Studies On Genetic Diversity And Population Structure In Wild Germplasm Collections Of Elymus Sibiricus L.

The understanding and knowledge of genetic variation within germplasm collections are useful for the efficient utilization of genetic resources in breeding programs.A prerequisite for an efficient conservation of biodiversity is that there is knowledge on genetic variation of native populations.As the type species of the genus Elymus,E. sibiricus L.(Siberian wildrye)is a perennial,self-pollinating and allotetraploid grass indigenous to Northern Asia,possessing the St and H genome.Its natural geographic distribution extends from Sweden to Japan and even to parts of Alaska and Canada,and that extends southerly to Qinghai-Tibet Plateau,which is the highest plateau in the world. E.sibiricus usually grows on wet meadows,riverside sands,and among open forest or shrubs.In the subalpine meadows with less than 4000m altitude in Qinghai-Tibet Plateau, E.sibiricus usually serves as an important forage species.Resource evaluation,cultivation technique,and seed production has been studied for E.sibiricus in China,whereas overseas studies of this species focused on biochemical and molecular mechanism of cold resistance, and phylogegenetic and evolutionary relationships of Elymus species including E.sibiricus. At present,very little is known about the information of genetic diversity of E.sibiricus germplasm collections or populations.The genetic diversity of worldwide germplasm collections of E.sibiricus was evaluated based on morpho-agronomic traits,gliadin markers,and SRAP markers.In addition,population structure and genetic variation among E.sibiricus populations from the southeast of Qinghai-Tibet Plateau of China.The main results showed as follows:1.Based on investigation of thirteen morpho-agronomic traits of 35 native Elymus sibiricus accessions including cultivar Chuancao No.2 as a check,Euclidean distances were calculated to performing cluster analysis for.The results showed that there were significant phenotypic differences among the studied accessions,indicating rich within-species biodiversity.According to the cluster analysis,the 35 accessions were classified into three groups with great morpho-agronomic differences.In groupⅢ,three accessions from Xingjiang Province and one accession from Hongyuan,Sichuan Province, had the highest performance in terms of forage and seed yields.The principle component analysis revealed a similar result to cluster analysis.The collection and conservation of native germplasm resources of E.sibiricus was also discussed in this part.2.Gliadin markers based on A-PAGE were used to analyze genetic diversity and genetic relationship among eighty-six Elymus sibiricus accessions from Asia and North America. Total of 52 gliadin bands were scored,of which 47 were polymorphic(90.4%).The generated similarity matrix showed that the genetic diversity within the accessions was fairly high(average similarity index=0.373).Similarity values among the accessions ranged between 0.108 and 0.952.Similar results were obtained when genetic diversity was estimated using the Shannon-Weaver index of diversity.The total genetic diversity across all accessions was 0.460.The proportion of variation explained by within geographic group and between geographic groups diversity was 0.559 and 0.442,respectively.Cluster analysis showed a clear demarcation between accessions from Qinghai-Tibetan Plateau, China and the others as separate groups.The extent of genetic diversity and genetic relationship among accessions is discussed.The clustering pattern was probably dependent on geographic origin and ecological adaptability of the accessions.3.SRAP markers were used to analyze genetic diversity and genetic relationship among eighty-four Elymus sibiricus accessions from Asia.A set of 23 primer combinations yielded 337 bands,of which 203 were polymorphic(60.24%).Genetic similarity values (GS)among the accessions ranged between 0.783 and 0.965 with a mean of 0.865.On the average,Mongolian and Russian accessions were the most similar while,Mongolian and Qingahi-Tibet Plateau accessions were the most distant ones.Cluster analysis grouped the 84 accessions into two clusters,which has quite a high fit(r=0.88)to the original similarity matrix.Results of cluster analysis which was supported strongly by the principal coordinate analysis.The molecular variance analysis(AMOVA)showed that the proportion of variation explained by within geographic group and between geographic groups diversity was 0.7962 and 0.2038,respectively.Similar results were obtained when genetic diversity was estimated using the Shannon's index of diversity.Based on pairwiseΦ_STbetween geographic groups,cluster analysis showed a clear demarcation between accessions from Qinghai-Tibetan Plateau and the others as separate groups.The clustering pattern was probably dependent on geographic origin and ecological adaptability of the accessions.The results of present study can be useful in collecting germplasm and the establishment of core collections of E.sibiricus.4.Inter-simple sequence repeats(ISSR)markers were used to assess the genetic diversity and population structure in eight populations of Elymus sibiricus L.from the southeast of Qinghai-Tibet Plateau of China.Of the 100 primers screened,13 produced highly reproducible ISSR bands.Using these primers,193 discernible DNA fragments were generated with 149(77.2%)being polymorphic,indicating considerable genetic variation at the species level.In contrast,there were relatively low levels of polymorphism at the population level with the percentage of polymorphic loci(P_P)ranging from 44.04% to 54.92%.The mean gene diversity(H_E)was estimated to be 0.181 within populations (range 0.164 to 0.200),and 0.274 at the species level.A high level of genetic differentiation among populations was detected based on Nei's genetic diversity analysis (33.1%),Shannon's index analysis(34.5%),Bayesian method(33.2%)and AMOVA analysis(42.5%).No significant statistical differences(analysis of molecular variance [AMOVA],P=0.08)in ISSR variation was found between the sample collection regions. However,among populations(42.5%of the variance)and within populations(57.5%of the variance),there were significant differences(P＜0.001).Populations shared high levels of genetic identity.This pattern of genetic variation was different from that for most of inbreeding Triticeae species reported.In addition,a geographical pattern of population differentiation,where the populations from south and north of sampling sites were clearly separated from each other,was revealed by both the cluster and principal coordinates analyses.Generally,the result of this study indicates that E.sibiricus contains high molecular variation in its populations.5.Random amplified polymorphic DNA(RAPD)markers were also used to assess the genetic diversity and population structure in eight populations of Elymus sibiricus L.from the southeast of Qinghai-Tibet Plateau of China.Of the 150 primers screened,25 produced highly reproducible RAPD bands.Using these primers,370discernible DNA fragments were generated with 291(78.65%)being polymorphic,indicating considerable genetic variation at the species level.In contrast,there were relatively low levels of polymorphism at the population level with the percentage of polymorphic loci(P_P)ranging from 46.49% to 53.78%.The mean gene diversity(H_E)was estimated to be 0.176 within populations (range 0.159 to 0.190),and 0.264 at the species level.A high level of genetic differentiation among populations was detected based on Nei's genetic diversity analysis (32.0%),Shannon's index analysis(33.7%),Bayesian method(33.5%).The partitioning of molecular variance by AMOVA analysis indicated significant genetic differentiation within populations(59.9%)and among populations(40.1%;P＜0.001).The average number of individuals exchanged between populations per generation(Nm)was 1.06.Populations shared high levels of genetic identity.The correlation between RAPD and ISSR gene diversity(H_E)showed a relative high correlation.In addition,a geographical pattern of population differentiation,where the populations from south and north of sampling sites were clearly separated from each other,was revealed by both the cluster,AMOVA,and principal coordinates analyses.Generally,the result of this study indicates that E.sibiricus contains high molecular variation in its populations.The implications of these results for the conservation of the species are also discussed.