Research Highlights

Understanding Nematode Populations is Key to Selecting Resistant Varieties

By Laura Temple

Countless nematode species can be found in all soil types, but just a few plant-parasitic types attack crops like soybeans and reduce yields. 

“In my trials, resistant soybean varieties have the biggest impact on protecting yield potential for growers,” says David Langston, professor and extension plant pathologist for Virginia Tech. “It’s proven to be the best tool to manage the nematodes found in Virginia and Mid-Atlantic fields.”

The Virginia Soybean Board supports Langston’s survey work and nematode management trials with soy checkoff funding. His research started in 2021, as his role expanded to include soybean diseases. He provides state and regional soybean farmers with information and management recommendations for nematodes and sudden death syndrome, based on learnings from on-farm strip trials and research station test plots.

“I also have been trying to understand the value of seed treatment nematicides in managing nematodes,” he says. “Over the last couple years, I have seen inconsistent results with those options. I’ve observed no major effect on yield or nematode damage from nematicide treatments, especially on later-planted soybeans. Varieties with nematode resistance usually perform best in my trials.”

Different Nematodes Create Different Challenges

Langston explains that many fields have soybean cyst nematode, or SCN, pressure, like most soybean-producing states. He adds that Virginia fields have higher populations of root-knot nematode than much of the U.S.

“The biggest difference between SCN and root-knot nematode is that SCN is specific to soybeans, so farmers can rotate crops to reduce populations,” Langston says. “Root-knot nematode can affect a lot of crops, including corn, cotton and peanuts, so it’s hard to reduce populations in a soybean–corn rotation.”

He believes farmers need more information than just nematode type or species to determine how to best protect soybean yields. 

Langston focuses on conducting a test known as HG Typing, an abbreviation of Heterodera glycines, the scientific name for SCN. This greenhouse test determines how well SCN populations isolated from problem fields reproduce on resistant soybean lines.

“Many soybean varieties have Race 3 SCN resistance, but we are seeing populations shift in races so nematodes can overcome that type of resistance in soybeans,” he explains. “This testing lets growers know if Race 3 resistance will still work in fields. While this has become more common in the Midwest, we haven’t done much of this testing in Virginia and the Mid-Atlantic. This knowledge improves variety selection.”

He also characterizes root-knot nematode populations using a polymerase chain reaction test, commonly called a PCR test, which detects unique genetic material to identify species present in a sample. 

“We know we have southern root-knot nematode, or SRKN,” Langston says. “Though we have other species in Virginia, like the northern root-knot nematode, we don’t have much data about them yet.”

Check Resistance Genetics

Langston says some soybean varieties have resistance to both SCN and root-knot nematode, though different genetics produce each trait. 

“Race 3 SCN resistance is most common,” he explains. “With shifts in SCN populations, varieties with resistance to more races of SCN typically perform best in my trials.”

The resistance to multiple races is known as Peking resistance. He encourages growers to select varieties with this type of resistance, especially if HG Type results from soil tests show multiple SCN races in a field.

“However, with Peking resistance, be sure to do your homework on overall yield potential of the variety,” Langston advises. “I have seen Peking varieties with low base yield potential, which were out-performed by susceptible varieties.”

He notes that Peking resistance exists primarily in Maturity Group 5 and 6 soybeans. Because most Virginia and Mid-Atlantic farmers plant MG 4 and 5 varieties, they may not find varieties that meet all of their needs. 

To manage root-knot nematodes, farmers rely on genetic resistance to SRKN.

“We have genetic resistance to SRKN in soybeans and cotton,” Langston says. “No resistance is available in corn, which makes planting resistant varieties in other crops critical to managing populations.”

He acknowledges that nematode resistance rarely tops the list of priorities for variety selection, but he points out an additional benefit of managing nematode pressure. 

“In our survey of sudden death syndrome outbreaks, 50% or more occurred in fields with high nematode populations,” he says. “Open wounds in roots caused by nematode feeding make plants more susceptible to other soilborne diseases. The link between SCN and sudden death syndrome has been documented, and we’ve observed the same with root-knot nematode.”

He plans to conduct greenhouse work to prove that a similar relationship exists between root-knot nematode and sudden death syndrome, as his additional work focuses on that disease. 

Other Resources

SRIN information page: Soybean Cyst Nematode

Published: Mar 20, 2023