By Greg Tylka
The soybean cyst nematode (SCN) is estimated to be present in at least 70 percent of Iowa fields. Growing SCN-resistant soybean varieties is critical to maintaining profitable soybean production in these fields.
Each year, ISU compiles information on the SCN-resistant soybean varieties available to grow in Iowa. The updated list is available as ISU Extension publication CROP1649. Collection and publication of this information is supported by soybean checkoff funds provided by the Iowa Soybean Association.
Over 900 resistant varieties available, more with Peking resistance than ever
The publication contains information on 920 SCN-resistant soybean varieties among maturity groups 0, 1, 2, and 3. This is 54 more varieties than last year and a near-record high number (figure 1). The varieties are from 33 brands offered by 25 companies.
In the early 1990s all SCN-resistant soybean varieties available in Iowa had SCN resistance from a breeding line named PI 88788, and this breeding line was used almost exclusively for 30 years (figure 2). Growing varieties with PI 88788 SCN resistance for decades caused SCN populations to develop high levels of reproduction on the varieties, leading to significantly reduced soybean yields.
Soybean varieties with SCN resistance from the breeding line named Peking have become available in recent years. Research results reveal these varieties can yield 20 bushels per acre more than varieties with PI 88788 resistance in fields with SCN populations having high reproduction on PI 88788 resistance.
Have we “turned the corner”?
There has been an increase in the number of varieties with Peking SCN resistance since 2021 (see figure 2). The updated list includes 200 varieties with SCN-resistance from Peking, which is more than twice the number that was available last year.
Peking has been the only source of resistance other than PI 88788 available in commercial soybean varieties since 2013 except for two varieties in 2020-2021 that had SCN resistance from PI 89772.
There are 30 brands with at least one variety having Peking SCN resistance listed in CROP1649 this year. It is especially notable that currently there are 32 varieties with Peking SCN resistance available in maturity group 3; last year there were only 8 such varieties. Also, Champion Seeds has five offerings that are blends of varieties with PI 88788 and with Peking SCN resistance. Farmers now have many choices of varieties with Peking SCN resistance from many brands.
The varieties listed in CROP1649 are organized by maturity group. The genetic source of SCN resistance, herbicide resistance or tolerance, relative maturity score, and iron deficiency chlorosis tolerance rating of each variety in the publication is provided. Also, numerous varieties listed have no herbicide resistance/tolerance.
Avoid too much of a good thing
Soybeans with Peking SCN resistance likely will produce much higher yields in SCN-infested fields relative to varieties with PI 88788 resistance. And it may be enticing to grow varieties with Peking SCN resistance every time soybeans are grown in SCN-infested fields. However, doing this is strongly discouraged.
Prolonged use of Peking SCN resistance will result in SCN populations developing high levels of reproduction on Peking resistance genetics, possibly quicker than what occurred with PI 88788 resistance. A long-term and economically sustainable approach to maintaining high soybean yields in SCN-infested fields is to alternate growing varieties with Peking SCN resistance and PI 88788 resistance.
The ISU SCN-resistant soybean variety evaluation program, funded by the soybean checkoff through the Iowa Soybean Association, evaluates nearly 200 varieties in experiments conducted across Iowa each year. See ISU Extension publication IPM52 for results from last year’s evaluations.
SCN-resistant varieties missing from the publication?
If you are aware of SCN-resistant soybean varieties in maturity groups 0-3 for use in Iowa that are not in the updated CROP1649 publication, contact Greg Tylka at 515-294-3021 or gltylka@iastate.edu to specify the seed brands that could be added to next year’s publication.
No endorsement is intended of varieties included in the list nor is criticism implied of varieties not listed.
Source : iastate.edu