The distribution of the A2 mating type of Phytophthora infestans in potato fields in Hebei province

isolates of Phytophthora infestans collected from late blight potato fields in Weichang county and Kangbao county of Hebei province during 1996—1997 were examined for mating type on Baiyun bean -V8 juice media. The results showed that 10 of 28 isolates were A2 mating type, the frequency of A2 mating type was 35.7%; 18 of 28 isolates were A1 mating type, the frequency of A1 mating type was 64.3%. The results also indicated that A2 mating type was all found in Weichang county and Kangbao county which were major potato-producing area of Hebei province. And we found that the average number of mature oospores produced per unit area varied from 10 to 2 300 per square centimeter. This article also described the characteristics of oogonium, antheridium and oospore.