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Research Highlights

Research Highlights
Progress in developing IPM tools for diagnosis and management of soybean seedling diseases

Effective control of seed and seedling rots is becoming increasingly important to protect the value of seed, currently the largest single expense in soybean production.

Fusarium root rot,  Rhizoctonia seedling blight, Phytophthora root rot, and Pythium damping off are examples of widespread seedling diseases of increasing concern. We now know there are many species of each of these organisms that can affect stand establishment, weaken seedlings, and reduce yield.  The root rot pathogen, Fusarium graminearum, and various Pythium species which can infect both corn and soybean are becoming more prevalent in corn-soybean rotations.

With checkoff funding provided by the North Central Soybean Research Program and the United Soybean Board, a interdisciplinary team of researchers from nine states (AR, KS, IA, IL, IN, MI, MN, NE, SD) and Canada have worked collaboratively to address the production constraints caused by seedling diseases and developed region-specific management recommendations to minimize yield loss. 

The significant progress made by this team in the past four years in rapid diagnostics, development of resistant soybean varieties, and development of screening tools that ensure fungicide seed treatments remain effective are providing a solid foundation for future seedling disease management.

New diagnostic assays provide a powerful decision tool

A diagnostic assay to determine the presence of Phytophthora in soil and plant roots has been developed and is in the final stages of testing before commercialization. The results have been published in the journal Plant Disease

 Plant clinic diagnosticians have already been trained with kits that can be used in the field with relatively simple equipment, with detection and identification being achieved in a matter of minutes.

The ability to quickly and accurately identify other key seedling pathogens is right around the corner. Diagnostic assays are in final stages of development for the fast identification and accurate quantification of Fusarium species and Rhizoctonia species from soil, roots and soybean stem. The ability to quickly and accurately identify and quantify  key seedling  pathogens will provide a powerful IPM tool for farmers and researchers.

Progress in identifying northern germplasn with resistance

With the exception of Phytophthora soja, no varietal resistance  is yet available. Over the past several years, a major goal for plant pathologists and soybean breeders has been to identify and develop varietal resistance to common seedling pathogens as a cost-effective management tactic, and considerable progress has been made.  

In Minnesota, significant differences were detected among northern cultivars and breeding lines for reaction to Rhizoctonia solani.  At least 15 soybean lines with partial resistance to seedling blight and root rot caused by Rhizoctonia solani have been identified and incorporated into the soybean breeding program.

In South Dakota, eight soybean accessions with significant resistance to Fusarium graminearum were identified for use in soybean breeding programs.

An additional project  supported by checkoff funding provided by the United Soybean Board and NCSRP has resulted in numerous sources of resistance to Phytophthora sojae,  Pythium spp. and Fusarium graminearumidentified by screening theentire USDA plant introduction (PI) germplasm collection.  Plant breeders now have a wealth of germplasm material to work with.

Efficacy of seed treatment fungicides and preventing resistance

Each year, the multi-state team tests and reviews the efficacy of seed treatment fungicides by field-testing the materials over multiple years and locations. The results are published and updated each year in the publication Fungicide Efficacy for Control of Soybean Seedling Diseases (NCERA-137, last  updated February 2019). Ratings summarized from national fungicide trials published in Plant Disease Management Reports by the American Phytopathological Society (aps.org) are also included.

To keep in front of potential resistance to fungicide tools, a fast, automated fungicide sensitivity assay has been developed and shared with a number of  labs.  The fungicide assay has enabled improved monitoring for fungicide resistance among oomycetes ( particularly the common seedling pathogens Pythium and Phytophthora ), which will ensure that the seed treatments in use are effective.

The baseline sensitivity of the common seedling pathogen, Rhizoctonia solani, to fungicide active ingredients is now established so that fungicide resistance can be monitored.

Species of Fusarium and Pythium that are not sensitive to major seed treatment fungicides have already been detected. Research soon to be published clearly demonstrates the need for multiple chemistry seed treatments for the management of mixed oomycete populations (mainly Pythium) and  Phytophthora species).

Resources

The state of our knowledge about seedling diseases, best management practices, and diagnostics have been compiled into several new publications. These are available as free downloads.

Factors to Consider Before Using a Soybean Seed Treatment. CPN 4003, 2018.

Fungicide Efficacy for Control of Soybean Seedling Diseases – NCERA-137, updated February 2019
Scouting for Soybean Seedling Diseases and Disorders – CPN 1009, 2015
Soybean Seedling Diseases – CPN 1008, 2015
Scouting for Phytophthora Root and Stem Rot in Soybean  CPN 1014B, 2015
Soybean Seed Treatments: Questions that Emerge When Soybean Plants Don’t – CPN 1016 , 2016
Development and Application of qPCR and RPA Genus- and Species-Specific Detection of Phytophthora sojae and P. sansomeana Root Rot Pathogens of Soybean.  Plant Disease, 2017

Also view three videos about soybean seedlings diseases on the SRIN YouTube channel.

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.