Details of DPV and References

DPV NO: 133 July 1974

Family: Geminiviridae

Genus: Mastrevirus

Species: Maize streak virus | Acronym: MSV

Maize streak virus

K. R. Bock Overseas Development Administration, Crop Virology Project, East African Agriculture and Forestry Research Organisation, Nairobi, Kenya

Contents

Introduction

Described by Storey (1925) and Bock, Guthrie & Woods (1974).

Selected synonyms

Maize streak virus A (Rev. appl. Mycol. 29: 614)

Sugarcane streak virus (Rev. appl. Mycol. 4: 442)

A small isometric virus, probably containing RNA, with particles c. 20 nm in diameter, usually occurring in pairs measuring 30 x 20 nm. Transmitted by leafhoppers (Cicadulina spp.) in the persistent manner but not by inoculation of sap. Host range is apparently confined to the Gramineae. The virus occurs throughout Africa south of the Sahara and in southeast Asia.

Main Diseases

Causes severe streak disease of maize (Zea mays) (maize streak; Fig. 1), sugarcane (Saccharum officinarum (Fig. 2), millet (Eleusine coracana) and many grasses (Fig. 3), and stunt of wheat (Triticum aestivum).

Geographical Distribution

Maize streak virus occurs in Africa south of the Sahara, and in Mauritius and Madagascar; it has been reported from India and probably occurs elsewhere in southeast Asia. It does not occur in the New World.

Host Range and Symptomatology

All known hosts are in the Gramineae, among which many species can be infected. In Africa, streak disease has been recorded in species in the tribes Andropogoneae (Cymbopogon, Imperata, Saccharum, Rottboellia), Eragrosteae (Dactyloctenium, Diplachne, Eleusine, Eragrostis, Leptochloa, Setaria), Sporoboleae (Sporobolus), Zoysieae (Tragus), Maydeae (Zea, Euchlaena), Hordeae (Triticum) and Avenae (Avena) (Storey & McLean, 1930; McLean, 1947).

Transmission experiments must be done with leafhopper vectors because the virus is not manually transmissible.

Diagnostic species

For maize (type) strain: Zea mays (maize). First symptoms in young seedlings appear 3-7 days after inoculation as almost circular pale spots 0.5-2 mm diameter in the lowest exposed portions of the youngest leaves (Fig. 4). When the disease is fully developed the plants show narrow veinal streaks which range from a few mm to several cm long, from 0.5-1 mm wide and frequently fuse laterally.

For other strains: Several strains do not infect maize; diagnosis must include transmission by Cicadulina to the host species under study, and evidence on particle morphology and serology.

Propagation and assay species

Cultures of the various strains are best maintained and assayed in their own specific host: e.g. the maize (type) strain in maize; the sugarcane strain in susceptible varieties of Saccharum; the guinea grass strain in Panicum maximum. No host is known that produces local lesions, and assays must be done by recording the proportion of test plants that become infected following inoculation by means of the leafhopper vector.

Leafhoppers can be rendered viruliferous by feeding through membranes on crude sap or purified preparations and by intrahaemocoelic injection.

Strains

Although maize streak virus apparently has a wide host range among African species of Gramineae, the strains show considerable host adaptation (Bock et al., 1974). McLean (1947) distinguished several forms of streak-producing viruses on host range and reaction and on speed of symptom development in maize: a severe (A) and a mild (B) form from maize; a form from sugar-cane (Uba-virus) that afforded no protection in maize against either the A or B viruses; and three forms from wild grasses (Sporobolus, Eleusine and Paspalum viruses), transmissible to maize but not to sugarcane.

Bock et al. (1974, and unpublished) have shown that four streak-disease viruses (those occurring naturally in maize, sugarcane, Panicum and Eleusine) have identical particle morphology and are serologically related though distinguishable. In Africa, it seems that some strains which were adapted to wild hosts, such as those occurring naturally in Eleusine and Sporobolus, proved highly pathogenic to the exotic maize.

Transmission by Vectors

The known vectors of maize streak virus are confined to the genus Cicadulina. They are C. mbila, C. storeyi, C. bipunctella zeae, C. latens and C. parazeae (Ruppel, 1965; Storey, Howland & Prosser, 1966).

Storey (1925; 1928; 1932; 1933; 1938; 1939) studied vector transmission in great detail. The virus may be acquired in less than 1 h (minimum acquisition time 15 sec) and may be inoculated in 5 min; latent period in the vector is 6-12 h at 30°C, which coincides with the first appearance of the virus in the body fluids. Storey suggested that the vector remained viruliferous for life, but experimental proof that the virus replicates within the vector is lacking.

All five nymphal instars are able to acquire and transmit the virus; it is retained during moulting but is not transmitted through the egg. Races that are active (able to transmit) and inactive have been found for four of the five vector species of Cicadulina (mbila, storeyi, bipunctella zeae and latens); the gut wall of inactive races is impermeable to passage of the virus but inactive races are rendered active by injecting virus into the abdomen or by puncturing the gut wall. The ability to transmit is inherited as a simple dominant gene linked with sex. Employing conventional notation (A = major gene for activity, a for inactivity), the constitutions are active males (AX) (Y); inactive males, (aX) (Y); active females, (AX) (AX) or (AX) (aX); and inactive females, (aX) (aX). Individual insects of an active race are not equally efficient; there is evidence that a second gene, not sex-linked, modifies the effect of the major gene for activity.

