Insights into Bioactive Molecules in Rhododendron tomentosum: From Metabolomics to Biological Applications

<i>Rhododendron tomentosum</i> is an aromatic plant belonging to the Ericaceae family, widely used for different applications, but still lacking in its molecular signature. This work provides a complete chemical and biological characterization of the hydroalcoholic extract of <i>R. tomentosum</i> tips of twigs. Combining untargeted metabolomic analysis with bioassays, a correlation between chemical composition and biological activity was defined. To this regard, liquid chromatography high-resolution tandem mass spectrometry (LC-MS/MS) revealed a heterogeneous chemical composition, including flavonoids, such as quercetin, catechin, and their derivatives, as well as a first tentative identification of novel aesculin derivatives. Cell-based model experiments on stressed immortalized human keratinocytes demonstrated the antioxidant activity of the extract. Moreover, it exhibited significant antifungal and antibacterial effects against <i>Trichoderma atroviride</i> AGR2, <i>Botrytis cinerea</i>, and <i>Clavibacter michiganensis</i>, while promoting the growth of the beneficial bacterium <i>Bacillus amyloliquefaciens</i>. These findings highlight the rich diversity of bioactive molecules present in <i>R. tomentosum</i> hydroalcoholic extract, bridging its chemical composition to its functional properties. Overall, these results suggest its promising potential for applications in improving plant health, as well as in pharmaceutical, cosmetic, and agricultural industries.