This proposal addresses the priority area of Soybean Pest Management. It focuses on research into managing against yield and quality limiting effects of stem and root rots. Stem diseases are widespread and problematic across Minnesota. They are often clearly damaging to plants and yield, and other times they may be undetected and yet cause yield losses. If we understand when and where stem diseases occur and how to manage them more effectively, yield could increase in many areas. This proposed project targets management strategies for specific stem diseases, primarily brown stem rot (BSR) and pod and stem blight. The goals are to identify resistance to BSR and pod and stem blight in breeding lines and varieties adapted to MN and to understand the challenge and opportunities for disease management with fungicides and crop rotation. This project also addresses a longer-term goal of understanding the reasons for yield ‘drag’ in many fields and the role that disease plays. Changes in the occurrence and types of stem diseases (e.g., BSR, stem canker, pod and stem blight) require that soybean growers and their advisors better understand these risks to plan for and react with appropriate management. Thus, we aim to understand the distribution of these and other key stem and root diseases via surveys and disease diagnosis with plants collected from different areas. This proposed research will address short- and long-term goals to manage key soybean stem diseases.

1. GOAL: Evaluate tactics to manage brown stem rot (BSR)
OBJECTIVES: Evaluate soybean breeding lines and varieties for resistance to BSR and determine the effects of potential alternative hosts and crop rotation on risk and management of BSR

2. GOAL: Determine methods to manage pod and stem blight (PSB) of soybean.
OBJECTIVE: Determine if there are clear and consistent differences in susceptibility to the pod and stem blight pathogens and determine if seed treatments can reduce severity of pod and stem blight

3. GOAL: Determine distribution and prevalence of important soybean stem and root diseases/pathogens in Minnesota
OBJECTIVE: Conduct survey for soybean stem and root diseases to better understand their current distribution and risk to Minnesota soybean growers

• Identify the level of resistance to both prevalent types of the BSR pathogen in soybean breeding lines and varieties from the U of MN soybean-breeding program.
• Determine if new methods to evaluate soybean for resistance to BSR are more consistent and have higher throughput than current methods.
• Determine the effects of crop rotation and alternative hosts of the BSR pathogen on risk and management of BSR
• Identify the level of resistance to the pod and stem blight pathogens in soybean breeding lines from the U of MN soybean-breeding program and select commercial varieties.
• Improve understanding of the distribution and risks of key soybean stem and root diseases to Minnesota soybean growers.
• Develop and extend updated information on the management, distribution, and risks of key soybean stem and root diseases for Minnesota soybean growers.

Update:
Quarterly Progress Report for 2023-2024 Minnesota Soybean Research and Promotion Council Production Action Team


Project Title: Addressing Management Challenges with Soybean Stem Diseases in Minnesota
• Principle Investigator: Dean Malvick
• Department/Organization: Department of Plant Pathology, University of Minnesota, St. Paul, MN

• Dates of Reporting: May 1 – July 31, 2023

A summary of activity and progress is summarized below for each part of this project for this reporting period. Please let me know if you would like additional information about this project and the results. Thank you.

Project Objectives

1. Evaluate tactics to manage brown stem rot (BSR) of soybean.
2. Determine methods to manage pod and stem blight (PSB) of soybean.
3. Determine distribution and prevalence of important soybean stem and root diseases/pathogens in Minnesota.

Activity and Progress Report by Objective

Objective 1. Evaluate tactics to manage brown stem rot (BSR) of soybean.
Background. BSR is a common and important soybean disease in Minnesota. Crop rotations and resistant varieties suppress BSR, however, neither method is a complete solution to managing the disease. Because BSR is a continuing threat in Minnesota, more information is needed to understand risk factors and disease management options.

Goal A. Evaluate soybean breeding lines and varieties for resistance to BSR. Advanced breeding lines from the U of MN soybean-breeding program, as well as selected commercial soybean varieties, will be evaluated for resistance to BSR. In addition, because BSR resistance is difficult to evaluate, we also aim to compare different resistance testing methods with the goal of developing a method that is consistent and has higher throughput for breeding and research needs.

