Research HighlightsCombatting Soybean Seedling Diseases From Inside and Out
In this article, you’ll find details on:
- Ongoing research is revealing more information about soybean seedling diseases, which will lead to effective ways to reduce their impact.
- Researchers have identified three new species of Fusarium not found in U.S. soybeans before.
- The USB-funded project helps researchers fight seedling diseases through soybean genetics and fungicide advancements.
By Carol Brown
A team of researchers continues to investigate persistent diseases that prey upon soybean seedlings, such as Fusarium, Pythium, and Phytophthora. The pathogens that cause these diseases are widespread and complex, which makes it complicated when scientists delve into how they work. They are using essentially two approaches: from inside the soybean and outside.
Febina Mathew, a plant pathologist at North Dakota State University, leads the group comprised of researchers at 10 universities across the country through a project funded by the United Soybean Board and supported by several state soybean boards. The research has been ongoing for several years as they continue to uncover information about these diseases, and the group has made strides in their knowledge.
“Fusarium is an important pathogen because it infects everything,” says Mathew. “I don’t know of any crop that it doesn’t infect. It can also be found in our gardens, trees and even weeds. It’s a difficult group of pathogens to control. And a year like 2024 had the perfect conditions for seedling pathogens to cause disease in soybeans.”
New Fusarium Species Identified
Mathew says that farmers often struggle with a lack of options when it comes to managing Fusarium.Although fungicides and biological seed treatments are available, the data on their effectiveness is limited. While cultivars that offer partial resistance to Fusarium virguliforme are available, there is still no resistance to other Fusarium species. Additionally, crop rotation may not be a solution since all crops rotated with soybeans are susceptible to Fusarium.
Through a project supported by the North Dakota Soybean Council, she and her student Nitha Rafi have isolated eight species of Fusarium in soil samples collected from 75 fields in the state in 2023. Three of those eight — Fusarium caucasicum, F. curvatum and F. clavus — have not previously been reported in soybeans in the United States.
“With these newly identified Fusarium species, we still need to determine the ability of these organisms to cause disease as well as determine their prevalence in the state,” comments Mathew.
As the North Dakota team finds answers about new pathogens, others are exploring how to combat seedling diseases through fungicides applied to the soybean seed and using genetics to fight disease from the inside of the seed.
Seed Treatment Effectiveness
The new pathogen species identified by Mathew’s team are research breakthroughs, but each new species adds to the disease’s complexity. Currently, there are a few fungicides in the form of seed treatments on the market that can effectively control these diseases. That’s what plant pathologists Teddy Garcia-Aroca and Dylan Mangel are working on at the University of Nebraska-Lincoln. They are testing different seed treatments for their effectiveness on seedling pathogens.
“In the beginning, we didn’t have a good idea of which pathogens were in our Nebraska soils,” explains Garcia. “We’re surveying soils around the state to gain a better sense of what pathogens we have that cause those seedling diseases.”
Through funding from the Nebraska Soybean Board, they are collecting soil samples from across the state and identifying the pathogens found in the samples. They are then testing numerous soybean seed treatments against those pathogens for effectiveness, including those with two and three active ingredients, says Garcia, and also testing different levels of seed treatment concentrations.
“The active ingredients within the seed treatments target different sites in the fungal cells to kill the pathogen,” Garcia says. “When a fungicide has more than one active ingredient, it targets multiple locations in the cells to be more effective.”
The team’s research shows some of the fungicide concentrations at which they saw effectiveness for some pathogens were relatively low, but higher concentrations were needed to be effective against others. If the fungicide is applied to the seed at a higher concentration, Garcia cautions, it will still be effective but may cause the pathogen to become more resistant, creating a vicious cycle. The pair is also exploring useful alternatives so farmers don’t rely exclusively on fungicides for seedling disease control.
This fall, Mathew’s lab will start fungicide sensitivity work on Fusarium and Rhizoctonia species. They have already obtained isolates from different states, including Nebraska, for the work.
Fighting Disease from the Inside
“A problem we are facing with soybeans is we don’t necessarily have seed treatments that are labeled against specific Fusarium species,” Mathew says. “At the same time, soybean seeds have partial genetic resistance to only Fusarium virguliforme, the pathogen that causes sudden death syndrome.”
Resistance to F. virguliforme does not promise resistance to the other species of Fusarium, Mathew says. Her team is exploring whether the soybean genes that confer resistance to F. virguliforme are compatible with genes conferring resistance to other species.
“We wanted to answer the question, ‘Is there a gene common across multiple species?’ and we have found that answer is no,” she remarks.
Knowing this answer makes things a little clearer for a soybean breeder, but not easier. As breeders stack soybean genes resistant to various pathogens, they will learn the limitations.
“Breeders might not be able to stack four genes at the same time, but maybe they could stack two,” says Mathew.
These project components work together to help soybeans fight Fusarium. The genetics work from Mathew’s team can help the soybean breeder. The fungicide efficacy results can be shared with the chemists who develop them. That small soybean seed will have layers of armor, inside and out, to battle seedling diseases.
It may take a few years before farmers can see these results, but once they learn which pathogens are in their soils, they will know which soybean varieties and seed treatments they need to mitigate seedling diseases.
Other resources:
No common candidate genes for resistance to Fusarium graminearum, F. proliferatum, F. sporotrichiodes, and F. subglutanins in soybean accessions from maturity groups 0 and 1: Findings from Genome-Wide Association Mapping. Nitha Rafi et al. APS Plant Disease, April 19, 2024
Fungicide Efficacy for Control of Soybean Seedling Diseases – Crop Protection Network publication
Understanding How Fusarium Affects Soybean in ND and Development of Disease Management Strategies– National Soybean Checkoff Research Database
Multi-dimensional Approaches for Improved Productivity, Sustainability, and Management of Major Soybean Diseases in the North Central U.S. – National Soybean Checkoff Research Database
Published: Sep 26, 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.
