Identification and Characterization of Pythium deliense Causing Sugar Beet (Beta vulgaris) Root Rot in Grand Forks, North Dakota

Damping-off disease caused by multiple species of soilborne pathogens causes severe economic losses to sugar beet production. Thus, identifying the causal agent is important to formulating effective disease management. During a July 2021 disease survey in a sugar beet field at Grand Forks, North Dakota, we observed that approximately 15% of plants located in low areas of a commercial field showed wilting leaves that were pale green and slightly blighted in color, and the roots were dark brown to black, along with irregular necrotic lesions. The isolated pathogen had the characteristic morphology of Pythium deliense. The sequences of the internal transcribed spacer (ITS) region and the cytochrome c oxidase subunit 1 mitochondrial (cox1) genes were 100% homologous to corresponding sequences in the NCBI database, which confirmed its P. deliense identity. Moreover, the ITS phylogeny confirmed its identity as P. deliense and its close relationship with P. aphanidermatum. A disease screening trial with four sugar beet varieties was done. Growers and breeders could benefit from accurate information about the sugar beet pathogen in a given field to formulate effective disease management practices.