Progress and results to date: This research will be conducted in a greenhouse under controlled conditions this fall, winter, and spring when the greenhouse is consistently cool enough to conduct this work.

Goal B. Determine the effects of potential alternative hosts and crop rotation on risk and management of BSR. The BSR pathogen (Cadophora gregata) is thought to only infect soybeans, but this is poorly documented and understood. Thus, we need more information to determine if other plant species can become infected and sustain the BSR pathogen in soil and crop rotations in the absence of soybean.

Progress and results to date; A diverse set of legumes and weed species was tested to determine if they can serve as hosts of BSR pathogen. Twenty-seven different species of weeds and crops were inoculated (via stem injection and root dip) with C. gregata at early growth stage V1 and then grown for approximately 7 weeks before assessing BSR incidence and severity. The preliminary results suggest that some Phaseolus vulgaris cultivars including black bean, pinto bean, and navy pea may be newly discovered hosts of C. gregata. In agreement with one previous report, red kidney and red clover do not appear to be hosts of C. gregata. Further analysis of the plant samples and data is required to confirm these results and fully assess all species tested.



Objective 2. Determine methods to manage pod and stem blight (PSB) of soybean.
Pod and stem blight is a widespread and problematic disease in Minnesota soybean fields. The pod and stem blight pathogens are also common as latent pathogens in asymptomatic plants. Soybean varieties can vary in resistance and crop rotation may be beneficial. but the disease is still widespread and often kills plants. Overall, this disease and how to manage it are poorly understood.

Goal: Evaluate tactics to manage pod and stem blight of soybean. The goals are to determine if there are clear and consistent differences in susceptibility to the pod and stem blight pathogens and to determine if seed treatments can reduce severity of pod and stem blight.

Progress and results to date: Selected commercial soybean varieties are current in a trial in progress and have been inoculated for evaluation for resistance to pod and stem blight. These studies of resistance are being conducted in the greenhouse and field (St. Paul). Disease development and severity have been and are continuing to be monitored. Some of the plants developed clear symptoms, and full results should be available in October.



Objective 3. Determine distribution and prevalence of important soybean stem and root diseases/pathogens in Minnesota.
Increasing and maintaining soybean yields in the presence of new and evolving pathogens and diseases requires continued improvements in soybean varieties, fungicides, and crop management practices. New pathogens and new disease management practices require more information to manage and use them most effectively. Thus, there is a need for increased disease/pathogen survey activity to detect and understand how risks from key soybean diseases are changing and where and when they occur.
Goal: Survey for soybean stem and root diseases to better understand their current distribution and risk to Minnesota soybean growers. Plants samples will be diagnosed in a laboratory to identify symptoms and the presence of key pathogens using pathogen isolation methods and specific DNA diagnostic tests.
Progress and results to date: The dry/drought conditions in Minnesota have been suppressing development of soybean diseases, and so far, we have obtained only a few samples that are useful. Samples with charcoal rot were obtained from one field and broader surveys will be conducted in September to determine the prevalence of key diseases.


Information Dissemination of data/information from this research during this reporting period

During the period from May – July for this report information dissemination has been focused on email and telephone conversations with growers, consultants and others with questions and concerns.

Update:
see uploaded file

View uploaded report

Update:
Minnesota Soybean Research and Promotion Council

Research Progress Report
February 29, 2024

Project Title: Addressing Management Challenges with Soybean Stem Diseases in Minnesota

