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ARS Home » Northeast Area » Frederick, Maryland » Foreign Disease-Weed Science Research » Research » Publications at this Location » Publication #419075

Research Project: Discovery and Development of Microbial-Based Biological Control Agents for Use Against Invasive Weeds in the United States

Location: Foreign Disease-Weed Science Research

Title: Emergence of a novel Alternaria species infecting invasive garlic mustard (Alliaria petiolata) in the United States

Author
item Tancos, Matthew
item Thomas, Jami
item MCCAUSLIN, SYDNEY - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2025
Publication Date: 5/12/2025
Citation: Tancos, M.A., Thomas, J.L., Mccauslin, S. 2025. Emergence of a novel Alternaria species infecting invasive garlic mustard (Alliaria petiolata) in the United States. Plant Disease. https://doi.org/10.1094/PDIS-03-25-0653-SC.
DOI: https://doi.org/10.1094/PDIS-03-25-0653-SC

Interpretive Summary: A novel Alternaria species was recently isolated and identified as the pathogenic agent of garlic mustard. Garlic mustard is a non-native invasive plant that is rapidly spreading across North America, displacing native flora, and damaging diverse agroecosystems. A severely diseased garlic mustard population was recently identified in Maryland, leading to the discovery of a new pathogenic Alternaria species. Sequence analysis determined that this strain appears unique and is not related to other known Alternaria species. The origins and host range of this novel Alternaria strain currently remain unknown. This first report of a new and pathogenic Alternaria species isolated from a widely distributed invasive weed highlights the indirect risks of invasive plants in harboring new or emerging plant pathogens.

Technical Abstract: The Brassicaceae invasive weed, garlic mustard (Alliaria petiolata), is a Eurasian biennial herb that has rapidly spread across North America infesting forests and field borders, and negatively impacting plant biodiversity and agroecosystem health. In 2022, a severe garlic mustard dieback event occurred in a limited section of a large, forested garlic mustard population in Maryland, United States. Diseased plants were heavily defoliated with remaining intact leaves having irregular-shaped necrotic and chlorotic lesions. Two isolates of an unknown fungal pathogen were collected, sequenced and identified as Alternaria, and confirmed to be pathogenic to garlic mustard. All inoculated garlic mustard plants rapidly developed severe symptoms within 72-hours, mimicking the symptoms observed in the field. A multilocus sequence analysis identified the two strains as a distinct species that appears to be a new monotypic sister lineage to Alternaria section Sonchi and most closely related to the Japanese Apiaceae pathogen A. triangularis. This study reports the first documentation of a novel, pathogenic Alternaria species identified from the introduced range of the invasive weed garlic mustard. In addition to its potential use as a garlic mustard bioherbicide, future studies will provide critical insights in the role non-native invasive weeds play in harboring and selecting for novel pathogenic microbes, as well as biosecurity risks to U.S. agriculture.