| Broomcorn millet(Panicum miliaceum L.)is an annual herbaceous plant in the genera Panicum L.of the family Gramineae,and it has 2n = 36 chromosomes.Broomcorn millet is an annual cereal of the grass genus Panicum,which has the shortest growing period of and cereal and an exceptionally low water requirement,so used as an important crop in semiarid regions where other crops fail.There have more than 8700broomcom millet germplasm which conserved in China National Collection Center,provide an abundant germplasm base for the genetic research and breeding work.In this study,we assess the genetic diversity of broomcorn millet accessions which collected from China and abroad,and to construct the mini core collection of broomcorn millet which including 253 accessions by SSR markers.The aim is to protect the germplasm resources more effectively.The results were as follows:1.Five hundred pairs of SSR primers developed in the authors' laboratory by high-throughput sequencing were used to identify polymorphisms in six representatives randomly selected from the total of accessions.A total of 63 primer pairs produced clear and reproducible polymorphic fragments among the six accessions and then were used to analyze the genetic diversity and relationship of 192 broomcorn millet landrace and wild accessions.A total of 161 alleles were detected with an average of 2.56 alleles per locus,and the mean Shannon-Weaver index(I),mean Nei and mean PIC were 0.6275,0.3874 and 0.4855,respectively.The results indicated that there is a significant difference among the 10 populations of broomcorn millet resources in genetic diversity from diverse geographic origins.The variance range of effective allelic number is 1.2407(South region)-1.8846(Inner Mongolia).In domestic populations,the rank of Shannon-Weaver index is Inner Mongolia Plateau>Tohoku>Loess Plateau>Northwest>southern regions,and the rank of foreign populations is the former Soviet Union>Europe>Mongolia>India>United States.The results of Nei's genetic heterozygosity analysis showed that the minimum and maximum of observed(Ho)and expected heterozygosity(He)is 0.2372 from Indian and 0.3966 from Inner Mongolia as well as 0.3114 from the Unite State and 0.4622 from Inner Mongolia Plateau,respectively.The effective number of alleles(1.9285±0.5101),Shannon-Weaver index(0.6948±0.2852)and Nei gene diversity index(0.4373±0.1773)of the wild germplasm are much higher which in domestic and foreign accessions.For domestic population and alien population,the effective number of alleles(1.8145±0.4519)of domestic resources,Shannon-Weaver index(0.6657±0.2413),and Nei gene diversity index(0.412±0.1574)of domestic accessions were higher than that in foreign resources(1.6862±0.4527,0.5897±0.2469,0.3652±0.1655).UPGMA cluster analysis showed that the 10 geographic populations could be clustered into three categories,the accessions from the Inner Mongolia Plateau,the Loess Plateau,northeast,northwest,Mongolia area were clustered as one group,the former Soviet Union,the United States,India,Europe together as one group,and southern region of China clustered as one independent group.The wild millet(34)which is from Qiqihaer is separated from others at 0.37,the wild millet from Gansu(19)was divided into an independent individual at 0.34,indicating that there are significant genetic variances between the two wild accessions and others.In general,genetic division of population is not significant for 192 domestic and foreign accessions,and there have material interpenetration among different groups.2.34 polymorphic SSRs were used to study the genetic diversity of core collection of broomcorn millet which including 636 accessions.The result identified 101 alleles,with an average number of 2.971 alleles/locus and values of Shannon-Weaver index(I)varied from 0.301(LMX1940)to 1.487(LMX1072)per locus,with an average of 0.843.Genetic similarity analysis showed that much greater genetic distances exist between domestic and foreign populations than among domestic populations.The UPGMA cluster analysis was employed and 17 populations were divided into two discrete groups,according to their cultivation system and origin.The most divergent subgroup identified was the accessions from Shanxi,with the highest values for gene diversity(0.807),and average number of alleles/locus(2.912).A mini-core collection(MC)containing 256 accessions was extracted based on SSR data,the diversity index and the polymorphism information content(PIC)for the MC were significantly higher than for the CC,suggested that the MC provides a good representation of the genetic diversity of original CC.This study provides a comprehensive characterization of the genetic diversity of the broomcorn millet core collection in China.A MC may aid in reasonably and efficiently selecting materials for broomcorn millet breeding and for genotypic biological studies,and may also be used as a population for association mapping in broomcorn millet. |
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