Principal Investigator(s): Dean Malvick

Project Period: October 31, 2023 – Feb 29, 2024
Research Question/Objectives: This project addresses the priority area of soybean pest management. It focuses on research into managing against yield and quality limiting effects of stem rots. Stem diseases are widespread and problematic across Minnesota. They are often clearly damaging to plants and yield, but at other times they may be undetected and yet cause yield losses. Understanding how to manage soybean stem diseases more effectively could potentially result in yield increases in many areas.
This project targets management strategies for the diseases brown stem rot (BSR) and pod and stem blight. BSR is a common, widespread, and important soybean disease in Minnesota. Crop rotations and resistant varieties can suppress BSR, however, neither method is a complete solution to managing the disease. Because BSR is a continuing threat to soybean production in Minnesota, more information is needed to understand risk factors and disease management options. Pod and stem blight is also a common and problematic disease in Minnesota soybean fields and likely causes more damage and yield loss than is recognized. The widespread distribution and high prevalence of these diseases in Minnesota were documented in recent and published surveys (listed below). Soybean varieties can vary in resistance to pod and stem blight and crop rotation may be beneficial, but this disease and the best methods to manage it are poorly understood.
The primary project goals addressed in this project period were to understand the challenges and opportunities for disease management with fungicides, crop rotation, and host resistance. This research is based on a few key points. First, the BSR pathogen (Cadophora gregata) is reported to only infect soybean, adzuki bean, and mung bean, but this is poorly documented and understood. Second, little to nothing is known regarding the efficacy of seed treatment fungicides for managing BSR. Third, soybean varieties with resistance to BSR are available but do not provide complete control.
In summary, this project is addressing short and long-term goals to manage two common and damaging soybean stem diseases. 1. Evaluate tactics to manage brown stem rot (BSR) of soybean. 2. Determine methods to manage pod and stem blight (PSB) of soybean. The following is a brief summary of activities and progress, but please contact me if you would like additional information.

Results and Project Updates for project period November – February 2024.
Objective 1. Experiments are underway to determine the impact of potential alternative hosts and seed treatments on risk and management of brown stem rot (BSR) of soybean. A diverse group of 27 crop and weed species is being evaluated for the second time in large greenhouse experiments to determine if they can serve as hosts of the BSR pathogen. Analysis of the plant samples and data from the first experiment are nearly complete but are not yet summarized or analyzed. Studies are also underway in the laboratory to determine if common seed treatment fungicides in different activity classes can suppress growth of the BSR pathogen. The preliminary results obtained earlier in this project suggest that some fungicides may suppress growth of the pathogen but may not reduce development of BSR in the field. All of these experiments are expected to be completed in the upcoming project period. The objectives related to identification of resistance to BSR and pod and stem blight in breeding lines and varieties is underway in the greenhouse and will also continue until spring.

Objective 2. In the previous project period, the work identified likely differences in susceptibility to the pod and stem blight pathogens. Field studies revealed how plant age/growth at inoculation and pathogen species can influence infection and disease development in the field. Sets of soybean varieties are being evaluated in a greenhouse in St. Paul for resistance to pod and stem blight and that work will be completed by April.

Materials and Methods: For objective 1. A diverse set of legumes and weed species are being evaluated to determine if they can serve as hosts of the BSR pathogen. The varied species of weeds and crops were inoculated via stem injection and root dip with C. gregata at early growth stage V1 and then grown for approximately 7 weeks before assessing BSR incidence and severity. To evaluate efficacy of seed treatment fungicides, laboratory assays using amended growth media are underway to assess sensitivity of the BSR pathogen to different fungicides and fungicide mixtures that are used to treat soybean seed. For the pod and stem blight studies, plant stems of breeding lines in replicated pots in the field and greenhouse were inoculated with the pathogen and disease is assessed over time.

Economic Benefit to a Typical 500 Acre Soybean Enterprise: Both BSR and pod and stem blight can cause substantial soybean yield reductions, and effective methods to reduce these diseases could have significant benefits where these diseases develop. More specifically, given that BSR is managed in part by rotation with non-host crops, a more complete understanding of the hosts of the BSR pathogen will have direct impact on survival and disease risk of BSR. If seed treatments can be used to reduce/manage BSR and pod and stem blight, they could have a significant benefit along with improved levels of partial resistance in soybean varieties.

