Research Highlights

Research Highlights
Kansas Researcher Working to Reduce Soybean Root and Seedling Diseases

In Little’s lab, a seed plate test shows the control seeds (left) and M. phaseolina-inoculated seeds (right) of a charcoal rot-susceptible soybean variety. Note the discolored, ungerminated seeds and shorter hypocotyls in the inoculated treatment. Photo: Christopher Little

By Carol Brown

Soybeans are a key commodity crop grown in more than half the United States, but they have their enemies both above and below ground. Chris Little, a plant pathology professor at Kansas State University, is focusing on the battle below ground. He is researching ways to mitigate root and seedling diseases through projects funded by the Kansas Soybean Commission and the North Central Soybean Research Program.

“My lab is interested in the ‘big three’ soil-borne soybean diseases: sudden death syndrome (SDS), Fusarium seedling diseases and charcoal rot. I think these are some of the most important issues for soybeans in Kansas,” Little says. “We’re looking at a lot of varieties so we can see which are going to be most tolerant to disease — and they may be different depending on the disease.”

Little has been researching several methods to evaluate many varieties quickly, called high throughput assays, which are effective in the lab, growth chamber or greenhouse. He uses these assays to efficiently test more than 160 different soybean varieties for tolerance to these yield-robbing diseases. The tests take advantage of seed from the Kansas Soybean Variety Trials, which includes breeding varieties from KSU agronomy professor William Schapaugh’s lab as well as other public and commercial varieties.

“There are two stages of sudden death syndrome: the root rot stage is caused by the fungus Fusarium virguliforme producing toxins, then the toxins are translocated to the leaves of the soybean,” Little says. “We conducted fungal culture tests and seed germination tests that measure toxin reaction and root rot reaction to look at both these stages of the disease.”The research team ranked the varieties on a scale from 1-6, based on their response to the toxin assays in the lab for SDS, charcoal rot reaction or early seedling disease. The best and worst performing varieties were then tested in field plots. The examinations that Little used in his lab were effective in differentiating the varieties and determining how well they performed in the field for disease tolerance.

Figure 1. Screening of K-State breeding varieties using the toxin assay. Both senescence (declining ability to function) and toxin reaction were evaluated using a 1-6 scale. Overall ratings, in the third column of each set, represent the maximum value across reactions. The best performing varieties are represented by green on the left and light yellow on the right, and the value is boxed in black. Source: Christopher Little

Management Recommendations

In addition to testing soybean varieties to identify those with the most disease tolerance, Little notes that there are practical control strategies that can also help to curb disease severity. These strategies are disease specific and include:  

  • SDS: Select tolerant varieties; selected seed treatments 
  • Fusarium diseases (including seedling disease and root rot caused by a range of Fusarium spp.): Plant during conditions that promote rapid seedling development; plant at correct depth; commercial seed treatments 
  • Charcoal rot: Moisture conservation via lower plant populations, no-till, weed control, irrigation; plant later-maturing varieties 
  • Phytophthora root rot: Host resistance (via rps1k and rps1c genes) and tolerance; improved drainage; seed treatments for the seedling blight phase of the disease 

“Tolerance in host plants is the best management strategy to reduce infection and damage from disease,” comments Little. “Although success of finding good varieties depends on the disease. Genetic resistance to SDS, Fusarium diseases, and charcoal rot occurs using different mechanisms, but varieties exist that show moderate resistance to these diseases.” 

Little says that a catalog of varietal resistance will be required to integrate these traits into materials the Kansas State breeding program can release.

Working Group for Soybean Roots

To develop an ideal venue for collaboration among soybean researchers, Little is establishing a soybean root health working group on the KSU campus. He’s been exploring how soybean root health research can be packaged together and possibly use similar approaches and is hoping a working group could help.

“The group is just getting ramped up. I want to include people who focus on both the abiotic or environmental side, along with the biotic side: weeds, insect pests, plant pathologists,” Little says. “I want to put our heads together about how to improve soybean roots and, therefore, overall plant health. These disciplines can come together and have a voice for root health research.”

Little sees this group growing and making an impact on soybean research. The possibilities could include collaboration on research grants, a forum for formal discussion, and a place for students, postdoctoral staff and project investigators to discuss research and findings.

“Soil health is a key discussion point these days,” remarks Little. “We need to understand microbiomes, suppressive soils, green manures and all the interactions plants have with these. There is great potential in exploring this underground world for better soybean health and better yields.”

Published: Oct 24, 2022

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.