Pokeweed mosaic virus
R. J. Shepherd
Department of Plant Pathology, University of California, Davis, California 95616, USA
- Described by Woods (1902) and Allard (1918).
- 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
Causes a mosaic and mottle disease of pokeweed, Phytolacca americana.
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
- Assay species
- Chenopodium quinoa is a suitable local lesion host for bioassay of some
isolates of the virus.
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.
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.
The virus may be distantly related serologically to tobacco etch
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
10 days; dilution end-point, 10-5
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
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,
; Edwardson, Purcifull & Christie, 1968
). Finely striated inclusions,
which are probably derived from pinwheel bodies in the cell, are numerous in
negatively stained leaf extracts.
- Allard, Phytopathology 8: 51, 1918.
- Duggar & Armstrong, Ann. Mo. bot. Gdn 12: 359, 1925.
- Edwardson, Am. J. Bot. 53: 359, 1966.
- Edwardson, Purcifull & Christie, Virology 34: 250, 1968.
- Kassanis & Kleczkowski, J. gen. Microbiol. 2: 143, 1948.
- Shepherd, Fulton & Wakeman, Phytopathology 59: 219, 1969.
- Woods, Bull. Bur. Pl. Ind. U.S. Dep. Agric. 18, 24 pp., 1902.
Systemic symptoms on Phytolacca americana.
Systemic symptoms on Gomphrena globosa.
Rod-shaped particles found in extracts of infected pokeweed. Bar
represents 500 nm.