Toxic action and baseline sensitivity of boscalid against Penicillium digitatum

Abstract

Baseline sensitivity and fungicidal activity of boscalid were investigated against the citrus postharvest fungus Penicillium digitatum. The frequency distribution of EC50 values for the total 189 isolates collected in 2017 and 2018 was unimodal, and the mean EC50 value was 0.099 μg/mL±0.041 (SD). Boscalid at 20 and 50 μg/mL significantly (P < 0.001) reduced sporulation on orange fruit, and pathogenicity of the spores produced on orange fruit treated with boscalid also reduced. Boscalid in potato dextrose agar (PDA) postponed the germination of spores. In the presence of boscalid at 20 μg/mL, spores did not germinate after 24 h of incubation; however, percent germination reached 93.7% after 60 h of incubation. Dipping fruit in boscalid solution at 100 and 200 μg/mL provided control efficacies of 67.3% and 79.4%, respectively. Light microscopic observations showed that boscalid in PDA caused hyphae to have more branches and more severe distortion than the nontreated control. Boscalid at 0.12 μg/mL in potato dextrose broth (PDB) significantly (P < 0.001) increased production of superoxide anion (O2−) in mycelia, whereas significantly (P = 0.001) reduced the concentration of hydrogen peroxide (H2O2). The activity of superoxide dismutase (SOD) decreased significantly (P = 0.039), while the activity of peroxidase (POD) increased significantly (P = 0. 003) for treatment with boscalid at 0.12 μg/mL. The activity of target enzyme succinate dehydrogenase (SDH) decreased significantly for treatments with boscalid at 0.03 (P = 0.027) and 0.12 μg/mL (P = 0.001). These results have significant implications for the control of green mold with boscalid and understanding the fungicidal action of boscalid against P. digitatum.