Sensitivity of Rhizoctonia cerealis to jinggangmycin and tolclofos-methyl in Henan province in China

The sensitivities of Rhizoctonia cerealis to jinggangmycin and tolclofos-methyl were determined by measuring the mycelial growth on the fungicide-amended media using 98 isolates collected from 15 cities in Henan province. The results indicated that 50% effective concentration (EC₅₀) values of all isolates to jinggangmycin and tolclofos-methyl ranged from 0.023 to 0.852, and 0.035 to 0.512 μg/mL, respectively. The results of the frequency analysis revealed that low sensitivity subcolony to jinggangmycin had been observed in the tested isolates. The mean EC₅₀ values of (0.424±0.081) and (0.124±0.043) μg/mL for 77.6% and 99.0% of all isolates showed a normal distribution, which was treated as the sensitivity baseline of R. cerealis to jinggangmycin and tolclofos-methyl, respectively. The mean EC₅₀ value of jinggangmycin was 3 times higher than that of tolclofos-methyl, which meant that R. cerealis was more sensitive to tolclofos-methyl. The isolates collected from different regions showed different sensitivities. It is noteworthy that the correlation efficient existed between jinggangmycin and tolclofos-methyl was very low, which implied that there was no cross-resistance between those two fungicides. The results provided a theoretical basis for the efficient application of the two fungicides in the control of wheat sharp eyespot in the field of Henan province.