Project Details:

Title:
Seedling Diseases: Biology, Management and Education

Parent Project: Seedling Diseases: Biology, Management and Education
Checkoff Organization:North Central Soybean Research Program
Categories:Soybean diseases, Education, Environmental stress
Organization Project Code:NCSRP
Project Year:2018
Lead Principal Investigator:Jason Bond (Southern Illinois University at Carbondale)
Co-Principal Investigators:
Leonor Leandro (Iowa State University)
Christopher Little (Kansas State University)
Martin Chilvers (Michigan State University)
Berlin Nelson (North Dakota State University)
Albert Tenuta (Ontario Ministry of Agriculture-Food & Rural)
Ahmad Fakhoury (Southern Illinois University)
John Rupe (University of Arkansas)
Kiersten Wise (University of Kentucky)
Loren Giesler (University of Nebraska)
Tony Adesemoye (University of Nebraska at Lincoln)
Sydney Everhart (University of Nebraska at Lincoln)
Heather Kelly (University of Tennessee-Institute of Agriculture)
Show more
Keywords:

Contributing Organizations

Funding Institutions

Information and Results

Click a section heading to display its contents.

Project Summary

Soilborne seedling and root diseases of soybean significantly reduce yields in the North Central region of the United States. Seedling diseases rank among the top 4 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. The challenges and failures of managing soilborne diseases and pathogens of soybean and other crops are based in part on limitations in knowledge and methods.

This project will address critical limitations in identifying and managing seedling diseases. Producers and industry will see benefits in the form of rapid diagnostics and management recommendations. This benefit will also help industry in their assessments in pesticides and germplasm development. Producers will also see their check-off funding being maximized by the synergy of this team, the USB seedling disease project and the USDA-NIFA oomcyete project. This project complements the USB seedling disease project.

Research themes of the USB seedling disease project are to:
• Determine the effect of temperature, soil type/texture and pH on infection by seedling disease
• Characterize the species complex associated with soybean iron chlorosis in field conditions
• Metagenomics analysis to improve our understanding of seedling biology and the environmental conditions that favor disease
• Establishing baseline inter- and intra-field variability for seedling pathogens
• Impact of cover crops on causal agents of seedling disease
• Outreach and Education
We propose to leverage the USB project to develop additional diagnostic tools to the genus and species level that rapidly identify soybean pathogens to improve seedling disease management. We also propose to develop and conduct metagenomics analysis to improve our understanding of seedling biology and the environmental conditions, including soil factors that drive disease. During the first cycle of the project, we used specific genetic barcodes to identify fungal species isolated from diseased soybean seedlings. We currently have a collection of 3,000+ isolates. The majority of these isolates are expected to be pathogenic on soybean and to be involved in the incidence and development of seedling diseases. We are also currently working on developing qPCR probes specific to the fungal species that were found to be most prevalent in the first three years of the project. In addition, we propose to enhance our understanding of various aspects of the biology of the interaction between seedling pathogens and soybean, which will enable us to develop more effective management options for improved stand establishment and yield.

Project Objectives

Objective 1: Development and deployment of a panel of QPCR probes to identify and quantify fungal seedling pathogens of soybean
Objective 2. Curate the collection of fungal pathogens collected during the first phase of this project
Objective 3: Improve understanding of the biology of Rhizoctonia solani as seedling pathogen of soybean
Objective 4. Improve understanding of the biology of Fusarium sp. as seedling pathogen of soybean
Objective 5: Improve understanding of the biology of Pythium as a seedling pathogen of soybean
Objective 6: Evaluate the effect of multiple pathogen interactions on seedling disease
Objective 7: Impact of seed treatments on the interaction of seedling pathogens
Objective 8: Communicate research results with farmers and stakeholders

Project Deliverables

Objective 1-2:
• Development of a QPCR panel to detect and quantify 5-10 fungal and oomycete pathogenic species.
• Optimization and validation of the panel in at least two laboratories with 3 different QPCR platforms.
• Development of standard operating procedures for the easy adoption of the panel by other users. SOP’s have been developed for the Phytophthora assays as part of the OSCAP project, these SOP’s can be adapted for additional assays.
• Maintenance of a collection of ~3,000 isolates of fungi collected from diseased soybean seedlings.
• Development and testing of long-term storage techniques for the different fungal species in the collection.
• Development and maintenance of a searchable database of collection of isolates.

