How to pick SCN-resistant varieties
Soybean varieties resistant to soybean cyst nematode, or SCN, are tremendously effective management tools. These resistant varieties produce greater yields and result in lower SCN numbers at the end of the growing season than nonresistant (susceptible) varieties.
Thanks to the hard work of plant pathologists and soybean breeders, there are literally hundreds of SCN-resistant soybean varieties for growers to choose from. That can be overwhelming. How do you choose a good SCN-resistant soybean variety to plant? Iowa State University Extension plant pathologist and nematode specialist Greg Tylka has some guidelines.
There is some debate about how to select the best variety, says Tylka. Do you need to consider SCN reproduction data from the field as well as yield data? To select high-yielding SCN-resistant soybean varieties that keep SCN numbers in check, he says to look for:
• data from as many different reliable sources as possible, including university variety trials and company-sponsored strip trials
• data from experiments that measured SCN reproduction on the soybean varieties in the field, as well as yield (High-yielding varieties don’t necessarily control SCN numbers the best.)
• SCN-resistant varieties that yielded consistently well in numerous SCN-infested fields (Yield data from noninfested fields are not useful.)
• SCN-resistant varieties that kept SCN population densities from increasing or that decreased numbers during the growing season
• consistently high-yielding SCN-resistant varieties with resistance from various sources, such as PI 88788, Peking, Hartwig, etc.
“There’s no way to ensure that you select the absolute best SCN-resistant soybean variety for your fields,” he sums up. “But using these recommendations should help you select SCN-resistant varieties that allow soybeans to be grown profitably for many years to come.”
Why resistance differs
If SCN-resistant bean varieties are grown repeatedly, SCN populations can build up over time with increased ability to reproduce on resistant varieties, says Tylka. This is especially a concern because almost all the SCN-resistant varieties on the market today have SCN-resistance genes from the same soybean breeding line, called PI 88788.
There are three different types or sources of resistance used to develop the
SCN-resistant bean varieties available in the Midwest. These sources of resistance are Peking, PI 88788 and PI 437654. The PI 437654 source sometimes is referred to as Hartwig and a version of this resistance is the branded CystX resistance. Each source of SCN resistance has several genes that provide resistance to the nematode. Not all of the resistance genes from a source need to be in a soybean variety for the variety to be resistant to SCN. So soybean varieties with the same source of resistance will not necessarily have the same level of resistance to SCN.
Resistance to SCN isn’t 100% effective; a few SCN females will develop on roots of resistant varieties. Exactly how many SCN females develop depends on the resistance genes in the soybean variety and also on the genetic makeup of the SCN population in the field.
One way to avoid SCN populations developing the ability to reproduce on SCN-resistant soybean varieties is to grow varieties with different sources of resistance in different years. If it isn’t possible to get seed of an SCN-resistant variety with a source of resistance different from what had been previously used, rotate among different SCN-resistant varieties with the same source of resistance.
It is no longer uncommon for SCN populations to have greater than 10% reproduction on PI 88788. But SCN-resistant soybean varieties with PI 88788 as the source of resistance continue to yield greater than susceptible varieties and also continue to prevent increases in SCN population densities throughout the growing season. “So growing resistant varieties is still an effective SCN management strategy,” says Tylka.
Source: ISU Extension
This article published in the February, 2010 edition of DAKOTA FARMER.