cherry leaf roll,
cocoa necrosis,
grapevine Bulgarian latent,
grapevine chrome mosaic,
grapevine fanleaf,
mulberry ringspot,
myrobalan
latent ringspot,
peach rosette mosaic,
raspberry ringspot,
strawberry latent
ringspot,
tobacco ringspot (eucharis mottle strain),
tomato black ring
(Scottish and English strains) and
tomato ringspot. In further tests
(R.A.C. Jones, unpublished data; A. F. Murant, unpublished data), antiserum
to arracacha virus A failed to react with Andean potato calico virus
(=potato black ringspot virus) or tobacco ringspot virus (type strain).
Stability in Sap
In sap from infected
C. quinoa leaves, infectivity is lost after
dilution to 10
-5 or heating for 10 min at 65-70°C but is
retained for at least 15 days at 20°C (
Jones & Kenten, 1978).
Purification
Extract infected
N. clevelandii leaves in 0.05 M phosphate
buffer at pH 7.5 containing 0.05 M ethylene diamine tetra-acetate, and
clarify with chloroform, followed by differential precipitation with
ammonium sulphate and three cycles of differential centrifugation. Up
to 200 A
1cm,260 units of purified virus can be obtained
per 1 kg of infected leaf by this procedure (
Jones & Kenten, 1978).
Properties of Particles
In sucrose density gradients, purified virus preparations separate
into three components, apparently empty protein shells (T) and two kinds
of nucleoprotein with different amounts of nucleic acid (M and B). In
equilibrium sedimentation in CsCl at 2°C, B component is not
resolved into more than one class of particle (R. H. Kenten, unpublished
results).
Sedimentation coefficients (s°20,w) (svedbergs):
50 (T), 92 (M) and 125 (B) (Fig.5).
A260/A280: 0.65 (T), 1.50 (M) and 1.85 (B).
Buoyant density in CsCl (g/cm3): 1.32 (T), 1.45 (M) and
1.52 (B).
Particle Structure
Particles are isometric,
c. 26 nm in diameter with a hexagonal
profile. Electron micrographs show particles, some completely, some partially
and some not penetrated by negative stain (
Fig.4). Detailed structure of the
particles is not known.
Particle Composition
Nucleic acid: RNA, single-stranded. There are two species, with
M. Wt 2.5 x 10
6 and 1.4 x 10
6 (R. J. Barton, unpublished results).
From the sedimentation coefficients and buoyant densities, the nucleic acid
contents of the M and B particles were estimated at 30-35% and 43-44%
respectively. Although equilibrium sedimentation in CsCl detected only
one class of particle in B component, it is still possible that there are
two classes, one containing a single 2.5 x 10
6 dalton molecule
and the other containing two 1.4 x 10
6 dalton molecules.
Protein: The coat protein has a M. Wt of c. 53 000 daltons
estimated by electrophoresis in polyacrylamide gels containing sodium
dodecyl sulphate.
Relations with Cells and Tissues
No information.
Notes
Arracacha virus A and the type strain of
arracacha virus B
have similar
particle size, shape and properties in sap, and both infect arracacha crops
in Peru, sometimes occurring together in the same plant. However, they can
be readily distinguished by differences in host range and symptomatology in
indicator hosts; arracacha virus A causes the more severe symptoms in hosts
such as
C. quinoa, T. expansa and
N. clevelandii but fails to infect
Vigna unguiculata. Moreover, the two viruses are serologically
unrelated (
Jones & Kenten, 1978;
Kenten & Jones, 1979).
References
- Jones & Kenten, Ann. appl. Biol. 90: 85, 1978.
- Kenten & Jones, Ann. appl. Biol. 93: 31, 1979.
Local lesions and systemic necrosis in Chenopodium quinoa.
Ringspots (above) and rings (below) in inoculated leaves of Nicotiana clevelandii.
Necrosis and stunting in Tetragonia expansa; healthy plant on right.
Particles in neutral phosphotungatate. Bar represents 50 nm.
Schlieren pattern produced after centrifuging for 16 min at 29500 rev/min.
Schlieren angle 40°; sedimentation from left to right.
