114
July 1973
Family: Alphaflexiviridae
Genus: Potexvirus
Species: Hydrangea ringspot virus
Acronym: HdRSV


Hydrangea ringspot virus

Renate Koenig
Biologische Bundesanstalt für Land- und Forstwirtschaft, Braunschweig, Germany

Contents

Introduction
Main Diseases
Geographical Distribution
Host Range and Symptomatology
Strains
Transmission by Vectors
Transmission through Seed
Transmission by Grafting
Transmission by Dodder
Serology
Nucleic Acid Hybridization
Relationships
Stability in Sap
Purification
Properties of Particles
Particle Structure
Particle Composition
Properties of Infective Nucleic Acid
Molecular Structure
Genome Properties
Satellites
Relations with Cells and Tissues
Ecology and Control
Notes
References
Acknowledgements
Figures

Introduction

Described by Brierley (1954) and Brierley & Lorentz (1957).

A virus with filamentous particles of normal length c. 490 nm. Readily transmitted by inoculation of sap; no vector known. World-wide distribution.

Main Diseases

Many naturally infected Hydrangea macrophylla plants carry the virus without showing conspicuous symptoms. Crinkling, rolling and asymmetry of leaves (Fig.1), decrease in number of florets per inflorescence, severe dwarfing and ‘running out’ of hydrangea varieties have all been attributed to the presence of the virus. Experimentally infected hydrangeas may develop chlorotic or brown spots or rings on the leaves and may show distortion and buckling of the leaves several months after inoculation (Brierley & Lorentz, 1957; Hollings, 1958). Symptom expression probably depends on variety and environmental conditions.

Geographical Distribution

Reported from USA, Europe and New Zealand. Probably world-wide in cultivated Hydrangea macrophylla.

Host Range and Symptomatology

Hydrangea macrophylla seems to be the only natural host. Experimentally, the virus causes infections in more than 20 species in 12 dicotyledonous families. It infects Primula malacoides systemically (Hollings, 1958), often without inducing symptoms.

Diagnostic species

Gomphrena globosa. Local necrotic dots within 3-5 days, later enlarging and developing red margins (Fig.4).

Chenopodium quinoa. Local chlorotic spots within 5-7 days (Fig.2) sometimes becoming bright yellow or necrotic or developing into chlorotic ringspots.

Chenopodium amaranticolor. Local chlorotic dots with a central necrotic speck within 5-7 days.

Propagation species

Primula malacoides. Naturally infected hydrangeas can also be used as a source of virus for purification.

Assay species

Gomphrena globosa is the most sensitive indicator plant. Chenopodium quinoa and C. amaranticolor may also be used.

Strains

Minor variants can be distinguished on the basis of serology (Hollings, 1958; Belli & Belli, 1967) and symptom expression on Chenopodium quinoa (Koenig, 1970).

Transmission by Vectors

No vector known. Attempts to transmit the virus by the aphids Myzus persicae and Macrosiphum euphorbiae failed (Hollings, 1958).

Transmission through Seed

Not found (Brierley & Lorentz, 1957).

Transmission by Dodder

Apparently not tested.

Serology

The virus is strongly immunogenic, forming flagellar precipitates in tube or slide precipitin tests.

Relationships

Particle morphology and physical properties place the virus in the potexvirus group (Brandes & Bercks, 1965). It is distantly serologically related to potato X, cactus X, white clover mosaic and clover yellow mosaic viruses.

Stability in Sap

In sap from hydrangea, the thermal inactivation point (10 min) is between 70 and 75°C, the dilution end-point is about 10-5 and infectivity is retained at room temperature for 2-3 weeks (Brierley & Lorentz, 1957; Hollings, 1958).

