Study On The Multifoliate Trait And Genetic Structure And In Backcross Population Of Multifoliate Alfalfa

In order to study the Multifoliate trait and Multifoliate trait inheritance of a backcross population of alfalfa(Medicago sativa L.)with Multifoliate trait as the main target,The study chosen ’Huaiyin’ of trifoliolate alfalfa and ’PL34HQ’ of multifoliolate alfalfa as recurrent parent and nonrecurrent parent to obtained BC2 generation.We use variance analysis,correlation analysis,principal coordinate analysis and correlation degree analysis as study’s analysis method.Growth data and molecular data were combined to study the population foliage characteristics and population structure.We hope to understand the population’s foliage characteristics,explore the genetic characteristics of multifoliate alfalfa,study the population performance of multifoliate alfalfa after the secondary backcross and select excellent single plant from BC2 population as subsequent breeding material.The result is as follows:1.The maximum group multifoliate rate of 196 BC2 generation plants was 27.04%at budding period,followed by 26.02%at initial flowering stage.The single plant with the highest main branch multifoliate rate was 88%.The ’4+5+6+7’ type was the best in BC2 population,and the 5 leaf type was the most stable in BC2 population.2.In BC2 population,alfalfa’s multifoliate character had obvious primary advantage,and the expression of multifoliate leaves of new leaflets at the same stem node decreased gradually.Multifoliate alfalfa leaf rate will be reduced with the growth of alfalfa.Flowering had bigger influence on the multifoliate characteristics.Single plants with multifoliate traits at seedling stage had better performance of multifoliate leaves than other single plants in subsequent growth.When choosing multifoliate leaves traits as the main goal for breeding,selecting only the alfalfa with multifoliate traits at seedling stage could improve breeding efficiency and effect.3.In BC2 population,multifoliate rate of single plant was very significantly positively correlated with multifoliate rate of main branch(P<0.01).multifoliate rate of Main branch and multifoliate rate of single plant was positively correlated with the yield related traits such as height of plant,number of branch,fresh weight and dry weight,but the correlation was not significantly.Multifoliate rate of main branch and multifoliate rate of single plant were positively with fresh-dry ratio.Multifoliate rate of main branch was significantly negatively correlated with stem-leaf ratio(P<0.05),and multifoliate rate of single plant was negatively correlated with stem-leaf ratio.Multifoliate characteristics of alfalfa’s effect on the yield was limited,but it had a significant positive effect on improving the quality of alfalfa.4.A total of 74 allelic variation were detected by 15 pairs of SSR primers in BC2 population,with an average of 4.93 allelic per pair of primers.Among the 15 pairs of SSR primers,MES 50 and MT 66 had the most allelic and MES 37 was the least.The average polymorphism ratio of 15 pairs of SSR primers was 84.96%,and the average Polymorphism information content was 0.7653.5.According to the population genetic structure analysis,BC2 population can be divided into four groups.The highest genetic diversity was found in group 3,with genetic diversity of 0.2934 and Shannon index of 0.4380.This is followed by group 4.Group 2 had the best multifoliate characteristic,followed by group 4.The average plant height and branching number of group 4 were 77.15 and 13.62,respectively,which were better than those of the other three groups.The multiple leaf rate of single plant and main branch of group 4 was significantly higher than that of group 1 and group 3.Combined with agronomic traits and genetic diversity,group 4 had the best comprehensive performance,which could provide high quality parent material for genetic improvement.6.After the secondary backcross,the mean value of each agronomic character in BC2 population was less than the median parental value and the comprehensive traits of BC2 population were Limited improvement effect.According to the comprehensive character and genetic relationship of the population,the proportion of ’cyclic parents’per plant was relatively high in the population,and the gene homozygosity of cyclic parents was improved,BC2 population was more close to the cyclic parents.The backcross population still has the potential for further improvement.Some of the individual plants in the population were better than the high parent in some characters,and the comprehensive performance was better than that of the parents,which could be used as the parent materials for further improvement.