| Alfalfa(Medicago sativa L.)is one of the most widely planted forage legumes because of its high yield,good quality,good resistance and broad adaptability.Analysis of genetic characteristics of important traits and QTL mapping of alfalfa provide the theoretical guide for genetic improvement of new alfalfa cultivars.In this experiment,paternal parent exhibits good phenotypic performance for early-flowering but poor forage production.Maternal parent exhibits good performance for forage yield but late-flowering.Crossing paternal parent and maternal parent resulted in a segregating full sib F1 population.The agronomic traits of parents and hybrid populations were test over many years in different locations.Multiple regression analysis and mixed major gene plus ploy-genes model were used to analyze the genetic traits of agronomic traits.We finished the construction of a molecular genetic linkage map and QTLs analysis of some agronomic traits,and we cloned MsLEAFY gene from Medicago sativa L.and verified its function.The results are as follows:1.The statistical analysis of different agronomic traits of alfalfa F1 individuals showed frequency distribution of eight traits,including the fresh weight,dry weight,branch number,plant height,internode length,stem diameter,internode number and the ratio of stem and leaf exhibited normal distribution.The correlation analysis showed that the branch number and plant height were positively correlated to fresh weight and dry weight.The broad heritability of flowering date,leaf type,the ratio of stem and leaf,and node number were all above 90%,the values of yield and plant height were 67%and 60.3%,and the minimum of branch number is only 20%.2.Mixed major gene plus ploy-genes model showed that the suitable genetic model for the stem diameter was 2MG-ADI in two years,and the heritability of major genes were 93.24% and 34.32%,respectively.The optimum model for the ratio of stem to leaf was 2MG-ADI,and the heritability of major genes were 71.61% and 32.68% in two years.Thus,the stem diameter and the leaf stem ratio were mainly controlled by two pairs of major genes besides additive and epistatic effects.The optimum models for dry weight,branch number and plant height were various in different years.3.The genetic linkage map was constructed using 176 SSR polymorphic markers by the special analysis software Teraploidmap for tetraploid.The genetic linkage map of paternal parent was constructed,consisting of 79 polymorphic markers onto 8 linkage groups and covering a total of 1102 cM with an average distance of 13.95 cM.The genetic linkage map of maternal parent was constructed,consisting of 78 polymorphic markers onto 8 linkage groups and covering a total of 1148 cM with an average distance of 14.72 cM.4.Nine hundreds and sixty SNP markers were obtained for genetic linkage map construction,with 484 and 476 for paternal and maternal plants.The genetic linkage map of paternal plant covered the map distance of 3993.3cM,and average genetic distance is 8.25 cM per marker.The genetic linkage map of maternal plant covered the map distance of 3769.4cM,and the average genetic distance is 7.92 cM per marker.SNP site information were used to construct the physical map.The average male chromosome covered physical distance of 47.42 Mb and the average physical distance is0.78 Mb between the two markers;the average male chromosome covered physical distance of 46.83 Mb and the average physical distance is 0.79 Mb.5.QTL mapping and genetic effect analysis were conducted for yield and other traits of alfalfa.Nineteen QTL were detected for yield and located in linkage group of 1,2,3,4,5,7,8.Fourteen QTL were for the branch number in linkage groups of 1,2,3,4,5,7and 8.Twelve QTL for plant height exists in the chromosome 1,2,3,4,5,7and8.Six QTL for flowering date were located at chromosome 1,3,4,5,with five for the length of internode and three for stem diameter in chromosome 1 and 8. |
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