Research Highlights

Progress in Developing IPM Tools for Diagnosis and Management of Soybean Seedling Diseases

Jason Bond (Project Leader, University of Illinois)
Co-investigators:  Ahmad Fakhoury (Southern Illinois University),Christopher Little (Kansas State University), Martin Chilvers (Michigan State University), Febina Mathew (South Dakota State University), Dean Malvick (University of Minnesota), Tony Adesemoye, and Sydney Everhart (University of Nebraska), Gary Munkvold, and Alison Robertson (Iowa State University)

Effective control of seed and seedling rots is becoming increasingly important to protect the value of seed, currently the largest single expense in soybean production.

Fusarium root rot, Rhizoctonia seedling blight, Phytophthora root rot, and Pythium damping off are examples of widespread seedling diseases of increasing concern. We now know there are many species of each of these organisms that can affect stand establishment, weaken seedlings, and reduce yield. The root rot pathogen, Fusarium graminearum, and various Pythium species which can infect both corn and soybean are becoming more prevalent in corn-soybean rotations.

With the exception of Phytophthora soja, no varietal resistance is yet available. Over the past several years, a major goal for plant pathologists and soybean breeders has been to identify and develop varietal resistance to common seedling pathogens as a cost-effective management tool.

With checkoff funding provided by the North Central Soybean Research Program and the United Soybean Board, researchers throughout the region have worked collaboratively to address the production constraints caused by seedling diseases and develop the IPM tools that are needed for future prevention and control.

Here are some major findings to date:

• A diagnostic assay to determine the presence of Phytophthora in soil and plant roots is in the final stages of testing before commercialization. Plant clinic diagnosticians have already been trained with kits that can be used in the field with relatively simple equipment. Detection and identification can be achieved in a matter of minutes.
   
• Diagnostic assays are in final stages of development for the identification of other key seedling pathogens from soil, roots and soybean stem. The ability to quickly and accurately identify and quantify key seedling pathogens will provide a powerful decision tool for farmers and researchers.
   
• Significant progress has been made in identifying northern germplasm with resistance to seedling pathogens. In Minnesota, significant differences in susceptibility to Rhizoctonia solani were detected among northern cultivars and breeding lines. Researchers in South Dakota have identified eight soybean accessions with resistance to Fusarium graminearum. Companion projects supported by USB and NCSRP have identified numerous sources of resistance to Phytophthora sojae, Pythium spp. and Fusarium graminearum.Plant breeders now have a wealth of germplasm material to work with.
   
• A fast, automated fungicide sensitivity assay has been developed and shared with a number of labs. The fungicide assay has enabled improved monitoring for fungicide resistance among oomycetes (particularly the common seedling pathogens Pythium and Phytophthora ), which will ensure that the seed treatments in use are effective. Research soon to be published demonstrate clearly the need for multiple chemistry seed treatments for the management of mixed oomycete populations.
   
• The soybean seed treatment efficacy bulletin was updated in March 2019.

Resources
Rapid diagnostics, germplasm for the development of resistant soybean varieties, and screening tools that ensure fungicide seed treatments remain effective are providing a solid foundation for seedling disease IPM. The state of our knowledge about seedling diseases and best management practices have been compiled into several current publications. These are available as free downloads.

Published: May 9, 2019