Cinchona-based liquid formulation exhibits antifungal activity through Tryptophan starvation and disruption of mitochondrial respiration in Rhizoctonia Solani

This study investigates the antifungal properties of a liquid Cinchona-Based Formulation (CBF) against Rhizoctonia solani. CBF, a stable acidic extract of Cinchona bark (0.1 N HCl), effectively suppressed mycelial growth (58.75 ± 0.48%) and sclerotia biomass (22.1 ± 0.65 mg), with an EC₅₀ of 217.14 µg/mL. GC-MS and HPLC revealed quinine as the primary active alkaloid. Molecular docking revealed a strong binding affinity of quinine to the fungal tryptophan (Trp) transporters (- 6.5 to - 7.8 Kcal/mol). Supplementation of 400 µg/mL Trp in the media reversed the fungal growth with increased fungal dry weight (33.33 ± 1.53 mg), and sclerotia weight (67.67 ± 3.06 mg), highlighting Trp starvation as a key factor for reduced growth of the fungus. Expression of amino acid permease (rhAAP-I/II) increased 4-9 fold during Trp scarcity in fungus. CBF also elevated levels of ROS, which results in loss of Mitochondrial Membrane Potential (MMP). CBF reduced Cyt. P450 expression (2.73-fold) while increasing mitochondrial QCR and COX expression, indicating a combined impact of Trp scarcity and oxidative stress, demonstrating a dual antifungal mechanism of the CBF on the fungus. These results suggest CBF as a promising eco-friendly biopesticide for long-term disease management.