Objective  Interspecific hybridization and introgression often occur among species of Quercus, especially among sympatric Quercus more frequently. In this paper, the genetic structure and genetic variation of three species of Quercus in the mountainous area of Beijing were studied. It will provide effective data for gene introgression, germplasm resources and management of Quercus species naturally distributed in Beijing.

  Method  304 natural oak samples of Quercus mongolica, Quercus dentate and Quercus aliena from Yunmeng Mountain, Shangfang Mountain and BUA (Beijing University of Agriculture) Forest Farm were selected as the material, and six pairs of SSR primers were used to study the genetic diversity, genetic structure and introgressive hybridization among populations.

  Result  A total of 105 alleles were detected, the average number of alleles (Na) of each locus was 17.5, the expected heterozygosity (He) was 0.660−0.911, the polymorphism information content index (PIC) was 0.632−0.903. The three oaks had high genetic diversity at the overall level. At the species level, the average allele number (Na) of the three oaks was 12.667−14.167, the expected heterozygosity (He) was 0.743−0.849, the polymorphism information content index (PIC) was 0.725−0.826, the genetic diversity level of the three species of oaks was Q. mongolica > Q. dentate > Q. aliena. The genetic structure analysis of 7 populations of Quercus showed that most of the genetic variation was in local populations. The genetic introgression analysis by structure software found that the gene introgression occurred among three pairs of Q. mongolica, Q. dentate and Q. aliena.

  Conclusion  There is a common and complex phenomenon of introgression hybridization among Q. mongolica, Q. dentate and Q. aliena in Beijing mountainous area.