Purification

1. Mince 100 g hydrangea leaves with 20 ml 0.5 M borate buffer pH 7.8, add 0.2 g sodium sulphite and 0.2 g ascorbic acid and centrifuge expressed sap at low speed. Add 1 volume 0.1% silver nitrate to 6 volumes of the supernatant fluid, stir for 10 min and leave at room temperature for several hours. Centrifuge at low speed, add 1 volume of 20% polyethylene glycol 6000 in 0.5 M borate buffer, pH 7.8, to 4 volumes of the supernatant fluid, leave at 4°C for several hours. Centrifuge at low speed, resuspend the pellets in 15 ml of 0.5 M borate buffer containing 0.5 M urea and 0.1% 2-mercaptoethanol. Subject the virus to 1 or 2 cycles of differential centrifugation (R. Koenig, unpublished).

2. The ether-carbon tetrachloride method of Wetter (1960) can be used with extracts from infected Primula malacoides (Bercks & Brandes, 1961).

Properties of Particles

Electrophoretic mobility: -3.9 x 10-5 cm2 sec-1 volt-1 in 0.05 M sodium phosphate buffer at pH 7.0 (Sisler et al., 1957).

Absorbance at 260 nm (1 mg/ml, 1 cm light path): 3.08 (calculated from Sisler et al., 1957).

A260/A280: 1.22 (calculated from Sisler et al., 1957).

Particle Structure

Particles are flexuous filaments (Fig.3) with normal length c. 490 nm (Bercks & Brandes, 1961).

Particle Composition

Nucleic acid: Probably single-stranded RNA for which a M. Wt of 2.5 x 106 is found by polyacrylamide gel electrophoresis (R. Koenig, unpublished).

Protein: SDS-polyacrylamide gel electrophoresis yields two bands corresponding to M. Wt of 1.9 and 2.2 x 104. Thin layer gel chromatography with Sephadex G 200 in the presence of 6 M guanidine hydrochloride and 0.1% 2-mercaptoethanol yields a single spot corresponding to a M. Wt of about 2.4 x 104 (R. Koenig, unpublished). As with the proteins of other potexviruses (Koenig, 1972) the meaning of multiple band formation in SDS-polyacrylamide gel electrophoresis is still unclear.

Relations with Cells and Tissues

No specific inclusions are seen in hydrangea, but chloroplasts are often clumped together. Epidermal hair cells of infected Primula malacoides often contain oval or elongated vacuolate bodies ranging from 13 x 32 to 11.5 x 50 µm. These inclusions stain intensely with 0.5% phloxine and sometimes contain discrete granules (Hollings, 1958).

Notes

Hydrangea ringspot virus can be differentiated from other viruses infecting Hydrangea macrophylla (i.e. tomato ringspot, tobacco ringspot, tobacco necrosis, cucumber mosaic and alfalfa mosaic viruses) by its inability to infect tobacco and other solanaceous hosts (but see Dunez, 1963) and by its elongated shape.

References

  1. Belli & Belli, Riv. Patol. veg., Pavia, Ser. IV, 3: 163, 1967.
  2. Bercks & Brandes, Phytopath. Z. 42: 45, 1961.
  3. Brandes & Bercks, Adv. Virus Res. 11: 1, 1965.
  4. Brierley, Phytopathology 44: 696, 1954.
  5. Brierley & Lorentz, Phytopathology 47: 39, 1957.
  6. Dunez, Annls. Épiphyt. 14: 103, 1963.
  7. Hollings, J. hort. Sci. 33: 275, 1958.
  8. Koenig, NachrBl. dt. PflSchutzdienst., Stuttg. 22: 34, 1970.
  9. Koenig, Virology 50: 263, 1972.
  10. Sisler, Chang, Reagan & Brierley, Phytopathology 47: 491, 1957.
  11. Wetter, Arch. Mikrobiol. 37: 278, 1960.

Acknowledgements

Fig.1 courtesy of Dr M. Hollings, Littlehampton; Fig.3 courtesy of Dr D. Lesemann, Braunschweig


Figure 1

Leaf of infected Hydrangea macrophylla.

Figure 2

Local lesions on Chenopodium quinoa.

Figure 3

Virus purified from hydrangea and negatively stained with sodium phosphotungstate. Bar represents 500 nm.

Figure 4

Local lesions on Gomphrena globosa.