Project Details:

Title:
Enhancing Sclerotia stem rot research capacity and exploring new avenues of disease through soybean canopy architecture traits

Parent Project: This is the first year of this project.
Checkoff Organization:Minnesota Soybean Research and Promotion Council
Categories:Soybean diseases, Agronomy, Breeding & genetics
Organization Project Code:10-15-44-22010
Project Year:2022
Lead Principal Investigator:Megan McCaghey (University of Minnesota)
Co-Principal Investigators:
Aaron Lorenz (University of Minnesota)
Keywords: canopy , plant shape, Sclerotinia sclerotiorum, Soybean Diseases, White Mold

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

Sclerotinia stem rot (SSR), is caused by the soilborne fungal pathogen Sclerotinia sclerotiorum and consistently ranks in the top ten diseases that reduce soybean yields in the United States (Bradley et al., 2021). The interaction of environmental conditions in the canopy including light, temperature, and humidity favor SSR development. The impact of soybean canopy architecture on these conditions and SSR development is an understudied area of research. If identified, plant architecture traits to reduce disease development may be useful for future resistance breeding efforts, especially when combined physiological resistance.
To enhance disease resistance breeding in Minnesota, I propose foundational work to characterize Sclerotinia sclerotiorum isolates, collected throughout the state, that can be used to comprehensively screen soybean lines and study fungal biology. I also propose developing and comparing field techniques for infesting research fields to conduct applied SSR research. Lastly, this project aims to define relationships between canopy architecture and sclerotinia development, to provide another, underexplored consideration for disease resistance breeding to avoid yield losses from SSR.

Project Objectives

1. GOAL: Characterize the aggressiveness of S. sclerotiorum isolates for use in future pathogen biology and resistance screening assays
Obj. 1) Collect a panel of S. sclerotiorum isolates from Minnesota soybean fields and researchers
Obj. 2) Characterize their growth and relative aggressiveness on soybean lines known to have differential resistance

2. GOAL : Define relationship between canopy architecture and SSR development
Obj. 1) Characterize the branching angle of lines in the field
Obj. 2) Define the genetic, SSR resistance of architecturally diverse lines
Obj. 3) Measure canopy closure and light penetration along with apothecia and SSR development

3. GOAL: Develop reliable S. sclerotiorum nurseries for future SSR field trials

Project Deliverables

1. GOAL: Characterize the aggressiveness of sclerotinia isolates for use in future pathogen biology and resistance screening assays
I aim to collect a panel of S. sclerotium isolates from soybean-growing fields throughout Minnesota that can be characterized and used in pathogen biology assays and to screen breeding and commercial lines for resistance to SSR. Diverse isolate populations have been documented across US soybean fields (Aldrich-Wolfe et al. 2015 and Willbur et al. 2017).
Aggressiveness, as indicated by the severity of infections, is often different between isolates and soybean genotypes resistance rankings can also shift, depending on the isolate used in screenings (Willbur et al. 2016). Due to these differences, Willbur et al. (2017) concluded that multiple isolates with a range of characterized responses are recommended to screen for resistance to SSR. Additionally, biological studies will benefit from a representative isolate collection, as isolates are not uniform. For example, the number of sclerotia that can produce apothecia and the rate of apothecial production differ by isolate (Lui and Paul 2007). Additionally, the reference isolate for which we have sequenced genome (isolate 1980) is not as aggressive as several other isolates, and oddly, does not have mycelial compatibility with isolates that it was assayed with (Willbur et al. 2017). Due to these differential characteristics, this study aims to characterize Minnesota isolates in soybean to establish a range of native, biologically relevant isolates for germplasm screening and fungal biology assays in Minnesota.

Obj.1) Collect a panel of S. sclerotiorum isolates from Minnesota soybean fields and researchers
In the summer of 2021, isolates from 10 or more soybean fields will be collected from throughout the state. I will collect isolates through visits to research sites and through communications with growers. Sclerotia from diseased plants will be plated on PDA and sclerotia will be collected after approximately 14 days. New sclerotia will be collected and stored at 4° C, in the dark with desiccator beads, as described in Pottinger et al. (2008).

