New European distribution of Coleosporium inulae (Coleosporiaceae) on Dittrichia graveolens (Asteraceae) and considerations for weed biological control

Authors: SFORZA, RENE - European Biological Control Laboratory (EBCL); BREUGNOT, D - European Biological Control Laboratory (EBCL); TANNIERES, M - European Biological Control Laboratory (EBCL)

Submitted to: Botanica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2025
Publication Date: 3/17/2025
Citation: Sforza, R., Breugnot, D., Tannieres, M. 2025. New European distribution of Coleosporium inulae (Coleosporiaceae) on Dittrichia graveolens (Asteraceae) and considerations for weed biological control. Botanica. 31(1): 39-47. https://doi.org/10.35513/Botlit.2025.1.4.
DOI: https://doi.org/10.35513/Botlit.2025.1.4

Interpretive Summary: Classical biological control is defined by the use of host specific natural enemies collected and tested in the native range of a pest, then released in the invaded range after the obtention of appropriate permits. One category of these natural enemies is plant pathogens that are one way to control alien weeds. This study reports the first observation of the rust fungus Coleosporium inulae in Cyprus, France, and Portugal on the Asteraceae, Dittrichia graveolens (stinkwort). Foreign exploration was conducted in 2023/24. Stinkwort originating from north Africa and Mediterranean Europe is reported as an invasive alien weed in many parts of the world like western USA, South Africa and northern Europe. The authors collected samples from three European countries and conducted molecular identification to confirm the identity of the fungus. The results show that the sequences obtained from the samples are closely related to other C. inulae sequences reported on close related plant species in the same tribe and on pine tree species. The authors discuss the potential use of the rust fungus as a biocontrol agent for stinkwort but note that the complex life cycle of this rust fungus may be an obstacle to further implementation of a biological control programme.

Technical Abstract: As part of a classical biological control program, investigation on potential plant pathogens is one way to control alien weeds. This research note reports the first observation of the rust fungus Coleosporium inulae in Cyprus, France, and Portugal on the Asteraceae, Dittrichia graveolens (stinkwort). Stinkwort originating from north Africa and Mediterranean Europe is reported as an invasive alien weed in many parts of the world like western USA, South Africa and northern Europe. The authors collected samples from three European countries and conducted molecular identification to confirm the identity of the fungus. The results show that the sequences obtained from the samples are closely related to other C. inulae sequences reported on Inula and Pinus species. The symptoms observed on the infected plants ranged from mild to severe, with some populations exhibiting high levels of infection and plant mortality. The authors discuss the potential use of C. inulae as a biocontrol agent for stinkwort but note that the heteroecious life cycle of the fungus, which requires two unrelated host plants, may complicate its development as a biocontrol agent outside the borders of Europe. The study extends the known distribution of C. inulae and provides insights into the natural enemies of the invasive weed D. graveolens in its native range. Further development is needed to investigate the host specificity and potential impact of C. inulae on non-target plant species.