Development of a Sclerotinia sclerotiorum Isolate Panel to Screen for Soybean Resistance to Sclerotinia Stem Rot in Minnesota

Sclerotinia sclerotiorum is a significant threat to soybean ( Glycine max ) production in the northern United States, where cool growing conditions favor Sclerotinia stem rot (SSR) development. This study aimed to identify a panel of S. sclerotiorum isolates that can be applied to screen for resistance to SSR in soybean lines adapted for Minnesota. Twenty-one isolates were collected from throughout Minnesota from 2002 to 2022. Lesion size and standardized area under the disease progress curve (sAUDPC) values were used to quantify the aggressiveness of each isolate on a susceptible cultivar, Dwight. A five-isolate screening panel representing high, medium, and low aggressiveness on soybean was selected and validated using soybean lines with known differential resistance. The expected differentiation between the susceptibility of lines was observed using the panel. Aggressive isolates such as SSMM2 and SSPotter induced severe infections across all cultivars and MNSS6 induced moderate infections. In addition, MNSS4 and WISS47 exhibited milder infections. This study resulted in a panel of five Minnesota S. sclerotiorum isolates with varied levels of aggressiveness which can consistently differentiate soybean resistance in future screening efforts.