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

As part of a classical biological control programme, investigating potential plant pathogens is one way to control alien weeds. This research study reports the first observation of the rust fungus Coleosporium inulae in Cyprus, France, and Portugal on the Asteraceae Dittrichia graveolens (stinkwort). Dittrichia graveolens, originating from North Africa and Mediterranean Europe, is reported as an invasive alien weed in many parts of the world, like the western USA, South Africa, and central and northern Europe. The authors collected samples from three European countries and conducted molecular identification to confirm the identity of the fungus. The results showed that the sequences obtained from the samples were closely related to other Coleosporium 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 infection levels and plant mortality. The authors discuss the potential use of Coleosporium inulae as a biocontrol agent for Dittrichia graveolens 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 Coleosporium inulae and provides insights into the natural enemies of the invasive weed Dittrichia graveolens in its native range. Further development is needed to investigate the host specificity and potential impact of Coleosporium inulae on non-target plant species.