References:
• Floyd, C.M. and Malvick. D.K. 2022. Diaporthe species associated with symptomatic and asymptomatic infection of soybean stems in Minnesota; identity, virulence, and growth. Can J Plant Pathol. 44:858-873.
• Malvick, D.K., and Grunden, E. 2008. Association between genotypes of the brown stem rot pathogen Phialophora gregata and resistant and susceptible soybean cultivars in the north-central United States and Ontario. Can J Plant Pathol 30:581-587.

View uploaded report

Updated May 31, 2024:
Minnesota Soybean Research and Promotion Council

Research Progress Report
May 31st, 2024


Project Title: Addressing Management Challenges with Soybean Stem Diseases in Minnesota

Principal Investigator(s): Dean Malvick

Project Period Ending May 31, 2024
Research Question/Objectives: This project addresses the priority area of soybean pest management. It focuses on research into managing against yield and quality limiting effects of stem rots. Stem diseases are widespread and problematic across Minnesota. They often clearly damage plants and yield, but other they may be undetected and cause yield losses. Understanding how to manage soybean stem diseases more effectively could potentially result in yield increases in many areas.
This proposed project targets management strategies for the diseases brown stem rot (BSR) and pod and stem blight. BSR is a common, widespread, and important soybean disease in Minnesota. Crop rotations and resistant varieties can suppress BSR, however, neither method is a complete solution to managing the disease. Because BSR is a continuing problem for soybean production in Minnesota, more information is needed to understand risk factors and disease management options. Pod and stem blight is also a common and problematic disease in Minnesota soybean fields and likely causes more damage and yield loss than is recognized. Soybean varieties can vary in resistance to pod and stem blight and crop rotation may be beneficial, but this disease and the best methods to manage it are poorly understood.
The primary project goals addressed in this project period were to understand the challenges and opportunities for disease management with fungicides, crop rotation, and host resistance. This research is based on a few key points. First, the BSR pathogen (Cadophora gregata) is reported to only infect soybean, adzuki bean, and mung bean, but this is poorly documented and understood. Second, little to nothing is known regarding the efficacy of seed treatment fungicides for managing BSR. Third, soybean varieties with resistance to BSR are available but do not provide complete control.
In summary, this project is addressing short and long-term goals to manage two common and damaging soybean stem diseases: brown stem rot (BSR) and pod and stem blight (PSB).


The two photos on the left show the internal stem and leaf symptoms of brown stem rot (BSR), although the leaf symptoms do not always develop. The photo on the right shows symptoms of pod and stem blight: note the black fungal structures in rows on the stem and the nodal lesion.


Results and Project Updates:
Objective 1 focused on brown stem rot.

• A diverse group of 20 breeding lines from the U of MN soybean breeding program and four public varieties were evaluated in a greenhouse for resistance to the A and B types of the BSR pathogen (Cadophora gregata). The breeding lines and varieties differed in their resistance/susceptibility to BSR, with severity scores ranging from below 10 (partially resistant) to nearly 80 (susceptible). The lines and varieties differed in resistance to the A and B types of the pathogen, indicating the resistance to one pathogen type does not consistently confer resistance to the other pathogen type. This work supports development of BSR-resistant soybean varieties for Minnesota and provides further support for the importance of breeding for and evaluating resistance to both the A and B types of the pathogen to obtain widely effective resistance to BSR.

• Our work to develop an improved method to evaluate soybean lines and varieties for resistance to BSR has provided results indicating that it may be feasible to evaluate resistance within a month after planting in a greenhouse vs about 2 months. The final results are still being obtained and analyzed, but this method based on quantity of the pathogen in soybean stems, could potentially reduce cost, time, and challenges with evaluating resistance to BSR caused by both types of the BSR pathogen.

• The host range of the BSR pathogens is largely unknown, which could have strong implications for management of BSR with crop rotation. Twenty-seven crop and weed species were evaluated in greenhouse experiments to determine if they can serve as hosts of the BSR pathogen. Initial results confirm that mung bean is a host, and they suggest that some edible bean (Phaseolus vulgaris) varieties may also be hosts of C. gregata. Further analysis of the plant samples and data is underway to confirm these results and to determine if other plants are hosts of the BSR pathogen.

