Research HighlightsSearching for Southern Root-Knot Nematode Resistance
Highlights:
- Southern root-knot nematode is the No. 2 threat to Southern soybeans, and genetic resistance is not commercially available in soybeans.
- University of Tennessee research aims to screen for and identify soybean genes that carry resistance to this pest.
By Laura Temple
From Kentucky to Florida and from Texas to Virginia, southern root-knot nematode has become the No. 2 threat to soybeans. Though this pest gets less attention than soybean cyst nematode, it reduces yield and is difficult to manage.
More than 2,000 plant species can host the microscopic southern root-knot nematode, including other major regional crops like corn, cotton, grain sorghum, rice and tomato. Unlike with SCN, crop rotation has limited value for reducing pressure.
Southern root-knot nematode causes patches of yellow, stunted soybeans that can eventually die late in the season. Below ground, it causes galls, or swollen growths, on plant roots. The pest can reduce yields 50 to 100%.
“When looking at soybean roots, it is easy to see galling caused by southern root-knot nematode,” says Tarek Hewezi, professor of plant molecular biology at the University of Tennessee. “However, genetic resistance to this pest is not commercially available in soybeans.”
With support from the Tennessee Soybean Promotion Board, he initiated research to address that gap.
Screening to Identify Genetics
Hewezi’s team screened hundreds of soybean plant introductions, or PIs, looking for lines that did not host southern root-knot nematode.
This work revealed two PIs with that demonstrated resistance. They then developed populations containing about 500 recombinant inbred soybean lines. The next step is screening these lines for resistance.
The research team is observing the performance of each line against southern root-knot nematode, or phenotyping for level of resistance. Then, because so much genetic information is available for soybeans, his team will focus on genotyping.
“Comparing genetic data from lines with strong resistance will allow us to find locations and genes linked to that trait,” Hewezi explains. “We are aiming to identify the first confirmed southern root-knot nematode-resistant genes.”
With that information, genetic markers can be developed to quickly identify the presence of these genes through the breeding process. Eventually, he believes breeders will be able to incorporate proven resistance into new soybean varieties that can withstand soils infested with southern root-knot nematode.
Hewezi notes that the process is moving forward slowly. He is looking for opportunities to leverage Soy Checkoff funding into additional support for this research. In the meantime, his team is making progress toward helping farmers address this critical nematode challenge.
Additional Resources
Hewezi Laboratory – website
New Map Charts the Distribution of Southern Root-knot Nematode – SRIN article
Arkansas Research Arms Soybean Farmers Against Southern Root-Knot Nematode – SRIN article
“Let’s Talk Todes” Southern Root-Knot Nematode Collection – SCN Coalition videos
Root-Knot Nematode of Soybean – Crop Protection Network
Meet the researcher: Tarek Hewezi SRIN profile | University profile
Published: Sep 1, 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.
