There are no reports of complete resistance in soybean against Sclerotinia sclerotiorum, the cause of white mold (Sclerotinia stem rot). Most commercial soybean varieties are susceptible to white mold, but a limited number of varieties express partial resistance defined as low plant mortality in field and controlled environments.

We achieved our goal to develop soybean lines that express zero plant mortality in greenhouse trials. Nineteen lines were identified to express complete resistance. An additional 105 lines expressed 10% or less plant mortality. Of 751 lines evaluated, 124 or 17% expressed resistance significantly higher than observed among commercial varieties rated as tolerant to white mold. A value of 17% signifies the difficulty of selecting highly resistant lines in a breeding program. Although experiments are needed to verify, we hypothesize that selection after 8 generations of self-fertilization contributed to the ability to identify breeding lines highly resistant to white mold. The vast majority of soybean breeders are selecting lines after 5 generations. Advanced lines are available for licensing through the Wisconsin Alumni Research Foundation. All 751 lines are now part of an NCSRP- funded project to identify genetic markers associated with genetic resistance to white mold. Brian Diers, University of Illinois, heads this project.

All collaborators have met several times over the past few years to complete projects for this objective. There are three main outputs from this project: 1) a complete updated management guide that was distributed to each of the north central states; 2) this management guide was expanded to become a referred journal article in the Journal of Integrated Pest Management; and (3) a series of podcasts were completed and loaded onto iTunes (go to iTunes and search “white mold soybean”). One of the outcomes of this project has been the development of a framework for doing collaborative extension projects. During the 2013 summer, the group will be collecting and identifying apothecia look-alike mushrooms. We will be developing a scouting card and an educational activity for pre-collegiate students from the results. We will also be collecting short videos on common management questions as opportunities arise.

The core group of Extension educators also has given several talks about white mold and management using foliar fungicides. Information about white mold efficacy was predominately driven by the north central region. A second national project was the Fungicides for Field Crops publication through the American Phytopathological Society http://www.apsnet.org/apsstore/shopapspress/Pages/44204.aspx).