Mining The QTLs For Increasing Thousand Grain Weigh From Synthetic Wheat

Common wheat is one of the most important crops in the world.During the long domestication process for common wheat,its genetic diversity has been narrowed by bottleneck effect and selection.Wild species are likely to contain favorable genetic factors that can increase the yield of modern varieties.Broadening the genetic base of common wheat by using exotic germplasm resources is an important germplasm development goal. In common wheat,thousand-gain weight(TGW) is an important component of grain yield. Increasing thousand-gain weight is one way to improve grain yield.However,it is negative correlation frequently with grain number per spike and spike number per plant, positive correlation with plant height.Am3,a synthetic wheat from crossing Triticum carthlicum(2n=28,AABB) with Aegilops tauschii(2n=14,DD),was used as donor lines and Laizhou953,a commercial Chinese cultivar used as recurrent parent in this study. After five generations of backcrossing,two BC₅F_2:3 populations(high TGW population consisting of 85 lines and low TGW population consisting of 75 lines) were employed for genotyping and phenotyping in the present study.Our goal is to detect the favorable TGW alleles of the synthetic wheat and to fine map QTLs for TGW in the future.The results obtained were listed as below.1.Two parents,Lalzhou953 and Am3,were screened for polymorphism with 648 SSR markers by using fluorescence and silver-staining detection systems of microsatellite markers.Among them,348 of them detect polymorphism between the parents.66 of the 348 SSR markers detected polymorphism in the high TGW population.The frequency of polymorphism was 18.96%.63of the 348 SSR markers detected polymorphism in the low population.The frequency of polymorphism was 18.1%.2.Using Map Manager software,a map of 58 markers distributing on 8 chromosomes was constructed in the high TGW population.The total length of the linkage map was 344.6 cM with an average genetic distance of 5.9 cM.In the low population,a map of 52 markers distributing on 9 chromosomes was constructed.The total length of the linkage map was 366.9 cM with an average genetic distance of 7.1 cM.3.The QTL analysis was performed with software Windows QTL Cartographer 2.0 based on composite interval mapping(CIM).QTL was claimed to be significant at a LOD value of 2.5.A total of 10 putative QTLs were detected in the high TGW population including 3 QTL for TGW located on chromosomes 1A,3D and 4B;1 QTL for grain length located on chromosome 7B;2 QTLs for grain width located on chromosomes 1A and 4B;2 QTLs for spike per plant located on chromosomes 4B and 7B;2 QTLs for plant height located on chromosomes 3D and 4B.A total of 17 putative QTLs were detected in the low TGW population including 3 QTL for TGW located on chromosomes 1A,4B and 7B;4 QTL for grain length located on chromosomes 1A and 2D;1 QTL for grain width located on chromosome 7B;2 QTLs for spike per plant located on chromosomes 4B and 7B;2 QTLs for plant height located on chromosomes 2D and 4B;5 QTLs for day to heading located on chromosomes 2A,2D,6B and 7B.4.In the high TGW population,3 new QTLs(QGw.caas-1A1,QGw.caas-3D,QGw.caas-4B1) for TGW were detected.QGw.caas-1A1 was detected in two environments with phenotypic variation explained(PVE) from 21.4%to 33.8%and increasing TGW 2.7-3.8g.QGw.caas-3D was detected in three environments with PVE 18.1%-31.8%and increasing TGW 2.3-4.8 g.QGw.caas-4B1 was detected in two environments with PVE 10.9%-30.2%and increasing TGW 3.9-4.8 g.TGW was not corrected to other traits except for GINS.A significant positive correlation between TGW and GNS was found in Luoyang (r=0.232,P＜0.05),but it was not significant in Beijing.QTL mapping revealed that the QTL of TGW detected here were not located in the same regions with the other yield components and plant height except for the Qph.caas-3D,suggested that we can select these favorable traits/QTL separately and pyramid them with the other yield components, such as SP and SN.Those QTLs were not correlated with other agronomic traits.We could select the favorable traits/QTLs separately and pyramid them with the other yield components,so the QTLs were the favorable QTLs conferring increasing thousand-grain weight.5.Despite inferior agronomic traits of donor parent Am3 to the recurrent parent Laizhou953,in the populations,some of ILs have superior agronomic traits to the recurrent parent Laizhou953,such as IL6 with:TGW 60.5g,GNS 53.3,PH 83.6 cm,SP 5.8;IL39 with:GNS 83.6,TGW 45.9g,SP 5.3,PH 84.3 cm.In this study,some of favorable lines have been distributed to breeders for improving grain yield.