Bacterium and Fungicide Combo Curbs Soybean Root Rot Fungus

A soilborne fungus newly linked to diseased soybean fields in Korea can be brought under control by pairing a beneficial soil bacterium with a reduced dose of a modern fungicide, according to a peer-reviewed study published in Chemical and Biological Technologies in Agriculture. In pot experiments, the combined treatment suppressed disease more effectively than either the biological or the chemical agent alone, and a new DNA-based test now allows the pathogen to be tracked directly in soil.

The pathogen at the center of the work is Fusarium ipomoeae, a recently reported soybean-associated species within the Fusarium incarnatum–equiseti species complex. Soybean production worldwide is continually threatened by soilborne Fusarium diseases such as damping-off and Fusarium root rot, but management information for this particular species has remained limited, and the taxonomic complexity of the genus has made diagnosis and control difficult, especially for emerging or less-studied species.

To map the local threat, the researchers sampled soybean fields in Korea and recovered 38 Fusarium isolates representing five species complexes: the F. fujikuroi, F. solani, F. nisikadoi, F. incarnatum–equiseti, and F. oxysporum species complexes. The isolates were identified by molecular phylogenetic analysis, and representative isolates were selected to give broad coverage across the identified complexes and clades before being tested for their ability to cause disease on soybean.

Among all the isolates screened, one stood out for its aggressiveness. Fusarium ipomoeae strain CMML23-33, belonging to the F. incarnatum–equiseti species complex, caused the most severe disease on soybean in the study’s pathogenicity evaluations, making it the primary target for the control experiments that followed.

In pot assays, Pseudomonas brassicacearum strain CMML23-51 provided the greatest disease suppression among the biological treatments, reaching 49.5 percent control efficacy on its own. That level of protection is meaningful for a standalone biological agent, but the study’s central question was whether it could be improved by combining it with chemistry.

On the chemical side, the team focused on succinate dehydrogenase inhibitor (SDHI) fungicides. As single treatments, fluopyram at 5 mg per liter achieved the highest efficacy at 83.3 percent, followed by pydiflumetofen at 4.59 mg per liter with 76.1 percent. These figures establish both compounds as effective stand-alone options against the fungus under the assay conditions used.

The strongest result, however, came from integration. Applying P. brassicacearum CMML23-51 together with pydiflumetofen at 2.29 mg per liter — half the concentration that performed best as a single treatment — produced the highest overall control efficacy of the study at 89.5 percent. The combination outperformed the best single fungicide treatment while using a reduced fungicide rate, a pattern consistent with the goals of integrated disease management programs that seek to lower chemical inputs by pairing them with biological control agents.

Beyond treatment testing, the study addressed the diagnostic gap that has hindered work on this pathogen. The researchers developed a species-specific TaqMan quantitative PCR assay targeting the translation elongation factor 1-alpha gene, enabling sensitive quantification of F. ipomoeae. When the assay was applied to pot soils, the quantities of F. ipomoeae DNA detected were inversely related to disease suppression, meaning soils with better disease control carried less detectable pathogen DNA. That relationship suggests the qPCR assay could serve as a quantitative readout of how well a management strategy is suppressing the pathogen, not merely as a presence-or-absence test.

The authors frame the work as foundational rather than as a finished field prescription. Their conclusions state that the study provides biological, chemical, and molecular diagnostic components that may contribute to integrated disease management strategies for soybean Fusarium root disease. The efficacy figures reported here come from controlled pot assays, and the isolates were recovered from Korean soybean fields, so translating these results into grower practice would require further validation under field conditions and in other production regions.

Even so, the study fills several gaps at once. It documents the diversity of Fusarium species complexes present in Korean soybean fields, identifies F. ipomoeae CMML23-33 as a highly aggressive soybean pathogen, demonstrates that a Pseudomonas biological control agent can complement a reduced rate of an SDHI fungicide, and supplies a species-specific qPCR tool for monitoring the pathogen in soil.

Subject of Research: Integrated biological and chemical control of the soilborne fungus Fusarium ipomoeae, an emerging cause of soybean root disease in Korea

Article Title: Integrated biological and chemical control of soybean root disease caused by Fusarium ipomoeae

Article References: Hong, G., Park, S.-W., Lee, J. G., Cho, M., Chilvers, M. I., & Sang, H. (2026). Integrated biological and chemical control of soybean root disease caused by Fusarium ipomoeae. Chemical and Biological Technologies in Agriculture. https://doi.org/10.1186/s40538-026-01100-0

Image Credits: AI Generated

DOI: 10.1186/s40538-026-01100-0

Keywords: soybean, Fusarium ipomoeae, root rot, biological control, Pseudomonas brassicacearum, SDHI fungicides, pydiflumetofen, fluopyram, qPCR diagnostics, integrated disease management, Korea, plant pathology