Distribution and occurrence frequency of mating type of Phytophthora infestans from potato in Yunnan

isolates of Phytophthora infestans collected from twelve major potato production regions from 1998 to 1999 were inspected of their mating types with A1 and A2 standard strains in order to study their distribution and occurrence frequency. The results indicated that out of 253 isolates forty-one samples were found to be A2 mating type,possessing obout 16.2 percent of all isolates. Although the A1 mating type isolates are the predominant pathogen,the A2 mating type ones spread out in all potato production districts except Zhaotong,Zhanyi,Shongming,Xundian and Dali.Eight self-fertile isolates were detected on Lima-V8 Juice agar and their morphological features and sexual organs were described respectively.Since both mating types are present in Yunnan,potential threat to potato was discussed and some suggesitons on how to transfer seed potatoes were also proposed based on the results.