Soybean diseases can cause substantial yield losses and influence variety selection and crop rotation. In North Dakota there are important diseases of soybean such as Phytophthora root rot, Fusarium root rots, soybean cyst nematode (SCN), and a new disease called sudden death syndrome (SDS). SDS is caused by a fungus Fusarium virguliforme that infects the roots and causes both a root rot and above ground foliar symptoms. This project will focus on identifying resistance to Phytophthora root rot and sudden death syndrome and incorporating resistance into adapted germplasm for this northern region through cooperation with the soybean breeder. These are two diseases where resistance is available within the soybean germplasm. Because sudden death syndrome is a new disease for ND, resistant varieties have not been developed for this area. This project will identify sources of resistance in maturity groups for this region that can be used in the NDSU soybean breeding programs. In addition, for the 2022 growing season we will have ready a protocol using molecular techniques for processing plant samples to identify SDS in soybean fields. There will be a request sent out to the NDSU extension personal, farmers and to crop scouts to look for evidence of SDS in fields and send plants in for verification of the pathogen. This is intended to provide a better understanding of the distribution of the disease in the state.

1. Screen NDSU breeding lines for resistance and identify lines with high levels of resistance to Phytophthora root rot.
2. Screen adapted soybean germplasm for resistance to sudden death syndrome and identify sources of resistance that the soybean breeder can use in the development of resistant varieties for this area.
3. Process plant samples with suspected SDS symptoms to verify the presence of the disease in ND fields.

1. Identification of soybean breeding lines with high resistance to Phytophthora root rot.
2. Identification of sources of high levels of resistance to sudden death syndrome in maturity groups for this area.
3. Provide information on distribution of SDS in soybean fields in ND.

Update:
FY 2023 Mid-Year Report North Dakota Soybean Council
November 2022

Jack Rasmussen (with Berlin Nelson)

Project Title: Resistance to Important Soybean Diseases
Project dates: July 1, 2022 to June 30, 2023.
Objectives:
Objectives:
1. Screen NDSU breeding lines for resistance and identify lines with high levels of resistance to Phytophthora root rot.
2. Screen adapted soybean germplasm for resistance to sudden death syndrome and identify sources of resistance that the soybean breeder can use in the development of resistant varieties for this area.
3. Process plant samples with suspected SDS symptoms to verify the presence of the disease in ND fields.

Completed work:

In May 2022 a microplot experiment was initiated to verify field resistance of two NDSU soybean varieties, Bison and Benson, to sudden death syndrome (SDS). These two varieties were previously shown in controlled experiments to have resistance to Fusarium virguliforme, the causal agent of sudden death syndrome. The microplot experiments consisted of Barnes, the susceptible check, MN 0807 (moderately susceptible), MN 1606SP (resistant check) and Bison and Benson. These were grown in naturally infested soil in pots buried in the soil on the NDSU campus. Each pot consisted of 8 plants and there were 5 replications. The plants were watered daily for the first month to maintain soil moisture conducive to disease development. Unfortunately, herbicide drift from an adjacent crop resulted in serious damage to the soybean plants. By September it was apparent that no SDS symptoms developed in our susceptible check or on the other plants and the experiment was terminated.
Greenhouse experiments were continued on our efforts to develop a reliable test to screen for resistance to SDS using an artificial inoculation technique under greenhouse conditions. These experiments used the same soybean varieties as used in the field experiments. The general method to infest the soil consisted of using pathogen colonized sorghum seed and putting 20 grams of dried inoculum in 20 inches of furrow, planting 8 seeds in the furrow and watering the plants daily for 5 weeks. We take stand counts to know if there is pre-emergence damping-off, then grow the plants to maturity with scoring of SDS around R3 growth stage. SDS symptoms on each plant are then rated on a 1 to 9 scale with 1 = no disease and 9 = plant dead. These experiments, therefore, require a minimum of three months to complete. Although SDS foliar symptoms will develop with this method, obtaining high levels of SDS has not been consistent. High levels of disease on the susceptible check are required to identify varieties with resistance to SDS and to verify the level of resistance. The research on SDS is being taken over by Dr. Febina Mathews, who will be working on Fusarium diseases on soybean. Dr. Mathews will decide on the future direction of SDS research on soybean. The previous research results from Dr. Nelson’s program and the cultures of Fusarium virguliforme from North Dakota were handed over to Dr. Mathews.
Preparation for screening Dr. Miranda’s breeding material for resistance to Phytophthora root rot is currently underway. The cultures of races 3 and 4 of P. sojae were recovered from storage and are being evaluated for pathogenicity. Generally, the actual screening of Dr. Miranda’s breeding material begins in January, but preparation of the races begins earlier. All the screening is conducted under controlled conditions in the greenhouse and laboratory and the results are provided to Dr. Miranda. Only breeding lines that have 80% survival of inoculated plants are rated as resistant to a race of this root rot.

