| Moso bamboo, Phyllostachys edulis (Carrière) J. Houz.(Poaceae), native to China, is themost economically and ecologically important bamboo species. Since the economic interests andthe strong clonality, it has been widely cultivated in southern China, which inevitably reduces thenatural stands and leads to gene lost of this species. An accurate assessment of genetic diversityand structure within and between populations is crucial in order to design and implementappropriate conservation strategies and utilization of biodiversity in natural and domesticatedspecies. Previous RAPD studies revealed a low genetic diversity in this bamboo, but detailedinsights into the population genetics are largely missing. In this study, twenty polymorphicmicrosatellite (SSR) markers, developed from cDNA sequences of moso bamboo (Phyllostachysedulis) and fluorescently labeled, were used to evaluate the genetic diversity, putativephylogenetic relationships and population structure of Ph. edulis including34representativepopulations (804individuals) from across the geographic range of the plant in China. The mainresearch results and conclusions were as follows,(1) SSR PolymorphismFrom Phyllostachys edulis cDNA sequences available in NCBI, twenty polymorphicmicrosatellite loci were successfully developed to assess the population genetics of Ph. edulis.All twenty loci were polymorphic and revealed a total of169alleles across all34populations.The number of detected alleles (Na) varied from4~15, with an average of8.5alleles per locus.Polymorphism information content (PIC) was0.034~0.663(average,0.318) which shows thatall loci are informative. Range of allele size (R) at SRR loci were found to vary from12~51bp.75%of loci variation followed infinite allele mutation (IAM) which creates a new allele, and20%and5%were resulted from stepwise mutation model (SSM) with increase or decrease byone repeat type and from insertion-deletion event in the flanking regions, respectively.(2) Genetic diversity, differentiation and gene flowPh. edulis possessed middling a middle level genetic diversity and population differentiation.Gene diversity (H) and differentiation (Gst) at the species level were0.376and0.162respectively,in keeping with the majority of the genetic diversity occurring within populations (84.55%)according to the AMOVA results. Despite all this, compared with other forest trees, the geneticdifferentiation in Ph. edulis is till high. Rich gene diversity was detected in HN5(0.538), GD1(0.524) and GZ2(0.465), and mean allelic richness and gene diversity within population were2.31and0.32. There was no significant correlation between genetic variation level and thepopulation locations (latitude and longitude), through which it’s difficult to exposit thephylogenetic relationships of Ph. edulis. Most loci in the34populations significantly deviatedfrom HWE, and inbreed coefficient at individual population and total population level were-0.440and-0.192due to heterozygotes excess in Ph. edulis. It revealed that heterozygotes have stronger vitality than homozygotes under selective pressure, besides, the heterozygote advantagecould be fixed in this species with long generation period. An overall estimated number of geneflow (Nm=1.203) may indicate human activities promoted gene flow among populations ofmoso bamboo, which characterized by particularly extensive vegetative reproduction.Furthermore, a significant positive correlation of the genetic distances with the geographicdistances between populations was found (r=0.247/0.215, P <0.05). This ruled a simpleisolation by distance model and implied that migrations from human occurred in a limited regionand did not significantly changed the whole genetic structure of Ph. edulis.(3) Clonal diversityAll34Ph. edulis populations were multiclonal. The vasted clone distributed across14populations and the maximum clone size was107ramets indicating the strong clonality.Relatively medium to low clonal variation, compared with other sexual vs. clonal plants, wasfound in this bamboo species, which possibly resulted from its long flowering interval. A total of261multigenotypes (genets) were identified by genotyping804individuals (ramets) and theclone size at species level is3.08. Within populations, the proportion of distinguishablegenotypes (PD) and Simpson index (D) were0.38and0.74, respectively.(4) Population structureStructure analysis exhibited that there were two gene pools among populations, althoughsome individuals had mixed ancestry. Main cluster (C1) included the majority of populationswith high mean posterior probability (0.95) and a few populations were assigned to another (C2).While hierarchy AMOVA indicated a strong genetic differentiation (Fst=0.253) between the twoclusters. Bayesian model-based structure analysis revealed the presence of two clusters thatbasically consistent with the clustering results based on genetic distance. By neighbor-joining(NJ), principal coordinate analysis (PCoA) and Structure analysis when K=3, two subgroupswere detected within the main cluster (C1). They consisted of17and13populations respectivelyand did not correlate with geographic regions. However, We found that masses of populations ina limited region belonged to the same subgroups.(5) Partial populations relationshipsMoso bamboo has a very long cultivation history in China. SSR analysis revealed that somecultivation populations had different introduced sources. For two populations (SX and SD)introduced from different sources in the1960~70s, SX showed the similarity with HN5, GD1and GZ2, while SD was similar to populations from ZJ and JX. The higher genetic diversity inSX population, linked to the document, indicated that it might be introduced from variouslocations (including HN5) for many times. According to historical materials, Ph. edulispopulations on the border of Yunnan, Guizhou and Sichuan province, in south-western China,might be introduced and cultivated long long time ago. Once there was no moso bamboo inChishui of Guizhou province. GZ1population was introduced initially from Fujian province andfounded in the year A.D.1769. Together with the geography distribution and SSR analysis, weconcluded that populations in south-western China might originate from FJ5population in south-eastern China.(6) Conservation strategiesThe genetic structure in this study suggested some ideas for the protection and managementof Ph. edulis populations. Some populations in HN5, GD1and GZ2should have the first priorityin preserving of the habitats. SC2population with higher private alleles and other distinctivegenetic resources distributed in any populations should have the highest preservation in ex situconservation. For some cultivated and highly disturbed populations, the low genetic diversityrequires careful consideration. |
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