Baseline sensitivity of Sclerotinia sclerotiorum to metconazole and the analysis of cross-resistance with carbendazim, dimethachlone, boscalid, fluazinam, and fludioxonil

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a devastating fungal disease in oilseed rape. Chemical control with fungicides is the primary method of controlling this disease. Metconazole is a demethylation inhibitor fungicide that has high activity against mycelial growth of phytopathogenic fungi. In this study, 119 isolates of S. sclerotiorum were collected from oilseed rape fields in different regions of Henan Province, China, in 2015 and 2016 prior to exposure to metconazole. The sensitivities of the S. sclerotiorum isolates to a range of concentrations of metconazole were determined based on mycelial growth inhibition in 90 cm Petri-dishes containing Potato dextrose Agar to which the fungicide was added. The 50% inhibition of mycelial growth (EC50) values of the S. sclerotiorum population to metconazole ranged from 0.0469 to 0.3912 µg mL− 1 and the mean EC50 value was 0.1875 ± 0.0058 µg mL− 1 (mean ± standard error). The frequency distribution range curve was unimodal with a narrow range. Spearman’s rho (ρ) for the log10 of the EC50 values of 22 isolates of S. sclerotiorum between metconazole and carbendazim, dimethachlone, boscalid, fluazinam, and fludioxonil showed that there was no cross-resistance between metconazole and the other test fungicides. The results from this study provide important information for the control of Sclerotinia stem rot and sensitivity monitoring of S. sclerotiorum to metconazole in this area.