First Soybeans With Complete Nematode Resistance Developed

A consortium of six agricultural seed companies has announced that it will be the first to sell soybean varieties that offer high yield and complete resistance to all known types of soybean cyst nematodes. The first soybeans have been planted to obtain seed, and the resistant soybeans will be available to farmers this fall for the 2001 planting season.

The new varieties are bred from a special soybean line called CystX, which was developed by researchers from Purdue and from the Indiana Crop Improvement Association. CystX is a licensed and patent-protected soybean line that crop breeders can cross with elite, modern soybean varieties to develop nematode-resistant soybeans. The research was funded in part by the Indiana Soybean Board.

Clyde Sylvester of Sylvester Ranch Inc. in Ottawa, Kan. (one of the member companies of the Midland Genetic Group consortium) says the parent variety of CystX soybeans will be available for the next planting season. Improved varieties will be available for the 2002 season. "We'll have several new varieties using this technology coming out as the years click by," he says.

Nationwide, annual losses from soybean cyst nematode infestations are estimated to be almost $270 million; losses in Indiana are an estimated $30 million to $50 million annually.

Soybean cyst nematode, known as SCN, is a microscopic roundworm that infests the roots of soybeans, forming cysts that contain up to 500 eggs and the juvenile worms. The worms feed on the roots of the soybeans. A field of soybeans can be infected by up to three generations of the nematodes during one growing season and can lose up to 40 percent of its yield.

Before the CystX lines, only one soybean variety was known to be completely resistant to the nematodes, according to Richard Vierling, director of the Indiana Crop Improvement Genetics Laboratory and adjunct professor of agronomy at Purdue. But that variety, Hartwig, is a poor performer and isn't planted by soybean producers. "Purdue researchers were able to separate the SCN resistance genes from the genes that caused poor agronomic performance," Vierling says.

Virginia Ferris, professor of entomology, says that Hartwig is a wild-type soybean variety that does not cross well with modern domesticated soybeans. "The SCN resistance gene is so close on the chromosome to a pairing control gene, which prevents some genes from being moved out of the variety, that formerly you couldn't successfully breed the trait into high-yielding lines of soybeans," she says.

By using genetic markers, the scientists were able to breed plants that contained the resistance gene from Hartwig combined with pairing genes from the domesticated soybeans. The CystX line of soybeans was then crossed with other lines through standard breeding practices.

"Strictly speaking, this isn't old-fashioned plant breeding because we used molecular markers to find the progeny plant line that had the resistance," Ferris says. "But the breeding itself is just regular breeding, and this isn't a genetically modified line of soybeans."

Vierling says that CystX is not a transgenic product, and the first varieties of SCN-resistant soybeans are not considered genetically modified. "Through the use of highly virulent in-bred nematodes and unique screening procedures, we were able to separate resistance genes from genes that had a deleterious effect," he says.

Although Vierling foresees widespread adoption of the technology by soybean breeders, he says this will not cause a dangerous narrowing of the crop's genetic base. "It's just a handful of genes that we're dealing with here, out of hundreds of thousands of genes in each soybean variety. This will not affect genetic diversity."

Dennis Brown of Brown Seed Enterprises in Neoga, Ill., is the project coordinator for Midland Genetics. He says his company was first because it believed in the technology when other companies were skeptical. "There were a lot of preconceived ideas about Hartwig, and because this product is derived from that, other companies didn't work with it as aggressively as we did," he says. "We're all farmers, and we've seen what SCN can do to soybean fields, so there's an emotional response in dealing with the problem. We were willing to look at anything that would give resistance to this."

Brown says that although other soybean varieties offer resistance to certain types of soybean cyst nematodes, their resistance isn't what it was when the products were introduced. "We're seeing levels of resistance break down and seeing more cysts on the roots all the time," he says.

With current SCN-resistant varieties of soybeans, farmers must try to match the crop variety to the particular race of nematodes in their fields. That chore is eliminated with the CystX soybeans. Jamal Faghihi, research nematologist in Purdue's Department of Entomology, and the late John Ferris, professor of entomology and husband of Virginia Ferris, tested the CystX soybeans on 150 populations of nematodes, including several highly virulent races created in Ferris's laboratory. "We've never found any population that can overcome it," says Virginia Ferris.