Application of Priestia megaterium strains isolated from nongerminating tar spots to maize seeds can inhibit the disease severity caused by biotrophic and necrotrophic maize pathogens

Authors: Johnson, Eric; Dowd, Patrick

Submitted to: International Journal of Pest Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2025
Publication Date: 1/22/2026
Citation: Johnson, E.T., Dowd, P.F. 2026. Application of Priestia megaterium strains isolated from nongerminating tar spots to maize seeds can inhibit the disease severity caused by biotrophic and necrotrophic maize pathogens. International Journal of Pest Management. https://doi.org/10.1080/09670874.2025.2612368.
DOI: https://doi.org/10.1080/09670874.2025.2612368

Interpretive Summary: Tar spot and Fusarium rot are fungal diseases of corn that together can cause over a billion dollars of losses in the U.S. in a single year. These pathogens, especially the one causing tar spot, are difficult to control using fungicides, so new disease management tools are needed. Two strains of bacteria called Priestia megaterium, were isolated from dead tar spots of corn and thus had the potential to control tar spot, and potentially other fungal diseases such as Fusarium rot. The strains were grown in the laboratory and applied to corn seeds. Plants whose seeds had received either of the two bacterial strains had smaller lesions caused by the Fusarium rot fungus when inoculated compared to plants whose seeds were not treated with bacteria. In another experiment, seeds that received either bacterium were sowed into a field along with untreated seeds in 2022 and 2023. In 2022, the overall incidence of corn plants with tar spot was reduced 42-54% in the corn plants that received either bacterium seed treatment compared to the untreated plants. In 2023, all corn plants had tar spot, but the occurrence of greater than 20 tar spots on the lowest leaves of the plants was reduced by 42-72% in plants that had received a bacterium seed treatment compared to the plants that were untreated. This study shows that these two bacterial strains have the potential to reduce the damaging effects of the tar spot and Fusarium rot diseases of corn and thereby contribute to higher grain yields, increased profits and lower costs for farmers and consumers.

Technical Abstract: Tar spot, caused by Phyllachora maydis, and Fusarium rot, caused by Fusarium graminerum, can be devastating diseases of corn, and new management strategies are needed. Two strains of Priestia megaterium were isolated from nongerminating tar spot stromata and applied to seeds of different maize inbreds. In a laboratory study, mean lesion size caused by the necrotrophic pathogen F. graminearum on leaves of maize inbred N6 was significantly reduced by 28.6% and 38.7% compared to controls when either P. megaterium strain 10 (NRRL B68352) or P. megaterium strain 11 (NRRL B68353) were applied, respectively. In a two-year field study, the overall incidence of tar spot disease caused by the biotrophic pathogen P. maydis on leaves was reduced by 41.6% and 53.9%, respectively, when P. megaterium strain 10 and strain 11 were applied to seeds of maize inbred GE440 the first year of the study. The incidence of lower leaves with greater than 20 tar spots was significantly reduced by 41.9% and 72.3%, respectively, when P. megaterium strain 10 and strain 11 were applied in the second year of the study. Additional experiments determined that neither bacterium strain caused damage to sheep red blood cells or corn leaves, suggesting that nontarget effects would be unlikely. Thus, these strains of P. megaterium have potential of significantly reducing maize pathogen effects, resulting in higher yields, more profitable production and lower cost for end users and consumer.