K-State Researchers Tackle Common Bunt from the Spore to Seed

On the upper floors of Throckmorton Hall at Kansas State University, a nondescript gray cabinet
and set of freezers hold a collection of spores gathered from across the world to help Kansas
wheat producers better manage common bunt.

“We have had, in the last five years, more fields affected by common bunt, and these fields have
had substantial yield loss,” said Kelsey Andersen Onofre, assistant professor of plant pathology
in K-State’s College of Agriculture, who leads this research project along with fellow K-State
plant plathogists Erick De Wolf and Sanzhen Liu, and Robert Bowden, supervisory research
plant pathologist with USDA’s Agricultural Research Service (ARS). “We want to be able to
help producers with making management decisions, choosing the right fungicide seed treatments,
having them properly applied and working with the breeding material to understand if there are
resistance genes that exist in current Kansas varieties.”

Also known as stinking smut, common bunt occurs regularly in Kansas at varying levels.
According to K-State Research and Extension, the fungal disease causes moderate deformation
of wheat kernels, which can have a gray color and a strong fishy odor. Infected kernels are also
filled with black powdery spores, known as teliospores, versus white starch.

In addition to yield losses, common bunt negatively impacts milling and baking quality. Too
much infected wheat results in dockage or rejection at the elevator, leaving producers without
good alternatives for selling the lower-quality wheat.

In the 2019-2020 wheat growing season, wheat producers in parts of Kansas and Oklahoma had
decade-high levels of yield loss due to common bunt. The bunt spores also looked different
under the microscope when examined by grain inspectors. As a result, the Kansas Wheat
Commission and U.S. Wheat Associates, the wheat industry’s export market development arm,
approached K-State researchers with a challenge — learn everything about common bunt and the
fungal pathogens that cause the disease, including how to better identify it and manage for it.

“We need to develop a better test and be sure we do not have isolates of something other than
common bunt,” Andersen Onofre said. “We also need to make sure we’re still making the right
management recommendations to our producers here in Kansas. So, we want to make sure the
biology is still holding true and that we can still make the same recommendations about seed
treatments and planting timing to keep common bunt under control.”

Common bunt is caused by two closely related, but easily distinguished fungal pathogens
— Tilletia tritici and T. laevis. Onofre and her team started their research by gathering spore
samples of these pathogens from Kansas and Oklahoma. The team also collected isolates for T.
controversa — the fungal pathogen that causes the highly regulated TCK or dwarf bunt — and T.
fusca — another related species that infects wild grass species. These isolates came from across
the United States, including the Pacific Northwest, Michigan and New York. Researchers also
obtained special pathogen permits to collect samples from Canada, Europe, Asia and Australia.

Once the isolates were gathered into that gray cabinet in Throckmorton Hall, each in an individual drawer marked with a scannable QR code, the real work could begin. Onofre’s team is categorizing each sample by phenotype (how it looks under the microscope) and genotype (DNA analysis). Teliospores — which look like tiny spiky soccer balls — from the samples are measured for reticulation depth and diameter before being run through germination experiments. The physical appearance of these teliospores has been the key indicator of distinguishing common bunt from other pathogens, making correct classification a priority of the research project.

Combined, this research has built a reference library. By better understanding these pathogens from a microscopic level and by putting them to the test under different germination conditions in the lab, researchers are constructing a file on common bunt — what it looks like, how it behaves and how it can be controlled.

Onofre and her team are already assessing the first field trials for the two existing management recommendations for controlling common bunt — using fungicide seed treatments and early planting to avoid the cool soil’s favorable to disease development.

“The first year of field trials where we’re comparing fungicide treatments for these different isolates has been planted and is underway this year,” Andersen Onofre said. “That will be some pretty exciting data we will have to share this coming winter.” “We don’t want to miss the opportunity to educate about managing these pathogens while we’re doing some of these genetic studies. We need to get the message out about management as well. We’ve included some new recommendations about fungicide seed treatments and the importance of using products that have the triazole class of fungicides in the mix.”

The research project funded by the Kansas Wheat Commission, the Kansas Wheat Alliance and the Kansas Crop Improvement Association is now backed by a second grant from USDA’s National Institute of Food and Agriculture (NIFA) that will focus on an expanded set of objectives. That includes the development of better diagnostic tools for distinguishing common bunt from its trade-restricted relative TCK and the identification of resistance genes within the K-State wheat breeding pipeline. 

“We’re working on a test that can be used by diagnostic labs,” Andersen Onofre said. “The most irrefutable way is to look to the DNA of these pathogens; that’s how we do a lot of different diagnostic tests across pathogens. We find these segments in their genomes that are different, and then we can use tests like a rapid PCR test. You can have a test that can actually tell us what’s there based on these segments of DNA and also how much is present in a sample.” From the gray cabinet in Throckmorton to farmers’ fields, the combination of lab work, field studies and new diagnostic tools will provide powerful data for wheat producers to combat common bunt.

Keep track of the project’s progress and the latest updates to management recommendations at https://eupdate.agronomy.ksu.edu/.

###

Written by Julia Debes for Kansas Wheat.