Biological control properties of two strains of Priestia megaterium isolated from tar spots in maize leaves

Authors: Johnson, Eric; Dowd, Patrick; Moser, Jill

Submitted to: Agriculture Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2025
Publication Date: 11/28/2025
Citation: Johnson, E.T., Dowd, P.F., Moser, J.K. 2025. Biological control properties of two strains of Priestia megaterium isolated from tar spots in maize leaves. Agriculture Journal. https://www.mdpi.com/2077-0472/15/23/2465.
DOI: https://doi.org/10.3390/agriculture15232465

Interpretive Summary: Corn is one of the most important crops in the United States, but diseases like tar spot threaten farmers’ yields and increase production costs. Tar spot caused $1.2 billion in economic losses in 2021 in the United States. Spraying chemicals on plants can reduce the amount of tar spot disease but consumers want farmers to use less chemicals on their crops. We identified two strains of bacteria that reduced the incidence of tar spots in field corn when either bacterium was applied to the seeds prior to sowing. We are currently conducting studies to understand how the bacteria reduce tar spot occurrence. Laboratory experiments determined that natural gases produced by the bacteria slowed the growth of fungi. Chemicals released by the bacteria into their surroundings completely inhibited the growth of one fungus. Lastly, we determined that the bacteria, when coated onto seeds, made the corn leaves more resistant to the fungi causing northern corn leaf blight, southern corn leaf blight and anthracnose disease. Seed treatments with these bacteria appear to be the most practical way forward. This study provides farmers and the corn industry a new tool to protect their corn, reduce dependency on fungicides, and align with USDA’s priority of protecting food security.

Technical Abstract: Priestia megaterium is an endophyte of maize that may help the plant defend itself against bacterial and fungal pathogens. In a previous investigation, coating maize seeds with one P. megaterium isolate, FS10 or FS11, reduced the incidence of tar spot disease in field corn, but the source of fungal resistance in the leaf has not been thoroughly characterized. This study aimed to identify any antifungal molecules produced by the two P. megaterium isolates and determine if seed coating with either strain could increase pathogen resistance to additional maize diseases. Volatiles emitted by both isolates reduced the hyphal growth of several fungi 17 – 76% in Petri dish assays. Gas chromatography of the headspace in small glass vials determined each strain emitted isovaleric acid (IVA) and 3-methyl-1-butanol (3MB) after two days of bacterial growth. Both 3MB and IVA are antifungal and antibacterial compounds. Volatiles produced by each P. megaterium isolate inhibited the growth of plant pathogenic bacteria, especially Clavibacter michiganensis ssp. michiganensis (Cmm), 96-99% in Petri dish assays. IVA killed all Cmm cells at 208 µl L-1 while 3MB inhibited growth of these bacteria 51% at 208 µl L-1 in Petri dish assays. Diluted cell-free extracts from FS10 and FS11 cultures grown for 4 days stopped growth of Cmm, Erwinia amylovora and Ustilago maydis but did not arrest growth of Fusarium verticillioides. The treatment of corn seeds with FS10 or FS11 reduced leaf damage 38-84% in young plants caused by the pathogens Bipolaris maydis, Colletotrichum graminicola, Exserohilum turcicum and Pythium sylvaticum. The P. megaterium FS10 and FS11 isolates exuded volatile and soluble compounds that were more effective in slowing growth of bacteria than fungi, which suggests that these compounds do not contribute greatly to leaf resistance to the fungus causing tar spot. It is likely that corn seed treatment with FS10 and FS11 bacteria triggers induced systemic resistance which mitigates leaf damage caused by several fungi and one oomycete. This study validates the hypothesis that P. megaterium can be an effective biological control agent for controlling multiple fungal diseases in corn.