Research Highlights

Searching for Answers to Reduce Severity of Soybean Stem Diseases

In this article, you’ll find details on:

• Minnesota researchers are looking further into better management of brown stem rot and pod and stem blight soybean diseases.
• Management practices such as crop rotations and fungicides can reduce the severity, and researchers are exploring if other crops serve as disease hosts.
• Researchers are also searching for new breeding lines that offer resistance to these diseases.

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By Carol Brown

Diseases can be devastating to a soybean crop, which translates to yield and profit loss for farmers. Plant pathologists are researching soybean diseases to find ways to improve the crop’s defenses against them. Dean Malvick, professor of plant pathology at the University of Minnesota, is focusing on soybean stem diseases and the management practices that could reduce disease severity. 

“Soybean stem and root diseases are common and problematic in Minnesota,” Malvick says. “Pod and stem blight and brown stem rot are two diseases we are focusing on to find the prevalence of these diseases and effective disease management options.”

These diseases are caused by soilborne fungi, with symptoms typically occurring later in the season at R4 to R5 growth stages. Brown stem rot symptoms, such as leaves yellowing between the veins, are similar to other diseases including sudden death syndrome, which adds to the difficulty of detection. The best way to diagnose brown stem rot is to slice the soybean’s stem lengthwise and look for brown discoloration in the pith.

Through a research project supported with checkoff funding from the Minnesota Soybean Research and Promotion Council, Malvick collected soybean plants from across the state with the help of farmers, extension specialists, and crop consultants who sent him samples of diseased soybeans. He also worked with the plant disease clinic at the University of Minnesota. Malvick will map the disease locations to find the areas with high disease prevalence. This helps him to prioritize focus areas for further study and to notify soybean farmers so they can adjust their management plans. 

Reducing Brown Stem Rot

An objective of this project was to find the best ways to manage brown stem rot. 

“Brown stem rot has been studied since it was first discovered in central Illinois in the 1940s, and it’s still a widespread problem,” comments Malvick. “Seed companies and breeders have made a diligent effort and progress in developing resistance. Today, there are more varieties with clear resistance to brown stem rot. But we’ve noticed that even in some of the resistant varieties, brown stem rot still occurs.” 

He attributes this to two pathogen types: one mainly causes internal stem browning and the other causes stem browning, leaf discoloration and plant damage. Malvick believes there are different levels of resistance in the soybean varieties, as some may have been bred for resistance to one pathogen but not the other.

He teamed up with University of Minnesota colleague Aaron Lorenz, a soybean breeding and genetics specialist. They are looking at soybean lines from Lorenz’s breeding program for varieties resistant to brown stem rot as well as pod and stem blight.

“We’ve completed greenhouse work this winter and have definitely found different levels of susceptibility to brown stem rot,” he confirms. “This will help Dr. Lorenz as he continues to develop soybean lines and make selections to improve soybean resistance.”

In addition to working with Lorenz on finding resistance through soybean breeding lines, Malvick has explored the effects of crop rotation and alternative hosts of this disease. The tests are ongoing to see what crops could also be hosts of the brown stem rot pathogen. Answering this question will help farmers in making crop rotation decisions.

Fighting Pod and Stem Blight

Another project objective is evaluating management practices that reduce pod and stem blight. Crop rotations and soybean varieties with resistance can suppress this disease, but it is not enough to keep the disease away.

Pod and stem blight is caused by fungi in the Diaporthe genus. Symptoms include lines of small dark brown or black dots along the stems of mature soybeans. Other Diaporthe diseases include stem canker and seed decay.

Malvick has several unanswered questions when it comes to finding management practices that work well to reduce this disease.

“Seed treatments may be beneficial, although we need to understand this better, as much of the infection may occur after seed treatments have had their main effect,” he says. “Also, we’re not clear on how well fungicides work as research results have been inconsistent. We have much more to learn as we continue to look for answers.”

Meet the Principal Investigator on this project: Dean Malvick

Published: Jul 29, 2024