Inventory,Diversity Assessment And Conservation Strategy Of Genetic Resource Of Dalbergia Cultrata In China

Dalbergia cultrata Graham ex Benth was an important high economic and ecological values tree species.Its natural distribution has sharply declined in recent decades.The threatened level has increased from Near threatened（NT）to Vulnerable（VU A2c）.Information on the genetic diversity in remnant populations is urgently needed to support conservation planning of this species.In this study,the population structure and natural regeneration of D.cultrata in China were studied based on field survey method.The habitats sutablitity and major environmental limiting factors for its distribtion were revealed,and the dynamic trend of its habitats sutablitity under climate change scenarios were predicted by the species distribution model（SDM）.Moreover,the genomic characteristics of D.cultrata were preliminarily estimated using Illumina sequencing,and a set of genomic SSR（g SSR）markers with high polymorphism and stable amplification were developed for futher population genetics studies.Then,the level of genetic diversity,spatial patterns of genetic varations,and mating system of wild population of D.cultrata in China were assessed using the above g SSRs.This study was intended to provide guidelines for conservation and restoration of the genetic resources of D.cultrata.Through the above research,the main results are as follows:（1）A total of 570 individuals were collected from 37 quadrates of 13 populations.D.cultrata was mainly distributed in the 21°58’～24°05’N,98°03’～101°43’E in the southwest of Yunnan Province in China,and the elevation of its distibution ranges from 600 to 1 600m.This species mainly grows on acidic latosol or red soil.The habitat condition of D.cultrata indicated it has a certain ability of shade-tolerance,but prefers to for warm and sunny habitats.The distribution pattern was sporadic and the habitat fragmentation was serious and its habitats have been limited to a small area because of disturbing by land use change,overcutting etc.,while this species need face to botic stress,e.g.pests or interspecific competition.The mode of natural regeneration of D.cultrata includes root sprouting and seed propagation,the former is more common in the field survey,and the regeneration rate of root sprouting was 25.0～112.50%.The existing population of D.cultrata consists of a large number ofⅠ～Ⅲdiameter class individuals（88.95%）,and a small number ofⅣ、Ⅴdiameter class individuals（11.05%）.The dynamic change index of the populations of D.cultrata was V_pi>V`_pi>0,it indicates a trend of growth for its wild popualtion.The disturbance sensitivity index of the population was 1.33%which indicated that the population has weak anti-interference ability and poor stability was due to the lack of individuals of large diameter class.（2）We used the Max Ent model to simulate habitats suitability and future species distribution under predicted climate change scenario using ten environmental variables.Our results showed that the modelled distribution of D.cultrata was mainly influenced by isothermality（Bio3）,temperature annual range（Bio7）,precipitation of warmest quarter（Bio18）,temperature seasonality（Bio4）,precipitation of wettest month（Bio13）,and precipitation seasonality（Bio15）etc.The resutls showed the distribuiton of D.cultrata was limited by the above ecologial facoters,and it also suggests the sepceis may be sensitive to temperature fluctuation and seasonal precipitation.Habitats suitability prediction of D.cultrata under climate change scenario showed the habitats of high suitability may decrease by 8.8×10⁴ km² in the face of climate warming.This findings indicates populations at the habitats of high suitability species range edge will be particularly face to greater risks from climate change（such as WD,etc.）.Hence,these populations should be prioritized for ex-situ conservation and a population restoration plan should be developed in the near future.Stable and highly suitable habitats in the global warming scenario could be a potential area to implement in situ conservation plans,e.g.Southern Yunnan,eastern Myanmar,north-western Laos and northern Thailand.（3）A genome survey and preliminary assembly of D.cultrata were performed using Illunima sequencing,and a total of 92.54 Gb of clean data were obtained.The reuslts showed the estimated size of D.cultrata genome was 706.92 Mbp,the heterozygosity was calculated to be1.26%and the repeat rate was estimated as 55.74%,the average GC content was 34.11%.It was a highly heterozygous complex genome.On the basis of the contigs from preliminary assembly of genome,27 g SSRs markers were developed.（4）Sampling strategy and genetic diversity of 13 wild populations of D.cultrata were anlayzed based on g SSR markers.The result showed the minimum sizes of sampling should be reached 25～30.Hence,in this study,30 individuals were selected from each popualtion to perform genetic diversity analysis.Finally,a total of 13 wild poplations of D.cultrata in China were performed to assess the geneitc divesity and genetic strucuture.The reuslts indicated the wild populations of D.cultrata in China had moderate genetic diversity（mean H_e=0.503）,and moderate differentiation(mean F_ST=0.114 and G_ST=0.099),with high gene flow（mean N_m=2.347）.and the wild populations of D.cultrata in China were clustered into three groups（GroupⅠ～Ⅲ）based on Po CA,clustering and STRUCTURE analysis,and the isolated by distance were detected by Mantal test,the result showed there is significant geographic isolation between populations,and the spatial pattern of genetic diversity of D.cultrata showed a tendency to decrease from center to margin.The AMOVA result showed the majority of genetic variation of D.cultrata comes from within the population,with up to 85%.The correlation analysis of genetic diversity and environmental factors showed its genetic diversity were significantly correlated with environmental factors such as temperature and latitude,suggesting that the ecological factors may play an important role in maintaining the genetic diversity of D.cultrata and promoting the generation of genetic variation.（5）Studies on mating system of D.cultrata populations showed that the multi-locus outcrossing rate（t_m）,the single-locus outcrossing rate（t_s）and the biparental inbreeding（t_m-t_s）were 0.760,0.643 and 0.117 respectively,these results indicated its mating mechanism was mainly outcrossing,and there were inbreeding in wild population.（6）Finally,conservation strategies of D.cultrata in China were proposed on the basis of the above work.Firstly,we should establish nature reserve planning and consider to no less than three in-situ conservation units in China based on population genetic composition and cluster analysis results,while populations with high genetic diversity need to be given a high priority,e.g.population DDG and MM.Secondly,we should establish ex-situ conservation stands and the facility preservation bank.Stable and highly suitable habitats in the global warming scenario could be a potential area to implement ex-situ conservation plans,e.g.Puer and Xishuangbanna of Southern Yunnan.We also can collect seeds from wild populations,especially vulnerable populations（such as WD,etc.）,to keep the seeds in the seed bank for long-term storage.Finally,forest restoration studies and genetic improvement and breeding practices should be carried out.In the practice,we also should consider to perform assisted migration or provenance introduction for increasing population size,improving genetic diversity.Through the implementation of scientific research projects to achieve genetically improved varieties,construction the improved variety base of D.cultrata.