关键词: 光核桃, 西藏, 遗传多样性, 遗传结构, SSR

Abstract: [Objective] In order to provide a theoretical basis for effective conservation and rational utilization of Amygdalus mira resources in Tibet, genetic diversity and population structure of 21 populations of A. mira were studied using SSR markers, and correlation between genetic structure and geographical distribution, altitudinal gradient were also analyzed.[Method] A total of 420 individuals from 21 populations were assayed by 25 pairs of SSR primers. Genetic diversity parameters, principal coordinates analysis (PCoA), and analysis of molecular variance (AMOVA) were carried out using GenAIEx 6.5 and Arlequin v3.1 software. NTSYS software was used for cluster analysis based on the matrix of Nei's genetic distance. STRUCTURE, STRUCTURE Harvester, CLUMP, and Distruct software were used to analyze genetic structure.[Result] Result showed that both genetic diversity and inbreeding were moderate within A. mira populations. The average number of alleles, effective number of alleles, expected heterozygosity, observed heterozygosity, Shannon's information index, and inbreeding coefficient were 3.8, 2.5, 0.52, 0.44, 0.95, and 0.17, respectively. The highest level of genetic diversity was in the P17 population (N_e=4.7, H_e=0.63, H_o=0.56, and I=1.57), while the lowest was in the P18 population (N_e=1.7, H_e=0.30, H_o=0.22, and I=0.49). According to STRUCTURE, Principal coordinates analysis (PCoA) and UPGMA cluster analysis, 420 individuals could be divided into three genetic clusters, which were significantly correlated with geographic altitudes. Mantel test showed that the genetic distance among the populations was significantly correlated with geographic distance (r=0.50, P<0.01) and geographic altitude (r=0.61, P < 0.01). AMOVA analysis showed that 16.3% genetic variation was among the populations, which indicate that the level of genetic differentiation among population is moderate, while, a high genetic variation (83.7%) was within populations.[Conclusion] It was suggested that the genetic diversity of A. mira in Tibet plate was moderate. The impact of geographical isolation and elevation gradients on genetic diversity was shown within populations. The degree of genetic differentiation was high, which could be due to the habitat fragmentation, elevation gradient, and the mountains block that caused by the effect of geographical isolation. The natural resources of A. mira in Tibet was seriously disturbed by human activities, and inbreeding among individuals was frequent. Therefore, the genetic diversity will gradually decrease if protection measures are not taken in time. Based on the genetic structure analysis, three protection units of A. mira in Tibet have been determined, and the human activities should be prevented. We suggest that it be conserved in situ and the exchange of genes between different groups should be promoted to protect the genetic diversity of A. mira in Tibet.

Key words: Amygdalus mira, Tibet, genetic diversity, genetic structure, SSR