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Research Highlights
Uncovering Hidden Sources of Soybean Cyst Nematode Resistance

In this article, you’ll find details on:

  • Soybeans contain thousands of “hidden,” or inactive, genes that could address challenges like additional sources of soybean cyst nematode resistance.
  • Innovative University of Tennessee research uncovered seven promising new genes carrying SCN resistance that don’t impact soybean growth, yield or quality.

Tennessee soybean field infested with soybean cyst nematode. Photo: Tarek Hewezi

By Laura Temple

When crop margins tighten, farmers must decide where and how to invest limited resources.

The tradeoffs are real: Apply fertilizer or in-season fungicide? Upgrade the planter or the combine? Own a sprayer or rely on the local co-op?

Plants — including soybeans — face similar decisions, according to Tarek Heweziprofessor of plant molecular biology at the University of Tennessee. 

“Plants have limited resources,” he explains. “They decide what genes to activate, while many other genes are suppressed as not needed.”

According to Hewezi, soybean breeders have focused on selecting genes that promote development and yield for decades, so that those genes are more likely to be highly active. That has come at the expense of genes that help soybeans manage stress.

He believes that soybeans contain “hidden” or inactive genes that could help the plant cope with various stress factors. He works in epigenetics, which refers to mechanisms that act “above” or “beyond” genetics to modify when and how genes activate. This research aims to uncover, identify and activate these genes to address key agricultural challenges.

Hewezi is applying this innovative approach to look for new genetic sources of soybean cyst nematode resistance, thanks to Soy Checkoff funding from the Tennessee Soybean Promotion Board.

“SCN is the top soybean pest, causing $2 billion in yield loss every year,” he says. “Sources of resistance are limited. The source of genetic resistance we have been using for more than 30 years, PI88788, is no longer effective as SCN becomes more virulent and develops the ability to overcome it.”

Transgenic Technology Aids Search 

With a high number of completely or partially inactive soybean genes to search, Hewezi needed a starting point and a timely testing method. He started with two isogenic soybean lines, meaning they were nearly genetically identical, except for a controlled difference. In this case, that difference was SCN resistance and susceptibility.

“In addition to these isogenic lines, we looked at the parents of these lines to identify genes that might be responsible for that SCN resistance,” he says. “To test those genes relatively quickly, we created composite plants with transgenic roots.”

Current technology allowed his team to select and overexpress the genes within transgenic material. They introduced the overexpressed genes into the roots of soybeans planted in SCN-infested soil in the lab. Inserting the transgenic material caused test plants to activate the gene in question. 

“In about six weeks, we were able to compare SCN reproduction on various transgenic roots,” Hewezi explains. “We validated responses over a few years, and we have identified seven separate previously unidentified genes that confer very high levels of SCN resistance.”

Trials Show No Tough Tradeoffs

Hewezi took the next step: Creating stable transgenics with the promising genes for further testing and validation. A few years of greenhouse tests confirmed previous findings. These genes deliver new sources of SCN resistance.

In 2024, he secured permits to conduct field trials with two of the previously hidden types of SCN resistance genes. Conducted at the East Tennessee Research and Education Center in Knoxville, Tennessee, these trials allowed his team to look for tradeoffs in other traits as the soybeans activated these genes for SCN protection.

“We didn’t see any yield loss,” Hewezi reports. “The effective SCN resistance helps soybeans perform as expected in growth, yield and protein content.”

Given these observations, he aims to conduct field trials with three more of the previously hidden genes, and move the other genes along in the testing process. At the same time, he is acquiring patents and working with seed companies to make the fully tested new sources of SCN resistance available for commercial soybean variety breeding.

“We found excellent sources for genetic SCN resistance,” he says. “With all our discoveries, we have enough options for protection for many years, replacing or augmenting PI88788.”

Hewezi believes that with these newly identified genes, soybean breeders will be able to combine genes to create a variety of options for farmers to use to rotate sources of SCN resistance. This will prevent or slow the breakdown of SCN resistance over time. Plus, the soybean varieties bred with these genes likely will activate resistance without compromising yield and quality potential.

Additional Resources:

Hewezi Laboratory 

Soybean Cyst Nematode – SRIN information page

Lessons Learned from Decades of Overuse of a Single Source of SCN Resistance – SRIN article 

Researchers Continue to Strengthen and Refine Soybean SCN Resistance – SRIN article 

“Let’s Talk Todes” Research Collection – The SCN Coalition 

Meet the Researcher: Tarek Hewezi

Published: Jul 14, 2025

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.