SDH mutations confer complex cross-resistance patterns to SDHIs in Corynespora cassiicola.

Area of Science:

• Agricultural Science
• Plant Pathology
• Biochemistry

Background:

• Succinate dehydrogenase inhibitors (SDHIs) are crucial fungicides for managing cucumber leaf spot in China.
• Previous research noted varied sensitivity of Corynespora cassiicola to SDHIs, but the underlying resistance mechanisms were unclear.

Purpose of the Study:

• To investigate the molecular mechanisms of SDHI resistance in Corynespora cassiicola.
• To identify specific mutations in sdhB/C/D genes conferring resistance.
• To understand how these mutations affect succinate dehydrogenase (SDH) activity and fungicide binding.

Main Methods:

• Fungicide sensitivity assays (EC50 determination) for four SDHIs (boscalid, fluopyram, fluxapyroxad, isopyrazam).
• Sequence alignment of sdhB/C/D genes from resistant C. cassiicola strains.
• Analysis of sdhB/C/D gene expression and SDH enzyme activity.
• Molecular docking to assess the impact of mutations on SDH-ligand interactions.

Main Results:

• High resistance frequencies observed for boscalid, fluopyram, fluxapyroxad, and moderate for isopyrazam.
• Eight single and three dual amino acid mutations in sdhB/C/D identified as key resistance factors.
• Mutations significantly altered gene expression, SDH activity, and the binding affinity of SDHIs to the target enzyme.
• Molecular docking confirmed that mutations disrupt the interaction between SDH and fungicides.

Conclusions:

• Amino acid mutations in sdhB/C/D are the primary drivers of SDHI resistance in C. cassiicola.
• These mutations lead to complex cross-resistance patterns and varying levels of resistance.
• Understanding these mechanisms is vital for developing effective fungicide resistance management strategies for Corynespora leaf spot.