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Research Highlights

Research Highlights
Exploring Sudden Death Syndrome Pathogens and SCN Connections

By Carol Brown

Finding out how soybean pathogens work in order to stop them is a daunting task. Researchers across the country are making strides to mitigate soybean yield loss from soybean cyst nematode and Fusarium virguliforme, the pathogen that leads to sudden death syndrome.  

Michigan State University plant pathologist Martin Chilvers leads several research projects, funded by the Michigan Soybean Promotion Committee, that are investigating these two yield robbers and the relationship between them. One project looks at whether SCN pressure plays a role in triggering SDS, and another project focuses on developing an SDS prediction tool. These two projects intertwine when it comes to field and lab work, as researchers use similar procedures to detect Fusarium virguliforme and SCN. 

The research included a two-year field study to see if Chilvers and his team could predict SDS development in a field based on the amount of F. virguliforme DNA that was found in soil samples. 

“We developed a real-time PCR assay to determine if we could predict the risk of SDS based on how much F. virguliforme DNA we could detect in the soil and it turns out that we could,” he explains. “We are continuing this study to develop a risk prediction tool using this PCR assay. We’ve proved it in one location and we’re now collecting soil samples from several states to test the model on different soil types.”

The PCR technique, which stands for polymerase chain reaction, has been in use since the 1980s. It enables scientists to replicate DNA in the lab using enzymes. Through PCR, they can amplify the amount of DNA to be able to tell if a gene or species of interest is present or absent, such as the Fusarium virguliforme fungus.

If the study finds that the model developed to predict SDS works in multiple soil types, eventually it could be used in a similar fashion as SCN testing, where farmers can send in soil samples to test for the presence of both SCN and SDS pathogens. 

Chilvers and his team found other intriguing results through PCR testing of soybean roots. They tested soybean varieties that were susceptible as well as resistant to SDS. One might think that the resistant variety soybeans would harbor only low levels of F. virguliforme, but Chilvers found this was not the case. So, what does that mean for the farmer?

“It means that even if you grow a resistant variety soybean, it’s not necessarily decreasing the amount of F. virguliforme inoculum in your field,” Chilvers explains. “This is important for a farmer’s long-term plan. If you plant a soybean resistant variety for a few years and forget about SDS, then plant a susceptible variety, it could be disastrous, because that inoculum has been building in the soil.”

The SDS–SCN Relationship

Other research conducted through the field study looked at the interactions between F. virguliforme and SCN. There have been at least 20 different studies across soybean-growing states that have explored the roles of and relationships between SDS and SCN, Chilvers says. Some of those studies found connections and others did not, which illustrates how many factors there are to consider when conducting research including soybean variety, the type of nematode, weather and greenhouse experimental conditions. 

“Former Ph.D. student Mitchell Roth looked at these interactions in the lab to get a sense of what happens between SDS and SCN in the soil system,” says Chilvers. “The study provided additional evidence that SCN pressure is important in terms of how much SDS develops. The other interesting outcome was that the SCN number correlated with the developed SDS and yield loss.”

Figure 1: Contour plots determined via kriging of the grid-sampled data representing Fusarium virguliforme(Fv) DNA quantities, SCN egg quantities, soybean reproductive growth stage R5 foliar SDS disease index ratings, and soybean yield in 2014 (top) and 2015 (bottom). F. virguliforme quantities are shown as a proportion of F. virguliforme DNA detected (femtograms) from total DNA extracted (nanograms). SCN eggs are shown as the quantity of eggs detected per 100 cm3 of soil. R5 foliar SDS disease index is expressed on a scale from 0 to 100. Yield is shown in kilograms per hectare. In all plots, white represents low values and green represents high values.

“We know that fields can get SDS without SCN, but maybe soybean cyst nematode feeding makes the plant more susceptible to SDS. Or that SCN are potentially vectoring or creating wounds for F. virguliforme,” he remarks. “We don’t know the answer, but these are questions worth pursuing, because if we understand this, we have a better chance of managing through breeding, seed treatments, or biologicals.”

Seed Treatment Tests

In another project, Chilvers is testing two seed treatments for fungicide sensitivity to F. virguliforme. The team looked at ILeVO and Saltro products to ensure these treatments continue to be effective, as chemistries and susceptibility can change over time. He knows that both products have been effective in the field, but he and his students are conducting tests for their continued efficacy. 

“Many of these projects are connected to multi-state projects, such as the testing of fungicide efficacy across the soybean growing region organized by Daren Mueller at Iowa State University,” explains Chilvers. “These field trials are being done again this season.” 

For more information on this research, visit the Crop Protection Network website.

Research resources:

Predicting Yield and Sudden Death Syndrome Development Using At-Planting Risk Factors
https://pubmed.ncbi.nlm.nih.gov/31090498/

Diagnostic qPCR Assay to Detect Fusarium brasiliense, a Causal Agent of Soybean Sudden Death Syndrome and Root Rot of Dry Bean
https://apsjournals.apsnet.org/doi/10.1094/PDIS-01-19-0016-RE

Improved Diagnosis and Quantification of Fusarium virguliforme, Causal Agent of Soybean Sudden Death Syndrome
https://apsjournals.apsnet.org/doi/10.1094/PHYTO-06-14-0177-R

Temporal Dynamics of Fusarium virguliforme Colonization of Soybean Roots
https://apsjournals.apsnet.org/doi/10.1094/PDIS-03-18-0384-RE

Influence of Fusarium virguliforme Temporal Colonization of Corn, Tillage, and Residue Management on Soybean Sudden Death Syndrome and Soybean Yield
https://apsjournals.apsnet.org/doi/10.1094/PDIS-09-20-1964-RE

Published: Sep 26, 2022

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.