Mating Type Distribution and Sensitivity to Several Chemicals of Phytophthora infestansfrom the West of Inner Mongolia

The isolates of Phytophthora infestans were collected from the west of Inner Mongolia in 2008.The mating type and response of the isolates to three chemicals were then determined.Among 94 isolates tested,82 isolates belonged to A1 mating type,accounting for 87.2%;8 was A2 mating type,accounting for 8.5%;4 was A1A2 mating type,accounting for 4.3%;13 was self-fertil mating type,accounting for 13.8%.Seven strains of A2 mating type were detected in Hohhot area and only one was detected in wulanchabu,This result showed that A2 mating Type existed in potato producing area in the west of Inner Mongolia.Among 94 isolates tested,91.49% were highly resistant,8.51 % were intermediate resistant.No isolate resistant were sensitive.Also it was found that the vegetative growth of some re sistant isolates was stimulated by metalaxyl.The sensitivity of 14 isolates to dimethomorph and 28 isolates to silver power with different levels of metalaxyl resistance were determined.EC50 values ranged from 0.002 μg/mL to 0.021 μg/mL to dimethomorph,the mean EC50 values was 0.005 μg/mL;EC50 values ranged from 0.081 μg/mL to 0.192 μg/mL to silver power,the mean EC50 values was 0.143 μg/mL,and the resistance to metalaxyl did not correlate to the resistance to dimethomorph or silver power.