Transmission through Seed

Not seed-transmitted in maize.

Transmission by Dodder

Not reported.

Serology

Maize streak virus is moderately to strongly immunogenic; Bock et al. (1974) obtained an antiserum with titres of 1/256 and 1/1024 in gel-diffusion and tube precipitin tests respectively.

Relationships

Strains of the virus from maize, sugarcane, guinea grass and millet are identical in particle morphology and are serologically related though distinguishable (Bock et al., 1974). The millet and sugarcane strains are closely related to the maize strain, the guinea grass strain more distantly. Strains differ greatly in host range and virulence; even serologically closely related strains do not cross-protect (Storey & McLean, 1930; McLean, 1947; Bock et al., 1974). For example, the maize (type) strain induces a mild transient streak in sugarcane; the sugarcane strain causes a mild permanent infection in maize. Neither of these strains infects guinea grass, nor does the guinea grass strain infect maize or sugarcane.

Stability in Sap

Studied by allowing vectors to feed through membranes on crude sap containing the type (maize) strain and transferring them to maize seedlings. Thermal inactivation point is not less than 60°C; dilution end-point not less than 1/1000; longevity at room temperature not less than 24 h (K. R. Bock & E. J. Guthrie, unpublished data).

Purification

The different virus strains may be purified satisfactorily from their preferred hosts (Bock et al., 1974). Homogenize 100 g infected leaf tissue in 200 ml 0.01 M phosphate buffer containing 0.1 % thioglycollic acid, pH 3.9-4.1. Clarify with n-butanol (7 ml/100 ml extract), concentrate by ultracentrifugation, and resuspend the virus in 0.01 M phosphate, pH 7.7.

Properties of Particles

(Bock et al., 1974). Sedimentation coefficent, s°_20,w: 76 S for paired and 54 S for single particles.

Particle Structure

Particles are isometric, 20 nm in diameter, but are usually paired (30 x 20 nm) (Fig. 5). The ratios of paired to single particles was approximately 8:1 (chloroform preparations) or 3:1 (n-butanol preparations). In paired particles, individuals seem to be 5-sided, whereas single particles appear hexagonal (Bock et al., 1974).

Particle Composition

Tests using acridine orange staining (Cowan & Graves, 1968) indicate that the nucleic acid is single-stranded, probably RNA (Bock et al., 1974).

Relations with Cells and Tissues

Storey (1928; 1938) found that virus was restricted to chlorotic areas of the leaf, and was not acquired from mesophyll or phloem of green areas. Infection depends on the stylet of the vector penetrating the phloem of the plants inoculated. Passage of virus down a leaf from the point of inoculation is rapid, and can exceed 40 cm in 120 min (Storey, 1928).

Crystalline nuclear inclusions occur in infected maize and sugarcane leaves (Fig. 6) (Bock et al., 1974; Sylvester, Richardson & Nickel, 1973); they contain particles c. 18-20 nm in diameter.

Notes

Smith (1957) and Martyn (1968) cite maize mottle virus as a strain of maize streak virus. However, there appears to be insufficient evidence to warrant this assumption (Storey, 1937). Recent work on the morphology of beet curly top virus, which is transmitted by the leafhopper Circulifer tenellus, suggests that its particles may be similar to the single particles of maize streak virus (Duffus & Gold, 1973).

In Africa, maize streak disease may be confused with diseases caused by maize line or maize stripe viruses (Kulkarni, 1973). These viruses are transmitted by Peregrinus maidis (and not by Cicadulina spp.); they also differ in particle morphology, having spherical particles of 35 and 40 nm diameter respectively. Maize mosaic virus (Herold, 1972) also induces leaf symptoms that could be confused with those of maize streak but it has bacilliform particles and is transmitted by Peregrinus maidis.

Figures

References list for DPV: Maize streak virus (133)

1. Bock, Guthrie & Woods, Ann. appl. Biol. 77: 289, 1974.
2. Cowan & Graves, Virology 34: 544, 1968.
3. Duffus & Gold, Phytopathology 63: 1107, 1973.
4. Herold, CMI/AAB Descriptions of Plant Viruses 94, 4 pp., 1972.
5. Kulkarni, Ann. appl. Biol. 75: 205, 1973.
6. Martyn, Phytopath. Pap. 9, 204 pp., 1968.
7. McLean, Sci. Bull. Dep. Agric. For. Un. S. Afr. 265, 1947.
8. Ruppel, Publs Mich. St. Univ. Mus. Biol. Ser 2: 385, 1965.
9. Smith, Textbook of Plant Virus Diseases, London, Churchill, 1957.
10. Storey, Ann. appl. Biol. 12: 422, 1925.
11. Storey, Ann. appl. Biol. 15: 1, 1928.
12. Storey, Proc. R. Soc. B. 112: 46, 1932.
13. Storey, Proc. R. Soc. B. 113: 463, 1933.
14. Storey, Ann. appl. Biol. 24: 87, 1937.
15. Storey, Proc. R. Soc. B. 125: 455, 1938.
16. Storey, Proc. R. Soc. B. 127: 526, 1939.
17. Storey, Howland & Prosser, Rec. Res. E. Afr. Agric. For. Res. Org., 1965: 123, 1966.
18. Storey & McLean, Ann. appl. Biol. 17: 691, 1930.
19. Sylvester, Richardson & Nickel, Pl. Dis. Reptr 57: 414, 1973.