- Described by Vovlas, Martelli & Quacquarelli (1971) and Quacquarelli
et al. (1972c).
- A virus with angular isometric RNA-containing particles c. 30 nm in
diameter, which sediment as several components when centrifuged. It is readily
transmitted by inoculation of sap to a moderate range of hosts and is seedborne,
but no specific vector has been found.
Main DiseasesCauses bright yellow mottle, ringspot and line pattern in the leaves of
chicory (Cichorium intybus) (Fig.1) (Vovlas et al., 1971) and
obvious foliar alterations in parsley (Petroselinum crispum) (Fig.2)
(Avgelis & Quacquarelli, 1974a).
Geographical DistributionReported from Southern Italy.
Host Range and SymptomatologyIn nature, found only in chicory and parsley. Transmitted experimentally to
32 species in 12 dicotyledonous families (Vovlas et al., 1971; Avgelis
& Quacquarelli. 1974a). Several Nicotiana species are infected symptomlessly.
Readily transmitted by inoculation of sap.
- Diagnostic species
- Phaseolus vulgaris (French bean). Erratic yellowish local lesions
develop in inoculated leaves. Systemic symptoms consist of chlorotic mottle,
and yellow spots and blotches (Fig.3).
- Cucurbita pepo (squash). Occasional yellow local lesions followed by
a conspicuous systemic mosaic, ringspots, deformation of the leaf blades, and
small necrotic areas.
- Propagation species
- Cucurbita pepo is a good source of virus for purification.
- Assay species
- No reliable local lesion host known. Some strains may be assayed by
recording the proportion of Chenopodium quinoa plants becoming infected.
StrainsTwo major variants are described:
Type strain (Vovlas et al., 1971). Causes chlorotic local
lesions and a characteristic wilting in Chenopodium quinoa (Fig.6). Plants
at the 6-8 leaf stage wither and die in less than a week. Older plants also wilt
but may recover. Gomphrena globosa reacts with whitish red-rimmed local
lesions and no systemic infection; Cucumis sativus develops yellowish local
lesions and a mosaic mottle. Parsley is not a host. A minor variant of the type
strain induces obvious concentric ringspots in inoculated leaves of Nicotiana
glutinosa (C. Vovlas, unpublished data).
Parsley strain (Parsley carrot-leaf virus) (Avgelis & Quacquarelli, 1974a).
Induces chlorotic local lesions and systemic mottle but no wilting
in C. quinoa, necrotic target-like local spots, systemic mottle and necrosis
in G. globosa, and yellowish local rings, systemic mosaic and enations in
C. sativus. Chicory is not a host.
Transmission by VectorsNo vector known. Attempts to transmit the major strains using the aphid Myzus
persicae were unsuccessful (Avgelis & Quacquarelli, 1974a).
Transmission through SeedThe type strain was transmitted to a small proportion of chicory seeds (Vovlas,
1973). No seed transmission of the parsley strain was found in several species
(Avgelis & Quacquarelli, 1974a).
Transmission by DodderNo information.
SerologyEmpty protein shells (top centrifugal component) are moderately immunogenic,
yielding antisera with precipitin titres no higher than 1/128. Nucleoprotein
fractions (bottom centrifugal component) are good immunogens, producing antisera
with titres up to 1/1024 following intramuscular and intravenous injections of
rabbits (Vovlas et al., 1971; Quacquarelli et al., 1972c).
Top and bottom components are serologically indistinguishable. Tube-precipitin
(granular precipitates) or gel-diffusion tests (single precipitin bands) can be
used for comparing strains (Quacquarelli et al., 1972c; Avgelis
& Quacquarelli, 1974b).
RelationshipsThe chicory and parsley strains share most but not all antigenic determinants
(Avgelis & Quacquarelli, 1974a, 1974b); no serological differences
occur among minor variants of the same strain. No relationship was detected to
23 viruses with isometric particles including several members of the nepovirus,
cucumovirus, tymovirus, comovirus and tombusvirus groups (Vovlas et al.,
Stability in SapAll strains behave similarly, irrespective of the assay host used. In
expressed sap, infectivity is lost after dilution to 10-3-10-5,
heating for 10 min at 53-56°C or storing for 3-4 days at 22°C (Vovlas
et al., 1971; Avgelis & Quacquarelli, 1974a).
