Sensitivity to difenoconazole and tebuconazole of Rhizoctonia cerealis in Henan province in China

The sensitivities of Rhizoctonia cerealis to difenoconazole and tebuconazole were evaluated by measuring the mycelial growth on the fungicide-amended media using 95 isolates collected from 15 cities within Henan province, China. The results indicated that 50% effective concentration (EC50) values of all isolates to difenoconazole and tebuconazole ranged from 0.014 to 1.609 μg/mL and 0.002 to 0.064 μg/mL, respectively. The results of the frequency analysis revealed that subpopulation, which is less sensitive to difenoconazole had been discovered in the tested isolates. However, most of isolates were sensitive to tebuconazole. The mean EC50 values of (0.165±0.101) μg/mL and (0.019±0.008) μg/mL for most isolates showed a unimodal curve distribution, which was treated as the sensitivity baseline of R. cerealis to difenoconazole and tebuconazole respectively. The mean EC50 value of difenoconazole was 26 times higher than that of tebuconazole, which meant that R. cerealis was more sensitive to tebuconazole. The isolates collected from different regions demonstrated different sensitivities. Especially, the correlation efficient existed between difenoconazole and tebuconazole was very low. The results provided a theoretical basis for the efficient application of fungicides in the control of wheat sharp eyespot in the field in Henan province.