One important consideration in dealing with SCN is the need to rotate various sources of resistance.
"The most common source of SCN resistance for varieties in Illinois comes from a line known as PI88788," said Brian Diers, soybean breeder in the Department of Crop Sciences at the University of Illinois. "Our research indicates that there is little if any yield drag associated with the major resistance gene from that source."
Diers pointed out that this resistance gene produces a significant yield increase in fields with high SCN pressure and keeps the SCN populations from increasing during the growing season.
"The yields of many resistant varieties now match those of susceptible varieties in fields without SCN," Diers said. "As a result, the planting of resistant varieties is an insurance policy that most farmers in the state should be looking at."
He noted, however, that there is a danger that Illinois growers have become too dependent on this single source of resistance.
"Among the commonly grown varieties in Illinois, about 93 percent of them have PI88788 as the sole resistance source," Diers says. "If we depend too much on this single source of resistance, we run the real risk that SCN populations in the state will overcome this resistance."
As a result, breeders are attempting to fill the need for resistance genes from new sources.
"Unfortunately, it has been difficult to combine resistance from those new sources with high yield," Diers said. "At the same time, we continue to make significant progress, and there are now high-yielding varieties that have resistance from PI 437654, which is also known as the Hartwig, or CystX, source."
He pointed out that breeders are also working with resistance from PI 468916, a wild soybean (Glycine soja) resistance source.
"We have identified new resistance genes from this source and we are now breeding them into new soybean varieties," Diers said. "We hope that bringing these new genes into high-yielding varieties will help us keep resistance ahead of the nematodes and allow profitable soybean production to continue in Illinois."
Primary support for this important breeding research is provided by the soybean checkoff through the Illinois Soybean Association.