Obj. 2) Characterize their growth and relative aggressiveness on soybean lines known to have differential resistance
New isolates will be characterized alongside isolates currently used by researchers at UMN, including isolates in the Malvick Lab, and with the isolate for which we have sequenced genome, isolate 1980 (Amselem et al. 2007). Isolate growth will be characterized by measuring four replicated fungal cultures of each isolate over time. Area under the growth curves will be assessed for 3-4 days, until the edge of plates are reached. To evaluate isolate aggressiveness, susceptible cultivar Dwight will be challenged with all isolates in the greenhouse using a cut petiole technique (Peltier and Grau 2008), where an agar core is collecting from the leading edge of mycelia and introduced to the petiole. These inoculations will be repeated three times and lesions will be measured 7-14 days post-inoculation, at three intervals, to assess disease progress (McCaghey et al. 2017 and Willbur et al. 2017). The study will be organized in a randomized complete block design.
Once we identify a panel of isolates with different levels of aggressiveness, we can test whether isolates will distinguish the resistance ranking of cultivars. Using three representative isolates, we will inoculate soybean check lines (Webster et al. 2021, Figure 2) developed by Dr. Damon Smith’s Lab at University of Wisconsin-Madison with known low, moderate, and high levels of resistance (compared to susceptible controls) to see if resistance rankings are similar when challenged with the new, UMN isolates.

2. GOAL : Define relationship between canopy architecture and SSR development
In addition to physiological resistance, plant architecture may be an important component of avoiding infection by S. sclerotiorum in the field. The development of SSR and the production of apothecia that cause disease in soybean are highly dependent on environmental conditions. Two of these particularly important conditions include moisture and light wavelength penetration to the surface of the soil, where apothecia develop. Developing a better understanding
of plant architecture in relation to disease development may lend to future possibilities of screening for architecture traits, combining genetic and architecture traits while breeding. Additionally, wide rows and high seeding rates are associated with decreased SSR development, but yields are reduced in this planting scenario (Webster et al., 2021). However, it may be possible to identify architecture traits that allow planting densities to remain high without enhancing disease or harming yields. In soybean, branch angle is the primary trait associated with canopy architecture. This trait impacts canopy closure and light penetration.

Obj. 1) Characterize the branching angle of lines in the field
To quantify branch angle, the angles between two branches growing in opposite directions near the base of 20 fully mature individuals from each line in this study will be measured in the field with a protractor; average branch angles will be calculated and compared for the lines. Lines used in this study will be from Dr. Aaron Lorenz’s research program and include 1) a branch angle diversity panel of 10 mutant lines, 2) near isogenic lines (lines with nearly identical genetic makeups except for branch angle loci), and 3) an “era panel” of historical soybean accessions. Evaluations will occur both in the greenhouse, in a randomized complete block design, and in the field. Evaluations in the field will occur within existing trials of Dr. Aaron Lorenz, and postdoctoral researcher Dr. Suma Sreekanta. The lines will be grown in two locations per group of lines, for a total of 6 trial locations. Research farm locations include St. Paul, Rosemont, Waseca, and Lamberton, Minnesota.

Obj. 2) Define the genetic, SSR resistance of architecturally diverse lines
In addition to examining branch angle, the genetic resistance of lines will be assessed, independent of branch angle in the greenhouse. This will be helpful to observe whether infection rates in the field are different due to genetic/physiological resistance or because of disease escape from canopy architecture variation. To examine the genetic resistance of lines, they will be directly challenged with the pathogen, S. sclerotium, as described in Goal 1, Obj. 2. Greenhouse screenings will compare the resistance reactions of the lines measured in the field, and lines will be evaluated for resistance alongside defined check lines (Webster et al. 2021) that are susceptible, moderately resistant, and highly resistant lines (compared to the susceptible and moderate controls). Dr. Ashish Ranjan is developing check lines from Dr. Aaron Lorenz’s research program, and these may be used in comparisons as well.

