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