Genetic Diversity And Genetic Relationship Of Broomcorn Millet(Panicum Miliaceum L.) Germplasm

Broomcorn millet(Panicum miliaceum L.)is one of the earliest domesticated crops in the world.Northwest China and central Asia,west Asia and European countries are the important way for the ancient Silk Road as well as the main cultivation area of broomcorn millet.The objective of this study is to analyze the genetic diversity and population genetic structure of broomcorn millet in the region.It will promote the study of origin evolution and propagation path of broomcorn millet and the application of excellent accessions of broomcorn millet in germplasm innovation,breeding and production of new varieties.The objective of this study is to analyze the genetic diversity,genetic relationship and population genetic structure of broomcorn millet(including 85 domestic wild accessions,284 domestic local varieties and 61 foreign local varieties,all germplasm accessions were divided into 15 groups according to the geographical source)in the most countries and areas along the silk road by SSR markers and sequencing technology,and to discussed the domestication centers of broomcorn millet and provide available data for further evolutionary study of broomcorn millet.The main findings of this study are as follows:1.Genetic diversity and genetic relationship of broomcorn millet germplasm based on SSR markers137 SSR primers are used to identify polymorphisms in six representatives which selected randomly from the total of accessions.A total of 103 primers produce clear and reproducible polymorphic fragments among the six accessions and then are used to assess genetic diversity of 362 broomcorn millet accessions.103 SSR markers detect a total of 323 alleles(Na)with an average of 3.1359 for each SSR and the mean values of Shannon-Weaver index(I),Nei and PIC were 0.8240,0.4973 and 0.5502,respectively.Their resolution range was 0.334-4.002 and more than 77.67% distribution at intervals of 1-4,indicated the moderate resolving power of these SSR.In genetic diversity analysis of broomcorn millet accessions,the observed number of alleles(3.1068),Shannon-Weaver index(0.8023),expected heterozygosity(0.4842),and PIC value(0.5340)of broomcorn millet accessions in China were all higher than those in abroad,indicated more abundant genetic diversity in Chinese samples.In addition to the observed number of alleles and heterozygosity,the values of geneticparameters of wild accessionss were all higher than those of local varieties,indicating that the genetic diversity of wild broomcorn millet was rich.Among them,the genetic diversity of Hebei population in China was the highest,followed by Heilongjiang population in China.The genetic distance of the 14 populations ranged from 0.0600 to 0.5762 with a mean of 0.2821.The genetic identity ranged from 0.5620 to 0.9416 with a mean of 0.7504.We found that the genetic similarity had a certain correlation with geographical distribution.The closer geographical distribution,the smaller genetic distance,the higher genetic identity.The genetic distance between local varieties and Hebei accessions was the smallest,so Hebei might be the center of broomcorn millet domestication.In the clustering,the division of domestic and foreign resources,wild resources and local varieties was very significant.Two accessions of Asian(AMES32315 and PI163300)were located at the outermost group,which had a far-distance relationship with other resources.In addition,the remaining 360 broomcorn millet accessions were divided into three groups at a genetic distance of 0.51.Group A was foreign local varieties,group B was domestic local varieties,and group C was wild accessions.Group A and group B was divided into three subpopulations at a genetic distance of 0.39 and group C was divided into six subpopulations at a genetic distance of 0.44.There were closer genetic relationship between Asia and European accessions,as well as Heilongjiang and Liaoning accessions in China,Hebei,Shanxi and Inner Mongolia accessions in China,Xinjiang and Gansu accessions in China than other populations.In the population clustering,the local varieties and Hebei accessions of broomcorn millet were clustered into the same branch,and the genetic relationship was closest,confirming that Hebei region might be the domestication center of broomcorn millet.The result of genetic structure analysis showed that there was obvious genetic differentiation between the domestic populations and foreign populations.Three groups(group 1 to group 3)were unique genotypes which owned by Chinese wild resources;five groups(group 4 to group 8)were unique genotypes which owned by Chinese local varieties and three groups(group 11 to group 12)were unique genotypes which owned by foreign local varieties.The population structures of Ningxia,Shanxi and South America tended to be independent,and the population structures of Hebei,Gansu and Asia tended to be diversified.The genetic structure analysis results were consistent with the results of UPGMA clustering,and the genetic relationships were related to their geographical distribution.PCA analysis explained a total of 58.8% of the variance,in which PC1 could divide the genotypesof most populations.2.Genetic diversity and phylogenetic relationships of broomcorn millet based on trn T-trn L and GBSSI sequencesThe trn T-trn L sequence was highly conserved,containing 10 variable sites and 18 indel sites.The haplotype diversity was 0.0640,and the nucleotide diversity was 0.00014.The diversity of GBSSI sequences was significantly higher than that of trn T-trn L sequences;420 variable sites and 76 indels were identified.The haplotype diversity was 0.9976,and the nucleotide diversity was 0.11025.The nucleotide diversity and nucleotide polymorphisms of wild accessions from Shanxi,Inner Mongolia and Heilongjiang populations,China were higher than other populations;genetic diversity among these populations was abundant.The genetic relationship among local varieties and Hebei,China was relatively close;that between local varieties and Heilongjiang,China was larger.Phylogenetic analysis divided 430 broomcorn millet accessions into different groups.Most accessions from the same origin were clustered in adjacent or similar branches and regional characteristics were found.Accessions from Heilongjiang,Liaoning,Inner Mongolia and Shanxi were clustered into the same branch.Genetic relationships of Ningxia,Xinjiang,Gansu populations of China and abroad populations were close.This data indicated that broomcorn millet may have spread westward through the northwest of China to enter Eurasia and other foreign regions.