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Research Project: Biological Control in Integrated Weed Management of Invasive Weeds from Europe, Asia, and Africa

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Title: Submission of DNA sequences of a Coleosporium rust infecting Stinkwort (Dittrichia graveolens L. Greuter) in southern France and northern Greece

item BON, MARIE-CLAUDE - European Biological Control Laboratory (EBCL)
item KASHEFI, JAVID - European Biological Control Laboratory (EBCL)
item GUERMACHE, FATIHA - European Biological Control Laboratory (EBCL)

Submitted to: Genbank
Publication Type: Database / Dataset
Publication Acceptance Date: 10/4/2021
Publication Date: 10/21/2021
Citation: Bon, M., Kashefi, J., Guermache, F. 2021. Submission of DNA sequences of a Coleosporium rust infecting Stinkwort (Dittrichia graveolens L. Greuter) in southern France and northern Greece. Genbank. OK356493 -499.

Interpretive Summary: Stinkwort (Dittrichia graveolens L. Greuter) of the Asteraceae family is native to the mediterranean region. First reported in 1984 in Santa Clara county in California, the plant has since rapidly expanded its range thoughout the state, primarily along roadsides, but also in gravel mines, detention basins, riparian floodplains, and seasonal wetlands.This invasive is also a noxious weed that is poisonous to livestock and cause contact allergic dermatitis in humans, thereby prompting the need for a sustainable control. Of the various alternatives available to state and land managers, classical biological control remains a major component of integrated weed management. One key step in classical biological control is foreign exploration in the native range of the invasive for searching natural enemies. The latter are primarily macroorganisms such as insects but also microorganisms such as biotrophic fungi. Recent field surveys in southern France and Northern Greece evidenced stinkworts infested by biotrophic fungi. DNA analysis sorted these fungi from France and Greece into one single rust species belonging to the Coleosporium genus. Though there is report in the litterature of a rust species identified as Coleosporium inulae attacking stinkwort but also many host plants including Asteraceae, reducing the likelihood of its prospect for biocontrol, this is the first time that DNA information on a rust found on stinkwort is provided. The overall finding is important in deepening our understanding of the natural enemies assemblage of stinkwort in the native range from which future potential biocontrol agents will be selected.

Technical Abstract: Dittrichia graveolens L. Greuter, commonly named stinkwort, belongs to the Asteraceae family. This plant native to the Mediterranean region in Europe was first recorded in 1984 in Santa Clara county in California and has since spread throughout California. This invasive is also a noxious weed which can kill grazing animals and cause allergic reactions and severe dermatitis in people who come in contact. Dittrichia graveolens has been targeted for classical biological control based on the assumption that its abundance and spread can effectively be limited by its natural enemies in the native range. During exploration for natural enemies in the Mediterraean region, diseased plants were discovered by one of the authors at La Grande Motte in southern France and at Orestiada in Northern Greece and brought back to the laboratory. Microscopic examinations let think that disease symptoms were due to a biotrophic fungus, a rust of the Coleosporium genus which is widely distributed in the Asteraceae family in Europe. Microscopic examinations in particular with respect to urediniospore dimensions are inconclusive for identification purposes and for the characterisation or delimitation of taxa in this genus. Given that application of DNA analysis can partly address this challenge, we generated sequences of the Nuclear ribosomal internal transcribed spacer (ITS) region which is considered as a universal DNA barcode marker for Fungi in combination with sequences of the 28S nuclear ribosomal large subunit rRNA gene (LSU) in two rusts of Dittrichia graveolens in France and Greece as well as in one rust of Dittrichia viscosa which was co-occuring with D. graveolens at the french site. Similar ITS and LSU sequences were obtained in rusts collected on D. graveolens in France and in Greece, but ITS were slightly different from the rust collected on D. viscosa. All sequences were compared to reference Coleosporium sequences made publicly available in online databases such as GenBank and UNITE. Homology search assigned all sequences to Coleosporium inulae which has recently been synonymized with Coleosporium tussilaginis f.sp. inulae S. Helfer, f.sp. nov. and previously reported on the two Dittrichia species. As molecular taxonomic investigation of Coleosporium taxa is still at its infancy, the present molecular identification needs to be confirmed by taxonomic authorities and sequences were deposited in Genbank as Coleosporium sp. under Accession numbers (OK356493 to OK356499). Rust fungi are widely used in weed biological control given their typical high level of host specificity and efficacy. However, because most of the Coleosporium species are heteroecious, they are not usually considered for classical biological control of weeds because extensive testing would be required to demonstrate that the selected fungus does not pose a threat not only to species related to the target weed, but also to those related to alternate hosts in a completely different family. Nevertheless, the overall finding extends our knowledge of the composition of the assemblage of natural enemies of Dittrichia graveolens in the native range.