This project focuses on understanding and managing diseases caused by fungal-like organisms called oomycetes, specifically species of Phytophthora and Pythium, which impact soybean crops in North Dakota. These pathogens thrive in cool, wet conditions and can cause significant yield losses, especially as early planting trends expose seeds to higher disease risks. While Phytophthora sojae has been a known threat, recent surveys suggest that Pythium species are more prevalent than previously understood. Additionally, a newer pathogen, Phytophthora sansomeana, has been identified in other Midwestern states, but its presence in North Dakota is still unknown. The research aims to survey North Dakota fields to identify the diversity of oomycetes present. By understanding which pathogens and P. sojae races are most prevalent, the project will help soybean breeders and farmers select the most effective resistance genes (Rps) to manage disease. Field soil samples, already collected from over 170 fields, will continue to be analyzed, and the isolates will undergo further screening. The project will also evaluate breeding lines for resistance to these pathogens, providing data to support improved cultivar recommendations. Results will be shared with farmers through extension meetings and publications to guide disease management strategies. This study will provide practical solutions for protecting yields and profitability in North Dakota soybean production, especially in the face of changing environmental conditions and evolving pathogens.

1. The diversity of oomycete pathogens (Phytophthora sojae and Pythium species) present in North Dakota soybean fields will be examined.
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 examined.
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.

• Improved grower recommendations for appropriate cultivar selections
• Improved understanding of oomycete (Phytophthora and Pythium) populations present and their frequency in North Dakota, which will allow for more targeted soybean breeding efforts

Oomycetes are a major cause of premature soybean death across the entire growing season. However, it is unknown to what degree which oomycete populations are present in the early season of soybean production. Understanding if early season damping off of soybean seedlings is caused by Pythium species compared to Phytophthora species will dictate management strategies.
Further while resistance to P. sojae is present in many commercial soybean cultivars, the understanding of which Rps genes 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.