Obj. 3) Measure canopy closure and light penetration along with apothecia and SSR development
Within each of the evaluated lines, four plots will be monitored for canopy closure, wavelength at the ground, disease, and apothecia production. As the canopy closes, a favorable microclimate promotes sclerotial germination and SSR development by maintaining high humidity, prolonging leaf wetness, and lowering temperature (Blad et al. 1978 and Kurle et al. 2001). Light, temperature, and moisture are considered to be the three most important factors for the germination of sclerotia of S. sclerotiorum (Abawi and Grogan 1979; Letham 1975; Sun and Yang 2000). Measurements of canopy closure will start before beginning bloom growth stage (R1) until full pod (R4) and will occur in by pictures in three fixed spots at a height of 1.5m in each plot, as described in (Mamadou et al. 2018). For scale reference, every picture included a plastic ruler. The percentage of canopy closure will be calculated for each sampling day as: Canopy closure=1-(daily measured distance/row spacing distance).
Additionally, the wavelengths of light penetrating to the ground where apothecia germinate and the intensity of light will be measured using a portable, fibre optic spectrometer. The spectrometer will be placed at three positions relative to the soybean stem base, into the row, and at 3-5 locations in each sampling plots. Measurements will be performed on sunny days, within a three-hour window each sampling period. Disease severity will be monitored in each naturally infested plot (if disease pressure is present). Thirty arbitrarily selected plants in each plot of the field nursery at the R6 soybean growth stage will be evaluated. Plants were scored either 0 (no infection), 1 (infection on branches), 2 (infection on, but not girdling, the main stem), or 3 (infection on the main stem resulting in death or poor pod fill) (McCaghey et al 2017). The number of apothecia will be monitored during each growth stage. Apothecia counts will be collected from 3-5 squares placed randomly throughout plots so that the middle of each square was aligned with a row.
Importantly, Dr. Lorenz’s group will evaluate the lines for yield, which would be a priority consideration in line selection for breeding and further trialing.

GOAL: Develop reliable S. sclerotiorum nurseries for future SSR field trials
Currently, researchers do not have field sites with reliable and uniform inoculum where we can conduct SSR experiments (personal communication). High disease pressure across plots is often required to observe the impact of experimental treatments (such as variety resistance differences or fungicide efficacy).
To produce apothecia and simulate natural ascospore infections, sclerotia need to undergo a period of cold conditioning for about eight weeks (Pethybridge et al. 2008). This summer, I am interested in trialing three methods to develop disease pressure for trials in 2023. These include:
1) growing sunflowers, which are very susceptible to white mold, inoculating them the back of the head with a slurry of S. sclerotiorum, and then incorporating residue into the soil in the fall of 2022.
2) sprinkle sclerotia inoculum generated in the lab on sorghum/millet seed into the field during the fall before 2023 trials. Cold conditioning over the winter should allow the inoculum to produce apothecia in the following field season.
3) I will grow sclerotia in the lab, cold condition them in the fridge, and then spring-apply the sclerotia to the field.

Untreated, naturally infested plots will be left as controls to compare with plots treated with the described infestation methods. This trial will be conducted in strips, replicated three times per inoculation method at each site. SSR trials will be conducted in the disease nursery locations in 2023, and apothecia and disease incidence will be monitored in the untreated plots of next year’s trials.
The goals and objectives described in this proposal will set the stage for my soilborne fungi pathology lab to conduct biologically relevant SSR research in soybean and will open new, creative avenues to improve resistance to this challenging fungal disease.

Progress of Work

Updated April 13, 2023:
Report document attached for review

SYNOPSIS OF PROJECT AIM:
To enhance disease resistance breeding in Minnesota, I propose foundational work to characterize Sclerotinia sclerotiorum isolates, collected throughout Minnesota, that can be used to comprehensively screen soybean lines and study fungal biology. I also propose developing and comparing field techniques for infesting research fields to conduct applied Sclerotinia stem rot (SSR) research. Lastly, this project aims to define relationships between canopy architecture and S. sclerotiorum development, to provide another, under-explored consideration for disease resistance breeding to SSR.

PROJECT OBJECTIVES:
1. GOAL: Characterize the aggressiveness of S. sclerotiorum isolates for use in future pathogen biology and resistance screening assays

This study aims to characterize Minnesota isolates in soybean to establish a range of native, biologically relevant isolates for germplasm screening and fungal biology assays in Minnesota.

