Details of DPV and References

DPV NO: 342 December 1989

Family: Potyviridae
Genus: Potyvirus
Species: Sugarcane mosaic virus | Acronym: SCMV

This is a revised version of DPV 88

Sugarcane mosaic virus

D. S. Teakle Department of Microbiology, University of Queensland, St. Lucia, Qld. 4067, Australia

D. D. Shukla CSIRO, Division of Biotechnology, Parkville, Victoria 3052, Australia

R. E. Ford Department of Plant Pathology, University of Illinois, Urbana, IL 61801, USA

Contents

Introduction

Described by Brandes (1919).

Synonyms

Abaca mosaic virus (Eloja & Tinsley, 1963)
Maize dwarf mosaic virus strain B (Mackenzie et al., 1966; Louie & Knoke, 1975)

A virus with flexuous, filamentous particles about 750 nm long, which contain a single strand of RNA. It infects numerous species in the Gramineae. It is transmitted by inoculation of sap and in the non-persistent manner by aphids.

Main Diseases

Causes mosaic diseases in sugarcane (Saccharum spp.; Fig. 2; Koike & Gillaspie, 1989) and some other graminaceous plants (Teakle & Grylls, 1973).

Geographical Distribution

Occurs in most parts of the world where sugarcane is grown (Gillaspie & Mock, 1987). Strains adapted to perennial hosts other than sugarcane may occur remote from sugarcane plantations (Teakle & Grylls, 1973).

Host Range and Symptomatology

The natural host range is restricted to members of the Gramineae, with the exception of the abaca mosaic strain, which infects Musa textilis, a monocotyledon in the family Musaceae. Sorghum, maize and some wild grasses (Fig. 1) growing near infected sugarcane may be infected naturally (Koike & Gillaspie, 1989). Although sap transmission tests have shown that many graminaceous species are susceptible (Abbott & Tippett, 1964; Ford & Tosic, 1972; Tosic & Ford, 1972; Penrose, 1974), cultivated cereals such as wheat, barley, rye and rice are rarely infected naturally.

Diagnostic species

Saccharum spp. (sugarcane). Systemic mosaic, yellow striping and/or necrosis depending on cultivar and virus strain (Fig. 2).

Sorghum bicolor (sorghum) cvs Atlas, Rio and certain other lines are readily infected with most strains. Systemic mosaic or necrosis are produced.

Zea mays (maize). Seedlings of most varieties are readily infected with the various strains and show systemic mosaic symptoms.

Propagation species

Sugarcane or other perennial hosts are suitable for maintenance of cultures. Sorghum cv. Rio is a good source for maintenance and purification of most strains. Sweet corn cultivars yield adequate amounts of virus and are suitable for strains that cause necrosis in sorghum.

Assay species

Although some strains induce necrotic local lesions in Atlas sorghum (Dean, 1970; Fig. 3), assay is usually done in other sorghums, such as Rio, which show systemic mosaic, or in sweet corn cultivars, which also produce systemic mosaic symptoms.

Strains

Some viruses previously regarded as strains of sugarcane mosaic virus have now been reclassified (Shukla et al., 1989b) as separate viruses (see Relationships). The following strains are closely related serologically and have coat protein sequence homologies of greater than 90% (Shukla et al., 1987; Jilka, 1990).

Sugarcane strains (Brandes, 1919). Cause mosaic in sugarcane, but rarely infect Johnsongrass (Sorghum halepense). USA strains A, B, D, E and F may be differentiated on sugarcane cultivar C.P. 31-294, strain C on Co. 281 and strain A on C.P. 31-588 (Abbott & Tippett, 1966). Sugarcane strains from other parts of the world may differ somewhat from USA sugarcane strains (Abbott & Stokes, 1966), but have usually been included with them (Gillaspie & Mock, 1987; Koike & Gillaspie, 1989).

Queensland blue couch grass and sabi grass strains (Teakle & Grylls, 1973). Cause mosaic symptoms respectively in Digitaria didactyla and Urochloa mosambicensis, their perennial hosts, but do not infect sugarcane.

Maize dwarf mosaic virus strain B (Mackenzie et al., 1966; Louie & Knoke, 1975). Causes mosaic in maize, but does not infect Johnsongrass or sugarcane cultivars C.P. 31-294 and C.P. 31-588 (Snazelle et al., 1971).

Abaca mosaic strain (Eloja & Tinsley, 1963). Causes a mosaic in abaca (Musa textillis) and maize, and is considered a strain on the basis of its serological relationship.

Transmission by Vectors

Transmitted in the non-persistent manner by Dactynotus ambrosiae, Hysteroneura setariae, Rhopalosiphum maidis, Toxoptera graminum and a number of other aphid species (Kennedy et al., 1962; Teakle & Grylls, 1973). The virus is more readily transmitted to or from hosts such as maize and sorghum than to or from sugarcane.

