Detection of Sensitivity and Resistance Variation of Magnaporthe grisea to Kitazin P,Carbendazim and Tricyclazole

One hundred and twenty-nine isolates of Magnaporthe grisea from Guangdong, Guangxi, Anhui and Jiangsu provinces of China were tested for resistance frequency to kitazin P and carbendazim, respectively by the distinctive concentration method. The resistance frequency of the isolates to kitazin P which had not been used in practice for about ten years was as high as 79.1%, and only one carbendazim-resistant isolate was detected in Gaoyao, Guangdong Province (with a frequency of 0.78%). Meanwhile, the minimum inhibition concentration (MIC) of hyphal melanization was adopted to detect the sensitivity of M. grisea to tricyclazole. There existed several different degrees of sensitivity to tricyclazole in the melanin biosynthesis of M. grisea, but no relationship was found between these MIC values completely inhibiting melanization in hyphae and the EC50 values of tricyclazole against rice blast tested in vivo. After the isolates were induced by chemical taming or UV irradiation in laboratory, kitazin P-resistant and carbendazim-resistant mutants were recovered by both the methods, but none of tricyclazole-resistant mutant was obtained.