Obj. 1) Collect a panel of S. sclerotiorum isolates from Minnesota soybean fields and researchers
Towards this objective, we have developed a collection of 28 isolates. These isolates have been collected mostly from the Northwestern part of Minnesota (near Crookston). Isolates were surface sterilized using 10% bleach and 70% ethanol solutions. The isolates were then stored with desiccant beads in the refrigerator (4°C). Newly collected isolates were designated as "SSMM-" followed by a number indicating the order in which the isolate was collected. I have also approved a draft permit from USDA APHIS to ship isolates from surrounding states. Seth Naeve, Aaron Lorenz, and their staff have also agreed to help me to collect isolates during field activities. I intend to use additional resources to collect isolates from seed at harvest including grower outreach with David Kee, Twitter, Dean Malvick, and Regional Extension Educators such as Ryan Miller. These networks should lead to a robust isolate collection.

Obj. 2) Characterize their growth and relative aggressiveness on soybean lines known to have differential resistance

We have started screenings to compare the aggressiveness between isolates and will continue trials into the fall and winter semester. In our preliminary screening, seven isolates of Sclerotinia sclerotiorum were evaluated for their aggressiveness as indicated by lesion size on soybean over time. An “empty plug” of agar with no fungus was used as a control to show that lesions were caused by the fungus, not cutting of the petiole. Three plants were inoculated in a single pot and five pots were inoculated per isolate (15 plants per isolate) at the V4 growth stage. The treatments were arranged in a randomized complete block design in the growth chamber. Lesions were measured at 24, 96, and 120 hours post inoculation (HPI). An additional replicate of screenings will begin on 9/12/22 and screenings will continue through the fall and winter.

Consistent lesions formed on plants and allowed the isolates to be compared. Results of the initial screening indicated differing levels of aggressiveness per isolate. For example, MNSS4 P (light blue) appears to be less aggressive than MNSS4 V (bright pink) (See Figure 1 in report).

Once we identify a panel of isolates with different levels of aggressiveness, we can test whether isolates will distinguish the resistance ranking of cultivars. Using three representative isolates, we will inoculate soybean check lines developed by Dr. Damon Smith’s Lab at University of Wisconsin-Madison with known low, moderate, and high levels of resistance (compared to susceptible controls) to see if resistance rankings are similar when challenged with the new, UMN isolates.

I have received the check lines from Damon, and we are currently bulking seed in the greenhouse for future screenings to determine whether our isolate panel can differentiate resistant from susceptible lines.

2. GOAL: Define relationship between canopy architecture and SSR development
In addition to physiological resistance, plant architecture may be an important component of avoiding infection by S. sclerotiorum in the field. The development of SSR and the production of apothecia that cause disease in soybean are highly dependent on environmental conditions. Two of these particularly important conditions include moisture and light wavelength penetration to surface of the soil, where apothecia develop. Developing a better understanding of plant architecture in relation to disease development may lend to future possibilities of screening for architecture traits, combining genetic and architecture traits while breeding.

Obj. 1) Characterize the branching angle of lines in the field
The Lorenz Lab planted soybean panels (of diverse plant architectures) in Waseca on 5/16/22 and in St. Paul on 6/8/2022. They were also planted in Rosemount but due to seed contamination during planting, we are unable to evaluate these. In total, we are evaluating three trials, in both Waseca and St. Paul. Suma Sreekanta, the postdoctoral researcher in the Lorenz Lab, is collecting data on various phenotypic traits that impact light penetration to the ground (where apothecia form). These data will be examined in the fall. See report for a list of Phenotypic traits.

Obj. 2) Define the genetic, SSR resistance of architecturally diverse lines
Resistance screenings of plants inoculated with Sclerotinia in the greenhouse will begin in the winter, once we have complete phenotypic data from lines at the end of this growing season. Based on the data from Obj. 1 and Obj. 2, we will narrow down the number of lines to a panel with a range of the traits measured. We will compare their genetic resistance based on lesion progression over time.

Obj. 3) Measure canopy closure and light penetration along with apothecia and SSR development
Drone data for canopy coverage has been underway once or twice a week since planting. Currently the data is in the form of images, and they will need to be analyzed to be usable. This data will be analyzed at the end of the season when all the flights are complete.

