NASHVILLE, Tenn. — Gene replacement may be the solution to curbing soybean cyst nematode (SCN), a roundworm that burrows into the ground and infiltrates plants to feed before the females drop off to lay eggs – then stimulated into repeating the cycle, by the next soybean planting.<br>
Dr. Melissa Goellner Mitchum with the University of Missouri-Columbia is collaborating with researchers from universities in Georgia, North Carolina and Iowa to study SCN for weaknesses in its basic makeup that can be exploited against it. She shared a bit of their research at last week’s annual Commodity Classic conference in Nashville.<br>
Mitchum said SCN can be found in 80 percent of all farmland planted to soybeans in the United States, and is consistently the leading cause of soybean losses. It’s such a debilitating disease, she said, because the worm is widely distributed, lays several hundred eggs per cyst, can produce a new generation in 30 days and fields often lack noticeable early symptoms aboveground.
“Unless you are scouting your fields … you may find it’s too late, once you find it,” she said.<br>
Once worms find hospitable ground, they and their offspring set up house for a long time. There are limited means of fighting the pest, she said, because none address the root cause of its survival: Its ability to set up a sedentary feeding cell within the soybean plant and grow without being rejected or damaged.
“If we can prevent this step from occurring, we can hopefully devise strategies for resistance,” Mitchum said, adding the worm secretes special proteins from gland cells that allow it to be recognized as a friendly feeder by the plant.<br>
Past means of killing the SCN included application of methyl bromide, which is no longer an option for growers. Current methods are to rotate beans with non-host crops – “It really likes soybeans, but it doesn’t like corn,” she pointed out – and planting genetically engineered resistant varieties.<br>
The problem, she explained, is that no current variety is resistant to all types of SCN; there will be at least one kind of worm that adapts to that seed. This might not present much of a problem the first year a particular variety is planted, but it won’t take long of growing that same variety year after year to have the same problem as a non-resistant seed; it’ll just be supporting a more elite strain of larva.<br>
“You still have SCN in your field,” Mitchum said. “You haven’t wiped them out.”<br>
So, her research team is trying to find a way to interrupt the worm’s friendly feeding by blocking how its gland cells function.
They have identified about 30 percent of the gland genes and are developing a transgenic plant that would mix in bad RNA with a worm’s feeding-cell nutrients.<br>
The hope is these RNA pieces will replace RNA that allows the worm to feed, rendering it incapable of being “friendly” to the soybean plant – and, without the feeding cell, it should die. She credited this idea to RNA Interference (RNAi) research developed long ago.
“We’re very close, and we’re on the verge of developing something for this,” Mitchum said. “(And) this kind of approach can be used for other crop cyst nematodes.”