Synergistic Interaction and Effects of Mixture of Fluopicolide with Pyraclostrobin on Resistance of Pseudoperonospora cubensis to Fungicides

[Methods]The joint-toxicity of the mixture of fluopicolide with pyraclostrobin against Pseudoperonospora cubensis was determined by potted plant spray-leaf disc test.P.cubensis was tamed for seven generations by using fluopicolide,pyraclostrobin,propamocarb hydrochloride and two kinds of mixtures,respectively.The sensitivity of 3,5,7th generations of tamed P.cubensis to fluopicolide,pyraclostrobin and propamocarb hydrochloride were tested by leaf disc floating method.[Results]The results showed that the mixtures of 5:1,3:1,1:(1-7) exhibited synergistic interaction.P.cubensis tamed with mixture of fluopicolide and pyraclostrobin or propamocarb hydrochloride developed resistance more slowly than tamed with three single fungicides.The resistance factors of the mutants acquired by seven subcultures of P.cubensis on the leaf discs treated with two kinds of mixtures to fluopicolide,pyraclostrobin and propamocarb hydrochloride were up to 12.0-13.4,9.6 and 4.2 fold,respectively.However,the mutants acquired by seven subcultures of P.cubensis on the leaf discs treated with the three single fungicides showed 16.3,11.6 and 5.1 fold resistance factors.[Conclusions]The results suggested that synergistic interaction against P.cubensis existed in the mixtures of fluopicolide with pyraclostrobin;application of mixture of fluopicolide with fungicides(pyraclostrobin or propamocarb hydrochloride) of different action mechanisms could delay development of resistance of P.cubensis to fluopicolide.