Germplasm offers genetic resistance

Purdue University scientists recently hit a home run in the genetic resistance battle against soybean cyst nematode (SCN).

It's called CystX. This new germplasm contains the strongest-ever genetic SCN resistance of Hartwig variety, and makes it easy for breeders to transfer that resistance into much better high- yielding varieties for Northern and Southern growers.

The process is already going on, and Midland Genetics Group, with member companies in Illinois, Iowa and Kansas, will be the first to offer this new resistance source in Northern varieties on a limited basis late this year. Many other companies will follow soon.

Until now, there have been only three sources of SCN resistance available in commercial varieties. But in the Northern soybean growing area, about 95% have used the Fayette resistance, a good source but not as total in its protection as the Hartwig source. The problem with Hartwig is it hasn't offered agronomic characteristics that work well for the Corn Belt.

That will all change - and likely very quickly with the introduction of the CystX germplasm, which has been offered to all public and private-company breeders under a licensing agreement with Access Plant Technology, Inc.

"The really nice thing about this line that we found, which subsequently became the CystX germplasm after we had taken it through many generations to purify it, is that it crosses very easily with all of the elite varieties that breeders have," says Virginia Ferris, Purdue nematologist. "Hartwig was very difficult to cross."

That means even those growers in Minnesota and Wisconsin raising Group 0, I and II varieties will be able to utilize the Hartwig-based resistance.

The research milestone that led to unlocking the resistance potential of the Hartwig source didn't come easily or quickly. It took about eight years of very careful, painstaking phenotypic screening using molecular markers to find a single line they called the "zero cyst phenotype." That means absolutely no cysts developed on this line, and it displayed the agronomic characteristics the researchers were seeking, refined through back crossing.

The soybean nematode research team at Purdue, besides Ferris, included her late husband, nematologist John Ferris, nematologist Jamal Faghihi and molecular geneticist Rick Vierling.

To confirm that CystX would offer virtually total resistance to SCN, Faghihi subjected it to more than 150 SCN populations, including his own highly virulent inbred nematodes.

"Since day one I've subjected it to every field population of SCN I could find, and not a single population has been able to overcome CystX resistance," he notes.

"One thing we emphasize all the time, however," adds the scientist, "is that we are not considering this a cure for SCN. It's just another tool - but a very, very good one."

The CystX milestone resulted from a collaborative effort of Purdue University, the Indiana Crop Improvement Association and the Indiana Soybean Board, which paid for a lot of the research with grower checkoff funds.