Genetic Diversity Of The Fargeonia Species Complex Based On Microsatellite Molecular Markers

Fargesia belongs to Tribe Arundinariinae,Bambusoideae,Poaceae.The results of molecular phylogenetic analysis of three plastid DNA and two nuclear genes(rpb2 and nrITS)sequence data showed that this genus should be divided into two clades,spathe clade and non-spathe clade.The spathe clade is also called Fargesia spathacea complex including 15 species which distributed mainly in northern Sichuan,southern Shannxi,Gansu,Ningxia,Guizhou,Hubei and Henan.The Fargesia spathacea complex share the follow morphological characters:the inflorescences are conpressed,unilateral and subtended by a series of persistent and delicate leaf sheaths which expand as spathes;the pistil has three stigmas,the culms without longitudinal ribs and without bristles.Traditional taxonomy of the species of Fargesia spathacea complex is extremely difficult based on the vegetative characters as most morphological characters were continuous variation to some extent.The boundary between species of Fargesia spathacea complex was unclear based on previously molecular systematic studies.The current study was discussing the genetic diversity of Fargesia spathacea complex using fourteen SSR markers,and further analyzing the role of the vegetative character in delimitating the species and providing relevant taxonomic treatment.14 microsatellite markers were developing based on the whole genome high throughput sequencing data of four species from Fargesia spathacea complex.14 loci revealed a total of 103 alleles and 7 private alleles in 15 species across all 39 populations(750 individual).Average percentage of polymorphic loci(PPL)is 83.5%and average of polymorphism information content(PIC)value is 0.42.The number of alleles,effective number of alleles and excpected heterozygosity is 2.998,1.88 and 0.461 respectively,which means Fargesia spathacea complex have medium genetic diversity and genetic differentiation among populations and could adapt to changeable environment in contrast to other plant taxa.Gene diversity(H)and differentiation(Gst)were 0.374 and 0.179 respectively at the population level,in keeping with the majority of the genetic diversity occurring within populations(81.79%)according to the AMOVA results.Meanwhile it suggested the genetic diversity of Fargesia spathacea complex was highly.Most loci in the 39 populations significantly deviated from Hardy-Weinberg’s equilibrium(HWE).Inbreed coefficient at individual population and total population level were 0 and-0.248 respectively mean that there was heterozygotes excess in the complex.It suggested that heterozygotes have stronger vitality than homozygotes under selective pressure and the heterozygote could be beneficial to help species fixing with long generation period and vegetative reproduction.Genetic distances with the geographic distances were non-significant positively correlation under the Mantel test.Gene flow(Nm=1.181)of Fargesia spathacea complex were estimate by Fst indicated that the Nm between populations could restrain genetic drift and prevent genetic differentiation.The results of Structure based on Bayesian classification show that 39 population divided to two groups:branch A consisting of 8 species in 17 population and almost distributed in south Shaanxi,Gansu,Qinghai,Ningxia autonomous region and few populations in the northwestern Sichuan;while branch branch B including 11 species from 22 population which almost distributed in northwestern Hubei,northern Chongqing,southern Shaanxi,northwestern Sichuan and southern Gansu.The results of Principal Coordinates Analysis(PCoA)were consistent with the finding of Structure.The results of Neighbour-Joining tree also divided into branch A and branch B,consistent with the changes in the morphology characters.The young culm with white powder and leaf sheath with margin ciliate which are obvious characters of the species of branch B,are absent in branch A.At the sub-branch level,Species of Fargesia robusta sub-branch culm with Pole hollow,Faregsia brevissima sub-branch has sheathes with conspicuous transversal vein,other morphological characters also have some similarities and differences in the six sub-branches.The results of Mantel test indicated that the distribution pattern of Fargesia spathacea complex is insusceptible to geographical distance at branch A and population levels,which suggested that Fargesia spathacea complex may undergo a rapid radiation.