New corn viruses raise their ugly heads

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COLUMBUS – Ohio State researchers have discovered two new corn viruses, one which remains to be identified.

Researchers at Ohio Agricultural Research and Development Center and the U.S. Department of Agriculture have isolated, identified and characterized a virus known as maize necrotic streak virus. The name comes from the symptoms the virus incites. Although there have been no recorded outbreaks of the disease in Ohio, researchers are taking preventive measures to ensure farmers are aware of its potential threat.

“We want farmers to know that this virus exists, and we are working to make sure that it is never a problem with crops,” says 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.

It is estimated that crop losses from maize viruses range between 5 percent and 15 percent annually in the United States. Diseases are responsible for reduction in yield, as well as affecting grain and seed quality. Maize necrotic streak virus was discovered after 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 United States.

Further analysis revealed the new virus, characterized by pale green, yellow, or cream-colored streaks on the leaves, eventually become translucent and necrotic around the edges. In some respects, the virus still remains a mystery. It falls into a family of viruses that infect tomatoes and peppers, not grain crops, Redinbaugh says. In 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,” Redinbaugh said. “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 by 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.

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. The difficulty in transmission might be what keeps the virus at bay, Redinbaugh says.

“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 says 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. Molecular markers are currently being developed in the hope that resistant Ohio corn lines may be identified.

Researchers also have discovered a second corn virus, which has yet to be identified. First discovered in Georgia, the unknown 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, Redinbaugh says.

Insects – namely planthoppers and leafhoppers – easily transmit those diseases. Studies have yet to determine if an insect like the planthopper transmits the unknown virus, but Redinbaugh believes the virus may not be a likely Ohio invader because the insect appears to be isolated in the southern U.S. research on the unknown virus is ongoing.

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