Fungal pathogen Sclerotinia sclerotiorum is pathogenic to over 400 plant species, and is one of the most deadly pathogens to American soybean crops in the form of Sclerotinia stem rot (SSR), also commonly known as white mold. Because there is limited clear information about how different soybean varieties resist this pathogen, , many commercial farms rely on a combination of cultural practices and chemical management like fungicides. While effective, fungicides can be costly and contribute to environmental pollution, and application errors are possible.
UMN researchers led by PhD student Nick Talmo and PI Ashish Ranjan recently published the results of a strategic screening process of various soybean varieties’ resistance to different genetic isolates of SSR. With this more comprehensive comparative information, soybean breeders and growers can work to lessen reliance on fungicide applications and move towards a strategy that breeds and implements research-backed resistant varieties.
In this study, researchers had three objectives, each with useful take-aways. First, researchers evaluated 51 soybean varieties (including commercial cultivars and University breeding lines) in response to SSR in controlled conditions, characterizing their resistance. Talmo and colleagues built on that information by then testing varieties that the first phase identified as high, moderate, or low disease resistance from eight Sclerotinia sclerotiorum isolates collected from around the state. This approach allowed them to determine whether genetic variances in the S. sclerotiorum could influence how well a soybean variety resists disease. Finally, the team assessed the genetic diversity and differing virulence of S. sclerotiorum isolates found in Minnesota fields. For complete methodology and tables containing the findings by variety, region, and isolate, please read the whole publication in Plant Disease.
The results of this study provide valuable complications to existing knowledge of soybean SSR resistance in Minnesota. Importantly, these results showed that current disease-resistance ratings from seed companies may not always hold up when soybean plants encounter more aggressive or genetically distinct strains of the pathogen, a finding that demonstrates the value of screening with diverse pathogen strains. Additionally, the S. sclerotiorum isolates from different Minnesota counties and environments in this study showed notably different virulence, proving the importance of developing screening panels in addition to just screening isolates.
This research affirms the value of analyzing multiple factors when considering SSR in soybean that account for both soybean and pathogen diversity. Such approaches provide a strong case for investing time and resources into creating standardized panels for clear and applicable results to those working with soybean sustainability. Further research is needed to analyze pathogenicity and resistance interactions across a wider geographic area, as well as including more genetic diversity of both plant and pathogen to strengthen these efforts.
This research was supported in part by the Minnesota Soybean Research and Promotion Council.
Cited:
Nick Talmo, Jo Evans, Aaron Lorenz, Dean Malvick, and Ashish Ranjan. “Soybean screening identifies resistant lines, reveals virulence variation, and genomic diversity among Minnesota Sclerotinia sclerotiorum isolates.” Plant Disease First Look. https://doi.org/10.1094/PDIS-03-26-0637-RE