Transmission through Seed

Not reported for sugarcane, sorghum or certain grasses. However, maize dwarf mosaic virus strain B was transmitted to a small proportion of maize seedlings (Humaydan, 1979).

Serology

Antisera usually have titres of about 1/256. They give flagellar type precipitates in tests with intact virus in liquid. Immunodiffusion tests may be done in agar gels using purified virus treated with ethanolamine at pH 10.5 as the antigen (Bond & Pirone, 1971). Antisera to sugarcane mosaic virus have also been used in immunosorbent electron microscopy, enzyme-linked immunosorbent assay and electro-blot immunoassay (Shukla et al., 1983; Jarjees & Uyemoto, 1984; Shukla & Gough, 1984; Hewish et al., 1986; Shukla et al., 1989b). Monoclonal antibodies have been produced to maize dwarf mosaic virus strain B (Hill et al., 1984).

Relationships

Sugarcane mosaic virus is placed in the potyvirus group because of its filamentous particles c. 750 nm long and 13 nm wide, its induction of pinwheel inclusions in cells, and its mechanical and aphid transmissibility.

On the basis of an apparently distant serological relationship, sugarcane mosaic virus was thought to be related (see Notes) to maize dwarf mosaic virus strains A, D, E and F and sugarcane mosaic virus strains H, I, and M (Pirone, 1972; Ford et al., 1989; Shukla & Teakle, 1989; Shukla et al., 1989b). However, recent tests in electroblot immunoassay using polyclonal antibodies directed to the virus-specific N-termini of coat proteins have shown that these strains are not related to the strains of sugarcane mosaic virus from Australia and the USA (Shukla et al., 1989b). The distant serological relationships observed previously were due to antibodies directed to the core region of the coat proteins which show high sequence homology throughout the potyvirus group (Shukla et al., 1989a; 1989b).

Maize dwarf mosaic virus strain B shows a strong reciprocal serological relationship with the HAT strain of tobacco etch virus, a potyvirus with a host range mainly in the Solanaceae, and the epitope for this relationship is located in the surface-exposed, N-terminal peptide region of the coat proteins (Shukla et al., 1989a). Shukla & Ward (1989) suggested that this epitope comprises the eight amino terminal residues of the coat proteins, which are identical in the two viruses (Jilka, 1990; Allison et al., 1985).

Stability in Sap

In sorghum or sweet corn, the thermal inactivation point is usually 50-55°C; dilution end-point is 10-2 to 10-4 depending on the strain. Longevity in vitro is 1 day or less at 20°C (Bond & Pirone, 1971; Teakle & Grylls, 1973).

Purification

Bond & Pirone (1971). The following procedure does not always succeed and aggregation of particles is a problem. Homogenize each 300 g minced tissue in 300 ml water containing 0.3% ascorbic acid, 0.01 M sodium diethyldithiocarbamate and 0.3% 2-mercaptoethanol. Use each 300 ml extracting fluid to extract three successive 100 g amounts of leaf material, removing the pulp and retaining the liquid each time. Strain through cheesecloth and homogenize the filtrate with an equal volume of chloroform. Centrifuge at low speed and recover the aqueous phase. Centrifuge this phase at high speed and resuspend the pellets in borate-EDTA buffer (0.1 M borate, 0.01 M EDTA, pH 8.2), using a minimum volume to avoid the need for a second high speed centrifugation, which results in the loss of over 90% of the infectivity. After a second low-speed centrifugation, float the supernatant fluid on 10-40% sucrose gradients in borate-EDTA buffer, and centrifuge for 2 h at 90,000 g. The virus forms a single light-scattering zone.

A very similar procedure, in which the sucrose for density gradients was dissolved in 0.01 M sodium citrate, was used by Snazelle et al. (1971).

Preparations may be further purified by zone electrophoresis in sucrose gradients (Von Wechmar & Hahn, 1967) or by equilibrium centrifugation in sucrose gradients (Gillaspie, 1972).

Properties of Particles

A sedimentation coefficient of 176 ± 5 S has been calculated for strain D of sugarcane mosaic virus and 170 ± 5 S for maize dwarf mosaic virus strain B: buoyant densities in CsCl for these strains are 1.3327 and 1.3427 respectively (Tosic & Ford, 1974).

Particle Structure

Particles are flexuous filaments about 750 nm long and 13 nm in diameter (Teakle & Grylls, 1973; Fig. 4).

Particle Composition

Nucleic acid: A single ssRNA species of c. 3.4 x 106 daltons, c. 5% by particle weight (Berger et al., 1988; Jilka, 1990).

Protein: A single polypeptide species of 35,000 daltons consisting of 328 amino acid residues (Jilka, 1990). The amino terminus of the coat protein is blocked in maize dwarf mosaic virus strain B (Jilka, 1990) whereas in sugarcane strains it is not blocked (D. D. Shukla, unpublished data). The amino acid sequence of maize dwarf mosaic virus strain B is given by Jilka (1990); the amino acid composition is: ala 30, arg 19, asp 18, asn 14, cys 2, glu 16, gln 17, gly 43, his 8, ile 10, leu 14, lys 17, met 13, phe 8, pro 12, ser 28, thr 31, trp 3, tyr 10, val 15.

