Conservation Genetics Of Endangered Plant Rhododendron Rex Subsp. Rex:endemic To Southwest Of China

Genetic diversity is a critical factor for the population surviving and can reveal the species ability to adapt to the changing environment.Thus,species'genetic diversity plays an important role in the conservation and management of rare and endangered species.Rhododendron rex subsp.rex is a perennial woody species in the family of Ericaeae,It is only distributed in the south west of Sichuan and northeastern Yunnan with fragment pattern in China.The species is a famous ornamental plant in China.The current study mainly focus on the species' culture and acclimation.However,the population of Rhododendron rex subsp.rex is decling due to the high frequency of disturbance.Up to now,no studies about the genetic diversity,genetic variation and population demography of Rhododendron rex subsp.rex have been reported despite these information is important for the conservation of this plant.Thus,in the present study,we studied the genetic diversity,genetic structure,phylogeographical structure,population demography of 11 Rhododendron rex subsp.rex natural populations that distributed to southwest of China using cpDNA sequences and microsatellite markers.Furtheremore,we also defined its evolutionarily significant units based on cpDNA sequence and genetic distance analysis.Finally,some conservation strategies and management plan of Rhododendron rex subsp.rex were proposed.The main results are summarized as follows:1.Genetic diversity and population structure of Rhododendron rex subsp.rex based on microsatellite markerswe used fourteen polymorphic microsatellite loci to assess the levels of genetic diversity and genetic structure for 212 individuals from 11 populations of Rhododendron rex subsp.rex.A total of 236 alleles were identified with a mean value of 14.857 alleles per locus.The results showed that mediate genetic diversity(Ho=0.424,He=0.515,I=1.096,PPB=94.16%)and high levels of genetic differentiation among the populations(Fst=0.16245)were observed at the species level.AMOVA analysis results showed that genetic variation mainly distributed within the group,accounting for 83.75%.Mantel test showed that the genetic distance and geographic distance exists significant correlation(R2=0.5434,P<0.050);In addition,UPGMA,Structure and PCoA clustering analysis showed that the closer geographical groupswere firstly clustered,suggesting the effects of geographical isolation on genetic differentiation among populations.Bottleneck analysis showed that all populations have not experienced a recently genetic bottleneck.While,GWI index showed that the population of Rhododendron rex subsp.rex experienced contraction events in history.2.Genetic variation and population demography of Rhododendron rex subsp.rex.based on cpDNA sequenceBased on the three cp DNA fragments(rbcL?matK?Psba-trnH)sequence and analysis,we found that mediate levels of genetic diversity occurred in Rhododendron rex subsp.rex and one of the population(GDX)may be the genetic diversity center of this species.In addition,12 chloroplast genetic haploid type were identified.Three clear geographical distribution patterns were found based on the haplotype bayesian trees.The individuals from population DLT and BJS is one independent clade,while the population JZS,LZS,LJS,QIB1,QLB2 and QLB3 are one independent clade,and the remaining clade contained the individuals from population GDX and YS.Network analysis showed that the two assumed ancestral haplotypes were located in the internal nodes of networks,combined with ancestors haploid type of population distribution and geological history of the event,inferring that the LJS population probably may be refuge in Sichuan area in the quaternary glacial period.AMOVA analysis results showed that more than 84%the genetic variability was distributed within groups and there existed a significant phylogeographic pattern(Nst>Gst,P<0.01).Furthermore,results from mismatch and neutrality test failed to indentify population expansion in the history,and the population demography analysis showed that the populations of Rhododendron rex subsp.rex appear the rapid contraction event in the 50000 years ago,suggesting that the cold weather in the quaternary glacial period affect the species distribution of this species.In addition,we also speculate that the Rhododendron rex subsp.rex may be a kind of cold adaptation population due to its high elevational distribution.3.Evolutionarily significant units(ESU)and conservation strategyAccording to the the geographical distribution of haploid type,genetic distance,AMOVA,the most parsimonious and UPGMA trees from cpDNA sequence data The 11 population of Rhododendron rex subsp.rex can be divided into four ESUs(ESUA-ESUA).The gradation of conservation priority is ESUB,ESUA,ESUD and ESUC.Although the population LJS located in the national nature reserve,the status of ESUB is not optimistic because of high frequency of human disturbance.Another two ESUS including the group of QILB1 and QLB3 are mainly distributed in the region that under the local people's activities.Thus,we suggest these three populations(QILB1-QILB3)should be strictly insitu conservation.Although ESUA,ESUD and ESUC is distributed in the national nature reserve with well conservation,We still suggest that strengthen protection of these ESUs should be conducted due to the unique haploid type in these ESUs.