x 750 nm. There are antiserum kits that can confirm the viruses identity. There is resistance to MDMV. Maize plants can have up to five resistance genes in their genetic make up. There are commercially available hybrids that provide good resistance. The major gene for resistance is called mdm1 and it is found on chromosome 6. Mdm1 was identified in Pa405, an inbred line. This chromosomal region of mdm1 is also where resistance genes to two other phtyviridae viruses are located. The resistance conferred by mdm1 can be greatly altered with genetic, environmental, and developmental factors. At the University of Wisconsin–Madison there are breeding trials to help create new varieties that are resistant to MDMV. Environment MDMV prefers warm to average temperatures. Johnson grass infected with MDMV in the surrounding environment can increase the disease on maize. MDMV is a cultivated virus that mainly occurs in the United States and Australia. MDMV does not overwinter in Minnesota and Wisconsin, which makes the source of inoculum in these northern states unclear. During infection after periods of cool night temperatures, about 60 °F, the plants may exhibit signs of the disease such as blotches or streaks of red. Transmission Maize dwarf mosaic virus is spread by seed, by infected leaves rubbing on non-infected leaves and perhaps most commonly, via aphids (Lipps & Mills, n.d.). These aphids become carriers after they feed on plants such as Johnson grass, maize or sorghum, or other grass species that are infected with MDMV. Broadleaf plants do not become infected with MDMV (The CIMMYT Maize Program). Aphids transmit Maize Dwarf Mosaic Virus disease effectively fifteen to thirty minutes after feeding on infected plants when by spreading the virus to the susceptible plants after they have flown or are blown onto a nearby corn crop and will start to feed (“Maize Dwarf Mosaic Virus,” n.d.). Symptoms When looking for symptoms of MDMV in corn, one must also be aware of the plant’s growth stage as symptoms may affect the plant differently at various stages. Young leaves, may experience chlorotic spotting which may eventually turn into a mosaic or mottle pattern (“Maize Dwarf Mosaic Virus,” n.d.). Later in the growing season, the mosaic pattern may bleed into a general yellowing of the leaf and eventually areas of red streaks or blotches may appear if night time temperatures are consistently around 60 degrees Fahrenheit (Lipps & Mills, n.d.). Plants affected