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ARS Home » Northeast Area » Frederick, Maryland » Foreign Disease-Weed Science Research » Research » Publications at this Location » Publication #426732
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: A new species of Didymella from the eastern United States is a pathogen of invasive Reynoutria japonica

Author
item INDERMAUR, ELIZABETH - Cornell University
item Fulcher, Michael
item Szarka, Desiree
item JOHNSON, ALEXANDRA - University Of Rhode Island
item TEWKSBURY, LISA - University Of Rhode Island
item Tancos, Matthew
item SMART, CHRISTINE - Cornell University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2026
Publication Date: 1/11/2026
Citation: Indermaur, E., Fulcher, M.R., Szarka, D., Johnson, A., Tewksbury, L., Tancos, M.A., Smart, C. 2026. A new species of Didymella from the eastern United States is a pathogen of invasive Reynoutria japonica. Plant Disease. https://doi.org/10.1094/PDIS-05-25-1125-RE.
DOI: https://doi.org/10.1094/PDIS-05-25-1125-RE

Interpretive Summary: Invasive weeds carry plant pathogens that may pose a risk to agricultural crops or alternatively have value as biological control agents. A new species of plant pathogenic fungus collected from invasive knotweed was described by scientists from ARS in Maryland, University of Rhode Island, Cornell University, and the National Park Service. Because the pathogen was able to infect rhubarb, it is not proposed for direct biological control application to knotweed, however, the fungus may be evaluated for the production of novel herbicidal compounds. These findings benefit plant pathologists diagnosing disease on agricultural and invasive plant species, as well as weed scientists developing new management tools.

Technical Abstract: Reynoutria japonica (Polygonaceae) is widely considered one of the most persistent and problematic non-native invasive weeds introduced to North America. Conventional methods to manage infestations are labor-intensive and often require annual monitoring and re-treatment. Biological control agents (BCAs) present an alternative management strategy. Currently, few organisms are effective for managing Re. japonica, presenting a need to discover additional candidate BCAs. Recently, leaf spots were observed on Re. japonica in two locations in the eastern United States, and the causal agent was investigated as a potential BCA. In this study, fungi isolated from symptomatic Re. japonica were identified as belonging to a previously undescribed species of Didymella based on DNA sequence homology, phylogenetic analysis, and morphological characteristics. The host range of related Didymella spp. includes other polygonaceous plants, notably cultivated Rheum rhabarbarum. Therefore, the pathogenicity of isolates representing this new fungal species was tested on seedlings of Re. japonica and Rh. rhabarbarum ‘Victoria’. The novel species was capable of infecting both Re. japonica and Rh. rhabarbarum under artificial conditions. An isolate of D. rhei (Ellis & Everh.) Qian Chen & L. Cai, a close relative and known pathogen of Rh. rhabarbarum, was included in pathogenicity tests but failed to cause disease on Re. japonica. The pathogen from Re. japonica was described as D. polygonacearum sp. nov. This study suggests D. polygonacaeum is a poor candidate for biological control use and that Re. japonica may harbor crop pathogenic microbes.