Landscape Genetic Structure Of Astragalus Strictus Along Altitude Gradients In Tibet

Astragalus strictus, belonging to Leguminosae, is a kind of perennial herbaceous plant. Astragalus strictus is a kind of poisonous weeds in Tibetan, and it has a tendency to expand. Currently, the research of Astragalus strictus was mainly focused on its chemical substances and the toxic ingredients, but there was little information on its genetic diversity and genetic structure. In this study, we used Astragalus strictus as the experimental materials in this study, the technique of AFLP was exployed to detect the genetic structure and genetic diversity between22population including390individuals. These samples were collected from Milha Mountain in different elevation gradient. The experiment got508AFLP banks which scored from9primer combinations. The data was analyzed by GENALEX6.1、PopGene3.2and Structure2.2. The results of this research were summarized as follows:(1) The genetic diversity of Astragalus strictus was decreased with altitude gradient increasing in the east side of Milha Mountain, but in the weat side, the genetic diversity had no obvious change with the elevation gradient increasing.As a result, the percentage of polymorphic bans of22populations was86.61%. At species level, the Shannon diversity index (Ⅰ) was0.404. and the Nei’s index of genetic diversity (He) was0.265. The alleles gene (Na) was1.866, the effective number of alleles (Ne) was1.439. It was negative correlation between genetic diversity and altitude gradient in the east side of the Milha Mountain, but no significant correlation in the west side.(2) The genetic variation within population was higher than that of among population.There was a variation east and wast side of Milha Mountain.The results of AMOVA showed that, in the east of the mountain, the genetic variation in and between poputations were13%and83%, and the coefficient of gene differentiation among population (Gst) was0.155. Otherwise, the genetic variation in and between the west poputations were11%and89%, the Gst was0.140. At species level, the genetic variation in and between poputations were11.22%and83.01%, the genetic variation between regions was5.77%, and the Gst was0.174. Consequently, the genetic variation of Astragalus strictus was mainly from intra-populations. The results of PCA and STRUCTURE assignment showed that there was significant variation between the east and west of Milha Mountain.(3)There was a relationship between genetic distance and spatial distance.Along with the horizontal distance increasing, the genetic distance and variation also increased (R2=0.064, P<0.05). The correlation between genetic distance and horizontal distance and vertical distance were positive (R2=0.0335, P<0.05; R2=0.1843, P<0.05) in the east side of Milha Mountain. In the west, it is not significant between genetic distance and horizontal distance, but positive between genetic distance and vertical distance (R2=0.0155, P<0.05).To analyse the genetic diversity and landscape genetic structure of Astragalus strictus. it was conducive to understand its optimal living environment, way of diffusion, spreading way and the relationship between genetic diversity and space distance, it also can provide theoretical basis for the prevention and control of poisonous weeds-Astragalus strictus, in Tibet.