Objective 3:
• Establish collection of Rhizoctonia isolates from soybean fields in underrepresented states, including new production areas towards the west.
• Determine R. solani anastomosis groups recovered from soybean seedlings and soil and identify the dominant anastomosis group.
• Determine pathogenicity of Rhizoctonia isolated from soybean fields
• Develop 1-2 additional peer-reviewed publications on fungicide sensitivity, anastomosis group diversity, and pathogenicity of Rhizoctonia. Results will also be disseminated at grower meetings, field days, crop production clinic, online in CropWatch, and other Extension publications.
• Determine if early maturity group soybean germplasms vary in response to Rhizoctonia root rot and identify those with different levels of susceptibility

Objective 4:
• Improved understanding of Fusarium species causing seedling disease on soybeans
• Identification of a resistant genotypes to more than one Fusarium species that can cause damping off and root rot.
• Improved understanding of Fusarium species from soybeans can affect corn and vice-versa; this will have influence on disease management practices (crop-rotations) in future.
• Test at least 2 common seed treatment active ingredients against a large collection of Fusarium proliferatum isolates that originate from diseased seedlings and seeds from Kansas.
• Screen 20-30 entries in MG III, MG IV, and MG V (et al.) from the Kansas State University breeding program (and other public programs) for resistance to F. proliferatum using a high-throughput rolled-towel pathogenicity assay.
• Publish at least 1 journal article reporting sensitivity of F. proliferatum to seed treatment active ingredients and/or reactions of breeding germplasm to this pathogen.

Objective 5:
• Determine fungicide sensitivity of = 250 isolates (82 species * 3 isolates per species)
• Determine fungicide sensitivity to chemistries = 2 (mefenoxam, ethaboxam)
• Screen chemistries at temperatures = 2 (55F, 75F)
• Improved understanding of Pythium-soybean interaction
o Improved understanding of the effect of cold temperatures and Pythium spp. on stand establishment of treated soybean – experiments done; manuscript in progress
o Data regarding effect of cold (<50F) temperatures at varying intervals after planting on the emergence of 2 to 3 soybean varieties that vary in resistance to Pythium -
o Data regarding effect of cold (<50F) temperatures at varying intervals after planting on seedling diseases caused by two species of Pythium
o Data regarding effect of cold (<50F) temperatures at varying intervals after planting on the efficacy of two commercial seed treatments experiments done; manuscript in progress

Objective 6:
• Improved understanding of seedling disease pathogen complex
o Data on what species are often associated in the seedling disease complex experiments done; manuscript in progress
• Improved understanding of interactions between seedling pathogens and their contribution to seedling disease
o Emergence and disease data associated with the interaction of three or more Pythium species
o Emergence and disease data associated with the interaction of three or more Fusarium species
o Emergence and disease data associated with the interaction of two or more Pythium and two or more Fusarium species experiments done; data analysis and interpretation in progress

Objective 7:
• Data will be generated to characterize the effect of 2-3 seed treatments on the population of fungal species in the rhizosphere and their ability to infect soybean plants.
• Greenhouse protocols will be developed to test the effect of 2-3 seed treatments on the collective ability of 3-4 fungal species to infect soybean seedlings.
• Results from greenhouse experiments will be compared and contrasted to those from field experiments.
• A manuscript will be prepared to publish the data learned from the research. Data will also be shared with researchers and other constituencies through presentations.

Objective 8:
• Provide high-quality Extension materials for soybean seedling diseases:
o This will include two full length publications, 3 web-based videos and 1 slide set to help farmers and agribusiness professionals to understand seedling diseases and make informed decisions on best management practices.

Progress of Work

Updated April 7, 2018:
Objective 1: Development and deployment of a panel of QPCR probes to identify and quantify fungal seedling pathogens of soybean (A. Fakhoury-SIU, M. Chilvers-MSU, and D. Malvick-UMN)
Chilvers Lab - We have sent Pythium sequence data and DNA samples to collaborators Dr. Frank Martin (USDA) and Dr. Tim Miles (CMBU) for the development of Pythium genus specific marker. We have also continued to work with these collaborators in the validation of the isothermal RPA assay for genus level detection of Phytophthora. The testing of this assay will provide information to the diagnostic companies for commercialization of the kits. Which would allow wider deployment and use of this type of assay which can be used in the field with relatively simple equipment.

