Molecular Docking-Based Analysis of QoI Fungicide Resistance Mechanisms in Fungicide-Resistant <i>Cercospora</i> spp. Infecting Soybean

Azoxystrobin (AZ), pyraclostrobin (PYR), and trifloxystrobin (TFR) are widely used quinone outside inhibitor (QoI) fungicides to manage leaf spot and leaf blight diseases of soybean. However, QoI resistance is widespread among fungal field populations , mainly due to point mutations (G143A, F129L and G137R) in the cytochrome b–encoding cytb gene.This study employed computational molecular docking to screen three QoI fungicides and the natural substrate ubiquinol-6 for binding with wild-type fungal Cytb and its single, double and triple substitution variants. Ubiquinol docking revealed reduced binding affinity and altered contact residues in mostly double and triple variants, suggesting potential fitness penalties and impaired electron transport. Among QoIs, PYR exhibited the strongest affinity with wild-type Cytb (-8.63 kcal/mol). The number of Cytb residues predicted to contact with tested fungicides varied from 4 to 19, with PYR having the highest number.The substitutions dramatically altered the number of contact residues and the predicted binding energy by selectively favoring binding of one type of QoI while disfavoring another. The combined F129L and G137R substitutions wre predicted to block the binding of TFR completely, but only mildly reduce the binding of AZ and PYR. Conversely, the triple substitution was predicted to be most effective against AZ, whereas the G137R substitution was found to be most effective against PYR. Identifying predominant Cytb mutations in field fungal populations can support targeted and sustainable disease management by enabling rapid prescreening of QoI fungicide efficacy and predicting resistance development, stability, and sensitivity to existing and novel QoIs.