| Archidendron clypearia(Jack)Nielsen is an evergreen,precious medicinal tree species of the genus Archidendron(family Fabaceae)native to southern China.Its branches,leaves and fruits have been used as medicine which occupies an important position in the market of traditional Chinese medicine(TCM).With the increase of people’s attention to and demand for TCMs nowadays,the wild resources of A.clypearia are gradually degraded.Plantation development could meet to solve the problem of resource shortage,however,the establishment of A.clypearia plantations in southern China is recently based on the seeds collected from the wild in the field without appropriate selection,as a result,leads to the low productivity of its plantations in the later stage.Although many studies have been carried out on A.clypearia,little is known about the genetic diversity and genetic structure of its germplasm resources,and the selection of excellent germplasm is still in the early stage of study.Therefore,in this study,16natural populations of A.clypearia in Guangdong,Guangxi and Hainan provinces were sampled from July to October 2019 to deal with the above-mentioned research aspects.SSR molecular markers were used to analyze the genetic diversity and population genetic structure of A.clypearia,to reveal the characteristics of genetic diversity of A.clypearia germplasm resources,to clarify the genetic relationship and classification of A.clypearia germplasm,and to analyze their genetic changes.At the same time,the core collection of A.clypearia preliminarily constructed.All of these provide an important theoretical reference for scientific and systematic protection,research and rational utilization of A.clypearia germplasm resources.The main results are as follows:(1)A total of 208 alleles were detected in 211 germplasms of A.clypearia by 22 pairs of SSR primers.The number of alleles(N_a),effective number of alleles(N_e),Shannon diversity index(I)and polymorphism information content(PIC)at each locus were between 4-16,1.946-7.621,0.883-2.374 and 0.427-0.884,respectively.The average values of N_a,N_e,observed heterozygosity(H_o),expected heterozygosity(H_e),I,PIC and fixation index(F)of 22 loci were9.455,4.415,0.650,0.716,1.532,0.672 and 0.100,respectively.ARCe SSR95 showed the highest polymorphism.(2)The genetic diversity of 16 natural populations of A.clypearia were calculated based on22 pairs of SSR primers.The ranges of N_a,N_e,H_o,H_e,I and F of each population were 3.682-6.318,2.911-3.784,0.588-0.730,0.609-0.695,1.196-1.432 and 0.184-0.114,with averages of4.923,3.342,0.652,0.649,1.267 and 0.003,respectively.Among all populations in Guangdong province,the populations from Zengcheng of Guangzhou and Dinghu of Zhaoqing recorded higher genetic diversities,while Taishan population showed the lower.The results showed that the genetic diversity of A.clypearia was rich,and there were great differences among different populations.(3)The differentiation of A.clypearia populations was evaluated by 22 pairs of SSR primers.The average values of intra-population inbreeding coefficient(Fis),inter-population inbreeding coefficient(Fit),inter-population differentiation coefficient(Fst)and gene flow(Nm)were 0.002,0.093,0.090 and 2.689,respectively,indicating that there was a certain degree of genetic variation among A.clypearia populations,a certain degree of inbreeding within a population,the population was at a moderate level of differentiation and moderate gene exchanges inhibited the differentiation resulted from genetic drifts.Analysis of molecular variances(AMOVA)showed that the genetic variation of A.clypearia populations mainly came from individuals within a population.There was no significant correlation between genetic distance and geographical distance(longitude and latitude)(p>0.05).(4)According to the Nei’s genetic distance,the 16 populations of A.clypearia could be divided into four groups when the genetic distance was 0.20,and the similar result was also found in the principal coordinate analysis(PCo A).The optimal number of grouping of 16 A.clypearia populations analyzed by STRUCTURE was 3.The genetic lineages of Ledong population of Hainan,and Taishan and Chaoan populations of Guangdong were pure,and there was a certain degree of genetic mixing among other populations.(5)The core collection of A.clypearia was constructed by comparing the two sampling methods,and the genetic diversity indexes were analyzed.Based on the stepwise clustering random sampling strategy,the core collection was selected at 20%of sampling percent,and the preservation rates of Na,N_e,H_o,H_e,I and PIC reached 81.72%,101.91%,99.23%,101.40%,101.38%and 101.04%,respectively.The results of t-test showed that there were no significant differences in N_e,H_o,H_e,I and PIC between the core collection and the original collection.PCo A showed that the core collection was evenly distributed in the original collection,and the constructed core collection was more representative,which will provide a scientific basis for the preservation and selection of A.clypearia germplasm resources in the future. |
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