Fakhoury lab – we have added another universal assay targeting both Phytophtora and Pythium genera. The assay has been optimized and tested for efficiency and sensitivity. Multiplexing is still being tested for the probe panel, and if successful it will reduce the number of assays from 10 assays to 3 or less. A manuscript is under preparation entitled “A probe panel assay for the detection and quantification of seedlings pathogens in Soybean fields” is under preparation and will be submitted during 2018.

Objective 2: Curate the collection of fungal pathogens collected during the first phase of this project (A. Fakhoury-SIU)
The website that describes each isolate collection and allows for retrieval request is under construction.

Objective 3a: Characterize R. solani anastomosis groups affecting soybean seedlings throughout the U.S. (S. Everhart and T. Adesemoye-UNL)
Our results have expanded the collection of Rhizoctonia root and stem rot isolates, adding a total of 114 Rhizoctonia isolated from soybean fields in 2015, 2016, and 2017. Thus far, we have identified Rhizoctonia zeae (75), R. solani AG-4 (26), and 13 other R. solani identified as one of the following anastomosis groups: AG1-1 IA, AG-B, AG-3, AG-5, AG-K, and AG-2-1. Our work is further characterizing the level of pathogenicity of these isolates and has identified a surprising number of Rhizoctonia zeae that are pathogenic to soybean.

Objective 3b: Monitor shifts in fungicide sensitivity in R. solani populations (S. Everhart and T. Adesemoye-UN)
Fungicide sensitivity is being determined for four commonly used seed treatments in soybean and corn: azoxystrobin (QoI), fludioxonil (phenylpyrrole), prothioconazole (DMI), and sedaxane (SDHI). Average EC50 of 41 Rhizoctonia zeae isolates for fludioxonil was 0.1 ppm (range: 0.03 - 0.33 ppm). Average EC50 of 15 R. zeae isolates for prothioconazole was 0.17 ppm (range: 0.08 - 4.5 ppm). Preliminary screening for azoxystrobin showed that EC50 of 28 R. zeae isolates was more than 100 ppm.

Our population analysis is also underway. We obtained GBS data for 12 R. zeae was obtained from Dr. O. O. Ajayi-Oyetunde and Dr. C. Bradley. Data was filtered and 2,161 loci were identified as potential candidates for developing SNP markers. Further analysis is underway to identify loci that are polymorphic for at least 25% samples. Markers developed from this data will be used for analyzing population structure of R. zeae isolates obtained from Nebraska.

Publications and scientific presentations:
• Gambhir, N., Everhart, S., Kodati, S., and Adesemoye, T. 2018. Fungicide Resistance: Risk and Management. Nebraska Soybean Magazine. In Press.
• Kodati, S., Adesemoye, T., Gambhir, N., and Everhart, S. 2018. Rhizoctonia Diseases on Soybean. Nebraska Soybean Magazine. In Press.
• Everhart, S. and T. Adesemoye. 2018. Fungicide Resistance in Rhizoctonia Solani and Implications for Soybean Fields in Nebraska. Nebraska Soybean Board, Meeting January 10th, Columbus, NE.
• Kodati, S., and Adesemoye, A. O., 2018. Biology-based strategies for integrated management of Rhizoctonia solani in soybean fields. 9th International IPM symposium, Poster- 48, March 19-22, 2018.
• Kodati, S., Eskelson, M. J., and Adesemoye, A. O. 2017. Cross-pathogenicity of Rhizoctonia spp. isolated from multiple hosts to corn, soybean, and wheat. A PowerPoint presentation made during the Annual Meeting of the North Central Division meeting of American Phytopathological Society, Champaign, IL. June 14-16, 2017.
• Kodati, S., Gambhir, N., Everhart, S., and Adesemoye, A. O. (2017). Prevalence and pathogenicity of Rhizoctonia spp. from soybean in Nebraska. A poster presentation during the American Phytopathological Society (APS) Annual meeting (poster #546-P), which held at San Antonio, Texas. August 5-9, 2017.
• Adesemoye, A. O. presented a seminar in Lincoln, NE on September 29, 2017 titled: “Harnessing components of the root microbiome for integrated management of soilborne plant diseases” and findings from this study was part of the discussion. The seminar was part of the UNL Department of Agronomy and Horticulture fall seminar series, which was well publicized.
• Adesemoye, A.O., S. Kodati, and R. Werle. 2016. Herbicide Injury and Pathogen Infection on Soybean Seedlings. CropWatch June 17, 2016
• Kodati, S., and A.O. Adesemoye. 2016. Characterization, Anastomosis Grouping and Pathogenicity of Rhizoctonia solani on Multiple Plant Hosts in Nebraska. Department of Plant Pathology Seminar Series. Nov. 7, 2016.

