Round-leaved sundew (Drosera rotundifolia L.) is a protected glacial relict plant inhabiting Sphagnum bogs, which are endangered habitats in Hungary. In 2020 and 2021 greyish mycelium growth was observed on the hibernacula of D. rotundifolia in Czech Republic, Germany and Hungary. Samples have been collected in possession of the required permits. The fungus was isolated and identified with classical and molecular methods. Koch's postulates were fulfilled. The novel pathogen was identified as the highly polyphagous Botrytis cinerea in each sample. Simultaneously, field assessments of wild Hungarian populations were carried out. Throughout the survey of three different Hungarian collection sites, altogether 207 hibernacula were carefully examined for gray mold symptoms. Interestingly, only plants grown on milled peat substrate were affected by the pathogen. The antifungal and antimicrobial properties of Sphagnum mosses have been reported by other researchers, which could aid in the protection of D. rotundifolia hibernacula. These results indicate that live Sphagnum moss is a better substrate for this species than milled peat, both for commercial production and for in situ conservation. This information can be vital to the survival and conservation of this species. Sphagnum bogs may protect and allow the expansion and re-establishment of D. rotundifolia.

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