58
June 1971
Family: Alphaflexiviridae
Genus: Potexvirus
Species: Cactus virus X
Acronym: CVX


Cactus virus X

R. Bercks
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 Amelunxen (1958).

Synonyms

Cactus virus 1 (Rev. appl. Mycol. 38: 585)
Kakteen-Virus (Rev. appl. Mycol. 38: 192)

An RNA-containing virus with elongated particles, normal length c. 520 nm. Transmissible by inoculation of sap but no natural vector known. Reported from Europe and USA in cultivated cacti.

Main Diseases

Infected cacti probably show no macroscopic symptoms; those symptoms which are occasionally observed in cacti may be caused by other viruses.

Geographical Distribution

Reported from Europe and USA in cultivated cacti; in USA also in wild cacti (M. Chessin, personal communication).

Host Range and Symptomatology

Occurs in many cultivated cacti without causing macroscopic symptoms (Milicic & Udjbinac, 1961). Transmissible by sap inoculation and grafting. Some species in the Amaranthaceae, Chenopodiaceae and Caryophyllaceae can be infected experimentally. Infections of species in the Caryophyllaceae are latent. After inoculation with sap from cacti, symptoms in diagnostic test plants usually require several weeks to develop; after inoculation with sap from test plants, however, they appear within a few days (Plese & Milicic, 1966).

Diagnostic species

Chenopodium quinoa. The only species consistently infected systemically. Primary lesions necrotic or chlorotic. Systemic mottle with necrotic and chlorotic spots (Fig.2, Fig.3). Tip leaves usually without systemic symptoms.

Chenopodium amaranticolor. Necrotic or chlorotic primary lesions. Not systemic.

Amaranthus caudatus. Necrotic or chlorotic local lesions. Systemic infection frequent with necrotic spots and sometimes brown veinal necrosis in tip leaves; upper leaves may be infected without showing symptoms.

Gomphrena globosa. Necrotic primary lesions with red margins (Fig.4). Not systemic.

Propagation species

Chenopodium quinoa is a useful plant for maintaining cultures and as a source of virus for purification. The virus reaches high concentrations in systemically infected leaves.

Assay species

Gomphrena globosa (Fig.4) is a useful local lesion host, though Amaranthus caudatus and Chenopodium amaranticolor are better for some strains of the virus.

Chenopodium quinoa is useful for whole plant assay.

Strains

Isolates can be differentiated on the basis of their tendency to form either necrotic or chlorotic local lesions in most plants or a mixture of both types. Three strains have been clearly differentiated by serology; two of these strains also differ symptomatologically.

Transmission by Vectors

None reported.

Transmission through Seed

None with cacti (Milicic, 1960).

Transmission by Dodder

None reported.

Serology

The virus is strongly immunogenic. The slide precipitin test or the tube test give good results; the precipitates are flocculent (flagellar). The agar gel-diffusion test with virus fragments is less sensitive (Koenig, 1969).

Relationships

Some strains are closely related serologically, others distantly (Milicic et al., 1966; Koenig, 1969). A very distant serological relationship exists to the following viruses which have particles of the same or similar normal lengths: potato X, white clover mosaic, hydrangea ringspot and clover yellow mosaic viruses. These viruses form the potato virus X group (Brandes & Bercks, 1963, 1965).

Stability in Sap

In sap from Chenopodium quinoa, the thermal inactivation point (10 min) is about 82°C, dilution end-point 10-5, and infectivity is retained at room temperature for more than 6 weeks; in dried leaves infectivity is retained for more than 1 year (Plese & Milicic, 1966; Bercks, unpublished).

Purification

The following method gives good virus preparations: add ascorbic acid (to 0.2%) and sodium sulphite (to 0.2%) to sap from infected Chenopodium quinoa, adjust pH value of the sap to 6.5, 7.0 or 8.0 according to the strain used (Koenig & Bercks, 1968), shake with an equal volume of ether, centrifuge at low speed and discard ether phase. Shake aqueous phase for 5 min with an equal volume of carbon tetrachloride, centrifuge at low speed and discard carbon tetrachloride phase, add n-butanol (to 8% (v/v)) to the aqueous phase and store the mixture at 4°C for 16 h. Repeat treatment with carbon tetrachloride. Sediment and clarify by two cycles of high and low speed centrifugation (Wetter, 1960). Use 0.05 M sodium citrate at pH 7.5 for resuspension. Prolonged contact with crude sap results in degradation of protein subunits (Koenig et al., 1970).

Properties of Particles

No information.

Particle Structure

Particles are flexuous filaments (Fig.5), normal length c. 520 nm, diameter c. 13 nm (Brandes & Bercks, 1963).

Particle Composition

RNA: M. Wt 2.1 x 106 (Koenig, 1971).

Protein: Subunits in rapidly purified preparations have a M. Wt of c. 2.0 x 104 but, after prolonged contact with crude sap, values of c. 1.7 x 104 have been found (Koenig et al., 1970; Koenig, unpublished).

Relations with Cells and Tissues

Many inclusion bodies are found in the epidermis of cacti as well as in the epidermis and sometimes also in the mesophyll of leaves from other host plants. Usually they are spindle-shaped (Fig.1). In addition ring-, bow- and thread-shaped structures are formed. According to Amelunxen (1958) all these structures develop from X-bodies which are formed early in infection.

References

  1. Amelunxen, Protoplasma 49: 140, 1958.
  2. Brandes & Bercks, Phytopath. Z. 46: 291, 1963.
  3. Brandes & Bercks, Adv. Virus Res. 11: 1, 1965.
  4. Koenig, Phytopath. Z. 65: 379, 1969.
  5. Koenig, J. gen. Virol. 10: 111, 1971.
  6. Koenig & Bercks, Phytopath. Z. 61: 382, 1968.
  7. Koenig, Stegemann, Francksen & Paul, Biochim. biophys. Acta 207: 184, 1970.
  8. Milicic, Acta bot. croat. 18-19: 37, 1960.
  9. Milicic, Plese, Bercks, Brandes, Casper & Chessin, Phytopath. Z. 55: 211, 1966.
  10. Milicic & Udjbinac, Protoplasma 53: 584, 1961.
  11. Plese & Milicic, Phytopath. Z. 55: 197, 1966.
  12. Wetter, Arch. Mikrobiol. 37: 278, 1960.


Figure 1

Spindle-shaped inclusions in Amaranthus hybridus (x 600). (Courtesy of D. Milicic, Zagreb.)

Figure 2

Upper leaf of Chenopodium quinoa, systemically infected.

Figure 3

Lower leaf of Chenopodium quinoa, systemically infected.

Figure 4

Local lesions in Gomphrena globosa.

Figure 5

Shadowcast virus particles from a purified preparation. Bar represents 500 nm.