Studies On Genetic Characteristics Of Two Male Sterile Lines In Alfalfa (Medicago Sativa L.)

Alfalfa(Medicago sativa L.)is one of most important leguminous forages.To obtain heterosis using male sterile lines could significantly improve biomass,quality and resistance in alfalfa breeding.Therefore,putting forward the appropriate hybrid seed production system based on the research of genetic characteristics of alfalfa male sterile lines has important theoretical and practical significance.In this paper,two male sterile lines 10-9 and 4-10,which were selected from two alfalfa cultivars Western Giant and Graze401+Z in a national alfalfa breeding program respectively,were hybridized with pollens from fertile line 10-10 selected from Western Giant.The segregation populations Fi,F2,BC1 of 10-9 × 10-10 and F1,BC1 of 4-10×10-10 have been constructed.And genetic characteristics of 10-9 and 4-10 have been analyzed based on fertile pollen ratio,the results are as below:1.Genetic characteristic of male sterile line 10-9.Alfalfa is a kind of cross-pollinated crop with heterozygous genotype,so the phenotype would segregate in F1 population,which could be used for genetic analysis.In F,population of 10-9(?)×10-10(?),14 male sterile(MS)individuals and 84 male fertile(MF)individuals were observed,which proved that such male sterility did not belong to maternal inheritance.That is,male sterile line 10-9 should be divided into types of genic male sterility.According to Mendel's laws,actual and theoretical separation ratio of fertility in Fi population at different genetic modes were tested,the results showed that.male sterility of 10-9 was controlled by a recessive gene,and the genotypes of 10-10 and 10-9 were MslMslmslmsl and mslmslmslmsl respectively(?2=0.23).According to the parental genotypes above,three genotypes of F1 individuals were MslMslmslmsl(MF),Mslmslmslmsl(MF)and mslmslmslmsl(MS).Then self-fertilizing of male fertile F1 individuals should produce 2 kinds of theory segregation rate(MS:MF)as 1:35 and 1:3 respectively.The genetic test showed that actual ratio of fertile and sterile plants in F2 followed the theory segregation populations 1:35(?2=11.82)and 1:3(?2=0.67,0.68 and 0.98).Male sterile plants(mslmslmslmsl,MS)from F2 population were backcrossed with male fertile parent 10-10.Based on the recessive male sterile mode above,the ratio of fertile plants to sterile plants in BCi should be 1:5,and the actual ratio of MS and MF plants were observed as expected and was in accordance with theoretical ratio(?2 ?1.56 and 1.60).The analysis for taken together for F1,F2 and BCi segregation,suggested that the male sterility of 10-9 was controlled by single recessive gene.The genotypes of MslMslMslMsl,MslMslMslmsl,MslMslmslmsl,Mslmslmslmsl are male fertile,and genotype of mslmslmslmsl is male sterile.2.Genetic characteristics of male sterile line 4-10.To characterize the genetic pattern of 4-10 male sterile line,the fertility of all 56 Fi individuals and 85 BC1 individuals had been examined and the results showed that all plants of the F1 and BC1 populations were male sterile,which indicated the such sterile phenotype could be 100%delivered to its progenies and was maternal inheritance.Considering alfalfa is a kind of cross-pollinated crop with heterozygous genotype,the results proved that male sterile should be controlled by cytoplasmic gene,and male sterile line 4-10 belongs to the cytoplasmic male sterility.In conclusion,according to the genetic analysis based on fertility segregation in hybrid groups,the genetic pattern of 10-9 and 4-10 had been preliminary revealed:the male sterility of 10-9 and 4-10 were controlled by a recessive gene and cytoplasmic gene respectively.These discovers will enrich alfalfa male sterile resources,and have great significance for exploring male sterile mechanism and hybrid seed production in future.