Identification of Halo Blight disease on oat in Idaho and exploration of resistant sources in oat, barley and wheat

Authors: Yimer, Belayneh; Esvelt Klos, Kathy; SAPKOTA, SURAJ - Oak Ridge Institute For Science And Education (ORISE); BUTCHACAS, JULES - The Ohio State University; JAKOBS, JONATHAN - The Ohio State University; TOTH, HANNAH - The Ohio State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2025
Publication Date: 1/6/2026
Citation: Yimer, B.A., Esvelt Klos, K.L., Sapkota, S., Butchacas, J., Jakobs, J., Toth, H. 2026. Identification of Halo Blight disease on oat in Idaho and exploration of resistant sources in oat, barley and wheat. Plant Disease. https://doi.org/10.1094/PDIS-08-25-1717-RE.
DOI: https://doi.org/10.1094/PDIS-08-25-1717-RE

Interpretive Summary: Oat is an important healthy cereal crop grown worldwide. Its production is impacted by many biotic and abiotic factors. Diseases caused by fungi, bacteria and viruses are the major biotic constraints impacting oat grain yield and quality. In 2023, oat trial fields in Aberdeen, Idaho, were severely infected with an unknown disease. Series of experiments were conducted to identify the new disease and its causative agent, other crop species infected by the pathogen, and to evaluate the reaction of oat, barley and wheat germplasms to the disease. After thorough investigations using traditional and molecular approaches, the disease was confirmed to be bacterial halo blight (BHB) caused by a bacterial species. BHB is an important oat disease prevalent around the world. The disease has been infrequently reported in the United States, with historical records limited to the 1920s through the 1960s. This study marks the first detection of bacterial halo blight in Idaho, and the first detailed description of the pathogen in the United States after over half a century. The study determined that barley and corn are also susceptible to the disease. Evaluation of a set of oat, barley and wheat germplasm identified four oat and five barley germplasm with some level of resistance to BHB. Most of wheat germplasm tested were resistant to BHB. Early and accurate detection of such plant pathogens is crucial for effective disease management as the misidentification of a disease and its causal agent can lead to ineffective control measures, wasting resources and time. Hence, the results of the present study will provide a basis for further research towards better understanding and management of BHB.

Technical Abstract: Pseudomonas coronafaciens pv. coronafaciens (Pcc), the causal agent of Bacterial Halo blight (BHB) on oat, has been infrequently reported in the United States, with historical records limited to the 1920s through the 1960s. In 2023, oat trial fields in Aberdeen, Idaho, were severely infected with an unknown disease that formed necrotic lesions on leaves. Preliminary identification based on colony morphology suggested a pathogen belonging to the genus Pseudomonas. Subsequent whole-genome sequencing confirmed 99.6% average nucleotide identity (ANI) with Pseudomonas coronafaciens pv. coronafaciens (Pcc). This marks the first detection of Pcc in Idaho, and the first detailed description of the pathogen in the United States after over half a century. Host range and pathogenicity assessments on multiple cereal crops showed that Pcc was pathogenic on oat, barley, and corn. However, wheat, rye and triticale displayed chlorosis and early cell death in response to the pathogen. Evaluation of oat and barley genotypes revealed resistance in the two crop species to be rare with only 2.5, and 4.5% of oat and barley genotypes exhibiting some level of resistance. Notably, the four resistant and moderately resistant barley genotypes identified in this study: DH170472, Celebration, Legacy and Quest are the first to be reported as sources of resistance to BHB. Results of the present study provides a basis for further research toward a better understanding of disease epidemiology, the genetics of host-pathogen interaction and the management of BHB on oat, barley and corn.