Fluazinam Resistance in Colletotrichum gloeosporioides and Its Association with Metabolic Detoxification and Efflux

Colletotrichum gloeosporioides is a major pathogen causing anthracnose of pepper (Capsicum annuum). In agricultural production, it is typically managed using fungicides like fluazinam. However, the frequent use of fungicides raises concerns about the potential development of fungicide resistance. This issue has not been extensively documented. To address this, 102 isolates of C. gloeosporioides were collected from pepper in fields. The EC50 values of these isolates to fluazinam exhibited a unimodal distribution with a mean value of 0.18 ± 0.14 μg/mL, indicating the absence of naturally occurring resistance in the sampling region. Through fluazinam domestication, 35 fluazinam-resistant mutants were obtained from the parental strain Cg219. These mutants exhibited strong cross-resistance to the fungicide SYP-14288. Metabolic analysis revealed that C. gloeosporioides could metabolize fluazinam into compounds lacking antifungal activity. Genetic analysis showed that genes related to efflux and detoxification were upregulated to varying degrees in both fluazinam-resistant mutants and fluazinam-treated strains. By comparing fungal growth and pathogenicity between the mutants and their parent, the mutants showed impaired overall fitness. Therefore, C. gloeosporioides has a low risk of developing resistance to fluazinam. This study provides critical data for monitoring the emergence of fungicide resistance and developing resistance management strategies for fluazinam.