We scouted for apothecia in each row of soybeans using a t-shaped PVC push pole prior to flowering (in St. Paul and at early flowering stages (Waseca) through canopy closure, when apothecia begin to develop. The plots were checked in St. Paul on 7/13/2022, 7/22/2022, 7/27/2022, 8/4/2022, and 8/16/2022. We scouted for apothecia in Waseca on 8/2/2022, and 8/17/2022. No apothecia were observed. We are also conducting disease assessments at the R6, full pod growth stage. In Waseca, disease assessments were conducted on 8/17/2022 and we saw no SSR. We will conduct St. Paul evaluations on 9/1/22. The lack of apothecia and disease in Waseca is likely related to the drought experienced earlier in the summer, and we anticipate that our data collection will be improved with SSR nurseries in the future (Goal 3).

We collected light measurements using a UVB meter in St. Paul starting at beginning flowering, the time most important for Sclerotinia infection, and through canopy closure on 7/22/2022, 7/28/2022, and 8/4/2022. UVB captures that spectrum of wavelengths considered to be the most important for apothecia production. Measurements were conducted in the morning on days with no cloud cover that might block the UVB penetration to the ground. The samples were taken from the left row of each variety, while facing east. Measurements were captured in the center of each two rows at 0", 7.5", and 15" from the base of the plant. Comparisons of light conditions under the architecturally diverse lines will be made along with phenotypic comparisons that may contribute to SSR development this fall.

3. GOAL: Develop reliable S. sclerotiorum nurseries for future SSR field trials
Currently, researchers do not have field sites with reliable and uniform inoculum where we can conduct SSR experiments (personal communication). High disease pressure, across plots is often required to observe the impact of experimental treatments (such as variety resistance differences or fungicide efficacy).

This summer, I am interested in trialing three methods to develop disease pressure for trials in 2023. These include:
1) growing sunflowers, which are very susceptible to SSR, inoculating them the back of the head with a slurry of S. sclerotiorum, and then incorporating residue into the soil in the fall of 2022.
2) sprinkle sclerotia inoculum generated in the lab on carrot seed into the field during the fall before 2023 trials. Cold conditioning over the winter should allow the inoculum to produce apothecia in the following field season.
3) I will grow sclerotia in the lab, cold condition them in the fridge, and then spring apply the sclerotia to the field. 4) Untreated, naturally infested plots will be left as controls to compare with plots treated with the described infestation methods.

Towards this objective, plots were planted on June 3, 2022 at The Northwest Research and Outreach Center (NROC) in Crookston, MN. The variety used was an early, Phomopsis and SSR susceptible Nuseed variety, N4HM354. The trial is a randomized complete block design and each treatment is repeated six times. It was planted on 22” row spacing. Rows are 20 feet long and each treatment plot contained six rows. There is a four-foot buffer of untreated buffer between plots to prevent unintended inoculum spread. Five-foot alleys were left on the front and back of rows. These trials are misted during early flowering until beginning dry down to encourage disease development.

We inoculated plots with a slurry of Sclerotinia at full flowering when some plants were at R5 and others were at R6 on August 22, 2022. Slurry was a prepared with a mixture of cultures from three isolates. We chose isolates with a range of aggressiveness, based on the results displayed in Table 1 (see report). We have also bulked sclerotia on autoclaved carrots and will apply sclerotia in field plots in the fall, to cold condition in the field and in the spring after cold conditioning the lab refrigerator. We will apply 30 ml of sclerotia per plot.

In 2023, soybean will be evaluated in the plots and their incidence and severity of SSR infections will be compared. Apothecia debsity will also be monitored. It is expected that this work will allow for more uniform, consistent disease pressure in which to compare the performance of soybean lines and treatments for SSR.

IN SUMMARY:
The goals and objectives described in this proposal will set the stage for my soilborne fungi pathology lab to conduct biologically relevant SSR research in soybean and will open new, creative avenues to improve resistance to this challenging fungal disease.

Additional comments on students:
I recently hired two graduate students that will research soybean and SSR interactions.

