Activity of Anthracenediones and Flavoring Phenols in Hydromethanolic Extracts of <i>Rubia tinctorum</i> against Grapevine Phytopathogenic Fungi
Natalia Langa-Lomba | Eva Sánchez-Hernández | Laura Buzón-Durán | Vicente González-García | José Casanova-Gascón | Jesús Martín-Gil | Pablo Martín-Ramos
In this work, the chemical composition of <i>Rubia tinctorum</i> root hydromethanolic extract was analyzed by GC–MS, and over 50 constituents were identified. The main phytochemicals were alizarin-related anthraquinones and flavoring phenol compounds. The antifungal activity of this extract, alone and in combination with chitosan oligomers (COS) or with stevioside, was evaluated against the pathogenic taxa <i>Diplodia seriata, Dothiorella viticola</i> and <i>Neofusicoccum parvum</i>, responsible for the so-called Botryosphaeria dieback of grapevine. In vitro mycelial growth inhibition tests showed remarkable activity for the pure extract, with EC<sub>50</sub> and EC<sub>90</sub> values as low as 66 and 88 μg·mL<sup>−1</sup>, respectively. Nonetheless, enhanced activity was attained upon the formation of conjugate complexes with COS or with stevioside, with synergy factors of up to 5.4 and 3.3, respectively, resulting in EC<sub>50</sub> and EC<sub>90</sub> values as low as 22 and 56 μg·mL<sup>−1</sup>, respectively. The conjugate with the best performance (COS-<i>R. tinctorum</i> extract) was then assayed ex situ on autoclaved grapevine wood against <i>D. seriata</i>, confirming its antifungal behavior on this plant material. Finally, the same conjugate was evaluated in greenhouse assays on grafted grapevine plants artificially inoculated with the three aforementioned fungal species, resulting in a significant reduction in the infection rate in all cases. This natural antifungal compound represents a promising alternative for developing sustainable control methods against grapevine trunk diseases.
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