Construction Of Ultrahigh-density Molecular Genetic Linkage Map And QTL Mapping For Yield,and Quality Traits Such As Protein Content Of Tetraploid Crested Wheatgrass

Tetraploid crested wheatgrass is an excellent forage obtained by interspecific hybridization and chromosome doubling of diploid A.mongolicum Keng and diploid A.cristatumcv.Fairway,which has strong heterosis.It combines the advantages of drought resistance,cold tolerance,strong adaptability and barren resistance from A.mongolicum Keng with that of strong tillering ability,large amount of leaves and higher nutritive value from A.cristatumcv.Fairway.In the present research,a total of 246 F₂ individuals of tetraploid crested wheatgrass and their parents were used as materials.Combined with three types of molecular markers SRAP,SSR,and SNP,a ultrahigh-density molecular genetic linkage map of tetraploid crested wheatgrass was constructed using JoinMap 4.0 mapping software,and the QTLs for 11 traits such as yield per plant,stem and leaf ratio,crude protein content were identified.with a view to providing theoretical basis for the further development of gene cloning and functional analysis,QTL fine mapping and molecular marker-assisted breeding for other important traits such as yield,quality of crested wheatgrass.The main results were as follows:1.A total of 42 suitable primers were screened,including 32 SRAP and 10 SSR primers.The primers were used to PCR amplify the genomic DNA of 246 F₂ individuals of tetraploid crested wheatgrass and their parents,and a total of 997 polymorphic markers were obtained,including 753 SRAP and 244 SSR markers,with the polymorphic ratio of 88.8%and 92.4%,respectively.2.A total of 5035 mapped SNP markers were developed based on the genotyping by sequencing technology（GBS）.3.The segregation distortion analysis showed that 137 of all the 6032 polymorphic markers（112 SRAP and 25 SSR markers）deviated from the segregation ratio,with an segregation ratio of 2.27%.4.An ultrahigh-density genetic linkage map of tetraploid hybrid crested wheatgrass was constructed,containing 14 linkage groups and 6032 markers,which covered the total map length of 2624.43 cM,with an average distance of 0.44 cM between markers.5.The correlational analysis indicated that 11 traits such as yield per plant,crude protein content,crude fat content and crude fiber content showed significant or extremely significant correlations.The normality test showed that the phenotypic value of each trait in mapping population of crested wheatgrass were normally distributed,under the three environments and their average data.6.A total of 39 stable QTLs were detected for 11 traits of tetraploid hybrid crested wheatgrass,of which seven QTLs controlled fresh weight per single plant,five QTLs controlled dry weight per single plant and crude protein content respectively,four QTLs controlled stem-leaves ratio and crude ash content respectively,three QTLs controlled WSC content,two QTLs controlled crude fat content and crude fiber content respectively,three QTLs starch content and calcium content respectively,one QTL controlled phosphorus content.These stable QTLs could explain the phenotypic variation from 8.0%to 26.0%.6.Of all the 39 stable QTLs,a total of 13 were major QTLs,of which three QTLs controlled fresh weight per single plant（Qfwsp-3-1,Qfwsp-12-4 and Qfwsp-14-6）,one QTL controlled dry weight per single plant（Qdwsp-14-5）,one QTL controlled crude protein content（Qcpc-4-3）,one QTL controlled crude fat content（Qcfac-8-2）,one QTL controlled crude fiber content（Qcfic-6-2）,one QTL controlled crude ash content（Qcac-2-2）,one QTL controlled WSC content（Qwscc-7-3）,one QTL controlled starch content（Qsc-9-3）and one QTL controlled phosphorus content（Qpc-4-1）,two QTLs controlled calcium content（Qcc-4-1 and Qcc-12-3）.