Objective 3c: Identification and characterization of resistance and tolerance to Rhizoctonia root rot (D. Malvick-UMN)
The goals of this project are to identify common R. solani anastamosis groups on soybean in MN and determine if early maturity group soybean germplasms vary in response to the common isolate types. We have continued to test new isolates of R. solani from fields in MN. We have determined that the AG 2-2 IIIB type is common on soybean seedlings in MN and that these isolates vary widely in aggressiveness/virulence on different soybean varieties This work is continuing and preparations are underway for field studies.

Objective 4a: Pathogenicity of Fusarium species and identify resistant germplasm (F. Mathew-SDSU)
Screening soybean germplasm (performed in March to August 2017) = For F. graminearum, of the 160 soybean genotypes that were screened for resistance, the fungus caused significantly shorter lesions on 15 genotypes when compared to the susceptible check at P = 0.05. For F. proliferatum, of the 227 genotypes that were screened for resistance, the fungus caused significantly shorter lesions on 85 genotypes belonging to maturity group 0 and 43 genotypes belong to maturity group I compared to the susceptible check at P = 0.05. For F. sporotrichioides, of the 115 soybean genotypes, the pathogen did not cause significantly shorter lesions on any of the genotypes when compared to the susceptible check at P = 0.05. For F. subglutinans, the pathogen caused significantly shorter lesions on 21 genotypes when compared to the susceptible check at P = 0.05.

Publication
Okello, P. N., and Mathew, F. M. 201X. Interaction between Fusarium and soybean cyst nematode on soybean (Glycine max L.). Plant Dis. (PDIS-10-17-1570-RE; Accepted 16-Dec-2017).

Objective 4b. Improve understanding of the biology of Fusarium sp. as seedling pathogen of soybean (K. Little-KSU)
Previous work has shown that approximately 25% of F. proliferatum isolates were found to be resistant to fludioxonil. Work with azoxystrobin has shown that approximately 12.5% of F. proliferatum isolates and 6% of F. semitectum show some level of resistance to azoxystrobin. Of the three Kansas F. oxysporum isolates tested against azoxystrobin so far, all three (100%) are resistant to azoxystrobin. More work is needed on F. oxysporum in Kansas in this regard. Isolates of other Fusarium spp., including F. graminearum, F. thapsinum, F. tricinctum, and F. verticillioides did not appear to be resistant to this fungicide active ingredient, although more isolates of these species need to be tested. Although Fusarium proliferatum has showed potential to cause soybean seedling and root rots, its influence and conditions necessary to negatively affect seed quality still uncertain and underexplored. The objectives of this study were to evaluate the aggressiveness of Fusarium proliferatum and their inoculum potential on soybean seed quality. Screening for aggressiveness was conducted using laboratory and greenhouse assays. Eight F. proliferatum isolates were used and the results, from all of parameters tested, were compared with mock-inoculated controls. Overall, all of F. proliferatum isolates tested significantly decreased seed germination in laboratory (p < 0.001) assays. In greenhouse assays, most F. proliferatum isolates tested were also able to reduce seed vigor (p < 0.001) when compared with mock-inoculated control. Four F. proliferatum isolates were used to study the influence of inoculum potential treatment and its interaction with aggressiveness on soybean seed quality using the rolled-towel assay. There was a highly and significant interaction between the isolate aggressiveness and the inoculum potential treatment used on the percentage of artificially inoculated seeds (p < 0.001). Overall, the effects of seedborne F. proliferatum isolates on soybean seed germination decreases as the inoculum potential in contact with the seeds decreases. No significant reduction of seed germination was observed when soybean seeds were treated with low inoculum potential (2.5 x 10^1 conidia ml-1) with both moderate and highly pathogenic isolates, suggesting that F. proliferatum has the potential to reduce soybean seed quality, depending on the aggressiveness and inoculum potential of the pathogens present in seeds.

