Multidrug Resistance in Fusarium incarnatum from Maize Stalk Rot: Molecular Mechanisms and Fitness Characterization

Maize stalk rot is a severe soil-borne disease caused by Fusarium species. In this study, 73 isolates were collected and identified, among which Fusarium incarnatum accounted for 43.8%. Two isolates, HA32R and HA39R, exhibited multidrug resistance to tebuconazole (resistance factors of 19.71 and 8.00), carbendazim (RF of 56.65 and 52.65), and pyraclostrobin (RF > 100). The resistance mechanisms were associated with target-site mutations CYP51B-G464S, β₂-tubulin-F167Y, and Cytb-G143A. Site-directed mutagenesis confirmed that CYP51B-G464S confers low-level resistance to tebuconazole (RF values of 6.88 and 5.29). Moreover, the multidrug-resistant isolates exhibited significantly reduced fitness, as evidenced by a marked decrease in conidial production. This study provides the first report of field-derived multidrug-resistant F. incarnatum, offering important theoretical insights and practical guidance for the management of maize stalk rot.