97
October 1972
Family: Potyviridae
Genus: Potyvirus
Species: Pokeweed mosaic virus
Acronym: PkMV


Pokeweed mosaic virus

R. J. Shepherd
Department of Plant Pathology, University of California, Davis, California 95616, USA

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 Woods (1902) and Allard (1918).

Synonym
Phytolacca decandra mosaic virus (Rev. appl. Mycol. 5: 314).

A virus with elongated, flexuous particles averaging about 776 nm in length. It has a restricted host range, is transmitted by aphids in a non-persistent manner, and readily by inoculation with plant extracts. It is widespread in North America.

Main Diseases

Causes a mosaic and mottle disease of pokeweed, Phytolacca americana.

Geographical Distribution

Widely distributed in North America east of the Rocky Mountains.

Host Range and Symptomatology

Host range is restricted; only 3 species of higher plants have been infected experimentally. The virus is readily transmissible with plant extracts from pokeweed to pokeweed; pokeweed, however, contains a potent inhibitor of infection which may prevent mechanical transmission of the virus to unrelated species (Duggar & Armstrong, 1925; Kassanis & Kleczkowski, 1948). Aphids are useful for transmitting the virus from pokeweed to other hosts (Shepherd, Fulton & Wakeman, 1969).

Diagnostic species
Phytolacca americana (pokeweed, or pokeberry). No local symptoms may be induced. Systemic symptoms consist of pronounced chlorotic mottle or mosaic with conspicuous dark green islands (Fig.1). Large green islands are usually accompanied by puckering.

Gomphrena globosa. Feathery chlorotic mottle or faint generalized chlorosis with small necrotic spots on some leaves (Fig.2).

Chenopodium quinoa. Small chlorotic local lesions. Not systemic.

Propagation species
Pokeweed is a suitable host for maintaining cultures and for propagating virus for purification.

Assay species
Chenopodium quinoa is a suitable local lesion host for bioassay of some isolates of the virus.

Strains

Variants have not been distinguished or described.

Transmission by Vectors

The virus is transmitted in a non-persistent manner by aphids as shown by tests with Myzus persicae. Can be acquired and inoculated in 1-2 min. No latent period. Retained for 1-3 hr.

Transmission through Seed

The virus is not seed-borne in pokeweed.

Serology

The virus is a potent antigen in rabbits. Tube or micro-precipitin tests with clarified sap or partially purified virus preparations are the most useful because the virus does not diffuse well in agar gels. Intact virus particles give flagellar-type precipitates in tube tests.

Relationships

The virus may be distantly related serologically to tobacco etch, henbane mosaic and potato Y viruses as shown by tests with broad-spectrum antisera (Shepherd et al., 1969).

Stability in Sap

In sap from systemically infected pokeweed plants 3 weeks after inoculation: thermal inactivation point (10 min), 70-75°C; longevity (c. 25°C), 10 days; dilution end-point, 10-5-10-6.

Purification

Homogenize infected pokeweed tissue in 0.5 M borate, pH 8.2, containing 0.5% thioglycollic acid. Clarify by emulsifying with one-third volume chloroform and recovering the aqueous phase after low speed centrifugation. Ultracentrifuge the clarified extract for 2 hr at 30,000 rev/min and resuspend the pellets in 0.02 M borate, pH 8.2. Preparations can be further purified by (a) adjusting solutions to pH 5.0, followed by low speed centrifugation to remove impurities, and dialysis of the supernatant fluid against 0.02 M borate, pH 8.2, or (b) passing partially purified virus through a column of agarose heads (Bio-gel A-150 M, Bio-Rad Laboratories, Richmond, Calif.) equilibrated with 0.01 M borate, pH 8.2.

Properties of Particles

No information.

Particle Structure

Particles are slightly flexuous filaments (Fig.3) of diameter 12-13 nm and modal length about 776 nm (Shepherd et al., 1969).

Relations with Cells and Tissues

The virus induces ‘pinwheel’ inclusions in the cytoplasm of infected cells similar to those associated with potato virus Y group viruses (see Edwardson, 1966; Edwardson, Purcifull & Christie, 1968). Finely striated inclusions, which are probably derived from pinwheel bodies in the cell, are numerous in negatively stained leaf extracts.

References

  1. Allard, Phytopathology 8: 51, 1918.
  2. Duggar & Armstrong, Ann. Mo. bot. Gdn 12: 359, 1925.
  3. Edwardson, Am. J. Bot. 53: 359, 1966.
  4. Edwardson, Purcifull & Christie, Virology 34: 250, 1968.
  5. Kassanis & Kleczkowski, J. gen. Microbiol. 2: 143, 1948.
  6. Shepherd, Fulton & Wakeman, Phytopathology 59: 219, 1969.
  7. Woods, Bull. Bur. Pl. Ind. U.S. Dep. Agric. 18, 24 pp., 1902.


Figure 1

Systemic symptoms on Phytolacca americana.

Figure 2

Systemic symptoms on Gomphrena globosa.

Figure 3

Rod-shaped particles found in extracts of infected pokeweed. Bar represents 500 nm.