Molecular and biological characteristics of laboratory tebuconazole-resistant mutants in Sclerotium rolfsii

Abstract

Peanut southern blight, caused by Sclerotium rolfsii Sacc., significantly reduces both global yield and quality of peanut. Tebuconazole, a triazole fungicide, effectively inhibits S. rolfsii, but its resistance risk and molecular mechanisms remain unclear. In the present study, the EC₅₀ values for tebuconazole against 210 S. rolfsii isolates ranged from 0.0651 to 5.772 mg L⁻¹ with sensitivity exhibiting a multimodal distribution. Four tebuconazole-resistant mutants (Resistance factor: 17.50–33.50-fold) generated by laboratory adaptation showed fitness costs in salt tolerance and virulence, with diminished exopolysaccharide production. However, no fitness costs were observed in mycelial growth rate or sclerotia production compared to their corresponding parental strains. Tebuconazole showed positive cross-resistance with fluxapyroxad but negative with cyprodinil. No cross-resistance occurred to boscalid, thifluzamide, isopyrazam, prothioconazole, pyraclostrobin, fludioxonil, difenoconazole, epoxiconazole, azoxystrobin, propiconazole, fluxapyroxad or pydiflumetofen. The resistant mutants showed overexpression of the SrCYP51 gene, elevated ergosterol and glycerol content, but significantly reduced activities of peroxidase, superoxide dismutase, and catalase. These findings indicate that tebuconazole-resistant strains of S. rolfsii have emerged under field conditions. The overexpression of the SrCYP51 gene and elevated ergosterol levels may contribute to tebuconazole resistance in S. rolfsii. These findings elucidate S. rolfsii's tebuconazole resistance mechanism and provide field-applicable strategies to mitigate resistance evolution.