A look at SCN

By Dusty Sonnenberg, CCA, Field Leader, a project of the Ohio Soybean Council and soybean check-off.

Soybean cyst nematode (SCN) is a significant source of soybean yield loss in the state. What work is being done to address this?

There are numerous efforts to keep raising awareness of how important and damaging SCN is in North America. Horacio Lopez-Nicora is a plant pathologist and nematologist at the Ohio State University He has a laboratory on campus in Columbus in Kottman Hall to analyze soil samples submitted by farmer to assess their SCN levels. But work at the lab is more than just counting the number of eggs in soil samples. It is also about identifying specific SCN populations out there. It has moved beyond just identifying is a field has SCN populations. It is also about identifying those specific populations in the field.

Lopez-Nicora said the process starts with the soil sample.

“Collecting and processing those samples is a good start. We need to know if we have SCN. By knowing the numbers, we can target and plan a strategy to reduce numbers to below damage threshold. But just knowing if we have SCN limits our options of management. There are different SCN populations. Some of those that will be very easily managed with any source of resistance. There are other populations that have adapted and reproduced on the most commonly used source of resistance that we have in commercially available soybean cultivars.

It’s important to know this because if I know my numbers and I know what population of SCN I have, I will make a better decision on what varieties I will plant. That’s very important to reduce soybean systematic damage in our fields.”

Beyond the lab, what additional work is being done at Ohio State to address SCN?

Lopez-Nicora is working on a number of different studies. One of the more recent studies is a cooperative effort in north central Ohio with Eric Richer in OSU Extension and Jon Schoenhals with Pioneer looking at the SCN reproduction factor in fields to better assess what control treatments actually work to reduce numbers. 

“We have plots with less nematodes and some with more nematodes, so we have a range of nematode density in that field. We planted these different soybean varieties with different sources of resistance, some with seed treatments, some without. We collected samples at planting to obtain the initial population of the nematodes and then later we went and collected samples at harvest to obtain the final population of the nematodes. By collecting two samples at two different points, we can now obtain a new variable that is called a reproduction factor,” Lopez-Nicora said. “We divide the final population by the initial population. If you have the same population density at planting and at harvest, it will give you a reproduction factor of 1 — the nematode density did not increase and did not decrease. If we have a reproduction factor above 1, it means that at the end of the season the SCN was able to increase its population. Whatever we did, did not work. Whatever we planted, the nematode was able to reproduce. If we have a reproduction factor of 5, we ended up with five times more nematodes than at the start of the season. On the other hand, if I have a reproduction factor below 1, that means that whatever I did was able to reduce the level of SCN. That’s where we want.”

What other work is being done with SCN around the country?

The Society of Nematology recently held their annual meeting (SON 23) in Columbus, Ohio, on the campus of The Ohio State University. Plant pathologists and nematologists from across the country gathered for a week to discuss current research and efforts being undertaken to address issues caused by the over 7,000 species of nematodes in the United States and around the world.

For over five decades, George Bird has studied nematodes; first as an undergraduate student at Rutgers University working as a student researcher in the summers, and for the last 50 years as a researcher, university professor and extension specialist at Michigan State University. Bird is also one of the founders of the SCN Coalition.

Soybean Cyst Nematode (SCN) has been recognized as an agronomic pest in the United States since 1954.

“In the early years, SCN was very difficult to control and there were not many options,” Bird said.  

Out of those challenges emerged the SCN Coalition. The first objective was the idea of a campaign called “Take the Test, Beat the Pest.” The objective was to make farmers aware of the potential presence of SCN in their fields.

This first SCN Coalition campaign was successful at raising awareness of the nematode pest, and farmers adopted planting resistant varieties.

“It did not take long for the overuse of certain resistant varieties to lead to variety resistance among the nematodes,” Bird said. “The issue of SCN developing resistance to the resistance gene led to a second SCN Coalition. The new objective of the SCN Coalition is to manage resistance and encourage farmers to rotate the genetic source of resistance among varieties as well as identifying other potential issues in the field.”

The SCN Coalition is comprised of 28 states and 8 transnational corporations. The SCN Coalition has a marketing agency helping to get the message about SCN out to farmers and stakeholders. Because of the marketing arm, the discipline of nematology will sponsor the very first National Nematology Day on Oct. 2, 2023, in the United States.

Bird is excited about the future of nematology.

“Thanks to the work of the marketing agency, some big things are coming,” Bird said. “National Nematology Day will help to raise awareness. Also, the SCN Coalition has developed a soon to be released hand-held nematode calculator for smartphones. The new calculator app will help to estimate SCN yield losses based on population densities and provide management recommendations. The SCN calculator app is expected to be released this fall.”

Another example is Nathan Schroeder, who first became interested in nematodes as a PhD Student in the Department of Plant Pathology at the University of Wisconsin.

“That got me very focused on plant parasitic nematodes and is where I first started working on Soybean Cyst Nematodes,” said Schroeder, now an Associate Professor at the University of Illinois at Champaign-Urbana. “From there I became more interested in the innerworkings and learning how nematodes could find the plant roots in the soil and get into the roots. I started investigating it further and that put me on my current research program that looks at applied near term solutions to control parasitic nematodes, as well as expanding those basic concepts into developing new ‘outside the box’ control strategies.

“One of the tools we use in our research is electron microscopy. It’s not the typical microscope that was used in high school biology. Instead of using light, we use electron beams to get incredible detail and resolution down to the nanometer scale to be able to see individual cells and neurons and how the neurons connect. From that we can get a very detailed picture of how the nematode works. With that knowledge, we hope to learn how to control it while not harming other things that are in the soil.”

Seed treatment studies are also a part of the research Schroeder conducts.

“Part of the applied research we do is to test seed treatments,” Schroeder said. “We test seed treatments that are in development and also those on the market to test the efficacy in different geographical regions. We are also going to be testing commercial soybean varieties looking at their resistance in the field to SCN.”    

All this research is funded in part by soybean check-off dollars.