Partial coat protein sequences for sugarcane, Queensland blue couch grass and sabi grass strains are given by Shukla et al. (1987).

Genome Properties

(Jilka, 1990). The segment of the genome encoding the coat protein of maize dwarf mosaic virus strain B is adjacent to the 3' non-coding region. The nuclear inclusion protein gene is located upstream from the coat protein gene. The 3' non-coding region is 237 nucleotides long and is polyadenylated. The poly(A) tail consists of approximately 60 adenosine residues.

Relations with Cells and Tissues

Cytoplasmic inclusions of the pinwheel, scroll and laminated aggregate types, characterisic of subdivision III of the potyvirus group, have been found in cells of Zea mays after infection with sugarcane mosaic virus strains A, D or E, or maize dwarf mosaic virus strain B (Edwardson, 1974; Fig. 5). Although nuclear inclusions, found in plants infected with such potyviruses as tobacco etch virus and bean yellow mosaic virus, have not been observed with sugarcane mosaic virus, the presence of the nuclear inclusion protein gene in the genome of maize dwarf mosaic virus strain B (Jilka, 1990) suggests that this protein is produced in infected tissue but perhaps does not aggregate to form nuclear inclusion bodies.

Notes

Recent investigation on the taxonomy of aphid-borne potyviruses infecting species of Gramineae (Shukla et al., 1989b) has shown that virus isolates previously included as strains of sugarcane mosaic virus in fact comprise four distinct potyviruses, namely sugarcane mosaic virus itself (USA strains A, B, D and E, Australian strains SC, BC and Sabi, and USA maize dwarf mosaic virus strain B), Johnsongrass mosaic virus (Australian sugarcane mosaic virus strain JG, USA maize dwarf mosaic virus strains O and Kansas 1; Shukla & Teakle, 1989; McKern et al., 1990), maize dwarf mosaic virus (USA strains A, D, E and F; Ford et al., 1989), and sorghum mosaic virus (USA sugarcane mosaic virus strains H, I and M; Shukla et al., 1989b). The four viruses induce similar symptoms in some hosts, have host ranges usually restricted to the Gramineae and have some aphid vectors in common. However, they are serologically unrelated or only distantly related (Teakle & Grylls, 1973; Shukla & Gough, 1984; McDaniel & Gordon, 1985; Giorda et al., 1986; Hewish et al., 1986; Shukla et al., 1983, 1989b). Previous reports of serological relationships among these viruses and their strains are caused by the presence in polyclonal antisera of antibodies to epitopes located in the conserved core regions of potyvirus coat proteins; these antibodies recognize most potyviruses (Shukla et al., 1988b, 1989a, 1989b). The viruses also differ considerably in the amino acid sequence of their coat proteins; sequence homology of only 54% was observed between the coat proteins of Johnsongrass mosaic virus and strains of sugarcane mosaic virus (Shukla et al., 1987; Jilka, 1990; N. M. McKern & D. D. Shukla, unpublished data). The four viruses can also be distinguished by high performance liquid chromatography of coat protein digests (Shukla et al., 1988a; N. M. McKern & D.D. Shukla, unpublished data) and by their reactions on certain sorghum inbred lines (Teakle & Grylls, 1973; Persley et al., 1985; Giorda et al., 1986; Tosic et al., 1990). Strains of sugarcane mosaic virus induce necrotic stripes in inoculated leaves, and mosaic and necrosis of new leaves of Atlas sorghum, whereas sorghum mosaic virus induces typical red leaf symptoms and the other two viruses induce only mosaic symptoms. Johnsongrass mosaic virus induces necrotic red stripes in sorghum lines OK Y8 and SA 8735 whereas the other three viruses induce only mosaic symptoms. Maize dwarf mosaic virus induces mosaic and necrotic spots in systemically infected leaves of sorghum cv. Rio, whereas the other three viruses induce either mosaic or symptomless infection.

Figures

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Sorghum verticilliflorum infected by the sabi grass (Urochloa mosambicensis) strain showing a mosaic pattern.

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Sugarcane infected by the Australian sugarcane strain showing yellow stripes; (above), cv. C.P. 31-588, (below) cv. C.P. 31-294.

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Sorghum bicolor cv. Atlas showing necrotic local lesions after infection with the Australian sugarcane strain.

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Filamentous particles of the Australian sugarcane strain mounted in phosphotungstate. Bar represents 250 nm.

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Pinwheel, tube and scroll aggregates in a thin section of Zea mays infected with the Australian sugarcane strain. Bar represents 250 nm (courtesy Sunee Srisink).

References list for DPV: Sugarcane mosaic virus (342)

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