Corn leaves infected by Georgia Unknown virus. Below, electron micrograph of virus. Credits

Corn leaves showing first signs of maize necrotic streak virus. Leaves gradually turn papery and translucent, with brown spots, as they die. Below, electron micrograph of virus. Credits

Two New Corn Viruses Discovered

Agricultural Research Service scientists and cooperators at Ohio State University have discovered two new corn viruses, one in Georgia and one in Arizona. The Arizona virus is in a family of viruses previously known only to attack broadleaf plants such as tomatoes and peppers, not grain crops like corn.

Peg Redinbaugh, an ARS plant molecular biologist at Wooster, Ohio, and colleagues named the Arizona virus "maize necrotic streak."

The team of scientists receives and identifies viruses in samples of infected corn leaves from around the world. The service provides global producers of corn and corn seed a first line of defense against new diseases.

Maize necrotic streak is in the Tombusvirus family, which comprises viruses that tend to spread by soil rather than by insects, making them less likely to spread widely. Another reason this virus promises not to be spread beyond Arizona is that it doesn't seem to spread from plant to plant. Its symptoms first show as white- or cream-colored streaks on leaves. It eventually kills the leaves, turning them papery and translucent, with brown spots.

Lab tests indicate that a cornfield infected by the new virus would be unlikely to yield any corn. That's why scientists have to take it seriously. Other Tombusviruses, like tomato bushy stunt virus, cause growers significant losses.

The Georgia virus, temporarily called the Georgia Unknown, is one of the plant-infecting rhabdoviruses, a family of bullet-shaped viruses which includes maize mosaic virus, a major corn disease in the tropics. Viruses in this family tend to be transmitted by any of a number of different common aphids, thrips, mites and other insects.

The team is currently testing its living collection of insects to see which of them transmit the Georgia Unknown, which may be limited to the southern United States.

ARS is the chief scientific research agency in the U.S. Department of Agriculture.

Scientific contact: Peg Redinbaugh, ARS Corn and Soybean Research Unit, Wooster, Ohio, phone (330) 263-3965, fax (330) 263-3841, redinbaugh.2@osu.edu.

Images courtesy of Ohio Agriculture Research and Development Center (OARDC), Ohio State University. Photos: Margaret Latta (maize necrotic streak) and Ken Chamberlain (Georgia Unknown), OARDC Communications and Technology. Electron micrographs: OARDC Molecular and Cellular Imaging Center.