Objective 5: Improve understanding of the biology of Pythium as a seedling pathogen of soybean (A. Robertson-ISU and M. Chilvers-MSU)
Peer-reviewed papers accepted pending revision:
1. Serrano, M., McDuffee, D. and Robertson, A.E. XXXX. Seed treatment reduces damping-off caused by Pythium sylvaticum on soybeans subjected to periods of cold stress. Can. J. Pl. Path. (accepted pending revision).
2. Serrano, M. and Robertson, A.E. XXXX. The effect of cold stress on damping off of soybean caused by Pythium sylvaticum. Plant Dis. (accepted pending revision).
Presentations:
Robertson, A.E. 2018. Soybean Seed Treatments. ISUEO Crop Advantage Series: Waterloo. January 2018.
A manuscript describing fungicide sensitivity of four species from across the NC region is in progress.

Chilvers Lab - Manuscript describing the high-throughput fungicide sensitivity assay is being revised for resubmission to Phytopathology. An additional manuscript describing Pythium and Phytophthora species sensitivity to mefenoxam and ethaboxam is being written.

Objective 6: Evaluate the effect of multiple pathogen interactions on seedling disease (A. Robertson and G. Munkvold-ISU)

The following paper was submitted for review:
Lerch, E. and Robertson, A.E. XXXX. Effect of co-inoculations of Pythium and Fusarium species on seedling disease development of soybean. Can. J. Pl. Path.

Objective 7: Impact of seed treatments on the interaction of seedling pathogens (A. Fakhoury and J. Bond-SIU)
Fewer modifications were introduced to isolate the effect of each pathogen and in combination on plant health. Fusarium species were evaluated individually and under interaction in the following scheme: A; B; C; A+B; A+C; B+C and A+B+C (whereby A= F. oxysporum; B= F. proliferatum; C= F. sporotrichioides). Root length, surface area and projected area data were collected for each inoculation scheme.
Our results have shown that Fusarium proliferatum to be more aggressive than the other two species Fusarium oxysporum and F. sporotrichioides based on root morphology and pathogen density. On the other hand, F. oxysporum, and F. proliferatum data suggested that they have an additive (synergistic) effect when causing root rot on soybean.

Objective 8: Communicate research results with farmers and stakeholders (K. Wise-UK and others)

View uploaded report Word file

Updated November 3, 2018:
Objective 1: Development and deployment of a panel of QPCR probes to identify and quantify fungal seedling pathogens of soybean (A. Fakhoury-SIU, M. Chilvers-MSU, and D. Malvick-UMN)
Chilvers Lab - We have sent Pythium sequence data and DNA samples to collaborators Dr. Frank Martin (USDA) and Dr. Tim Miles (CMBU) for the development of Pythium genus specific marker. We have also continued to work with these collaborators in the validation of the isothermal RPA assay for genus level detection of Phytophthora. The testing of this assay will provide information to the diagnostic companies for commercialization of the kits. Which would allow wider deployment and use of this type of assay which can be used in the field with relatively simple equipment.

Fakhoury lab – we have added another universal assay targeting both Phytophtora and Pythium genera. The assay has been optimized and tested for efficiency and sensitivity. Multiplexing is still being tested for the probe panel, and if successful it will reduce the number of assays from 10 assays to 3 or less. We have validated the probe panel on a set of seedlings inoculated with a mix of seedlings pathogens (including Fusarium species and Rhizoctonia), and the assays were successful in detecting the inoculated pathogens. Currently, efficiency and sensitivity of the developed assays is also being tested on soil and root from diseased seedlings soybean.
A manuscript is under preparation entitled “A probe panel assay for the detection and quantification of seedlings pathogens in Soybean fields” is under preparation and will be submitted during 2018.

Objective 2: Curate the collection of fungal pathogens collected during the first phase of this project (A. Fakhoury-SIU)
The website that describes each isolate collection and allows for retrieval request is under construction.

Objective 3a: Characterize R. solani anastomosis groups affecting soybean seedlings throughout the U.S. (S. Everhart and T. Adesemoye-UNL)
Our results have expanded the collection of Rhizoctonia root and stem rot isolates, adding a total of 114 Rhizoctonia isolated from soybean fields in 2015, 2016, and 2017. Thus far, we have identified Rhizoctonia zeae (75), R. solani AG-4 (26), and 13 other R. solani identified as one of the following anastomosis groups: AG1-1 IA, AG-B, AG-3, AG-5, AG-K, and AG-2-1. Our work is further characterizing the level of pathogenicity of these isolates and has identified a surprising number of Rhizoctonia zeae that are pathogenic to soybean.

