| Late blight, caused by oomycete Phytophthora infestans, causing heavy losses to yield of tomato and potato worldwide. The composition and variation in population structure of P. infestans plays an important role in its appearance and prevalence, therefore the research on pathogen population structure has become the main part of the study on late blight disease. In this study, genetic diversity in some areas of Fujian province was revealed using SSR molecular markers, and genetic diversity of P. infestans populations on potato in three provinces of China was analysed with RAPD, and evolutionary dynamic models of different genotype P. infestans populations also studied using SSR, aiming to clarify genetic diversity of the population structure of P. infestans in tested areas. The main results are shown as below:1. A total of 10 pairs of SSR primers were selected for amplification of highly polymorphic and unambiguous bands. A total of 30 bands were identified based on 10 SSR markers in 70 P. infestans isolates from 11 areas in Fujian province, and 30 alles were detected, in which each pair of primers could detect two to six alleles, with an average of 3.0. The result of cluster analysis from UPGMA showed that the tested strains were divided into five cluster groups as a threshold of genetic distance of 0.37: Group I consisted of 2 isolates of P. infestans on potato representively from Changle and Zhouning; Group II consisted of 64 isolates from Putian and other 9 disricts; Group III consisted of 2 isolates representively on potato from Quanzhou and tomato from Zhouning; Both Group IV and Group VI only have one isolate of P. infestans on potato from Liancheng and tomato P. infestans from Dehua respectively. All the results above suggested that there is no obvious correlation between SSR grouping of P. infestans in Fujian province and geographic origins.2. A total of 10 pairs of random primers were selected for amplification of highly polymorphic and unambiguous bands. A total of 125 bands were identified based on RAPD markers in 70 P. infestans isolates from Heilongjiang, Inner-Mongolia and Fujian provinces. The numbers of bands amplified by a single pair of primers ranged from 9 to 15 and the range of polymorphic bands was from 8 to 15. The total number of polymorphic bands was 122 with a polymorphism detection rate of 97.6%. The cluster analysis of P. infestans in Fujian, Heilongjiang and Inner-Mongolia provinces showed that P. infestans populations from Heilongjiang and Inner-mongolia provinces were clustered in the same group, and populations from Fujian Province were clustered in one group alone, which indicates that populations from Heilongjiang and Inner-mongolia provinces are comparatively similar in population genetic diversity, wheras significantly different from Fujian province.3. A total of 308 P. infestans isolates were isolated from plants in 5 areas of different potato cultivars and quantitative distributions based on using marker-release-recapture. Thirty-nine alleles were detected through performing SSR analysis by using 14 pairs of primers, in which each pair of primers could amplify two to four bands with an average of 2.8. The distribution of Shannon information index ranged from 0.2000 to 0.2965 with an average of 0.2556. The analysis on genetic variation of P. infestans by using AMOVA1.55 showed that variation within population accounted for 94.45%, wheras that among poluations only 5.55%. The clutster analysis of five populations indicated P. infestans could be divided into three groups by a genetic distance of 0.04, in which area C and F were classified as one group, wheras area H, I and G were classified as another group. The results indicate that there is some correlation between genetic diversity of population structure of P. infestans in a certain area and the species and quantitative distribution of the corresponding hosts in the given area.
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