Utilization Of Male Sterile Line Heterosis In Alfalfa (Medicago Sativa L.)

Alfalfa（Medicago sativa L.）is a high quality leguminous forages,which is known as“king of the grass”and has high yield,tolerance to mowing,strong adaptability,high protein content,good palatability,and perennial.However,compared with annual crops,alfalfa yield breeding is slow work.Configured the hybrid with heterosis performance by alfalfa male sterile line will an effective way to improve the yield of alfalfa.Therefore,continuing to breed new good alfalfa male sterile line and exploring its potential application value in the process of heterosis utilization will help to promote alfalfa application in agricultural production.In this research,early breeding alfalfa male sterile lines ms₁～ms₆served as female parent in our research group.Meanwhile,six alfalfa cultivars with excellent properties served as male parent,configured to establish hybrid population.By measuring the hay yield and other agronomic character of alfalfa parents and its cross population,to analyze combining ability of hay yield and its main yield related traits of different cross combination and heritability of hay yield,and discuss utilization of male sterile line heterosis in alfalfa,as to screen the alfalfa male sterile lines with potential heterosis utilization value and provide theoretical basis and breeding material for the breeding of alfalfa varieties.The main research results were as follows:1)In the alfalfa male sterile lines,except for internode length,leaf length,leaf width,leaf area,the hay yield and other yield related traits of ms₃,ms₄,ms₅and ms₆were at a higher level;In the male parent,except for internode length,leaf length,leaf width,leaf area,the hay yield and other yield related traits ofⅡ,Ⅲ,Ⅴwere at a higher level;In the cross population,the hay yield of ms₃×Ⅴ,ms₄×Ⅱ,ms₄×Ⅲ,ms₅×Ⅲ,ms₅×Ⅴ,ms₆×Ⅰ,ms₆×Ⅲwas higher,and not less than 200g/plant.Except for internode length,leaf length,leaf width,leaf area,other yield related traits were at a higher level.2)The mid-parent heterosis and its correlation analysis of the hay yield and its main yield related traits of different cross combination showed that the mid-parent heterosis of hay yield of ms₃×Ⅴ,ms₄×Ⅱ,ms₄×Ⅲ,ms₅×Ⅲ,ms₅×Ⅴ,ms₆×Ⅰ,ms₆×Ⅲwas particularly strong.In addition,the mid-parent heterosis of plant height,branch number,leaf number,internode number and regrowth rate had extremely significant correlation with mid-parent heterosis of hay yield,showed that the mid-parent heterosis of these yield related traits had important influence on the formation of hay yield mid-parent heterosis.3)The combining ability analysis of hay yield and its main yield related traits of parent and their cross combinations found that in alfalfa male sterile lines,the GCA of hay yield and its main yield related traits of ms₄,ms₅,ms₆were higher,and SCA of hay yield and its main yield related traits of hybrid combinations that were configured with the three alfalfa male sterile lines were also at a higher level,thus the three alfalfa male sterile lines could served as excellent female parent in hybrid configuring,and their cross combinations would show a stronger heterosis potential and had a higher utilization value.In the cross population,the SCA of hay yield and its main yield related traits of ms₃×Ⅴ,ms₄×Ⅱ,ms₄×Ⅲ,ms₅×Ⅲ,ms₅×Ⅴ,ms₆×Ⅰ,ms₆×Ⅲwere higher,and mid-parent heterosis of hay yield and its main yield related traits of the seven cross combinations were at a higher level and had higher heterosis utilization value.4)The results of groups combining ability variance for hay yield showed that the genotype variance of parental GCA accounted for 70.58%of the total genetic variance,indicated that gene additive effect played a leading role on the formation of hybrid hay yield heterosis.In addition,male sterile lines and male parent accounted for 39.61%and 30.97%of GCA genotype variance respectively,showed that GCA of alfalfa male sterile lines played a main role in the formation of hybrid hay yield heterosis.Therefore,choosing alfalfa cultivars for hybrid configuring should give preference to higher GCA male sterile lines to served as female parent.5)Broad-sense heritability and narrow-sense heritability of hay yield were54.84%and 42.71%respectively,show that selection of excellent hybrid was more ideal in the early generation,namely the excellent characters of parents could be better inherited to F₁hybrids,and had higher application value in agricultural production.In conclusion,breeding of excellent alfalfa hybrid should give preference to high GCA male sterile line to served as female parent to conduct crossing experiment,which would have greater chance to obtain excellent hybrid.Meanwhile,plant height,branch number,leaf number,internode number,regrowth rate must be taken into account comprehensively for the formation of yield heterosis.