This survey has provided novel information, which shows that Rhizoctonia zeae (Waitea circinata var. zeae) is an important pathogen of soybean, which has not been well studied. We have identified Rhizoctonia zeae and Rhizoctonia solani AG-4 as the two most prevalent groups in Nebraska, among a total of more than 100 Rhizoctonia isolated. Our work is further characterizing the level of pathogenicity of these isolates and has identified a surprising number of Rhizoctonia zeae that are pathogenic to soybean. We are investigating this further and if confirmed, it will be a major finding. Different methods of isolation of Rhizoctonia and growth media were developed or evaluated, which will enable standardized approaches to future studies on this pathogen. Thus far, we have presented information to growers about conditions that may favor Rhizoctonia infection as well as information on disease management.

Objective 3b: Monitor shifts in fungicide sensitivity in R. solani populations (S. Everhart and T. Adesemoye-UN)
Fungicide sensitivity assays are nearly complete, with results from the entire first experimental replicate showing that Rhizoctonia zeae has a broad range of fungicide sensitivity to prothioconazole, sedaxane, and fludioxonil. However, these results also suggest that Rhizoctonia zeae is completely insensitive to azoxystrobin fungicide, which is currently one of most common fungicides used due to the expected high specificity of action. A greenhouse study will be used to determine if these results are repeatable for the fungicide applied in planta.

Our population analysis is also underway. We obtained isolates of Rhizoctonia zeae from Dr. O. O. Ajayi-Oyetunde and Dr. C. Bradley, collected from several North Central states. We obtained whole-genome sequence data for five isolates and are currently identifying polymorphic SSR loci to characterize the population structure of these populations across the region. These markers will be used to assess population structure of isolates obtained throughout the region.

Publications in 2018:
1. Adesemoye, A. O. 2018. Root and Soilborne Diseases Update. CropWatch July 2, 2018.
2. Adesemoye, A. O. 2018. Soilborne and early seedling pathogens and delayed planting in corn and soybean. CropWatch May 3, 2018.
3. Gambhir, N., S. Everhart, S. Kodati, & A. Adesemoye. 2018. Fungicide Resistance: Risk and Management. SoybeaNebraska Mag., Spring 2018, Page 22.
4. Kodati, S., A. Adesemoye, N. Gambhir, & S. Everhart. 2018. Rhizoctonia Diseases in Soybean. SoybeaNebraska Magazine, Spring 2018, Page 23.
Posters Presented in 2018:
5. Gambhir, N., Kodati, S., Adesemoye, A.O., and Everhart, S.E. 2018. Fungicide sensitivity of Rhizoctonia spp. isolated from soybean fields in Nebraska. Poster at ICPP Meeting in Boston, MA.
6. Kodati, S. and Adesemoye, A. O. 2018. Emerging understanding of the pathogenesis of Rhizoctonia zeae in row crops. ICPP-APS Joint Conference holding August 1 to 5 in Boston, MA.
Presentations in 2018:
7. Everhart, S.E. and Adesemoye, A.O. 2018. An update on the project presented during the 2018 Crop Production Clinics at the Sandhills Convention Center, North Platte, NE on January 11, 2018.
8. Gambhir, N., Kodati, S., Adesemoye, A.O., and Everhart, S.E. 2018. Fungicide sensitivity of Rhizoctonia zeae from soybean and corn in Nebraska. Presentation at International Rhizoctonia Workshop: Rhizoctonia at crossroads: research advances and challenges, Boston, MA.
9. Kodati, S. and Adesemoye, A.O. 2018. Diversity and pathogenicity of Waitea circinata on row crops. Presentation at International Rhizoctonia Workshop: Rhizoctonia at crossroads: research advances and challenges, Boston, MA.
10. Presentation during 2018 Nebraska Crop Management Conference at the Younes Conference Center, Kearney, NE on January 24 and 25, 2018.

Objective 3c: Identification and characterization of resistance and tolerance to Rhizoctonia root rot (D. Malvick-UMN)
The primary goals of this project are to identify common anastamosis groups (AG) of R. solani on soybean seedlings in Minnesota and determine if early maturity group (MG) soybean germplasms vary in response to R. solani. Based on our sampling, the predominant anastomosis group of R. solani infecting soybean in Minnesota is AG 2-2 IIIB. Our greenhouse studies have determined that isolates in this AG group vary in aggressiveness on soybean seedlings. Fungicide sensitivity studies ae underway with multiple isolates. In 2017, significant differences were detected among MG 1.5-2.0 cultivars and breeding lines for final plant population and yield in field studies in southern Minnesota, indicating that soybean cultivars and breeding lines differ in susceptibility to Rhizoctonia diseases. The field studies were repeated with the same varieties and breeding lines in 2018 in southern MN, and the study was expanded to include earlier maturity (~MG < 1) cultivars and lines at a site in northern Minnesota. Field conditions (warm and moist soil) were very favorable for Rhizoctonia root rot at both field sites this year, which created unusually severe disease pressure that killed most plants. Harvest was delayed due to wet weather and final field data from 2018 has not yet been analyzed.

