Effect of continuous application and taming in vitro on sensitivity of Botrytis cinerea in tomato to fludioxonil

To clarify the effect of continuous spraying of fludioxonil on sensitivity of Botrytis cinerea in tomato to fludioxonil,a fungicide spraying programming was conducted in selected tomato greenhouse where fludioxonil was sprayed at the recommended rate(active ingredients 67.5 g/ hm2,a.i.) for 7 times regularly since the initial occurrence of gray mould,the sensitivity of B.cinerea to fludioxonil was detected through mycelial growth rate test.The results showed that the B.cinerea was still sensitive to fludioxonil after 7 continuous sprays,with EC50 values ranging from 0.004 7 to 0.046 2 μg/mL. Two mutant strains (Rg-12 and Rdz-28) resistant to fludioxonil were selected from thirty sensitive strains of B.cinerea which were subcultured for 7 generations on the PDA medium that contained with fludioxonil.The EC50 value of Rg-12 to fludioxonil was 46 times of its parent strain g-12 and the EC50 value of Rdz-28 to fludionxonil was more than 500 μg/mL.The mycelial growth rate,sporulation and sclerotia of the two mutants decreased obviously,comparing with their parent strains.All the results showed that the level resistance of B.cinerea to fludioxonil is low,then fludioxonil could be used to control B.cinerea as an ideal fungicide.