PurificationSatisfactory purification is achieved by clarification of expressed sap with
7% (v:v) of magnesium-activated bentonite (Dunn & Hitchborn, 1965) followed by
cycles of low- and high-speed centrifugation and sucrose density gradient
centrifugation (Vovlas et al., 1971; Avgelis & Quacquarelli,
1974a). Virus yields range from 5 to 30 mg/100 g of infected squash
tissue. Spontaneous crystallization occurs at 4°C in purified virus
preparations of the type strain (Fig.5) (Quacquarelli et al.,
Properties of ParticlesPurified virus preparations contain protein shells without RNA (T) and
nucleoproteins containing different amounts of RNA (B). Sucrose density
gradient and analytical centrifugation resolve up to five classes of particles
in component B (B1-B5; Fig.4) (Quacquarelli et al., 1972c).
Equilibrium centrifugation in CsCl reveals that these components
are themselves heterogeneous because, in addition to component T, there are at
least 16 classes of particle in component B (Fig.9). Most of the heterogeneity
is in component B3 (Quacquarelli et al., 1973; A. Quacquarelli
& A. Avgelis, unpublished data). The relative proportions of the centrifugal
components varies with the virus strain, host and temperature (Fig.4) (A.
Quacquarelli & A. Avgelis, unpublished data). Infectivity is associated
with the fast-sedimenting nucleoprotein fractions (B4 and
B3). In infected tissues or purified suspensions, virus particles
dissociate into protein shells and infective RNA when frozen at -25°C
and thawed (Quacquarelli, Piazzolla & Vovlas, 1972a).
Sedimentation coefficients (s20,w) in 0.02 M phosphate buffer
with 0.1 M NaCl (svedbergs): 50 (T), 66 (B1), 78 (B2), 84
to 109 (B3), 117 (B4) and 126 (B5)
(Quacquarelli et al., 1973; A. Quacquarelli & A. Avgelis, unpublished
Buoyant densities in CsCl at 25°C: 1.279 (T), 1.298 to 1.464 (B1 to B3,
split into 12 separate isopycnic components), 1.481 (B4),
1.487 to 1.505 (B3, split into 3 isopycnic components) (Quacquarelli
et al., 1973).
M. Wt of T component particles is c. 3 x 106 daltons (A.
Quacquarelli & P. Piazzolla, unpublished data).
Electrophoretic behaviour: The virus does not move from the origin when
electrophoresed in 2.4% polyacrylamide gels or in immuno-electrophoresis,
irrespective of the agar concentration or the type and pH of buffer. In zone
electrophoresis it migrates to the anode in a single band with a R F
value of 0.10 (Quacquarelli et al., 1972c;
Avgelis & Quacquarelli, 1974b).
Absorbance at 260 nm (1 mg/ml, 1 cm light path): 9.5 (type strain,
Particle StructureParticles are isometric, c. 30 nm in diameter with angular
outlines (Fig.7). T particles are penetrated by negative stain (Fig.8).
Some of the B particles are partially penetrated by neutral sodium
Particle CompositionNucleic acid: single-stranded RNA, comprising the following
percentages of the particle weight:
Molar percentages of nucleotides in unfractionated virus (type strain) are about:
G28, A22, C23, U27 (Quacquarelli et al., 1973). Non-fractionated virus
preparations yield five RNA species with sedimentation coefficients,
calculated by sucrose density gradient centrifugation, of: 9, 16, 25, 31
and 35 S (Quacquarelli et al., 1972a; 1972b; 1973)
and M. Wt of 0.12 x 106; 0.5 x 106; 1.2 x 106;
1.9 x 106; 2.5 x 106, calculated from
s20,w values (Hull, Rees & Short, 1969).
