Citral-Based Acylthiourea Derivative as Antifungal Synergistic Agent: E14 Enhances the Antifungal Activity of Chlorothalonil against <i>Colletotrichum fructicola</i> by Interfering with Mitochondrial Complex I

The citral-based acylthiourea derivative <b>e14</b> was identified as a potent synergist for chlorothalonil (CT) against <i>Colletotrichum fructicola</i>. The optimized mixture (<b>ECS</b>, 25% <b>e14</b>) exhibited strong synergistic activity (synergistic ratio (SR) = 2.30), significantly enhancing disease control efficacy while enabling reduced fungicide dosage. Mechanistic studies revealed that <b>e14</b> specifically targets mitochondrial complex I by binding to the NADH dehydrogenase subunit 5 (ND5), thereby disrupting oxidative phosphorylation and inducing energy depletion and oxidative stress. This distinct mode of action differs from that of CT, minimizing the risk of cross-resistance. Importantly, <b>e14</b> exhibits low mammalian cytotoxicity. This study elucidates the synergistic mechanism of <b>ECS</b> and the enhancing role of <b>e14</b>, thereby providing a solid foundation for the development of effective fungicide synergists.