Scientific Presentations
1. C. M. Floyd, P. Sharma, A. K. Chanda, and D. K. Malvick. 2018. Soybean varieties and breeding lines differ in susceptibility to Rhizoctonia root and stem rot. Presented at the Annual Meeting of the North Central Division of the American Phytopathological Society in Fargo, ND. June 2018.

Objective 4a: Pathogenicity of Fusarium species and identify resistant germplasm (F. Mathew-SDSU)

Presentation:
1. Mathew, F. M. 2018. Improve understanding of the biology of Fusarium sp. as seedling pathogen of soybean. Meeting for Seedling Disease of Soybean (NCSRP and USB) Research Group, Excelsior Springs, MO. September 11-12, 2018.

Objective 2: Screening soybean germplasm (performed between April and September 2018).

1. Two accessions significantly less susceptible to F. graminearum; three to F. proliferatum and one to F. subglutanins.
a. PI 592907C was significantly less susceptible to F. graminearum and F. proliferatum
b. PI 361090 was significantly less susceptible to all the three pathogens
2. None of the accessions were significantly less susceptible to F. sporotrichioides

Publication –
1. Okello, P., and Mathew, F. M. XXXX. Screening soybean germplasm for resistance to Fusarium graminearum, F. proliferatum, F. subglutanins and F. sporotrichioides Plant Health Progress (Manuscript in preparation for submission by January 2019).

Objective 3: Cross-pathogenicity of species of Fusarium causing disease on soybean and corn (performed between April and September 2018).

1. On soybean, Fusarium proliferatum isolates from corn caused the greatest disease severity. Significant differences in disease severity were observed among soybean and corn isolates within F. graminearum, and F. proliferatum. However, significant differences in RTE were not observed among soybean and corn isolates within F. oxysporum, F. subglutinans, F. equiseti-incarnatum complex, F. solani, and F. acuminatum.
2. On corn, significant differences in root rot severity were observed among soybean and corn isolates within F. graminearum, F. subglutinans, and F. proliferatum. However, significant differences in disease severity were not observed among soybean and corn isolates within F. oxysporum, F. equiseti-incarnatum complex, and F. acuminatum.
3. 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.

Publication –
1. Okello, P., and Mathew, F. M. XXXX. Seven species of Fusarium from soybean and corn are pathogenic on the two hosts. Plant Health Progress (Manuscript submitted on 03-Oct-2018; PHP-10-18-0056-RS).

Objective 4b. Improve understanding of the biology of Fusarium sp. as seedling pathogen of soybean (K. Little-KSU)
Symptomatic and asymptomatic soybean seedlings were collected from the twelve environments located in central and eastern Kansas where the bulk of production occurs. Total fungi and Fusarium spp. were collected from seedling roots at the V2 stage. Inter- and interfield diversity measurements showed overall negative relationships between seedling-associated fungal species richness and dominance, and diversity and dominance. In an effort to characterize environmental parameters associated with certain seedling-associated Fusarium spp. with soybean seedling roots, air temperature, precipitation, wind speed, soil temperatures (2” and 4”), solar radiation, and evapotranspiration were collected from each environment. As a result, differences in favored environmental conditions could be determined for particular root-associated species. Frequency of Fusarium acuminatum and F. reticulatum on soybean seedling roots was positively correlated to increased air temperature. However, F. solani and F. fujikuroi were negatively correlated to air temperature, indicating that they prefered cooler temperatures for seedling colonization. This result was further confirmed as the same results for these species were evident when 2” and 4” soil temperatures were related to species frequencies. Peak isolation frequencies for F. oxysporum and F. solani occurred from environments where temperatures ranged between 45 to 69F and 44 and 69F, respectively. In addition to favoring cooler temperatures, these two species increased in frequency from environment where higher levels of precipitation occurred accompanied by less evapotranspiration during seedling development. On the other hand, F. acuminatum, which was found in abundance on soybean seedling roots, appeared to prefer higher temperatures in air and soil, and higher levels of evaptranspiration (ETo). It is possible that his species takes advantage of stressed seedlings, a situation that would certainly occur under higher soil temperatures and ETo. In a 15 day period, when ETo exceeded approximately 3.8 inches, F. acuminatum isolation frequencies were significantly higher than ETo were less than this value. Further, higher wind speeds, which can also create stress for seedlings, were correlated to higher isolation frequencies of F. proliferatum. In this case, average daily windspeeds of 8 mph or greater, were associated with the highest recovery of F. proliferatum. This too could be due to plant stress or damage, a situation of which F. proliferatum could take advantage.

