Study On Population Genetic Diversity Of Three Chinese Corylus Species And The Phylogentic Relationship Of Corylus Species

Wild species generally contain more genetic variations than the cultivars. Naturally occurring variation among wild species is an excellent valuable breeding resource in plant breeding.Although hazel germplasm resources are abundant and broadly distributed in China, including 8 species of Corylus mandshurica, Corylus heterophylla,Corylus Kweichowensis, Corylus ferox, Corylus yunnanensis, Corylus chinensis, Corylus fargesii, Corylus wangii and 2varietiesofCorylus ferox var. thibetica,Corylus kweichowensis var. brevipes,the most is still in the wild state with low yield and poor quality. Few researchwerereported on the phylogentic relationship and genetic diversity of Chinese hazelnut. In this work, the genetic diversity and genetic structure of 12 natural C. mandshurica populations were analyzed using SSRand AFLPmarkers; the genetic diversity and genetic structure of 21 natural C. heterophylla populations and 13 natural C. kweichowensis populations were analyzed using SSR markers; In addition, the phylogentic relationships and kinships of 17 Corylus species were analyzed using SSR markers, ITS and cpDNA sequence fragments. The aim of our study explores population genetic diversity of three chinesecorylus species andfurther clarify the phylogentic relationship of corylus species. The main results are as follows:(1) 10 SSR loci of Corylus mandshurica expressed a comparatively high level of genetic diversity. The average of percentage of polymorphic loci based on 6 pairs of AFLP primers were 99.18%. Both SSR and AFLP markers revealed that entire C. mandshurica populations possessed high degree of genetic diversity. NA and MJG populations expressed relatively higher level of genetic diversity than the remaining populations.The genetic differentiation coefficient of C.mandshurica(SSR=0.1215, AFLP=0.1064) indicated that genetic variation mainly reside within populations. This is supported by the results of AMOVA analysis based on SSR and AFLP markers. The gene flow(Nm>1) would be sufficient to counteract the impact of genetic drift.(2) The results of UPGMA, STRUCTURE and PCoAanalyses showed that C. mandshurica populations were divided into two clusters, Northeast China and North China. BARRIER analysisidentified three predicted barriers among thetwelve populations.The first barrier located betweenclusterⅠand clusterⅡ by SSR.The Mantel test showed a weak but still significantly positive correlation between Nei’s genetic distance and geographic distance(km) among populations(r=0.419, P=0.005).(3) Results evidenced that 11 SSR loci expressed a relatively high level of genetic diversity in C. heterophylla populations(Na=14.4545, Ho=0.7272, He=0.8216, PIC=0.8212), C. kweichowensis populations(Na=14.7273, Ho=0.6687, He=0.8218, PIC=0.8016). The C. heterophylla populations maintained a comparatively high degree of genetic diversity. Similar results were also found in C. kweichowensis populations. WC, MS, GJ populations of C. heterophylla expressed higher genetic diversity and ZY population of C. heterophylla was relatively low. In addition, WC, MS, GJ populations of C. kweichowensis showed higher genetic diversity and XE population of C. kweichowensis was relatively low.According to the coefficient of genetic differentiation and AMOVA, genetic variation within the populations of C. heterophylla populations, C. kweichowensis populations were remarkably higher than among the populations. There was a high gene flow among populations(C. heterophylla=4.0103, C. kweichowensis=2.6194).The clustering results of UPGMA, PCoA and STRUCTURE(k=2) showed that 34 of C. heterophylla and C. kweichowensis populations were clearly divided into two clusters,, namely C. heterophylla populations and C. kweichowensis populations. C. heterophylla populations were divided into two clusters, Northeast China and North China.(4)The result of UPGMA clustering by SSR showed that 17 Corylus species were divided into eight main groups. The first group consisted of eight Chinese Corylus species(varieties), the second groupcomposed of Corylus californicaand Corylus cornuta ofAmerican region,the third groupcomprised Corylus sieboldianaand Corylus mandshuricaofAsian region,the forth groupcomprisedCorylusavellana,the fifth groupcomprisedCorylusamericana,the sixth group includedCorylusfargesii,the seventh group includedCoryluscolurna.theeighthgroup includedCorylusjacquemontii.However, STRUCTURE analysis showed that dividing into two clusters was the most appropriate. PCoA was similar to the UPGMA clustering results. The clustering results of UPGMA and STRUCTURE revealed the kinship of C. fargesii was far from other Corylus species in China. Genetic relationships of C. mandshurica were not only far from sympatric C. heterophylla, but also distant from C. kweichowensis,C. yunnanensis, C. wangii,C. ferox,and C. ferox var. thibetica; it is though close to C. mandshurica.(5) A total of 19 haplotypes were found in Corylus species basd on cpDNA and ITS spliced sequences. Hap3 and Hap15 belonged to the original haplotype. Hap3 and Hap15 were distributed only in Asia hazel species(C. mandshurica,C. sieboldiana,C. yunnanensis and C. kweichowensis).C. kweichowensiswere more primitive thanC. heterophylla.C. mandshurica populationsusing SSRand AFLPmarkers and C. heterophylla populations andC. kweichowensis populationsusing SSR markersexpressed arelatively high level of genetic diversity. And the genetic variation mainly occurred within populations. There was a high gene flow among populations.A variety of clustering results revealed that 34 of C. heterophylla and C. kweichowensis populations were clearly divided into two clusters,, namely C. heterophylla populations clusters and C. kweichowensis populationsclusters. This supported the results that C. kweichowensis should be one independent species.reported by previous researcher. The clustering results of Corylus species showed that 17 Corylus species were divided into eight main groups.The kinship of C. fargesiiandC. mandshuricawas far from other Corylus species in China.The results of this research provided molecular theoretical basis for further clarifying the phylogentic relationshipof the Corylus genus.