Brome grasses represent the primary source of Claviceps purpurea inoculum associated with barley fields in the San Luis Valley of Colorado

Authors: WYKA, STEPHEN - Colorad0 State University; Broders, Kirk

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2022
Publication Date: 6/29/2022
Citation: Wyka, S., Broders, K. 2022. Brome grasses represent the primary source of Claviceps purpurea inoculum associated with barley fields in the San Luis Valley of Colorado. Canadian Journal of Plant Pathology. 45(1):15-29. https://doi.org/10.1080/07060661.2022.2091041.
DOI: https://doi.org/10.1080/07060661.2022.2091041

Interpretive Summary: The fungal pathogen, Claviceps purpurea, which causes ergot disease on grain heads, poses a significant threat to agriculture and food safety due to various toxic alkaloids present in the dark ergot bodies which can cause severe poisoning in humans and livestock. C. purpurea is known to infect a wide range grass species including barley, rye, and wheat as well as many native, invasive, and weedy grasses that grow in ditches along crop fields. An ARS researcher at Peoria, Illinois, worked with a scientist at Colorado State University to understand the role of non-crop grasses in the survival, reproduction and spread of the ergot fungus C. purpurea. Data from field surveys found that brome grasses, including smooth brome, were the most susceptible to infection by C. purpurea, were found in the greatest abundance near barley fields with a history of ergot, and had the greatest number of ergot bodies in the seed heads. Our findings indicate that smooth brome represents a significant source of pathogen inoculum and the amount of inoculum is capable of causing sporadic disease in nearby barley fields when environmental conditions are optimal.

Technical Abstract: The fungal pathogen Claviceps purpurea can infect numerous grass species including important crops like barley, rye, and wheat, but the ecology of ergot disease is rarely studied in non-crop grass species. Recent outbreaks of ergot in barley production systems in the western U.S. have implicated nearby grass hosts as reservoirs for inoculum and spread of C. purpurea into the barley crop. We survey the prevalence of ergot infections among native, invasive, and weedy grass species near barley fields in the San Luis Valley of Colorado over three years. We found that barley fields with a history of ergot disease were surrounded by grass community composed largely of smooth brome, that smooth brome was very susceptible to ergot infection and had the highest infection rates, and that disease severity among the grass community increased during the growing season. Our findings indicate that smooth brome represents a significant source of C. purpurea inoculum and inoculum levels increase as the composition of brome grass in the grass community increases. There is sufficient inoculum present in the brome grass population in the San Luis Valley to cause sporadic disease in barley fields when environmental conditions are optimal for infection. Future disease management strategies should take into account the large pool of inoculum in the grass population near barley production fields.