• Studies in the laboratory and field have been conducted to determine if common seed treatments in different activity classes can suppress growth of the BSR pathogen or reduce BSR development in the field. The initial results suggest that some fungicides suppress growth of the pathogen in the lab. However, the studies in the field with a more limited number of seed treatment fungicides suggest that the seed treatments do not reduce BSR development in the field. These experiments are also being repeated to confirm and solidify the results. Specific results will be available when we have completed the additional experiments analysis and have fully analyzed and confirmed the results.


Objective 2 focused on pod and stem blight.
• Field and greenhouse studies were conducted to study development and management of pod and stem blight of soybean. Field studies in St Paul showed how plant age/growth at inoculation and pathogen species can influence infection and disease development in the field. The results indicate that plants are highly susceptible up to at least 7 weeks post planting, although earlier plant stages appear optimal for inoculation of soybean with Diaporthe pathogens. This work enhances our ability to screen for and develop resistance to pod and stem blight against the prevalent types of this pathogen/disease.

• Another study focused on resistance to Diaporthe longicola and Diaporthe caulivora, both of which are common in soybean fields across Minnesota. In a selected set of public and private soybean varieties, differences in susceptibility to both of these pathogens were detected. This suggests that additional breeding and screening efforts could reduce damage by these pathogens. Additional testing with 20 breeding lines was delayed due to limited greenhouse space but is currently in progress.

• A third study focused on possible interactions between pod and stem blight and BSR in greenhouse experiments, which often occur simultaneously in the same soybean fields. The results suggest that Diaporthe longicola may increase development of BSR in soybean stems in some cultivars. There seems to be a synergistic reaction between the two pathogens/diseases rather than a competitive interaction.. Overall, the results suggest that dual infection by the two pathogens can result in more damage to soybean than either pathogen alone. More studies are needed to confirm these results with additional types of each pathogen and with additional soybean varieties.


Materials and Methods:
For objective 1. A diverse set of legumes and weed species were inoculated via stem injection and root di) with C. gregata at early growth stage V1 and then grown for approximately 7 weeks before assessing BSR incidence and severity. To evaluate efficacy of seed treatment fungicides, laboratory assays using amended growth media are underway to assess sensitivity of the BSR pathogen to multiple different fungicides and fungicide mixtures used to treat soybean seed. In addition, seed was treated with multiple fungicides prior to planting in May, and plants in replicated plots were evaluated in the fall to determine if they reduced development of BSR. Similar experiments are underway in a growth chamber with potted plants.
For objective 2, Plant stems for the pod and stem blight studies in replicated pots in the field and greenhouse were inoculated with toothpicks colonized by the pathogen and disease was then assessed over time.

Economic Benefit to a Typical 500 Acre Soybean Enterprise:
Both BSR and pod and stem blight can cause significant soybean yield reductions, and effective methods to reduce these diseases could have significant benefits where these diseases develop. More specifically, given that BSR is managed in part by rotation with non-host crops, a more complete understanding of the hosts of the BSR pathogen will have direct impact on survival and disease risk of BSR. If seed treatments can be used to reduce/manage BSR, they could have a significant benefit along with improved levels of resistance in soybean varieties.

Information Dissemination of data/information from this research during this reporting period

Information dissemination has included prsentations at Extension programs this winter and email and telephone conversations with growers, consultants and others with questions and concerns.

This project, as outlined with each of the deliverables, will address the need for improved understanding and management of key soybean diseases that reduce soybean yields across Minnesota. Enhanced understanding of where stem and root diseases occur and managing them more effectively should result in increased soybean yields in many fields. Thus, this research will produce information to improve disease management and reduce risk and yield-loss for soybean. Results will be transferred through newsletters, production meetings and field days, scientific meetings, and news outlets. The ultimate benefit to soybean growers will be increased yields and reduced risk of lost yields due to disease.