Updated December 10, 2019:
Soybean stem diseases, such as sudden death syndrome, white mold, charcoal rot, and stem canker can severely limit yield across the U.S. each year. Development of genetic resistance in soybean varieties and improved management practices are needed to protect soybean yield. The research conducted under this project will deliver soybean varieties with improved resistance to stem diseases and advance knowledge of the biology of the pathogens that cause those diseases, resulting in improved disease management. This information will be shared with stakeholders in multiple formats to ultimately improve soybean profitability.

The tasks of this study were:
1: Increase availability of genetic resistance to stem diseases
2: Understand diversity of soybean pathogens causing stem disease based on fungicide resistance
3: Improve our ability to predict stem disease development
4: Develop outreach materials to improve stakeholder awareness of stem disease pathogens and best management practices for diseases

Plant breeding efforts were undertaken to characterize advanced breeding lines for sudden death syndrome (SDS), charcoal rot, white mold and stem canker. Field trials were established in IA, MI, and SD. Successful disease symptoms developed allowed assessment of breeding lines, and a range of resistance levels were observed from replicated tests. These efforts will allow release of soybean varieties with disease ratings so that farmers can make decisions for their needs, as well as private seed companies can utilize this information for licensing public program lines to meet their requirements.

Genetic studies were conducted to determine the pathogenic variability, host preference and fungicide sensitivity among Macrophomina phaseolina isolates. Genomic regions related to fungicide insensitivity have been identified and are being analyzed from a collection of 96 isolates. Protocols were developed and optimized to conduct infection studies with Macrophomina phaseolina, charcoal rot pathogen, and Fusarium virguliforme, the SDS pathogen.

In order to expand white mold disease forecasting model nationally. Field trials were conducted in to refine the existing soybean Sclerotinia stem rot (SSR) advisory tool to incorporate model output for different forms of resistance. The goal is to improve the accuracy of a fungicide application decision tool for controlling white mold, by accounting for varietal resistance in soybean. The Sporecaster model was previously validated in field trials with good level of accuracy but we expect that this accuracy would be improved by modifying action thresholds based on resistance type. Trials were conducted in WI and MI during the 2019 field season in Wisconsin to test these new thresholds. Disease and yield data were collected and are being analyzed.

Field trials were conducted in WI, IA, and MS to study the importance of management strategies on disease development. One of the goals was to identify soybean varieties with a high level of resistance to white mold that are stable across locations in the North Central region. Several commercial varieties were identified that appear to have good physiological resistance in the greenhouse and acceptable field resistance in multiple environments. These varieties were again tested in Wisconsin, Michigan, and Iowa in the 2019 field season. Disease data was collected at these multiple sites, with yield data collection ongoing.

Extension efforts focused on developing outreach materials to improve stakeholder awareness of stem disease pathogens and best management practices for diseases. An article was released through CPN focused on diagnosing stem diseases (https://cropprotectionnetwork.org/resources/features/diagnosing-interveinal-chlorosis-in-soybeans-it-s-not-just-sds)