Coming: Best SCN resistance ever

The decades-old battle between soybean growers and the soybean cyst nematode (SCN) has been pretty much an advance-and-retreat situation: As breeders developed a variety with resistance to one or more races of the microscopic worm, growers planted them extensively, whereupon the nematodes selected for resistance and in a few years the variety's effectiveness was lost.

Nearly 30 years ago, the Pickett soybean came on the scene, giving growers SCN control they'd not been able to achieve previously. Taking advantage of a good thing, it was planted widely year after year and its resistance was lost.

Then along came Bedford. Same scenario: Good SCN control, widely planted year after year, resistance lost. More varieties followed, but over time the SCN resistance they offered was diminished by continuous planting.

Now what is being described as perhaps the best weapon ever against SCN is being introduced in new varieties. Where previous SCN varietal resistance was a .22 rifle bullet, the new CystX resistance is an A-bomb. It offers complete genetic resistance to all known races of SCN. And while it has thus far been mostly in Midwest varieties, you'll be seeing it in more and more southern varieties as breeders incorporate it into their gene pool.

CystX is patented and owned by the Purdue University Research Foundation, and was developed in cooperation with the Indiana Crop Improvement Association. The trademark is owned by Access Plant Technology, Inc.

The technology was achieved through traditional plant breeding methods, and thus carries no potential GMO stigma. Interestingly, for Mid-South growers, some of the genetic source material for CystX traces back to the work of the late Dr. E. E. Hartwig, pioneer soybean breeder at Stoneville, Miss., whose varieties blanketed much of the southern landscape for decades.

“CystX is absolutely the best source of SCN resistance in the U.S. that will also produce high soybean yields,” says James Thomas, soybean breeder for Hornbeck Seed Co., Inc., at Dewitt, Ark. “More and more growers are getting hammered by SCN as they're seeing selection for races that may not have affected them significantly in the past.

“They've all been planting basically the same resistance, which encourages selection for new races and then the loss of resistance.”

He told growers attending his company's field days that soybean breeders “really excited” about the potential for varieties incorporating CystX. “Compared to varieties available only two years ago, these will offer excellent resistance to any SCN race in the grower's fields — and they will also offer increased yield potential.”

Thomas says Hornbeck will be introducing one or two varieties next year that include CystX resistance. Other companies are also developing varieties to take advantage of the broad scale SCN resistance. CystX will be available in both conventional and Roundup Ready varieties.

“There may be limited availability next year, depending on how much seed companies were able to produce this season, but in 2003 CystX varieties should be widely available.”

Its developers say CystX “has redefined SCN resistance as zero — soybean cyst nematodes cannot establish themselves or reproduce on CystX roots. This means complete resistance.” In a university study, a CystX variety planted on the same field over three years reduced the SCN egg count by 87 percent.

While CystX has the potential to breathe new life into soybean production, Thomas says growers should still use it wisely and take steps to protect the resistance it offers.

“I would suggest using it in a rotation program to knock down the SCN populations; then come back in with other resistant lines. Where possible, alternate with non-host crops such as corn, cotton, and rice to reduce the populations even more. A good plan might be two years of a CystX variety, then rotate to another variety or non-host crop.

“This is the best thing growers have had for SCN — ever,” Thomas says. “If you see the CystX label on a seed bag, you've got some gold in your hands.”

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