Researchers Take Close Look at Emerging Corn Virus

January 3, 2003

WOOSTER, Ohio — Maize fine streak virus (MFSV) was first spotted three years ago in a sweet corn field in southwestern Georgia. Since then, scientists with the Ohio Agricultural Research and Development Center (OARDC) have learned enough about the disease to be prepared for its possible spread to the Corn Belt. Margaret Redinbaugh, a plant molecular biologist with OARDC and the U.S. Department of Agriculture (USDA), said the emerging corn pathogen is a rhabdovirus, genus Nucleorhabdovirus, that had not been characterized before. "We isolated the virus from fall-planted sweet corn leaves showing fine chlorotic (discolored) streaks," Redinbaugh said. "The isolated virus was bacilliform (bullet-shaped), with a knobby surface and obvious helical structure typical of rhabdovirus morphology." A number of rhabdoviruses have been found to infect maize worldwide. Of these, maize mosaic virus (MMV) and wheat American striate mosaic virus (WASMV) cause disease in North America. MMV was first reported in Hawaii and subsequently confirmed in Florida. Meanwhile, WASMV has been found in the northern plains of North America. Although maize fine streak virus was discovered in Decatur County, Georgia (near the northwest border of Florida), MFSV and MMV are serologically different. In addition, MFSV is transmitted by a leafhopper (the black-faced leafhopper, Graminella nigrifons), while MMV is spread by a planthopper (the corn planthopper, Peregrinus maidis). When leafhoppers feed on virus-infected corn, they suck the plant’s sugar-rich phloem sap where virus particles dwell. The insect then moves to other plants and, during feeding, injects the virus into the phloem of non-infected plants. "We tested different insect species but found that only the black-faced leafhopper transmits the virus," Redinbaugh explained. "This insect overwinters in the southeastern part of the country, but it travels to the Midwest and the northeastern corner of the United States." In the study, the same leafhopper also transmitted MFSV to barley, wheat, oat, giant foxtail and rye. Sorghum and Johnson grass were resistant to the virus. The black-faced leafhopper is also responsible for the spread of the maize chlorotic dwarf virus (MCDV), which stunts plants at maturity. MFSV also causes dwarfing, Redinbaugh said, which means that substantial yield reduction in infected plants is to be expected. "The insect is found in large enough numbers in Ohio that it can transmit other viruses, so there is potential for possible spread of the emerging virus," she added. "But on the other hand, we've never seen the virus before and it's only been found in fall-planted Bt sweet corn in Georgia. So whether the insect will transmit the virus to field crops remains to be seen." Researchers speculate that Georgia farmers who planted Bt sweet corn did not spray to control for insects like the fall armyworm and the corn earworm. "Because the black-faced leafhoppers don't do much damage to corn, farmers don't spray to control them," Redinbaugh said. "But any spraying done on non-Bt corn would normally keep leafhoppers out of the fields." There are no fall plantings of field corn or sweet corn in Ohio. About 20 percent of Ohio farmers grow Bt corn. Redinbaugh and colleagues have studied different corn lines to determine which are more resistant to the virus. In general, Corn Belt germplasm —especially B73 and Mo17— was easily infected. The good news is that Oh1VI, a recently released line with resistance to MCDV, had very low rates of infection by MFSV. "Lines used in the southeastern United States showed lower infection rates, especially those that have been resistant to other rhabdoviruses in the past," Redinbaugh explained. "But lines used in Midwestern states are more susceptible." However, Redinbaugh believes that the research done on MFSV will be a major factor in combating this pathogen if it moves northward. "Now we have the diagnostic tools to deal with the virus if there’s an outbreak," she said. "Our study will be useful for determining the virus’ distribution in maize and other hosts. I think we are ahead in the game." Redinbaugh is part of a joint program between OARDC and USDA scientists dedicated to tracking the emergence of corn diseases worldwide. The Wooster-based group is responsible for analyzing maize viruses from the United States and around the world. OARDC is the research arm of Ohio State University’s College of Food, Agricultural, and Environmental Sciences.

Mauricio Espinoza
Margaret Redinbaugh