Further, Fusarium isolates per seedling values were calculated from environments with differences in watering regime (dryland vs. irrigated), soil type, tillage, and crop rotation. For F. proliferatum, dryland environments, sandy- and silty-loam soils, and corn rotations yielded marginally significantly greater numbers of F. proliferatum isolates per seedling (P < 0.10). Tillage did not have a significant effect upon F. proliferatum isolation, but numerically greater levels of this pathogen were isolated from seedlings under conventional tillage regimes. Also, there is a positive relationship (r = +0.481, P = 0.0816) between seedling root length and F. proliferatum isolation across the environments tested. This may be due to seedling stage. However, the underlying reason for this relationship is not clear."

Publications (in progress):
1. Pedrozo, R., and Little, C.R. ####. Fusarium proliferatum inoculum potential affects soybean seed and seedling quality. Plant Disease: In preparation.
2. Pedrozo, R., Fenoglio, J., Waite, N., and Little, C.R. ####. Fludioxonil resistance in diverse seedborne Fusarium isolates from Kansas. Plant Health Progress: In preparation.

Objective 5: Improve understanding of the biology of Pythium as a seedling pathogen of soybean (A. Robertson-ISU and M. Chilvers-MSU)
Our research evaluating the effect of cold stress on soybean seedling disease caused by P. sylvaticum (see peer-reviewed manuscripts submitted below) did not take into account soil moisture. Preliminary trials were done in the growth chamber to include soil moisture. At high soil moisture, emergence of soybean was reduced. Inoculation with P. sylvaticum further reduced emergence.

Peer-reviewed papers accepted pending revision:
1. Serrano, M., McDuffee, D. and Robertson, A.E. XXXX. Seed treatment reduces damping-off caused by Pythium sylvaticum on soybeans subjected to periods of cold stress. Can. J. Pl. Path. (in press)
2. Serrano, M. and Robertson, A.E. XXXX. The effect of cold stress on damping off of soybean caused by Pythium sylvaticum. Plant Dis. 102: 2194-2200.

Chilvers Lab: Manuscript describing the high-throughput fungicide sensitivity assay is being revised for resubmission to Phytopathology. An additional manuscript describing Pythium and Phytophthora species sensitivity to mefenoxam and ethaboxam is being written.

Objective 6: Evaluate the effect of multiple pathogen interactions on seedling disease (A. Robertson and G. Munkvold-ISU)
Revisions are being made to the following paper that was submitted:
Lerch, E. and Robertson, A.E. XXXX. Effect of co-inoculations of Pythium and Fusarium species on seedling disease development of soybean. Can. J. Pl. Path.

Objective 7: Impact of seed treatments on the interaction of seedling pathogens (A. Fakhoury and J. Bond-SIU)
Fewer modifications were introduced to isolate the effect of each pathogen and in combination on plant health. Fusarium species were evaluated individually and under interaction in the following scheme: A; B; C; A+B; A+C; B+C and A+B+C (whereby A= F. oxysporum; B= F. proliferatum; C= F. sporotrichioides). Root length, surface area and projected area data were collected for each inoculation scheme.

Our results have shown that Fusarium proliferatum to be more aggressive than the other two species Fusarium oxysporum and F. sporotrichioides based on root morphology and pathogen density. On the other hand, F. oxysporum, and F. proliferatum data suggested that they have an additive (synergistic) effect when causing root rot on soybean. Rhizosphere soil tightly attached to roots and rhizome were collected for quantitative PCR. At a later stage of this set of experiments, fungicide seed treatments will be incorporated as an additional variable affecting the interaction between the different isolates and soybean.

Objective 8: Communicate research results with farmers and stakeholders (K. Wise-UK and others)

View uploaded report Word file

Final Project Results

Benefit to Soybean Farmers

Performance Metrics

Project Years