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Corn+Soybean Digest

Want Yield With That?

It's plain horse pucky that growers can't find SCN-resistant soybean varieties that are also good yielders.

“Many farmers have been convinced that cyst-resistant varieties are just so inferior that they aren't going to make up the difference even if they have cyst nematodes,” says Jim Orf, a University of Minnesota soybean breeder. “That flat out isn't so.”

In fact, late Group II-Group IV SCN-resistant varieties can give other beans a run for their money.

Doubt it? Consider this. In Purdue University's 2000 yield trials, a cyst-resistant, Roundup Ready variety topped all varieties in the Group III category. It was Dairyland Seed's DSR-395, yielding 84.1 bu/acre.

Another resistant entry, DSR-363/RR, hit 75.6 bu. If you do your homework, you can find high yielders in mid-Group IIs and even in Group Is, insist soybean breeders and nematologists.

Not every seed company or public breeding program can match those trial-topping performances. But many companies have a number of SCN-resistant varieties that will yield well — within about 5% of the top susceptible varieties on ground not infested with cyst nematodes.

“There are high-yielding SCN-resistant varieties out there if you really look for them using the data from many sources,” says Orf. He's even released a Group 0 that comes within 5% or less of the top-yielding susceptible varieties in that same maturity group.

Ellsworth Christmas, Purdue University soybean specialist, echoes Orf's comments: “Admittedly, you'll have to search for them — and they aren't going to be easy to find in the earlier maturities — but there are top-yielding cyst-resistant varieties out there. They're available in multiple maturity groups, too, not just in one or two.”

Greg Tylka, Iowa State University nematologist, hesitates to even mention yield lag with cyst-resistant varieties. “I don't think there is much of a lag and certainly not in a field that has cyst nematodes.

“In fact,” adds Tylka, “if a field has cyst nematodes, I believe 99 times out of 100 a grower is going to make more money by growing a good-yielding resistant variety. It's just that simple.”

Jim Smolik, South Dakota State University nematologist, seconds that observation. “I get a little concerned when I hear about this yield lag or drag,” he says. “A 5% yield lag is nothing compared to what's going to happen if you put a susceptible variety in an SCN-infested field with a fair cyst population. You're not talking a 5% yield hit then, but much higher, even 20% or more.”

What do seed company soybean breeders say about the yields of their SCN-resistant varieties?

On average, they maintain that from late maturing through the mid-Group II maturities, yield lag simply isn't a problem if you do your homework. However, they do admit that, on average, there's still a small yield lag in the earlier maturities — generally in the 5% range.

“I would say that, in the late Group IIs and IIIs, breeders have, on average, gotten back yield parity. But in the earlier maturities, it's still a struggle,” says Alan Walker, Monsanto's soybean breeding program director for Asgrow, Dekalb and Hartz varieties. Where cyst infestations are present, however, there's no contest, he says.

Monsanto's top-selling variety for northwestern Iowa in 2001 was a cyst-resistant Group II variety.

Hunt Wiley, a Dairyland Seed soybean breeder and research director, lets university yield trials speak for at least the company's Group III varieties.

“We have, however, two SCN-resistant Group II varieties that are excellent yielders and would definitely fall within that 95% yield level of non-cyst varieties,” Wiley notes. “We have some very strong lines in terms of yield in Group I, but they are not Roundup Ready.

“I'd agree that it's harder for us to close the yield gap the farther we go north in the early maturity groups. But we are slowly catching up to the high-yielding, non-cyst types in those maturities.”

John Soper, soybean researcher at Pioneer Hi-Bred International, Inc., concurs with his industry colleagues. “In the earlier-maturity groups, under non-cyst conditions using cyst-resistant varieties, there is about a 5% yield disadvantage. But under even moderate-level cyst infestations, there's a definite yield advantage with the resistant varieties.”

Of course there are exceptions to every rule, and some farmers may have tried cyst-resistant varieties that were yield busts, admit these experts.

Either way, ensuring that you have tested for SCN is the key. And if SCN is not present, no resistant variety is necessary and growers won't have to worry about possible yield lag.

Walker, however, seems to echo the good-news judgment of most soybean breeders. “With the breeding materials on the drawing boards of private and public breeders, in the not-too-distant future we'll have cyst-resistant varieties that will yield virtually equal with high-yielding susceptible varieties — even on non-infested ground. And non-infested ground is becoming much more uncommon all the time.”

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