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Update:
This study aims to screen soybean genotypes for resistance to two economically important soybean diseases in North Dakota: Phytophthora root and stem rot (PRSR) and sudden death syndrome (SDS). PRSR is caused by a water mold called Phytophthora sojae and has been a consistent threat to soybean production across the state for many decades. However, SDS, caused by Fusarium virguliforme, is a newer threat to North Dakota soybean growers. It was first confirmed in ND during the 2018 growing season in Richland County, and in 2020 SDS was also confirmed in Cavalier County. The three objectives of this study were 1) Screen NDSU breeding lines for resistance and identify lines with high levels of resistance to Phytophthora root rot, 2) Screen adapted soybean germplasm for resistance to SDS and identify sources of resistance that the soybean breeding program can use in the development of resistant varieties for ND, and 3) Process plant samples with suspected SDS symptoms to verify the presence of the disease in ND fields.

In the spring of 2023, 96 F2 NDSU soybean breeding lines (second generation) were screened for resistance to P. sojae race 3 and 4, which are the two most prevalent races as of 2016. The screenings revealed that 46% of the lines were resistant to both races, 28% were resistant to only race 3, and 26% were susceptible to both races. Continuing to screen these lines is crucial to ensure breeding populations are resistant to these pathogen populations. Each of these lines had ten individual plants inoculated with each of the two races. While the lines were reported as resistant if 80% of plants survived infection, several lines exhibited a survival rate of 30% to 79%, indicating partial resistance to the two P. sojae races. These lines could be highly beneficial for future breeding efforts. Currently, we are quantifying these lines following inoculations with the two races to better understand the current levels of partial resistance in these populations. Dr. Hope Becton, the newly hired research specialist in the Soybean Pathology lab, is currently performing this work, which is expected to be completed by the end of fall 2023.

Until recently, SDS has been primarily a concern for soybean growers in many parts of the United States, with limited reports from the Northern growing regions. As a result, there is a lack of knowledge regarding resistant germplasm specifically adapted to the North Dakota (ND) growing regions, particularly in maturity groups 00, 0, and 1. Consequently, there is a pressing need to screen soybean germplasm lines in order to identify potential parental lines for future breeding endeavors. Presently, the majority of SDS screenings are performed under field conditions, but due to specific environmental conditions necessary for disease development these trials are often inconsistent for SDS screening. As a result, screening for resistance to Fusarium spp. are often performed under greenhouse conditions. Currently the protocols for screening F. virguliforme in greenhouses are being optimized for consistent results. But other similar protocols have proven successful in assessing soybean resistance to other Fusarium species that cause root rots. Collaborating with Dr. Febina Mathew, we have conducted screenings on over 100 diverse soybean genotypes from maturity groups 0 and 1 to evaluate their resistance to Fusarium spp. in terms of root rot. The outcomes of this work will establish a fundamental basis for targeted screening initiatives aimed at identifying soybean lines with SDS resistance. Furthermore, continuous efforts are underway to gather samples of diseased soybeans from production fields, with a number of SDS identifications in Cavalier County in 2023. The collection of samples is currently in progress and will persist throughout the entire growing season. Subsequently, the fungi present in these samples will be isolated and subjected to PCR and sequencing analyses to confirm their species. The Fusarium isolates obtained during the 2023 growing season will then be employed for root rot ratings in order to screen for resistance in the germplasm. Going forward, research on SDS will be managed by Dr. Febina Mathew at NDSU.

This research will provide significant benefits to North Dakota soybean farmers and the soybean industry as PRSR and SDS pose serious threats to soybean production in North Dakota. By screening soybean genotypes for resistance to these diseases, this study identified lines with high levels of resistance to Phytophthora root rot and will lead to identification of potential sources of resistance to SDS. This information is invaluable for the soybean breeding program in developing resistant varieties specifically adapted to North Dakota's growing regions. The study also focuses on optimizing screening protocols for consistent results, addressing the challenges posed by field conditions and environmental factors associated with SDS. This ensures more accurate and reliable assessments of soybean resistance to Fusarium spp. and SDS, which cause root rots. Additionally, ongoing efforts to gather diseased soybean samples from production fields and confirm the presence of Fusarium isolates through molecular analysis contribute to a comprehensive understanding of the diseases and aid in future screening initiatives. Ultimately, these research outcomes empower North Dakota soybean farmers with enhanced disease management strategies, increased crop productivity, and improved resilience against PRSR and SDS.

