Research HighlightsExploring different ways to reduce the impact of soybean seedling diseases
By Carol Brown
Soybean seedlings are vulnerable to a host of things. Coaxing them to grow into a thriving plant takes the right combination of nutrients, water, warmth — and a good defense.
Jason Bond is leading a group of plant pathologists who are exploring ways to reduce soybean seedling diseases to help the little seed flourish.
“When we think of seedling diseases, such as Pythium, Fusarium and Rhizoctonia, plant pathologists have not spent a lot of time to seek their diversity within a state or across several states,” said Bond, a Southern Illinois University (SIU) professor in the plant, soil and agriculture systems department. “We discovered there was much more diversity of pathogens within a state — even across one field — than we had expected.”
Bond is working with a group of pathologists in the North Central region, and Arkansas, Tennessee and Kentucky. The group collected samples of sick soybean plants from farm fields and university research plots in as many as seven states. Each university cultured the organisms causing the symptoms in those collected plants. The cultures were divided by what was found. Martin Chilvers at Michigan State University focused on the oomycetes (Pythium and Phytophthora pathogens); Ahmad Fakhoury and SIU handled the fungi (Fusarium, Rhizoctonia and others).
The team observed that many of the organisms found in the roots of the soybean plants had not been reported before, and a lot of them are beneficial to the soybean. This discovery has developed into a follow-up study between several universities.
“There’s such a zoo of these organisms in the soil,” Bond said. “A lot turned out to be bio-control agents, which have activity against Pythium and also the pathogen that causes sudden death syndrome. There are good organisms in these sick plants that are trying to provide protection for the plant.”
Production practices and disease connection
Bond said that because the organisms, both beneficial and detrimental, are already naturally occurring in crop fields, the next step is to look at what farmers can do through their production practices to make the good organisms more prevalent for the soybean crop.
Through funding support from the United Soybean Board and the North Central Soybean Research Program, the team is researching how production practices including no-till and cover crops show promise for seedling disease reduction.
“One of our research stations at Southern Illinois has land that has been in continuous no-till for more than 30 years and it has been compared with tillage replication plots,” said Bond. “In the continuous no-till situation, there tends to be a high frequency and greater diversity of the organisms that are beneficial for crop production.”
The cover crop portion of the project includes research on how well a single species such as cereal rye helps to suppress seedling diseases when grown before soybeans. The team has found that some sites have had a dramatic impact on seedling disease reduction, but more work needs to be done.
Farmers have many cover crop management choices to make and the results from their choices can vary widely. Choices can include growing a single species or a mixture, time of growth before termination, how to terminate, whether to graze or use as a double crop. Variations in soil type, cover crop seeding populations and even cultivars can make it problematic to know what is happening in the field.
“It’s kind of like the wild west out there with regards to cover crops right now,” Bond said. “There’s so much unknown about their impact on plant pathogens, it’s difficult to make broad management recommendations yet regarding how they affect pathogens.”
Results influence new research
As the research team collected and studied the sick plants, they discovered that some pathogens normally associated with corn and wheat were also present in soybean roots. Bond said these pathogens probably don’t cause damage to the soybean, but the plant may act as a reservoir or a host when not growing corn or wheat.
“The implications of this are bigger than just soybean health,” Bond said. “This finding should be explored for corn and wheat pathogens.”
In 2019, the team added a component to their studies regarding seed quality. After the 2018 harvest, many farmers and grain processors were disappointed in the quality of the soybeans. Bond said several sources indicated that seedling disease pathogens attacking the seed right after planting, or within the first month of the plant’s life, could have a lingering impact on soybean quality in the fall.
“The seedling diseases could be weakening the plant’s health later in its development and making an impact,” said Bond. “Researchers at Iowa State University and the University of Arkansas are evaluating seed quality from the beginning and how the plant defends itself from these conditions that weaken it to see if this is accurate.”
This seed quality study includes two different components and at looking at both ends of the seed’s circle of life: the health of the seed for plant growth to reach a good stand and how seedling diseases affect the quality of the soybeans yet to be harvested.
To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.