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Ohioline

The
Ohio State
University

November 21, 2000

Two New Corn Viruses Discovered

By Candace Pollock
(330) 202-3550

Source: Peg Redinbaugh
(330) 263-3965
redinbaugh.2@osu.edu

WOOSTER, OH - Ohio State University researchers have discovered two new corn viruses, one of which remains to be identified.

Researchers at Ohio Agricultural Research and Development Center and the USDA have isolated, identified and characterized a virus known as maize necrotic streak virus, based on the symptoms it incites. The findings were published in the October issue of Plant Disease.

Although there have been no recorded reports of the disease and it may not pose a problem for Ohio corn growers, the researchers are taking preventive measures to ensure farmers are well educated.

"We want farmers to know that this virus exists and we are working to make sure that it is never a problem with crops," said Peg Redinbaugh, research plant molecular biologist. Redinbaugh is part of a joint program between OARDC and USDA scientists dedicated to tracking the emergence of corn diseases worldwide. The group, based at OARDC, is responsible for analyzing maize viruses throughout the United States and around the world.

It is estimated that crop losses from maize viruses range between 5-15 percent annually in the U.S. Diseases are responsible for reduction in yield, as well as affecting grain and seed quality.

Maize necrotic streak virus was discovered after the researchers analyzed corn crops from Arizona suspected of being infected with maize dwarf mosaic virus, a disease that has caused severe crop losses throughout the U.S. Further analysis revealed the new virus, characterized by pale green, yellow, or cream-colored streaks on the leaves, which eventually become translucent and necrotic around the edges.

But in some respects, the virus still remains a mystery. It falls into a family of viruses that infect tomatoes and peppers, not grain crops, said Redinbaugh. In the 18 months of studying the virus, researchers have yet to nail down specific vectors of transmission.

"Diseases don't get from plant to plant without some sort of help, whether it be an insect, nematode, or fungus," said Redinbaugh. "Using three different techniques we've only been able to transmit the virus through the soil. And we don't know what's in the soil that transmits the virus."Most plant diseases are transmitted via an insect. The researchers used several common crop insects, such as the corn root aphid, green peach aphid, potato aphid, oat bird cherry aphid, corn leafhopper, black-faced leafhopper, corn planthopper and western rootworm to spread the disease from one plant sample to another. But none of the insects proved to be a vector of transmission. The researchers also attempted to transmit the virus by rubbing healthy leaves with the disease, without success.

Redinbaugh said that the difficulty in transmission might be what keeps the virus at bay. "It may not be a big problem if it's not easily transmitted in nature," she said. "If the virus primarily is transmitted through the soil, like we think, then it could be just a local problem."

Redinbaugh said the researchers have found one corn line that is resistant to maize necrotic streak virus, but the tropical line is not well adapted to Ohio soil. She said molecular markers are currently being developed in the hopes that resistant Ohio corn lines may be identified.

Researchers have also discovered a second corn virus, which has yet to be identified. First discovered in Georgia, Redinbaugh said the virus has similar symptoms to several corn diseases including maize mosaic virus, maize chlorotic dwarf mosaic virus and maize rayado fino, so it can be easily misdiagnosed. Insects, namely planthoppers and leafhoppers, easily transmit those diseases.

"The Georgia unknown could be a problem if it's transmitted by insects, like the other viruses are," said Redinbaugh. Studies have yet to determine if an insect like the planthopper transmits the unknown virus, but Redinbaugh determines that the virus may not be a likely Ohio invader due to the insect's restricted southern U.S. geographical area. Studies on the "Georgia unknown" are ongoing.

Other researchers involved in the studies include OARDC researchers Ray Louie, Don Gordon, Dave Fulton, Bill Styer and Saskia Hogenhout and USDA OSU-based researchers John Abt, Robert Anderson and Kristen Willie.