Maize Dwarf Mosaic Virus (MDMV) and Sugarcane Mosaic Virus (SCMV)

Maize dwarf mosaic disease and sugarcane mosaic disease are caused by various strains of the Sugarcane mosaic virus potyvirus. These viruses are transmitted predominantly by several genera of aphids, but can also be transmitted mechanically and through seed. Yield losses due to maize dwarf mosaic disease and sugarcane mosaic disease can be extensive.

Pathogen

Sugarcane mosaic virus (SCMV) consists of at least 14 strains (designated ‘A’ through ‘N’) that differ in their host range and injury and are distributed worldwide. Maize dwarf disease is caused by strains C, D, E and F which are collectively known as maize dwarf mosaic virus (MDMV).

Vector: At least 15 species of aphids transmit MDMV and SCMV including Rhopalosiphum maidis, Schizaphis graminum and Aphis maidiradicis.

Symptoms

Symptoms of maize dwarf mosaic and sugarcane mosaic diseases vary widely depending on host genotype, time of infection, and viral strain. Generally, infected plants develop distinct chlorotic mosaics, mottles or streaks on green tissues (typically observed on young leaves). Infected plants are characterized by stunting and shortening of upper internodes. Ear development can be arrested, leading to incomplete grain filling and direct yield loss. Plants infected early may produce nubbins or can be totally barren. Foliage of plants infected with SCMV can turn purple or purple-red although this does not occur in plants infected with MDMV.

Confirmation

Both MDMV and SCMV are single stranded RNA potyviruses in Potyviridae. They are flexuous and rod-shaped, measuring 12 × 750 nm. Antiserum kits are commercially available to confirm virus identity.

Why and where it occurs

Maize dwarf mosaic and sugarcane mosaic virus occur where aphid vectors are prevalent and where alternate hosts are cultivated. Both diseases can also be transmitted through infected seed and mechanical injury, although these techniques are less common than aphid transmission. Mechanical transmission occurs predominantly in greenhouses and is not considered a major problem in the field. Disease incidence is highest where vector populations are high, large number of infected plants are present, and susceptible varieties are cultivated.

Host range

• MDMV strains are known to infect maize, sorghum and Johnson grass.
• SCMV strains infect maize, sugarcane, sorghum and a range of Graminaceous species.

Life cycle

Aphids (both adults and nymphs) transmit the virus during feeding. The virus is acquired by the aphid within seconds of feeding and a latent period is not required for transmission to new host plants. Aphids do not retain the virus after molting. The virus overwinters in alternate hosts.

MDMV and SCMV can also be transmitted to a lesser extent through seed and mechanically through plant damage. Mechanical transmission is considered to be a problem predominantly in greenhouses.

Damage

• Mechanism of damage: Yield loss is caused by the halting of ear formation and development, resulting in nubbins and incomplete grain filling. Stunting of plants also results in less harvestable biomass.
• When damage is important:Damage is most critical when plants are infected early, which can result in termination of ear development and production of barren ears. Damage is also critical when large population of aphid vectors are prevalent, susceptible hybrids are cultivated, and infected plants are widespread in the vicinity.
• Economic importance:Yield losses as high as 40% have been attributed to maize dwarf mosaic virus.

Geographical distribution

SCMV is documented worldwide (Figure 1) wherever maize and sugarcane are cultivated. MDMV strains, however, occur predominantly in the United States and Australia.

Figure 1. Global distribution of SCMV.

Management principles

Host resistance

• Resistant varieties are widely available and offer the best means of disease management.
• A major gene for MDMV resistance (mdm1) has been identified and is located on chromosome 6.

Management of insect vectors

• Use of insecticides, biological control agents and cultural practices (management of aphid refuges) that reduce aphid populations will reduce transmission of viruses.
• Excessive use of nitrogen fertilizer favors aphid reproduction. Application of nitrogen above recommended levels should therefore be avoided.

Management of alternate hosts

• Removal of volunteer plants and management of alternate hosts, such as Johnson grass and graminaceous weed species, will reduce sources of inoculum.

Certified seed

• Use of certified, virus-free seed will limit seed-borne transmission of the MDMV and SCMV.

References

Agrios, G.N. 1988. Plant Pathology. Third Edition. San Diego: Academic Press, Inc.

CAB International. 1974. Sugarcane mosaic virus. Distribution Maps of Plant Diseases. Edition 4 (October), Map 229. Wallingford, UK: CAB International.

CIMMYT. 2004. Maize Diseases: A guide for Field Identification. 4th Edition. Mexico, D.F.: CIMMYT.

Comstock, J.C. and R.S. Lentini. 2005. Sugarcane Mosaic Virus Disease. University of Florida IFAS Extension. Factsheet: SSAGR209. http://edis.ifas.ufl.edu/pdffiles/SC/SC00900.pdf  (4 September 2007).

Louie, R. 1999. Diseases Caused by Viruses. In Donald G. White (ed), Compendium of Corn Diseases. St. Paul, Minnesota: The American Phytopathology Society. Pp. 49-55.

Redinbaugh, M.G., R.E. Gingery and M.W. Jones. 2004. The genetics of virus resistance in maize (Zea mays L.). Maydica 49:183-90.

Shukla, D.D., C.W. Ward and A.A. Brunt. 1994. The Potyviridae. Wallingford, UK: CAB International.

Contributor: Biswanath Das