Sensitivity Evaluation of Botryosphaeria spp. Distributed in Apple Orchards to Benomyl and Tebuconazole Fungicides in Korea

The sensitivity of Botryosphaeria spp. to benomyl WP (active ingredient [a.i.], 50%) and tebuconazole WP (a.i., 25%) fungicides was investigated by comparing 238 Botryosphaeria strains isolated from 2005 to 2023 using the agar dilution method. The EC50 values of each isolate ranged from 0.07 to 3.04 μg/ml (average, 0.62±0.47) for benomyl and ranged from 0.05 to 1.94 μg/ml (average, 0.58±0.32) for tebuconazole. The mean and distribution of EC50 values were compared to determine the differences in sensitivity between groups by year, region and species. The mean EC50 values and distribution graphs were similar among all isolate groups, indicating no significant differences in sensitivity to both fungicides. As a result of analyzing the β-tubulin genes of 30 sensitive and less sensitive strains selected based on the EC50 values to benomyl, no mutations were found at codons 167, 198, and 200. In addition, the diameter of lesions was measured 7 days after inoculation of 6 strains of Botryosphaeria into apple fruits treated with benomyl or tebuconazole at the recommended concentration, and there was no significant difference between the sensitive and less sensitive strains. Based on the results, the 238 Botryosphaeria isolates are sensitive to benomyl and tebuconazole fungicides. These results may provide the guidelines for monitoring the fungicide resistance in Botryosphaeria populations in Korea.