Hsuan-Fu Wang is a PhD student who will be developing the isolate collection, characterizing these isolates, and developing a panel for soybean screenings. He brings experience in plant breeding, disease resistance screening, and molecular techniques in fungal biology from his MSc and work experience in agricultural industry.

Alisha Hershman, an MSc student, will work to understand the relationship between soybean architecture and disease infection. She has extensive field and lab experience in soybean genetics and has worked for the USDA and Calyxt (a plant gene editing company).

We’ve had a great crew of three undergraduate students- Jane, Leslie, and Ella- this summer that have helped with culture maintenance, plant care, disease evaluations, and project implementation.

These are promising students, and I appreciate MSRPC support for their research efforts and learning.

PROJECT DELIVERABLES/OUTCOMES
• Results will be presented at seminars and regional (Prairie Grains, Minnesota Ag Expo) and national meetings.
• Peer-reviewed research publications will be developed.
• A S. sclerotiorum isolate collection will be developed for future SSR work.
• A research education and outreach opportunity will be available to students in my lab who are assisting with the project. The next generation of soybean researchers and will be trained in grower-driven research.
• New breeding opportunities will be explored through enhancing disease escape with plant architectural traits and candidate lines for breeding will be identified.
• Improved SSR resistance screening methods (through the characterization of S. sclerotiorum isolates and improved nursery methods), can lead to improved SSR research across University of Minnesota and the Sclerotinia community.
• Identification of lines with unique branching phenotypes can lead to candidates for quantitative trait loci (QTL) studies to identify genes related to branching phenotypes and disease resistance.
• Collaborations between researchers of various departments and universities will build bridges of expertise in soybean research to enhance each other’s work in soybean improvement.

PERFORMANCE METRICS
1. GOAL: Characterize the aggressiveness of S. sclerotiorum isolates for use in future pathogen biology and resistance screening assays
• This goal will be successful if new isolates are collected (more than 10) and a better understanding of their characteristics is developed (at least two repetitions of aggressiveness and growth assays should be completed in the project year).
• Isolates should be effectively used to differentiate resistance between check lines.

2. GOAL : Define relationship between canopy architecture and SSR development
• Branching angles will be measured in the field, for all experimental lines.
• At least two experimental repetitions of greenhouse resistance screenings should be completed.
• Environmental data under canopies will be collected during the field season.
• These lines should be well characterized in their architectural and disease resistance traits by the end of the funding year.

3. GOAL: Develop reliable S. sclerotiorum nurseries for future SSR field trials
• Experiments will be established and implemented in 2022.
• In 2023, data will be collected and analyzed to compare infestation methods.

View uploaded report PDF file

View uploaded report 2 Word file

Updated November 30, 2022:
Please find report attached. This update will be presented at Prairie Grains on Dec. 8, 2022.

View uploaded report Word file

Updated February 28, 2023:

View uploaded report Word file

Final Project Results

Updated May 31, 2023:

