Study On Genetic Diversity Of An Endangered Plant Tetracentron Sinense Oliv.

In this paper,the genetic diversity of an rare and endangered plant Tetracentron sinense Oliv.was studied detailedly through the two methods of phenotypic markers and molecular genetic markers.Combining leaf phenotypic variation and its environment,the law of phenotypic variation was discussed.The ability to adapt to the environment and adaptation scope was speculated according to the level of leaf phenotypic variation;we also analyze the level of genetic diversity and genetic structure of the existing Tetracentron sinense population by ISSR molecular marker method.The final purpose is to discuss the mechanism causing its endangering from the perspective of genetic and the ability to adapt to hostile conditions in order to provide some references for effective conservation and management.The main results are as follows:?Analysis of nested variance for all traits showed significant differences among and within populations(F = 2.86-120.54;P < 0.01),but the variance between population is the main source of phenotypic variation of the species(Vst = 56.34%).The degree of phenotypic variation in 24 Tetracentron sinense populations is generally low,and the range of variation of 24 Tetracentron sinense populations was only 6.13%-6.13%.Of which,the degree of phenotypic variation was the highest in WFHH population,and the lowest level of phenotypic variation exist in SHS population.The variation of 17 kinds of leaf phenotypic characteristic ranged from 4.64% to 4.64%,the mean was 11.78%.The leaf phenotypic variation of Tetracentron sinense was related to the the environmental factors,such as mean temperature in July,mean annual precipitation,mean annual sunshine duration.The gradient rule of leaf phenotypic straits is presented along with longitude,latitude and altitude.According to the cluster analysis,24 natural populations of Tetracentron sinense could be divided into four groups.The first group included DFD?BDGS?DSH?WFHH?SNJ?LGS.To the second class belonged TJH,HK,BSJ,HG,HBY,SHS,JFS,MLZ,QZMS,FP,KKS,BH.In addition,KP,EM,ALS,GLGS clustered for the third class,and the FJS population clustered the fourth class lonely.?ISSR molecular variance analysis revealed variance between populations was greater than that within populations,suggesting that the variance between populations was the main source of the genetic variation of the species.At the species level,the percentage of polymorphic loci(PPL),Nei's gene diversity(h)and Shannon's information index(I)were 68.33%,0.1957 and 0.3004 respectively.The genetic variation parameter PPL,Na,Ne,H,I at 26 populations ranged from 9.44% ~ 30.56%,1.0944~1.3056,1.0743 ~1.2177,0.0410~0.1217,0.0589~ 0.1774 respectively,indicating that the genetic variation at populations were generally low.The BSJ population showed the highest genetic diversity.On the contrary,the KP population possessed the lowest genetic diversity.The coefficient of gene differentiation(Gst)was 0.6072,and the gene flow(Nm)between populations was 0.3235,which revealed the lower gene flow and the higher genetic differentiation between populations.The genetic structure analysis indicated that 26 Tetracentron sinense populations should be divided into three groups,which were separated by the Hengduan mountains and Qinling mountains.?On the whole,the results by leaf phenotype markers kept pace with that by ISSR molecular markers,but there were a little difference.In aspect of diversity,the most of phenotypic variation and genetic variation both existed in between populations.However,the phenotypic variation and genetic variation within populations were generally low.There was not significant correlation between phenotypic variation and genetic variation at all populations.In aspects of genetic structure,there was significant positive correlation between leaf phenotype distance matrix and genetic distance matrix.But the clustering result according to leaf phenotype did not quite fit in with that according to genetic markers.?The factors leading to Tetracentron sinense endangered included two parts.In the aspect of environment,the changes of water condition accounted for adaptation scope gradually shrinking.Human disturbance leaded Tetracentron sinense populations to decline into small populations.In the aspect of gene,the low level of gene flow gave rise to the low genetic variation between or within populations.The above factors could prevent Tetracentron sinense from adaptation,subsistence and evolution.?We came up with the following conservation strategies according to the above results.Firstly,three protection management units were established on the basis of genetic structure.The first category included KP,BMXS,GLGS,ALS.The second class was composed by HG?FP?BDGS?MLZ?QZMS?SNJ.JFS?TJH?HK?LGS?FJS?WL?BH?DFD?SHS?KKS formed the third unit.Then,BSJ population and TJH population could be as prior populations to protect because of their higher genetic variation.In addition,we also should pay attention to protecting existing Tetracentron sinense populations and their natural habitats.