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Update:
Nothing to report on object 3 at this time.

Update:
FY 2023 Final Report North Dakota Soybean Council
November 2023

Richard Wade Webster

Project Title: Resistance to Important Soybean Diseases
Project dates: July 1, 2022 to December 1, 2023
Principal Investigator: Dr. Richard Webster
Co-PI: Dr. Hui Yan

Objectives:
1. Screen NDSU breeding lines for resistance and identify lines with high levels of resistance to Phytophthora root rot.
2. Screen adapted soybean germplasm for resistance to sudden death syndrome and identify sources of resistance that the soybean breeder can use in the development of resistant varieties for this area.
3. Process plant samples with suspected SDS symptoms to verify the presence of the disease in ND fields.

With soybean production increasing across the entire state of North Dakota, the development of soybean diseases is inevitable. Two of the most yield limiting diseases of soybeans across the United States is sudden death syndrome (SDS) and Phytophthora root and stem rot (PRSR). Sudden death syndrome is caused by the fungal pathogen Fusarium virguliforme, and it has been historically a major disease in states such as Minnesota and Iowa. However, in 2018 a suspected SDS sample was reported in Richland Co., North Dakota. A few years later a second report was made for SDS in Cavalier Co., North Dakota on the Canadian border. It was not surprising to see this disease appear in North Dakota as soybean production has increased substantially over the recent decades. Phytophthora root and stem rot is caused by an oomycete pathogen, Phytophthora sojae, which thrives under high moisture soil conditions that are often found in North Dakota during the early spring and summer months. Having been present for many years, PRSR is still a major threat to North Dakota soybean production. In order to manage both of these diseases, the use of genetic resistance is incredibly important as a defense from potential devastating yield losses.
In May 2022, a microplot study was conducted to evaluate the field resistance of two NDSU soybean cultivars, Bison and Benson, against SDS. Previously controlled studies had indicated that these cultivars were resistant to F. virguliforme, the pathogen responsible for SDS. The microplot study involved a range of varieties: Barnes (susceptible control), MN 0807 (moderately susceptible), MN 1606SP (resistant control), and the two focal varieties, Bison and Benson. These were cultivated in pots with naturally infested soil, buried at NDSU Fargo research fields. Each pot contained eight plants, with a total of five experimental replicates. For the initial month, daily watering was essential to maintain soil moisture favorable for disease emergence. Regrettably, herbicide contamination from a neighboring field caused damage to the soybean plants. By September, it became clear that none of the plants, including the susceptible control, exhibited SDS symptoms, leading to the study's premature conclusion.
Concurrently, greenhouse experiments aimed at developing a robust SDS resistance screening test continued. These used the identical soybean varieties as in the field study. The inoculation process involved integrating pathogen-infested sorghum seed into the soil, with 20 grams of dried inoculum per 20 inches of furrow. Following the planting of 8 seeds per furrow and consistent daily watering for five weeks, stand counts were taken to assess pre-emergence damping-off, after which the plants were grown to maturity. At around the R3 growth stage, SDS symptom severity on each plant was evaluated on a scale from 1 (no disease) to 9 (plant deceased). These experiments spanned a minimum of three months. Although SDS foliar symptoms did manifest, achieving consistently high disease levels proved challenging. High disease incidence in the susceptible control is crucial for identifying and confirming resistance levels in other varieties. Dr. Febina Mathew is set to take over SDS research. Dr. Mathew will lead the future course of SDS soybean research, inheriting both the findings from Dr. Berlin Nelson’s program. Further complicating these results in the spring of 2023, molecular work performed by Dr. Guiping Yan discovered that previously collected isolates of the suspected F. virguliforme were in fact another fungal species, Clonostachys rosea, which had never before been reported as a pathogen of soybean in North Dakota. This leads to questions of whether F. virguliforme was ever present in North Dakota when first suspected in 2018.
In 2023, a comprehensive screening was conducted on 96 F2 (second-generation) NDSU soybean breeding lines to assess their resistance against P. sojae races 3 and 4, the most dominant races in North Dakota as of 2015. These screenings were performed by growing ten seedlings of the breeding lines in clear plastic cups. After roughly ten days, these plants were inoculated by induction of a wound on the hypocotyl of the seedling with a hypodermal needle. Then a slurry of P. sojae cultures were placed around this wound for inoculation. Seven to ten days after inoculation, cups were rated for the survival of individual plants which was used to calculate a survival percentage for each line. From these disease assays, we define a resistant line as having greater than 80% survival after inoculations. This evaluation showed that 46% of the lines were resistant to both races, 28% displayed resistance exclusively to race 3, while 26% were susceptible to both. This ongoing screening process is essential to ensure that the breeding populations are equipped to counter these pathogen races. Further, these lines were evaluated for presence of partial resistance or often called field tolerance. Several lines demonstrated a survival rate between 20% and 80%, indicating a degree of partial resistance to the P. sojae races, which could prove highly valuable for future breeding programs (Fig. 1 and 2). Future breeding efforts will be focused on precisely quantifying this partial resistance in soybeans lines post-inoculation with the two races. This will add value as we aim to stack both complete resistance via Rps genes and partial resistance for increased management of P. sojae.
The importance of genetic resistance in managing SDS and PRSR is critical for successfully protecting soybean crops. Although the presence of F. virguliforme in North Dakota is now potentially in question. The screening of NDSU soybean breeding lines has revealed that a high number of lines exhibit resistance to the dominant races of P. sojae, which is crucial for developing disease resistant varieties. Further, the identification of partial resistance in several breeding lines against P. sojae races highlights the potential for breeding soybean varieties with both complete and partial resistance, offering a more comprehensive approach to managing this disease.