View uploaded report Word file

The purpose of this work was to develop tools for white mold resistance breeding and research in Minnesota. White mold is caused by the soilborne fungal pathogen, Sclerotinia sclerotiorum and can cause severe yield losses when conditions are suitable for disease development. One of the most effective means to control white mold is the use of resistant cultivars. This work aimed to characterize Sclerotinia sclerotiorum isolates, collected throughout Minnesota, that can be used to comprehensively screen soybean lines and study fungal biology. We are also working to compare field techniques for infesting research fields to conduct research on white mold management under more consistent disease pressure. Lastly, this project aims to define relationships between canopy architecture and S. sclerotiorum development, to provide another, underexplored consideration for disease resistance breeding for white mold. The goals of this work will set the stage for my soilborne fungi pathology lab to conduct biologically relevant SSR research in soybean and will open new, creative avenues to improve resistance to this challenging fungal disease.
So far, we have developed an isolate collection of 34 isolates. Results of the initial screening indicated differing levels of lesion sizes and disease progression with each isolate. Once we identify a panel of isolates with different levels of aggressiveness, we can test whether isolates will distinguish the resistance ranking of cultivars. Using three representative isolates, we will inoculate soybean check lines developed by Dr. Damon Smith’s Lab at University of Wisconsin, Madison with known low, moderate, and high levels of resistance (compared to susceptible controls) to see if resistance rankings are similar when challenged with the new, UMN isolates and whether our isolate panel can differentiate putative resistant from susceptible lines.
In addition to physiological resistance, plant architecture may be an important for avoiding soybean infection by S. sclerotiorum in the field. Apothecia (the mushrooms required for infection of the pathogen) production is influenced by moisture and light (quality and quantity). This spring, we used differential light data in addition to phenotypic traits including branching angle, canopy closure, and leaf area from over 150 lines (measured in 2022) to select 20 lines for greenhouse resistance screenings and for field evaluations for white mold infection in 2023. This season, we aim to better understand the interaction between light and plant architecture so that it might be used as a breeding consideration to reduce infection.
Currently, researchers do not have field sites with reliable and uniform inoculum where we can conduct white mold experiments. High disease pressure, across plots is often required to observe the impact of experimental treatments. In 2022, we initiated a trial comparing three methods to encourage uniform disease pressure for trials in 2023. These include 1) growing sunflowers, which are susceptible to white mold, inoculating them the back of the head with a slurry of S. sclerotiorum, and then incorporating residue into the soil in the fall of 2022. We also added 2) sclerotia inoculum generated in the lab on carrot seed into the field during the fall before 2023 trials. Cold conditioning over the winter should allow the inoculum to produce apothecia in the following field season. In the third method, 3) we are growing sclerotia in the lab, cold conditioning them in the fridge, and then will spring apply the sclerotia to the field. 4) Untreated, naturally infested plots will be left as controls to compare with plots treated with the described infestation methods. In 2023, soybean will be evaluated in the plots and their incidence and severity of SSR infections will be compared. Apothecia density will also be monitored. It is expected that this work will allow for more uniform, consistent disease pressure in which to compare the performance of soybean lines and treatments for white mold.

Benefit to Soybean Farmers

Disease management options for Sclerotinia stem rot are limited, and genetic resistance is one of the most effective lines of defense against any plant disease. This project will aim to improve resistance screening methods by developing a collection of Sclerotinia fungal isolates that are typical of Minnesota, with a representative ability to cause disease symptoms in soybean. Additionally, uniform and reliable disease pressure developed in the field will allow me to share reliable data with growers due to consistent SSR disease pressure for variety and experimental trials. Finally, the development of SSR disease is very dependent on environmental conditions. Plant architecture may play an important role in creating conditions that are ideal for disease development. Through this work, I would like to examine the importance of plant architectural traits for disease development. This work may lead to opportunities to further improve soybean resistance to SSR by breeding for architectural traits that discourage SSR development and improve yield. Ultimately, I aim to explore genetic/architectural management tools for growers to use in SSR-infested fields to avoid yield losses.
Additionally, I am passionate about mentoring and anticipate recruiting graduate students during this spring’s recruitment cycle. I plan to have students assist with this project. Through this project, students will learn more about research in soybeans and will develop as budding experts to assist with future production challenges through science.
Additionally, this project is collaborative and uses resources (seeds and ideas) from researchers in different institutions and departments. These collaborative relationships will likely provide enhanced idea generation and pooled resources for future projects in Minnesota soybeans.

Performance Metrics

1. GOAL: Characterize the aggressiveness of S. sclerotiorum isolates for use in future pathogen biology and resistance screening assays
• This goal will be successful if new isolates are collected (more than 10) and a better understanding of their characteristics is developed (at least two repetitions of aggressiveness and growth assays should be completed in the project year).
• Isolates should be effectively used to differentiate resistance between check lines.

2. GOAL : Define relationship between canopy architecture and SSR development
• Branching angles will be measured in the field, for all experimental lines.
• At least two experimental repetitions of greenhouse resistance screenings should be completed.
• Environmental data under canopies will be collected during the field season.
• These lines should be well characterized in their architectural and disease resistance traits by the end of the funding year.

3. GOAL: Develop reliable S. sclerotiorum nurseries for future SSR field trials
• Experiments will be established and implemented in 2022.
• In 2023, data will be collected and analyzed to compare infestation methods.

Project Years