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Research Highlights
Soybean Cyst Nematode-Resistant Varieties Deliver Millions in Value

Soybean cyst nematode (SCN) is one of the most common, detrimental pests in soybeans. Each female, the round cream-colored objects on these soybean roots, contains hundreds of eggs. Photo: Iowa State University

By Laura Temple

Soybean farmers rely on varietal resistance to manage soybean cyst nematode (SCN), one of the most common, detrimental pests to the crop. When effective, SCN-resistant varieties can produce profitable yields and slow the buildup of nematode numbers in the soil. However, individual commercial varieties provide differing levels of SCN resistance. Research data helps farmers choose SCN-resistant varieties that best fit their needs.

Iowa State University runs the largest, most intensive, and longest-running SCN-resistant soybean variety evaluations in the country, according to Greg Tylka, a professor at Iowa State University (ISU) and the director of the Iowa Soybean Research Center. These trials evaluate hundreds of commercial soybean varieties each year. The work is funded by the Iowa Soybean Association. 

“These variety trials started in the early 1990s, and they currently include field experiments in nine locations throughout Iowa,” Tylka explains. “Every year, we publish the data from these trials to help farmers select soybean varieties that have strong SCN resistance. I’ve always been curious to know the monetary value of this information for farmers.”

The Iowa State University SCN-resistant Soybean Variety Trial Program tests soybean varieties for yield and SCN resistance in nine locations around Iowa each year. Photo: Iowa State University

Return on SCN Investments

Former ISU Ph.D. student Seungki Lee, now an assistant professor of agricultural economics at The Ohio State University, and his advisor GianCarlo Moschini, ISU distinguished professor of agricultural economics, conducted a study to assess the economic value of the SCN-resistant variety trial information to farmers. The research was published in the January 2022 American Journal of Agricultural Economics.

“The ag economists compared yield and SCN control data from several years of our variety trials with a dataset they acquired of seed purchase prices and quantities of seed sold,” Tylka says. “Their economic analyses estimated the value of growing soybeans with strong SCN resistance.”

The economic study matched seed sales information from 2011 to 2016 for farmers throughout Iowa and the northern third of Illinois, where ISU’s SCN-resistant variety trial results were distributed, with yield and SCN resistance scores for the same years. The economists conducted several analyses based on different sets of assumptions. Results of the most conservative data analysis found planting soybean varieties that ranked in the top half of the ISU variety trials in both yield and SCN suppression increased economic welfare for farmers by up to $205.5 million. 

“The results of their analyses using less conservative methods and assumptions had much greater dollar value estimates,” Tylka adds. “Their analysis illustrates the money to be made by selecting effective SCN-resistant varieties.”

The analysis also showed that farmers were willing to pay more for SCN-resistant soybean varieties. Seed sales data showed they would pay $2.69 per acre for seed of any SCN-resistant varieties, and up to $9.62 per acre for seed of soybean varieties ranked in the top half of ISU SCN-resistant trials for yield and SCN resistance. The more than $205 million surplus with these varieties demonstrates a strong return on those seed investments.

Soil samples are collected from each plot at planting and at harvest in the SCN-resistant Variety Trials conducted by Iowa State University. SCN egg counts in the soil samples reveal SCN population densities throughout the growing season. Photo: Iowa State University

Selecting Both SCN Resistance and Yield

When evaluating variety trials, yield attracts the most attention. However, that isn’t the only data Tylka recommends paying attention to when selecting soybean varieties for effective, long-term SCN management. The primary SCN resistance gene used in 95 percent of resistant varieties suppresses SCN reproduction and leads to lower SCN population densities at the end of the season. This gene occurs in different “doses,” or number of copies, among the hundreds of SCN-resistant varieties.

“Our team takes soil samples from each variety trial plot at the beginning and end of the growing season,” he explains. “We count SCN eggs to determine the levels of SCN in each plot and monitor how egg numbers change during the growing season. This data is included in our report.”

He encourages farmers to consider changes in SCN population densities as they choose varieties because lower SCN egg numbers in the soil mean less potential yield loss from SCN that season and in the future. Results from his trials list the SCN reproductive factor (RF), which indicates the season-long change in SCN numbers, next to the yield data for every variety evaluated. 

To learn more about detecting and managing SCN populations in their fields, farmers throughout the U.S. can access state-specific information, including soil testing options, from The SCN Coalition

“The economic analysis found the most value in soybean varieties with both high yields and strong SCN resistance,” Tylka says. “Soybean farmers will get real value from understanding their SCN pressure and planting soybeans that can withstand that pressure.”

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.