Inside Iowa State
June 30, 2000
Planting the seeds of virus-resistant soybeans
by Brian Meyer
In July, plant-disease experts from the north-central
states will sit around a table in Agronomy Hall to mull a new
disease in their region's soybean fields.
It could be a somber meeting.
Bean pod mottle virus is a disease that has scuttled northward from fields in the South. It's vectored by bean leaf beetles, which have greatly multiplied, thanks in part to the Midwest's less-than-bone-chilling winters the past few years.
In conjunction with other viral diseases, bean pod mottle virus cuts yield and produces lousy grain quality. That means fewer profits for farmers. So far little is known about the growing menace and how to manage it.
John Hill will be present at the July meeting and may offer a ray of hope.
The ISU plant pathologist and his research team have spent years studying the molecular identity of soybean mosaic virus, a disease found wherever soybeans are grown. Armed with that knowledge, they cloned a gene from the virus and, using biotechnology techniques, inserted the gene into soybeans. No small feat, since soybeans are a notoriously difficult crop to transform.
The strategy resulted in plants that fend off the disease. Hill has evaluated the transgenic beans in labs and greenhouses and found the plants effectively resisted several strains of soybean mosaic virus.
Last summer, in a collaboration with ISU colleague Forrest Nutter, the plants were grown in field plots for the first time. The researchers still are analyzing data from tens of thousands of leaf samples from the trials, but preliminary results look "very good," Hill said.
"To our knowledge, this is the first successful test of genetically engineered disease resistance in soybeans," he said.
"Our work on soybean mosaic virus has really helped us understand the interactions between a virus and a soybean plant. That understanding can spin off to similar approaches for diseases like bean pod mottle virus. We'll be able to move faster."
In the field, it's hard to tell the difference between infection from soybean mosaic virus and bean pod mottle virus. Both crinkle the leaves. Both have the potential to devastate yield. Both discolor the grain. Some severely infected seeds look scorched, as if someone mistook them for popcorn and threw them in a popper. Last fall, elevators docked farmers up to 17 cents per bushel for virus-mottled grain, according to the Iowa Soybean Association.
This summer Hill and Nutter are repeating field trials of the transgenic soybeans to harvest more evidence of their potential. But don't ask Hill how exactly the soybeans become resistant.
"The exact mechanism hasn't been tied down yet," he said. "To cause infection, the virus has to shed its coat protein. One theory is the gene we've inserted somehow messes up that uncoating process. But that's tough to prove."
In the future, Hill thinks the best disease protection may come by combining virus resistance that occurs naturally in soybeans with resistance that's genetically engineered. He said researchers elsewhere are studying the stacking of these two traits in rice.
When it comes to plant viruses, Hill is a respected source. He chairs a U.S. Department of Agriculture committee that keeps vigil on the status of plant viruses around the country. Last year he was named a fellow of the American Association for the Advancement of Science. And he is the only fellow of the American Phytopathological Society in the state of Iowa.
Much needs to be learned about the new threat from bean pod mottle virus. Hill and ISU entomologists Larry Pedigo and Marlin Rice are cooperating on studies to answer some basic questions.
"Right now my centrifuge is purifying the virus so we can work on developing a rapid method to detect the disease," Hill said. "We also want to know exactly where the disease is coming from -- if it's overwintering in bean leaf beetles and whether it can be transmitted by seed. We also want to know if legumes other than soybeans serve as hosts for the virus."
"Above all, we want to discover any information that would lead to management strategies for farmers," he added.
That link to real-world agriculture is important to Hill.
"With our work with mosaic virus, we've bridged the gap between molecular biology and practical applications in the field," Hill said. "Some research in molecular biology may be very interesting in itself, but the important thing is to take it to the furrow and help the farmer."
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