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View uploaded report 2

2023 Executive Summary on Resistance to Important Soybean Diseases
Project Title: Resistance to Important Soybean Diseases
Project dates: July 1, 2022 to December 1, 2023
Principal Investigator: Dr. Richard Webster
Co-PI: Dr. Hui Yan


Objectives:
1. Screen NDSU breeding lines for resistance and identify lines with high levels of resistance to Phytophthora root rot.
2. Screen adapted soybean germplasm for resistance to sudden death syndrome and identify sources of resistance that the soybean breeder can use in the development of resistant varieties for this area.
3. Process plant samples with suspected SDS symptoms to verify the presence of the disease in ND fields.

From July 2022 to December 2023, our team evaluated soybean varieties for resistance to Phytophthora root and stem rot (PRSR) and sudden death syndrome (SDS). One of the key elements of this study was a field evaluation of two soybean varieties, Bison and Benson, both believed to be resistant to SDS. This disease is caused by a fungus, Fusarium virguliforme, and the study aimed to confirm the varieties' resistance under field conditions. However, accidental herbicide damage occurred and no SDS symptoms developed by September in our susceptible checks, forcing the termination of this study.
Simultaneously, we conducted SDS greenhouse experiments using the same soybean varieties. These controlled conditions allowed for an observation of how the varieties reacted to the F. virguliforme. Although the plants did exhibit some SDS symptoms, the inconsistency in the severity of SDS posed a challenge for the validity of results. Adding to the complexities, a puzzling discovery was made in 2023. Molecular research revealed that the fungus initially thought to be causing SDS in North Dakota was actually a different species entirely. This revelation brought about new questions regarding the actual presence of F. virguliforme in ND since its first suspected appearance in 2018.
Another significant part of the research involved screening 96 soybean lines for their resistance to PRSR, focusing on the two most prevalent types in North Dakota. The findings were promising with nearly half of the lines showing resistance to both types, about a quarter were resistant to one, and the remaining were susceptible to both. Intriguingly, several lines demonstrated what is known as partial resistance, surviving the disease to varying degree but not completely immune. This data is important as it opens up new avenues for breeding with a combination of complete and partial resistance, offering a more robust defense against PRSR. This comprehensive study lays a foundation for future efforts of developing more resilient soybean lines, capable of withstanding major diseases of North Dakota more effectively.
Overall, this work suggests that growers should be aware of SDS symptoms in the field for identification of its presence. While questions on the presence of SDS in North Dakota are now surfacing, it is important to scout so that resistant varieties can be planted when needed. Additionally, this research helps to advance breeding efforts in a direction that allows for improved resistance to PRSR by selecting specific lines with both complete and partial resistance.

This is long term research which will benefit growers in the years to come when sources of resistance are incorporated into public and commercial soybean varieties. Resistance is the most valuable management tool for preventing major losses to important soybean diseases. To illustrate the importance of just one disease, in the United States in 2007 sudden death syndrome was estimated to cause losses of 22 million bushels of soybean.