Report shows need for diversity in soybean cyst nematode resistant varieties

A report analyzing nearly 20 years of field data collected by Iowa State University on soybean cyst nematodes shows the tiny, parasitic roundworm has continued to adapt to the industry’s most popular resistant variety. 

The analysis looked at PI 88788, a type of soybean cyst nematode resistance in seed varieties, and found the ability for the nematodes to reproduce on PI 88788 soybeans increased approximately 2%, annually, from 2001 through 2023. 

If the trend continues, varieties with PI 88788 resistance would have just 40% control of soybean cyst nematode by 2030. This could lead to an average yield loss of approximately 9 bushels per acre, according to the study. 

Annually, soybean cyst nematodes cause more than $1 billion in U.S. crop losses, and continue to spread across North America. 

Greg Tylka, ISU nematologist and co-author of the study, said if farmers don’t diversify how they manage the pest, they can “expect that trend to continue.” 

Soybean cyst nematodes live in the soil and have been present in every Iowa county since 2017. Soybean fields infected with soybean cyst nematodes often look healthy, but the parasitic nematodes will limit the plant’s ability to absorb nutrients and produce beans as it feeds on the roots. It can also make crop diseases like sudden death syndrome worse, by causing additional stress to the plants.

Farmers typically manage soybean cyst nematodes by rotating fields with a non-soybean crop, usually corn, in the field and planting soybean cyst nematode resistant varieties when they plant beans. 

According to the study, the majority of soybean seed varieties are marketed as resistant to soybean cyst nematodes, but these varieties mostly “possess resistance genes from the PI 88788 breeding line” meaning there is a “lack of genetic diversity” in SCN resistant varieties. 

Peking is the other genetic resistance used in soybean cyst nematode resistant seeds, and while not as common as PI 88788, its use in seed varieties is increasing, according to the SCN Coalition. 

Tylka, however, said it’s important that the agriculture industry doesn’t fully shift to Peking varieties or the same issue of increased virulence to the variety will occur. 

“We cannot afford to repeat the mistakes made with PI 88788,” Tylka said in a news release about the study. “Another wholesale shift to a single resistance source, like Peking, is likely to accelerate adaptation by SCN populations. The goal is long-term management that preserves the effectiveness of all available resistance sources.”

The study recommends farmers alternate between PI 88788 and Peking varieties, in addition to crop rotation, to prolong the effectiveness of the Peking resistance. 

“Soybean cyst nematode will continue to be a major management challenge for soybean farmers across Iowa and the rest of the Midwest United States,” researchers concluded in the study. “Although the results and trends reported herein were from Iowa, we believe they are broadly applicable throughout most, if not all, of the soybean-producing areas of the midwestern United States and Canada.”