Abstract:The population genetic structure of Phytophthora infestans collected from Guyuan of Ningxia Hui Autonomous Region was revealed by the combination of phenotypes and genotypes. The phenotypes of P.infestans i.e. mating types and metalaxyl resistance were investigated by means of dual culture with A1 and A2 testers on rye plates and radical growth assay on fungicide-amended media in vitro, respectively. Mitochondrial DNA haplotypes of isolates of P.infestans were detected with restriction fragment length polymorphism and polymerase chain reaction (PCR-RFLP). Genotypes of genomic total DNA of P.infestans were examined by simple sequence repeats (SSR) and amplified fragment length polymorphism (AFLP). Of tested 94 isolates, only one was A1, 86 ones were A2, and the seven ones were self-fertile. Nevertheless, all tested isolates were metalaxyl-resistant. Only one mitochondrial DNA haplotype (Ⅰa) and two SSR genotypes (named as typesⅠand Ⅱ) were determined among population, one (i.e. type Ⅰ) of which was absolute predominance. Then, two AFLP clades (i.e. α and β clade) were formed at a genetic similarity value of 0.68 and all isolates of P.infestans from Guyuan of Ningxia were included in β clade. All data indicated that the population structure of P.infestans from Guyuan was very simple and the level of genetic diversity was much less.