Phytophthora root and stem rot (PRSR) is a major disease of soybean that can cause yield losses of up to 40 million bushels in a single season in the United States and Canada. In North Dakota, farmers use commercial varieties having the resistance genes Rps 1c, 1k, 3a, and 6, however the study by Yan and Nelson (2019) indicate that there are pathotypes of the PRSR organism, P. sojae, that can defeat these genes. Thus, it is important to evaluate the virulence diversity in the P. sojae population and the effectiveness of Rpsgenes for long-term disease management. Additionally, there is no information on another PRSR pathogen, P. sansomeana, which has been reported in the Midwest (e.g., Indiana, South Dakota, Wisconsin). In this research, we propose to characterize the P. sojae pathotypes, identify and determine the prevalence of P. sansomeana (if present in North Dakota), and screen breeding lines for resistance to P. sojae. For the proposed research, surveys will be conducted to collect soil samples from commercial fields. The causal organisms will be baited using a variety susceptible to P. sojae, isolated, identified and pathotyped. After obtaining P. sojae isolates, lines from NDSU’s soybean breeding program will be screened for resistance to the prevalent pathotypes, race 3 and race 4.
Overall, this work will allow for the better understanding of P. sojae populations present in North Dakota and more targeted breeding efforts for resistance to this pathogen, as well as help us provide farmers with effective recommendations of cultivars to plant.

1. The diversity of Phytophthora sojae pathotypes present in North Dakota soybean fields will be determined.
2. Phytophthora sansomeana may be identified in North Dakota soybean fields.
3. The current status on the effectiveness of Rps genes against P. sojae will be determined.
4. The soybean breeding efforts will be improved by targeting the most important pathotypes of P. sojae.
5. Soybean farmers will have access to improved recommendations to manage PRSR, which includes cultivar selection.

1. Improved grower recommendations for appropriate cultivar selections
2. Improved understanding of P. sojae (and possibly P. sansomeana) populations, which will allow for more targeted soybean breeding efforts

Update:
FY 2024 Mid-Year Report North Dakota Soybean Council
November 2023

Richard Wade Webster

Project Title: Investigating Phytophthora sojae Populations Across North Dakota Soybean Production Systems
Project dates: July 1, 2022 to June 30, 2023.
Objectives:
Objectives:
1. The diversity of Phytophthora sojae pathotypes present in North Dakota soybean fields will be determined
2. Phytophthora sansomeana may be identified in North Dakota soybean fields
3. The current status on the effectiveness of Rps genes against P. sojae will be determined
4. The soybean breeding efforts will be improved by targeting the most important pathotypes of P. sojae.
5. Soybean farmers will have access to improved recommendations to manage PRSR, which includes cultivar selection


Completed work:
Despite widespread dry conditions in North Dakota in 2023, PRSR was surprisingly widespread with pockets of high stand loss due to PRSR. During the 2023 growing season, 147 soybean fields were sampled for soil through collaborations with county Extension agents, industry partners, and our own personnel (Figure 1). Our original goal was to attain 100 samples, and we well exceeded expectations. Beginning in September of 2023, an M.S. graduate student, Abdul-lateef Popoola, joined the Soybean Pathology program and is responsible for managing this project. At the end of November 2023, a total of 78 soil samples have been processed with a total of 67 isolates collected from these samples. We aim to complete all soil samples by March 2024. The currently isolated samples are also being processed for sequencing for the identification of the correct species. This will lead to the determination if P. sansomeana is present within our collection. Beginning in 2024, we will begin testing the collected isolates against our differential lines to determine races of these isolates. Once these isolates are fully tested and races determined, information can then be reported back to growers as to regional differences in the P. sojae populations present. Further, beginning in the spring of 2024, breeding lines from Dr. Carrie Miranda’s program will be screened for resistance to P. sojae races 3 and 4. This work will assist in selecting lines with complete resistance.

View uploaded report

While resistance to P. sojae is present in many commercial soybean cultivars, the understanding of which Rps are the most important for growers to plant is currently lacking. Therefore, this research will allow for the more informed decisions across North Dakota for choosing the proper cultivars. Additionally, this research will assist the soybean breeding efforts at NDSU in ensuring the proper resistance genes are being introgressed into advanced yield lines and future public releases for the farmers.