Maize chlorotic dwarf of maize is caused by Maize chlorotic dwarf virus (MCDV). The disease (Fig. 1) has been reported from Texas up to Missouri and Ohio covering 19 states of the United States and Mexico. The disease caused severe economic losses in the Midwest and Southern United States during the 1960s to 1970s. Although major yield losses in field (dent) corn due to MCDV have not been reported recently, it may affect corn production since the virus and its vector are still present in Ohio, and warmer conditions improve transmission efficiency in the vector. Few systematic studies to estimate yield losses in production fields have been conducted. Experimentally, losses caused by MCDV in susceptible hybrids have varied from 5 to 91%. MCDV is mainly found in regions where an overlapping distribution of Johnsongrass, the overwintering virus host, and the maize leafhopper Graminella nigrifrons, its main vector, occurs.
|Fig. 1. Corn plant in the field infected with MCDV showing chlorosis, vein banding and reddening of the leaf margins in Wooster, OH.|
MCDV can cause diverse symptoms including plant stunting, shortening of upper internodes, leaf reddening or yellowing, leaf twisting and tearing, and chlorosis or clearing of the smallest visible leaf veins (vein banding). Symptoms vary with the hybrid and with the virus strain. Infected leaves may also develop a rough “corduroy” texture instead of being smooth and shiny. Vein banding is the most diagnostic symptom for this virus (Fig. 2). This vein chlorosis may not be observed in older plants or with mild strain infections. Intensity of symptoms varies according to the virus isolate, maize hybrid, and plant developmental stage at the time of infection.
MCDV is mainly transmitted by the black-faced leafhopper Graminella nigrifrons. Corn is not the favorite host for the leafhopper since the insect prefers to feed on grasses such as ryegrass (Lolium perenne), barnyardgrass (Echinochloa crusgalli), crabgrass (Digitaria sanguinalis) and bermudagrass (Cynadon dactylon). The leafhopper has to feed on an infected plant for at least 15 minutes to several hours to acquire the virus before it can be transmitted. The insect carrying the virus can transmit the virus immediately and for up 4 days. Only some gramineous species are infected by MCDV, including sorghum and wheat, which do not show any symptom when infected. The virus survives the winter in the rhizomes of its only known perennial host Johnsongrass (Sorghum halepense). MCDV is not transmitted by seed or rub-inoculation.
Identification of virus diseases based on symptoms alone is usually inadequate. Vein banding is diagnostic for MCDV but symptoms vary according to corn cultivar/hybrid, virus strain, plant age, and environmental factors. For an accurate identification, samples of symptomatic leaves should be tested in a laboratory to confirm the presence of the virus. Serological and reverse-transcriptase PCR-based assays can detect virus. Spherical virus particles may also be detected by electron microscopy.
|Fig. 2. Sweet corn infected with a severe isolate of MCDV showing chlorosis of leaf veins (vein banding).|
- The control of Johnsongrass is the best way to avoid the disease. Apply herbicide to eradicate Johnsongrass within and adjacent to maize fields early in the season. MCDV survives winter in the rhizomes of Johnsongrass, the main reservoir for the virus.
- The use of foliar insecticides to control the vector is not recommended. Seed treatment with systemic insecticide produces optimum efficacy against the leafhopper and other pests.
- The CIMMYT Maize Maize Diseases: A Guide for Field Identification. http://apps.cimmyt.org/english/docs/field_guides/maize/pdf/Maizediseases...
- Stewart, L. R. 2012. Waikaviruses. www.apsnet.org/publications/apsnetfeatures/Pages/waikavirus.aspx
- University of Maize Chlorotic Dwarf Virus. cropdisease.cropsci.illinois.edu/corn/maizechloroticdwarfvirus.html
Laboratories testing or providing ELISA kit for MCDV identification
- Agdia: www.agdia.com