- calculated according to Reichmanns (1965) formula: 14% in
B1; 22% in B2; 25 to 37% in B3; 39% in
B4; 43% in B5;
- calculated from buoyant densities:
6 to 38% in isopycnic components B1 to B3; 40% in
B4; and 41.5 to 43% in isopycnic components of B5.
Infective RNA is easily obtained from purified virus preparations in 0.02 M
(Na-K) phosphate buffer by freezing for 10 min at -25°C and thawing
(Quacquarelli et al., 1972a, 1972b) or by heating at 71°C
for 90 sec (A. Quacquarelli, unpublished data). Only preparations containing
the 31 and 35 S RNA species are infective but it is not known whether both
species are necessary for infection (Quacquarelli et al., 1973).
Protein: No information.
Relations with Cells and TissuesElectron microscopy revealed abnormalities of the fine structure of infected
squash cells but virus particles could not be identified with certainty (G. P.
Martelli & M. A. Castellano, unpublished data).
NotesThe virus, owing to the distinctive symptoms induced in chicory, is easily
distinguished from other viruses infecting this host in nature. The dissociation
of its protein and RNA moieties in intact form, when frozen and thawed, is not
known to occur with any other isometric plant virus. Turnip yellow mosaic
(Kaper & Alting Siberg, 1969), peanut stunt (Western strain) (Mink, 1972),
grapevine chrome mosaic, radish mosaic and artichoke Italian latent viruses
(A. Quacquarelli, unpublished data) also release intact RNA when frozen but
their protein shells disintegrate. In its unusual centrifugal complexity,
chicory yellow mottle virus resembles preparations of tobacco ringspot virus
containing satellite RNA (Schneider, Hull & Markham, 1972). However, the
two viruses are not serologically related nor is there, at the moment,
sufficient ground for ascribing chicory yellow mottle virus to the nepoviruses.
- Avgelis & Quacquarelli, Phytopath. Mediterranea 13: 97, 1974a.
- Avgelis & Quacquarelli, Phytopath. Mediterranea 13: 160, 1974b.
- Dunn & Hitchborn, Virology 25: 171, 1965.
- Hull, Rees & Short, Virology 37: 404, 1969.
- Kaper & Alting Siberg, Virology 38: 407, 1969.
- Mink, CMI/AAB Descriptions of Plant Viruses 92, 4 pp., 1972.
- Quacquarelli, Piazzolla & Vovlas, J. gen. Virol. 17: 147, 1972a.
- Quacquarelli, Piazzolla & Vovlas, Phytopath. Mediterranea 11: 207, 1972b.
- Quacquarelli, Vovlas, Piazzolla, Russo & Martelli, Phytopath. Mediterranea 11: 180, 1972c.
- Quacquarelli, Piazzolla, Vovlas & Martelli, Mikrobiologija 10: 15, 1973.
- Reichmann, Virology 25: 166, 1965.
- Schneider, Hull & Markham, Virology 47: 320, 1972.
- Vovlas, Phytopath. Mediterranea 12: 102. 1973.
- Vovlas, Martelli & Quacquarelli, Phytopath. Mediterranea 10: 244, 1971.
A naturally infected chicory leaf with yellow mottle symptoms
Severe distortion in an infected parsley leaf (parsley strain).
Yellow spots and blotches in a systemically infected leaf of French
Ultraviolet absorption patterns of preparations of (above)
parsley strain and (below) type strain after sucrose density gradient
centrifugation, both purified from squash. Note the difference in the type
and relative amounts of B components.
Virus crystals from a purified preparation of the type strain.
Wilting of Chenopodium quinoa induced by the type strain.
Virus particles from a purified preparation of component B, mounted
in phosphotungstate. Bar represents 50 nm.
Particles of component T penetrated by negative strain. Bar represents
Schlieren diagram of equilibrium sedimentation analyses in CsCl of a
purified virus preparation: (a) initial density 1.3029, showing density
components T and 1-3; (b) initial density 1.3622, showing density components
3-7; (c) initial density 1.4154, showing density components 6-12; (d) initial
density 1.4498, showing density components 9-15; (e) initial density 1.5117,
showing density components 14-16.