Resistance investigation of Penicillium digitatum to imazalil in China

The demethylation inhibitor fungicide imazalil is a primary fungicide in China for controlling citrus green mold, a serious postharvest disease caused by the fungus Penicillium digitatum. Regular monitoring of pathogen resistance levels is crucial for effective disease control.

The fungicide sensitivity of 201 P. digitatum strains collected from 11 provinces across China to imazalil was determined. The results showed that EC₅₀ values of all strains ranged from 0.04 to 5.11 μg mL^-1. The strains were divided into three categories depending on insertions in their CYP51A/B gene promoters: 102 were imazalil-sensitive, exhibiting a mean EC₅₀ of 0.08 μg mL^-1; 15 belonged to imazalil-R2 type, with a mean EC₅₀ of 2.38 μg mL^-1; and the remaining 84 were classified as imazalil-R3, with a mean EC₅₀ of 0.95 μg mL^-1. In addition, all imazalil-R2 strains shared a common L298M substitution in the CYP51A gene, while some imazalil-R3 strains harbored point mutations (Q309H, Y136H, G459S, and F506I) in the CYP51B gene. The biological characteristics of the representative strains revealed that imazalil-resistant strains exhibited impairments in spore germination rate and adaptability to environmental stresses (NaCl, SDS, and high temperature).

This study investigated the sensitivity of the P. digitatum population in China to the DMI fungicide imazalil and assessed the resistance frequency and risk. These findings lay the foundation for understanding the population dynamics of P. digitatum under imazalil stress. © 2026 Society of Chemical Industry.