The Sensitivity of Phytophthora capsici to Metalaxyl and Cross Resistance between Fungicides

Sixty-four isolates of Phytophthora capsici collected from different regions of hebei province and Shijiazhuang were tested by measuring mycelial growth rate in order to explicit the sensitivity of Phytophthora capsici to metalaxyl.Sensitivity of 11 relatively sensitive isolates and 3 relatively resistant isolates to metalaxyl, mandipropamid,dimethomorph,azoxystrobin,and cymoxanil were determined by the same method to make sure that it existed cross resistance or not between metalaxyl and other diverse active mechanism fungicides.The results showed that metalaxyl to P.capsici has obvious inhibition,EC 50 of 0.1661-27.5572 mg/L,the highest and lowest difference of 165.91 times.Collected from different regions strains of P.capsici sensitive to metalaxyl there were very different.The linear regression showed that there were no positively-correlated cross resistance between metalaxy and other diverse active mechanism fungicides.