Sensitivity of Rhizoctonia cerealis to fludioxonil in Henan Province in China

In order to evaluate the sensitivity of Rhizoctonia cerealis to fludioxonil, 98 isolates were collected and identified from 15 cities in Henan Province in 2013. Their sensitivities to fludioxonil were determined by measuring the mycelial growth on the fungicide-amended media. The results indicated that the EC50 values of all isolates ranged from 0.009 to 0.079 μg/mL and the average EC50 value was (0.025 ±0.012) μg/mL. The sensitive frequency analysis of R. cerealis to fludioxonil distributed as a unimodal curve, which demonstrated that resistant subpopulation didn't exist among these isolates.So the average EC50 value was treated as the sensitive baseline of R. cerealis to fludioxonil. The results of both variance analyses by LSD test and hierarchical cluster analysis by SPSS indicated that the isolates collected from the same region exhibited different sensitivities. The ratio of the maximum and the minimum of EC50 values of isolates from the same region ranged from 1.0 to 4.1. However, there was no significant difference on the sensitivity to fludioxonil among the isolates from most of the regions. From all the regions, the average EC50 value of the isolates ranged from 0.015 to 0.060 μg/mL and the maximum value was 4 times of the minimum. Especially, the correlation efficient existed between the sensitivity to fludioxonil and the sensitivities to thifluzamide, difenoconazole, tebuconazole, propiconazole or jinggangmycin was very low, which implied that there was no sensitivity correlation between fludioxonil and these six fungicides. The results provided a theoretical basis for the rational application of fludioxonil in the control of wheat sharp eyespot in the field of Henan Province.