Seedling Diseases of Soybean: Characterization and Education
by Jason Bond, Southern Illinois University
Young plants infected by Rhizoctonia
Fusarium root rot, Rhizoctonia seedling blight, Phytophthora root rot and Pythium seedling blight are widespread fungal seedling diseases of increasing concern in soybean production. We now know there are many species of each of these organisms that can affect stand establishment, weaken seedlings, and reduce yield.
In a three-year research project funded by the United Soybean Board and the North Central Soybean Research Program, 16 soybean plant pathologists and breeders from eleven states (AR, KS, IA, IL, IN, MI, NE, MN, NE, TN) and Canada worked collaboratively to address the production constraints caused by seedling diseases and developed region-specific management recommendations to minimize yield loss.
Our goals were (1) to identify the fungi that cause seedling blights of soybean, (2) to perfect the tools needed for identification and soybean germplasm screening, (3) to determine the environmental factors that increase the risk of disease, and (4) to establish baseline fungicide sensitivities in order to monitor changes in resistance over time. Here are some major findings to date:
- From over 3,000 disease samples collected from soybean fields in all participating states, we developed quick molecular identification tools for Phytophthora species, several Fusarium species, and Rhizoctonia solani that will soon be available to diagnostic clinics.
- Many potential bio-control organisms were also isolated from soybean roots. We are following up on the potential of these organisms to control seedling pathogens.
- Reliable lab and greenhouse assays are now in place to test for pathogenicity of seedling fungal isolates. They are being used to compare pathogenicity among fungal species and isolates, and to test germplasm for resistance or tolerance to seedling disease.
- We have identified 15 soybean lines with partial resistance to seedling blight and root rot caused by Rhizoctonia solani. Progeny from resistant X susceptible parents can now be characterized for their resistance using QTL mapping.
- The baseline sensitivity of Rhizoctonia solani to fungicide active ingredients is now established. These baselines will allow us to monitor if shifts in sensitivity to DMI, SDHI, and QoI fungicides are occurring. We have already found species of Fusarium and Pythium that are not sensitive to major seed treatment fungicides.
- Soil temperature greatly impacts which seedling blight species will infect soybeans. Temperature can also influence how aggressive seedling pathogens will be on soybean, and affects the sensitivity of Pythium species to fungicides.
- We are in the process of determining the host range of specific pathogens so that the effect of cropping systems and rotations on pathogen survival and the risk of seedling disease can be determined.
The state of our knowledge about seedling diseases, best management practices, and diagnostics have been compiled into several new publications. These are available as free downloads.Soybean Seedling DiseasesScouting Soybean Seedlings Diseases and DisordersFungicide Efficacy for Control of Soybean Seedling Diseases
Also view three videos about soybean seedlings diseases on the SRII YouTube channel.