Genetic Diversity Based On SSR And Its Association Analysis With Phenotypic Traits In Germplasm Resources Of Castanopsis Hystrix

Castanopsis hystrix is an important local broad-leaved precious timber and high-efficiency multi-purpose tree species in South China.It combines various benefits such as timber,economy,landscape,ecology and consumption.It has excellent characteristics such as fast growth,excellent material quality,wide adaptability and high benefit.It is an excellent economic tree species with high economic benefit,social benefits and ecological benefits.In this paper,a total of 232 clonal samples of 17 populations from six main distribution areas which is Guangdong,Guangxi,Fujian,Hunan,Yunnan and Hainan Province were planted in the C.hystrix germplasm resources of Maofeng Mountain in Guangdong Province were used as the research objects,and 32 pairs of highly polymorphic SSR markers were selected to discover genetic diversity.20 indicators including growth,stem form,leaf and wood traits were observed,and the genetic diversity and population genetic structure of Castanopsis hystrix were also analyzed based on SSR markers and phenotypic traits.Moreover,association analysis between phenotypic traits and SSR molecular markers were performed using GLM and MLM models.The aim of this research is to provide a theoretical basis for the evaluation and utilization of germplasm resources,genetic improvement and establishment of high-quality and high-yield seed orchards in C.hystrix.The main results were as follows:（1）The 17 provenance populations showed higher levels of genetic diversity based on SSR markers.A total of 335 alleles were detected by 32 pairs of SSR primers.The average number of alleles（NA）was 10.458,and the number of effective alleles（Ne）was 7.115.The expected heterozygosity（He）was 0.824,the average polymorphism information index（PIC）was 0.889,and the PIC values of all loci were greater than 0.5,indicating that all loci have higher polymorphism within the population.The average genetic differentiation coefficient(F_ST)of all loci was 0.080,indicating that the locus was slightly differentiated.The average value of gene flow（Nm）was 2.952.The gene flow fluctuated between different sites,and there was a high degree of gene communication among the populations of C.hystrixs.（2）STRUCTURE cluster analysis divided 17 natural groups into 3 groups.Each group had obvious regional characteristics in geographical distribution,and the genetic diversity of each group was higher.The 17 natural populations had higher genetic diversity.The highest genetic diversity is P2 population of Guangxi Bobai provenance,and the lowest one is P13 population of Hunan Jianghua provenance.The average expected heterozygosity was0.824,and the average observed heterozygosity was 0.861.The results of molecular variance analysis（AMOVA）showed that the main variation source was from the population and group,accounting for 87%at the natural population level and 92%at the group level.Mantal test results revealed that the genetic distance between the C.hystrix population were significantly positively correlated（r=0.292,p=0.017）with the geographical provenance distance.Therefore,the provenance played an important role in the group division,and geographical isolation had important effects during the process of genetic evolution of different provenance populations of the C.hystrix.（3）The 20 growth,leaf and wood traits showed rich genetic diversity,especially these seven traits with higher coefficient of variation,including stem straightness,leaf area,petiole length,DBH,undergrowth,crown width and tree height.ANOVA results showed that except for the microfibril angle,the other quantitative traits were significantly different between both the provenances and the clones,indicating that the variation level was abundant and that the genetic improvemental potential was large.The overall correlation of each phenotypic trait is high,and polymerization improvement and chain effect can be considered,which could provide theoretical basis for subsequent orientational cultivation and variety breeding.（4）Principal component analysis divided 20 indicators into 9 principal components.Combined with principal component analysis and cluster analysis,the test C.hystrix populations were divided into three categories.The main performance of the first category were with high height,small leaves,high wood basic density and low stem straightness.The second category was characterized by large crown,medium height and stem form,low height under the branches,broad leaves,long and wide fibers,high wood basic density and high cellulose content.The third category was characterized by low height,straight stem form,high lignin content,low wood basic density,medium leaf size and low leaf shape index.（5）There was extensive linkage disequilibrium in the SSR locus of C.hystrix,LD signal was detected in 296 locus combinations（59.7%）,the Finsher test showed significant（p<0.05）locus combination 12.7%,and the paired linkage disequilibrium locus（D’>0.5）was 30.The overall linkage level was low（r²<0.1）,which may be caused by multiple generations of outcrossing and recombination in the history of C.hystrix.Based on the analysis results of two models of GLM and MLM,11 SSR loci（p<0.05）significantly associated with six quantitative traits of east-west crown,north-south crown width,leaf width,fiber length,fiber width and cellulose content were preliminarily obtained.