Genetic Diversity Analysis And Core Germplasm Constructi On Of Phoebe Bournei Based On SSR Molecular Markers

Phoebe bournei is an evergreen large tree grouped into the genus Phoebe Nees of the family Lauraceae,rare and ornamental tree endemic in China.Germplasm banks have been established by growth phenotype in provinces of southern China and studies on growth phenotype have been reported since the beginning of the 21^stcentury,however,there is a lack of knowledge on genetic diversity and genetic structure of germplasm resources in P.bournei,the construction of core germplasm of P.bournei is also rarely reported.This study used simple sequence repetition（SSR）markers to analyze the genetic diversity and population structure of16 natural groups in P.bournei,revealed the genetic diversity characteristics of germplasm resources in P.bournei at the molecular level,analyzed the genetic variation law of the germplasm materials in P.bournei,and initially constructed the core germplasm of P.bournei.It provides reference for the collection,research and rational utilization of germplasm resources in P.bournei.The main findings are as follows:（1）A total of 61 bands were amplified on 10 screened SSR loci with high polymorphism,and the number of alleles detected per bit（Na）and the number of effective alleles were 3～10and 1.02～3.07 respectively,and the loci polymorphism（PIC）is 0.46～0.83.The mean values of the genetic parameters of Na,Ne,I,Ho,He,PIC and F were 6.1,1.96,0.72,0.35,0.43,0.59and 0.28,respectively.（2）Genetic diversity analysis of 16 natural groups in Phoebe bournei was carried out by using 10 SSR sites screened.The range of the average allele number（Na）of each group was1.91～3.64.The range of the average effective allele（Ne）is 1.11～2.42.The range of observed hybridization（Ho）is 0.13～0.47.The expected hybridization（He）ranges from 0.25～0.51.The Shannon index（I）ranges from 0.42 to 0.91.The range of the immobilization index（F）is-0.24～0.59.Overall,the genetic diversity of CY population is the highest,and the genetic diversity of JGS and ZH is relatively low.The data show that the genetic diversity of the population in P.bournei is at a low level,but it is slightly higher than that of other endangered tree species,and there are great differences in genetic diversity among different groups of P.bournei.（3）Based on the analysis of the differentiation coefficient and gene flow of natural population in Phoebe bournei in 10 SSR loci,the gene flow（Nm）of the population between P.bournei is 0.835,and the degree of the gene flow is higher than that of other endangered species,but it is still at a lower level.The inter-group differentiation coefficient Fst is only0.287 and the Fis coefficient within the group is 0.198.Molecular variance analysis（AMOVA）showed that the Fis coefficient in the population of P.bournei is 0.206,the differentiation coefficient Fst among the groups is 0.289,the difference ratio between the groups is 29%,and the difference ratio of the variants in the group account for 15%.The high level of inter-group differentiation may be related to the small number of natural populations,habitat fragmentation,geographical isolation and so on in P.bournei.（4）Genetic structure analysis of 16 natural groups in Phoebe bournei was carried out.The16 groups in P.bournei can be divided into 3 large groups when the Nei’s genetic identity is0.60.The first category is only DT included,the second category includes populations of TH,SHX,SX,EN,ZP.The third category includes ten populations,i.e.CY,FY,SY,SC,YX,JO,JL,JGS,MX,JY,of which JGS,MX,JY three groups in Nei’s genetic identity of about 0.65can be separated from the other 7 groups divided into two subgroups.The results of PCo A Principal coordinate analysis are basically the same,but the JO population is allocated into the second largest category.（5）The core germplasm of Phoebe bournei was constructed by comparing four sampling methods,and the genetic diversity indexes were analyzed.After T test,a bank of core germplasm was established with the germplasm selected at 25%sampling scale based on stepwise clustering point priority sampling strategy,the allele number,average effective allele number,polymorphism loci percentage,and retention rate of Shannon diversity index are 98%,104.92%,90.09%,97.94%of the initial germplasm respectively for the core gemplasm.The 59core germplasm accessions selected represent well the genetic diversity of germplasm resources in P.bournei,and provide scientific basis for the conservation of germplasm resource in P.bournei.