Database Research SummariesSeedling Diseases: Biology, Management and Education
Research Focus
Soil-borne seedling and root diseases of soybean rank among the top four pathogen threats to soybean because their insidious nature makes them difficult to diagnose and control. It is nearly impossible to predict when they will take a heavy toll until it happens.
This project addresses critical limitations in identifying and managing seedling diseases. As a result of this research, producers and industry will see benefits in the form of rapid diagnostics and management recommendations. This will also help the soybean industry in the development of pesticides and resistant germplasm.
Objectives
- Develop and deploy a panel of QPCR probes to identify and quantify fungal seedling pathogens of soybean.
- Curate the collection of fungal pathogens collected during the first phase of this project.
- Improve understanding of the biology of Rhizoctonia solani as a seedling pathogen of soybean. Characterize Rhizoctonia solani anastomosis groups affecting soybean seedlings throughout the U.S. Monitor shifts in fungicide sensitivity in Rhizoctonia solani populations. Identify host resistance to Rhizoctonia root rot.
- Improve understanding of the biology of Fusarium as a seedling pathogen of soybean. Determine pathogenicity of Fusarium species and identify resistant germplasm.
- Improve understanding of the biology of Pythium as a seedling pathogen of soybean. Compare pathogenicity and fungicide sensitivity of Pythium species across the North Central region. Evaluate the effects of low temperature stress on soybean seedling susceptibility to disease and the contribution of seed treatments.
- Evaluate the effect of multiple pathogen interactions on seedling disease. Determine the impact of seed treatments on the interaction of seedling pathogens.
- Communicate research results with farmers and stakeholders
Results
Diagnostics
- An assay to determine the presence of Phytophthora in soil and plant roots has been developed and will likely be commercialized by a private diagnostic company. The kits can be used in the field with relatively simple equipment, with detection and identification being achieved in a matter of minutes. The commercialization of the Phytophthora assay will improve the in-field diagnosis capability of CCA’s and diagnostic services.
- Significant progress has been made in the development and deployment of a panel of molecular QPCR probes to identify and quantify fungal seedling pathogens of soybean. The probe panel can be used for fast identification and accurate quantification of key fungal seedling disease pathogens from soil, roots and plant stem. This will provide a powerful decision tool for farmers and researchers.
Seed Treatments
- Research soon to be published clearly demonstrates the need for multiple chemistry seed treatments for the management of mixed oomycete populations, such as Pythium and Phytophthora. This information can be used to refine seed treatment prescriptions based on a knowledge of the causal organisms.
- An efficient fungicide sensitivity assay has been developed to speed the process of fungicide sensitivity testing. The high-throughput fungicide assay will enable improved monitoring for fungicide resistance among oomycetes (Pythium and Phytophthora species), thereby ensuring seed treatments in use are effective. The assay has been taught to a number of other labs and will be made widely available.
- The Fungicide Efficacy for Control of Soybean Seedling Diseases publication was updated in March 2019. This publication is widely used in the soybean industry and by farmers for selecting the best seed treatments.
Rhizoctonia
- Significant differences were detected among northern cultivars and breeding lines for reaction to Rhizoctonia solani in greenhouse and field studies, suggesting that soybean germplasm in northern maturity groups differ in susceptibility to Rhizoctonia diseases.
Fusarium
- Eight soybean accessions (PI437949, PI438292, PI612761A, PI438094B, PI567301B, PI408309, PI361090 and P188788) were observed to be significantly less susceptible to Fusarium graminearum when compared to Williams 82 and Asgrow 1835. The eight soybean accessions will be used in breeding programs as sources of resistance to graminearum for development of resistant soybean cultivars.
- Cross pathogenicity studies show that South Dakota isolates of Fusarium acuminatum, equiseti, F. graminearum, F. oxysporum, F. proliferatum, F. solani, and F. subglutinans from either soybean or corn are pathogenic to both crops. The results indicate that the seven species of Fusarium are important root rot pathogens of corn and soybean and that the corn-soybean rotation may not help with the management of Fusarium root rot.
- Studies are in progress to determine environmental risk factors for Fusarium infection. Some Fusarium species colonize seedlings more readily when environmental conditions are stressful for seedlings, such as high temperatures, evapo-transpiration and wind speed.
Resources
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
Factors to Consider Before Using a Soybean Seed Treatment. CPN 4003, 2018.
Fungicide Efficacy for Control of Soybean Seedling Diseases – NCERA-137, updated March 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
Importance
The commercialization of the Phytophthora assay will improve the in-field diagnosis capability of CCA’s and diagnostic services.
The developed probe panel for fungi can be used for the fast identification and accurate quantification of key seedlings disease pathogens from soil, roots and stem and will be a powerful decision tool for farmers and researchers.
Work on fungicide sensitivity of seedling pathogens is yielding important insights that will be of great value in making seed treatment decisions and preventing fungicide resistance.
Soybean varieties with some resistance to key seedling pathogens are needed for effective management of seedling diseases. Significant progress has been made in identifying northern germplasm resistant to Fusarium, Rhizoctonia and oomycete species.
For more information about this research project, please visit the National Soybean Checkoff Research Database.
Funded in part by the soybean checkoff.
