Research Highlights

Research Highlights
Searching for Phytophthora Resistance in North Dakota Soybeans

In this article, you’ll find details on:

  • This project is surveying for Phytophthora prevalence across North Dakota soybean fields and which soybean varieties continue to carry resistance to the disease.
  • Farmers will gain knowledge of disease presence and which management practices and soybean varieties will help reduce Phytophthora in their fields.
  • Farmers who suspect Phytophthora presence can send in soil samples to help researchers improve their knowledge of this disease in the state and direct soybean breeding to continue to combat it.

A North Dakota soybean field shows the stand loss that Phytophthora root and stem rot can cause. Photo: Richard Webster

By Carol Brown

In North Dakota, soybeans are a relatively new crop, having been part of the state’s landscape since the late 1930s1, and then only in the southeastern part of the state. Today, soybean production is expanding west across North Dakota. With this expansion also comes soybean diseases such as white mold, sudden death syndrome, and Phytophthora root and stem rot.

North Dakota State University plant pathologist R. Wade Webster is assessing which Phytophthora populations are prevalent in the soil and whether they are tracking westward. The project, funded by the North Dakota Soybean Council, also includes screening soybean varieties for continued or decreased resistance to those pathogens.

“We want to understand what the populations look like across the state, and how they will impact the soybean resistance genes that should be used,” explains Webster. “This is important because there are typically four resistance genes we see in commercial varieties, and two of those genes have become ineffective. They’ve been used for so long that the pathogens are becoming insensitive to the resistance genes.”

Phytophthora root and stem rot is a seedling fungal disease that usually infects soybeans in wet and warm conditions, either after a heavy rain or wet season. Phytophthora sojae is part of a group of organisms called oomycetes, or water molds. Symptoms can also appear later in the season and cause brown lesions that move up the soybean stem from the soil. Leaves will wilt, become yellow and die on the plant.

Webster’s work will reveal which soybean resistance genes are still effective and whether the ineffective genes are getting worse, he says. His first goal is to create a distribution map that shows regional differences in the Phytophthora populations, as the team needs to know what they are dealing with and where before they can work to overcome the disease.

After collected soil samples are ground to a powder, they are put in cups along with small discs of soybean leaf tissue. The soil is then flooded, which leads to Phytophthora infecting the leaf tissue, which can then be analyzed for the pathotype. Photo: Abdul-lateef Popoola

In 2023, the team collected samples from 147 fields across the state. NDSU graduate student Abdul-lateef Popoola is processing the soil samples and conducting the pathogen screenings. Webster has shared this project at extension meetings and field days, encouraging farmers to submit soil samples, especially if they are seeing symptoms in their fields. This will help him and his team to increase state coverage, especially in the central and western portions. Webster also shares test results with the participating farmers to provide information on the disease severity in their fields and possible management practices to reduce the spread.

Farmers can take a soil sample any time, but Webster says the best time to collect one is after soybean emergence or at the end of the growing season.

“Phytophthora is distinct from other diseases as it can reproduce on the plant throughout the entire growing season, so sampling isn’t as stringent as it may be with other pathogens,” Webster comments. “Phytophthora is able to survive in the soil for up to five years, so even if farmers don’t see symptoms currently, we should still be able to discern through a soil sample whether the pathogen is present and which pathotype it is.”

Breeding Soybean Varieties to Combat Phytophthora

Webster is partnering with Carrie Miranda, leader of the NDSU soybean breeding program, to work on the other project objective of determining resistance gene effectiveness. 

“We’re screening Carrie’s early generations of soybean breeding lines for Phytophthora resistance,” says Webster. “In the screening process, if the resistance gene is present and effective, the soybean plants should survive. If the resistance gene is not present, we’ll see some death of the seedlings after emergence.”

The surveying done across the state will help Miranda update or alter her breeding lines to target the most representative pathotypes of Phytophthora. A decade ago, two particular isolates, or races, were prevalent in North Dakota, says Webster. But he cautions that things can change quickly, and 10 years is quick in the plant breeding world.

“We want to understand which soybean resistance genes are going to be effective in each of the state’s regions, and the map we’re creating should provide an accurate illustration,” Webster says. “We’ll have a good representative idea of what management tools will be effective for farmers in the different regions. And we’ll also know which soybean lines will be more durable in the fields to hold up to Phytophthora.”

For more information about collecting and sending a soil sample for this project, contact Webster at:

Other resources

Meet the Principal Investigator on this project: R. Wade Webster

Phytophthora Root and Stem Rot – SRIN information page

1 Soybeans In North Dakota. North Dakota Bimonthly Bulletin, Volume XII, No. 4, Mar.-Apr. 1950  

Published: May 6, 2024

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.