Study On Genetic Diversity Of Alfalfa(Medicago Sativa) Germplasm Phenotypes And SSR Molecular Markers

Alfalfa is the most leguminous forage planted in the world with the widest area and it has the highest economic value.Due to the lack of alfalfa germplasm resources in China and the unclear genetic background,the cultivation of new varieties is slow and it is difficult to meet the needs of China's market.Therefore,understanding the genetic characteristics of different alfalfa germplasm materials has important theoretical guidance for the breeding of new alfalfa cultivars.In this paper,the genetic diversity and population genetic structure of 96 alfalfa germplasm materials collected from different sources were analyzed by phenotype traits and SSR molecular markers.The research results are as follows:(1)There were obvious differences among 16 phenotypic traits of 96 alfalfa germplasm materials tested,the coefficient of variation was between 7.00%-28.48%,the diversity index H'was between 1.62-2.07,and it had rich genetic diversity.Among them,the six indicators of plant height,stem thickness,root neck diameter,number of first-level branches,leaf area and root neck soil depth have large differences between alfalfa germplasm materials,which are the main factors affecting the alfalfa variation and genetic diversity.(2)Through cluster analysis of 16 phenotypic traits of 96 alfalfa germplasm materials,we can know that 96 germplasm materials can be divided into 5 categories,of which No.10,No.12,No.55,No.6,No.8,No.34,No.26,No.28 and No.71 materials,these plants grow vigorously,grow well,grow best,and can be used as a raw material for alfalfa breeding.But the materials No.31,No.56 and No.57 have weaker plant growth,smaller plant type,small and narrow leaves,short petioles,thin stems and short intemodes in the fourth node,and the breeding value is not high.(3)12 pairs of SSR primers amplified a total of 499 bands in 240 individual plants of 30 alfalfa germplasm materials,of which 498 polymorphic bands,an average of 41.50 loci were amplified per marker and the point percentage reached 99.73%.The variation level of genetic diversity within the 30 alfalfa material groups was 0.0767-0.2006,the variation level of Shannon information index was between 0.1214-0.2832,and the genetic differentiation coefficient(Gst)was between 0.1133-0.2831,indicating that the tested alfalfa material group,there is a more obvious genetic variation.The number of effective alleles between 30 alfalfa germplasm materials is between 1.0787-1.1188,polymorphic sites are between 77-151,and the percentage of polymorphic sites is between 17.31%-31.70%,the Shannon information index ranged from 0.9758 to 1.5017.Sorted according to Nei's genetic diversity,the top 10 germplasms are:No.31s No.30,No.79,No.91,No.50,No.84,No.45,No.77,No.44 and No.28.(4)Analysis of the genetic similarity coefficient of alfalfa materials shows that the materials with more distant relationships are derived from the individual plants of Japan No.84 and Italy No.79;the materials with closer relationships are from the United States No.72 and the United States No.85 single plant material;and the genetic similarity coefficient of the single plant from Armenia No.31 material changed the most,followed by the United States No.67;(5)According to the UPMGA clustering method,30 parts of alfalfa germplasm can be divided into four categories.The first category includes 23 alfalfa materials;the second category is 5 alfalfa materials from the United States,Bolivia,and Libya;Grouped into one category are material No.31 from Armenia and material No.56 from China.(6)Analysis of the population genetic structure of the alfalfa germplasm materials tested showed that when K=4,the similarity value was the largest,so the test materials were divided into four groups.Taking the Q value? 0.6 as the dividing standard,the Q values of different alfalfa materials in different groups were analyzed.Among them,96.67%of the alfalfa germplasm materials had a Q value? 0.6 in the four major groups,and the genetic structure was considered to be simple;The genetic structure of alfalfa germplasm material has complex variability and belongs to a mixed group;while the alfalfa germplasm material divided into four major groups accounts for 40.00%,25.42%,14.58%,16.67%;Among the alfalfa materials of various groups,the genetic structure of individual alfalfa germplasm materials in the same group is quite different;from the principal component analysis,it can be seen that the genetic differentiation level of group? is relatively high,indicating that the alfalfa materials of this group are quite different.