Soybean diseases can cause substantial yield losses and influence variety selection and crop rotation decisions. In North Dakota Phytophthora root rot caused by Phytophthora sojae is a major disease generally associated with high soil moisture for extended periods. The pathogen is long lived in soil and resistance to the pathogen is the most effective way to reduce damage during conditions favorable for disease. The pathogen consists of various races, and each race can attack different genes in soybean for resistance. Understanding what races are found in soybean growing areas and which are most common is essential information for selecting the resistance genes most effective to manage the disease. This grant proposes to do a state wide survey to determine what races are most common in soybean fields.

1. Conduct a state-wide survey of the races of Phytophthora sojae and determine the virulence phenotypes on a selection of 8 differential varieties. The virulence phenotype is a list of resistance genes that an isolate of the pathogen can attack.

1. Identification of races of P. sojae in the principle soybean growing counties.
2. Identification of the most common races and which are most threatening to soybean cultivars in this area.

Updated November 19, 2021:

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Understanding which races occur in our state and which races are most common, impacts our decisions on which resistance genes need to be used for management of Phytophthora root rot using resistant varieties. This is information that can be used by both the private soybean seed companies and the NDSU soybean breeding program. It also impacts the research that NDSU conducts on other ways to manage this disease such as the use of partial resistance. Furthermore, growers often have questions as to why disease is showing up in a field that has a cultivar with resistance to Phytophthora root rot. The information from this project can help us better understand disease development in soybean growing areas of the state.