Plants with resistance to soybean cyst nematode (SCN) shouldn’t allow more than 10% of the nematode population to survive—but in many states they are. PI 88788, the most common form of SCN resistance, is failing at alarming rates and researchers are scrambling to find the next solution for farmers. “In the most recent survey, 100% of the SCN populations we tested in Missouri had elevated reproduction on PI 88788,” says Melissa Mitchum, nematologist in the division of plant sciences at the University of Missouri. “In fact, a majority of Missouri SCN populations are capable of reproducing 50% or more on PI 88788.” Fortunately, researchers have identified new resistance genes. Brian Diers, plant breeder at the University of Illinois, found two new resistance genes from wild soybean varieties. These are being bred into commercial varieties for testing, where they’ve proven to be highly effective.
“We found that by combining genes from different resistance sources we could obtain much higher levels of resistance compared to using one source,” Diers says. He’s created a four-gene stack to control the pest. In addition to Illinois, Missouri researchers are testing the new gene combination in greenhouse trials. Mitchum says they’re exploring different rotations. “When we took the four-gene stack and rotated that with the Peking source of resistance, we were able to slow down SCN reproduction of populations adapted to PI 88788 over generations,” Mitchum adds. Next steps for this four-gene discovery is to get it into today’s genetics. It won’t be difficult for commercial breeding companies to integrate the stack into their lineup because the base germplasm is PI 88788—the oldest and most common form of SCN resistance on the market today, according to researchers. Don’t worry about yield drag, Diers says—they’ve tested for it and found it doesn’t exist. In fact, there is often a yield advantage in fields with high SCN populations.