Abstract：Potato late blight caused by Phytophthora infestans is one of the most destructive diseases. Crop losses and costs of late-blight control constitute a significant financial burden on the potato industry. However, understanding the mechanisms, processes and rates of P. infestans evolution are important factors in predicting the durability and effectiveness of new management practices. Microsatellite marker is regarded as a perfect molecular marker for studying biogenetics, syngenetic succession of population and diversity. Hence, microsatellite marker developed based on the genome system is particularly important for understanding of the genetic diversity of P. infestans. Single-copy microsatellite (more than 25 bp in microsatellite sequence length and more than 20 bp in adjacent interval) sites and sequences at both ends were screened in the genome of P. infestans by using SciRoKo, Clustal X and Primer Pair Specificity Checking from Primer-BLAST. And then the microsatellite specificity and polymorphism were detected by using 9 P. infestans strains of different years and geographical origins. Finally, 115 appropriate sites were obtained for developing microsatellite markers. Among them, 64 microsatellite markers were validated by feasibility test, including 33 polymorphic ones (14 intergenic ones, 13 Flank5', 7 Flank3', 15 exons and 6 introns) and 31 non-polymorphic ones(whose electrophoretograms included 4 situations——cluttering bands, no bands, bands appearing in some strains as well as three or more bands appearing in some strains). The determination of the number of alleles and evaluation of polymorphism were made for polymorphic microsatellite markers developed by using 40 P. infestans strains of different years and geographical origins. It was found that polymorphism–tagged microsatellite polymorphic information content(PIC) values ranged from 0.164 to 0.614. There were 7 markers with PIC≥0.5 (highly polymorphism), most of which belonged to the intergenic region; I-00408, I-10840 and E-04958 had 4 alleles, and I-01408, I-07111, I-06861 and F5-22735 had 3 alleles. There were 25 markers with 0.25＜PIC＜0.5 (moderately polymorphism) and there was only one with PIC≤0.25 (low polymorphism). The 9 polymorphic microsatellite markers were selected for genetic diversity analyses on 35 (from Hebei, Heilongjiang, Jilin, Yunnan, Sichuan, Chongqing, Ningxia, Inner Mongolia and Fujian) and 5 (from Poland, Switzerland and the U.S.) P. infestans strains of different years. UPGMA cluster analysis found a high genetic diversity of P. infestans in China and a significant interpopulation differentiation in different regions. Moreover, it was also found that P. infestans genome microsatellite genotype was correlated to its mating type and geographical origin to some extent but not correlated to metalaxyl sensitivity. These genomic microsatellites could provide rich and polymorphic markers for gene location, clone and genetic diversity of P.infestans.
