Daphne virus X
R. L. Forster
Plant Diseases Division, D.S.I.R., Private Bag, Auckland, New Zealand
K. S. Milne
Dept. Horticulture and Plant Health, Massey University, Palmerston North, New Zealand
- Described by
Forster & Milne (1975,
A virus with flexuous filamentous particles c. 500 x 12 nm. No vector is known
but the virus is spread by vegetative propagation.
The virus occurs naturally in Daphne cneorum
and D. odora
but is not
associated with symptoms in either species.
Recorded only from New Zealand.
Host Range and Symptomatology
The virus infected 19 of 34 species in 6 of 11 dicotyledonous families (Amaranthaceae,
Chenopodiaceae, Cucurbitaceae, Leguminosae, Scrophulariaceae, Solanaceae). Only 7 species
were systemically infected (Chenopodium quinoa, Cucumis melo, Cucumis sativus, Cucurbita
maxima, Datura stramonium, Pisum sativum, Nicotiana clevelandii).
- Cucumis sativus
(cucumber). Sunken chlorotic local lesions in cotyledons; faint
chlorotic spotting on first systemically infected leaf, later leaves being symptomlessly
Dolichos biflorus. Small necrotic local lesions; no systemic infection.
Gomphrena globosa. Necrotic local lesions, often with red haloes; no systemic
Nicotiana clevelandii. Chlorotic and necrotic local lesions; systemic chlorotic
rings or mottle.
Pisum sativum (pea). Necrotic local lesions; systemic chlorotic mottle and
sometimes blackening of the stem in the region of inoculated leaves.
The virus is best maintained in Nicotiana clevelandii; inoculated leaves of
this host are a good source of virus for purification.
Cucumis sativus, Dolichos biflorus and Gomphrena globosa consistently
give local lesions.
Transmission by VectorsThe virus was not transmitted from pea to pea by the aphid Myzus persicae.
Transmission through SeedNot reported.
SerologyThe virus is a good immunogen; flocculent precipitates were observed in microprecipitin
tests at antiserum dilutions up to 1/2048.
(Milne & Forster, 1976)
indicated a distant serological
white clover mosaic virus
but later experiments
(Forster & Milne, 1978b)
have shown no serological relationship to this virus or to
clover yellow mosaic,
narcissus mosaic or
potato X viruses.
Stability in SapInfectivity was retained in N. clevelandii sap held at room temperature (c.
20°C) for 5 weeks but not for 6 weeks, in sap diluted to 10-5 but not
10-6, and after heating for 10 min at 80°C but not 85°C.
PurificationInoculated leaves of Nicotiana clevelandii infected for 7-10 days were
homogenised in 0.5 M phosphate buffer, pH 7.1, containing 0.01 M disodium
ethylenediamine-tetraacetate (EDTA), 0.01 M sodium diethyldithiocarbamate (DIECA) and 0.3%
2-mercaptoethanol. Extracts were emulsified with chloroform and n-butanol and
clarified by low speed centrifugation. The virus was sedimented by high speed centrifugation,
resuspended in 0.05 M borate buffer, pH 8.2, containing 0.01 M EDTA and further purified
by sucrose-gradient centrifugation.
Properties of ParticlesThe virus sediments in the analytical ultracentrifuge as a single component with
a sedimentation coefficient (s°20,w) of c. 110 S.
Buoyant density: 1.28 g/cm3 in CsCl.
Particle StructureParticles are flexuous filaments c. 500 x 12 nm
In uranyl acetate
many particles show distinct cross-banding.
Particle CompositionNucleic acid: c. 6% of particle weight (estimated spectrophotometrically).
Protein: In limited tests using polyacrylamide gel electrophoresis with sodium
dodecyl sulphate, a single polypeptide was observed with M. Wt c. 23,000.
Relations with Cells and TissuesIn ultrathin sections of systemically infected pea leaflets, virus-like particles were
observed in large aggregates
or as unaggregated particles scattered through the
NotesIn New Zealand, no D. cneorum plants have been found free of daphne virus X out
of more than 100 tested. The virus has properties typical of members of the
but can be distinguished from other members of the group by host range,
symptomatology and serology. Only two other viruses infecting daphne have flexuous
(Forster & Milne, 1975);
daphne virus S
has particles c. 720 nm long
(Forster & Milne, 1978a),
daphne virus Y
has particles c. 730 nm long
(Forster & Milne, 1976).
Unlike daphne virus X, these viruses do not infect Cucumis
sativus or Gomphrena globosa. None of the other viruses recorded in daphne
give a range of symptoms resembling those of daphne virus X on the species listed under
- Forster & Milne, N. Z. Jl agric. Res. 18: 391, 1975.
- Forster & Milne, N. Z. Jl agric. Res. 19: 359, 1976.
- Forster & Milne, N. Z. Jl agric. Res. 21: 131, 1978a.
- Forster & Milne, N. Z. Jl agric. Res. 21: 137, 1978b.
- Milne & Forster, Acta Hort. 59: 95, 1976.
(Left) Local lesions and (right) systemic symptoms in cucumber.
Virus particles from sap of D. cneorum flowers, negatively stained
with neutral phosphotungstate. Bar represents 200 nm.
Local lesions in Gomphrena globosa.
Aggregates of virus-like particles in a systemically infected pea leaf cell.
Bar represents 300 nm.