Research Highlights

Research Highlights
Delaying Onset of Sudden Death Syndrome Could Protect Soybean Yield

Sudden Death Symptoms in soybeans. Photo: Leonor Leandro

By Laura Temple

Sudden death syndrome, or SDS, thrives during wet springs and summers. This disease, caused by the soilborne pathogen Fusarium virguliforme, is one of the most economically damaging soybean diseases in the Midwest, according to Leonor Leandro, professor of plant pathology at Iowa State University. She has spent more than 15 years researching SDS, working with soybean breeders who screen for resistance and exploring ways for farmers to protect soybean yield.

“One of my recent Ph.D. students addressed research questions to understand when SDS starts and how that timing impacts the plants,” she says. “His work monitoring a single soybean variety in both field and greenhouse trials found a strong correlation between the onset of SDS, or when it first appears in a variety, and yield loss. Every day of delay in SDS infecting the plant reduced yield loss a consistent, measurable amount.”

Based on this work, Leandro’s team is now exploring if the correlation applies across soybean varieties. She hypothesizes that understanding the relationship between the onset of SDS and total yield loss could become a tool to gauge the effectiveness of SDS treatments. The Iowa Soybean Research Center is funding her current research to test this concept, which means that the checkoff dollars invested by the Iowa Soybean Association are being matched by the companies partnering with the ISRC.

SDS symptoms in soybeans. Photo: Leonor Leandro

Varietal resistance most effectively minimizes SDS yield loss, and a couple seed treatments are labeled to help manage the pathogen. Leandro adds that practices that improve drainage and help manage soil moisture can also reduce the impact of SDS.

Value of Correlating Timing and Yield Loss 

Leandro explains that breeders and seed companies typically rate plots for SDS resistance at the end of the growing season. They determine visual ratings for each variety based on the percentage of leaf area exhibiting SDS symptoms. 

“The current system doesn’t take into account when SDS symptoms started,” she says. “However, if onset timing and plant damage do correlate, monitoring SDS onset could indicate resistance or treatment efficacy better than end-of-season ratings.”

She says that multiple varieties or treatments could have the same visual ratings toward the end of the growing season, despite very different disease progressions. If SDS affected a plot during flowering or pod set, yield could be reduced to almost nothing. However, if SDS didn’t appear in another plot until the pod fill stage, yield reduction would be significantly less. “If what was observed during previous research holds true across varieties, onset timing would provide better information to select genotypes and rate varietal resistance,” Leandro adds. “For example, soybean breeders could more efficiently screen new germplasm and develop varieties with SDS resistance.”

Figure 1. Hypothetical progression of SDS in two different soybean varieties based on research from Leandro’s team. End-of-season ratings would be the same, but Variety 1 is likely to have a higher yield than Variety 2 because of the delayed onset of the disease. Source: Leonor Leandro

Conditions Challenge Research Trials

Leandro’s team used a combination of field and greenhouse trials to test this concept, with research starting during the 2021 growing season. They selected existing commercial soybean varieties with varying levels of SDS resistance and planted them in field trial plots and in the greenhouse. 

In 2021, a cooperating farmer hosted one field trial in a field with a history of SDS pressure. The team planted another field trial at an Iowa State research farm, where they could introduce SDS inoculum. In 2022, they added several more field trials located around Iowa.

Leandro’s team monitored the field plots and greenhouse plants for SDS throughout the season.

“Iowa experienced drought conditions in both 2021 and 2022, so field conditions were not ideal for the development of SDS,” she says. “In the greenhouse, the ideal conditions and disease inoculation made it too easy for SDS to develop, regardless of resistance rating. Even the checks, or control plants, did not behave as expected. Because of these factors, the results we gathered in 2021 were not sufficient to draw reliable conclusions.” 

Based on feedback from growers, her team is looking into using plant scanning technology to monitor plants. This method may help detect SDS earlier than the naked eye, providing more reliable data to examine for a correlation between onset timing and yield loss.

“We use modeling to look for patterns and determine correlation, if there is any,” she adds.

The ISRC awarded Leandro funds to continue this research through at least 2023. The additional years of data from a wider variety of field conditions should help determine if choosing varieties and treatments that delay the onset of SDS can protect soybean yield. 

Additional Resources

Sudden death syndrome:

Related SRIN resources:

Published: Dec 12, 2022

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.