Identification And Validation Of QTL For Grain Related Traits In Common Wheat

Wheat is one of the most important cereal crops in the world.Grain related traits,such as thousand grain weight?TGW?,grain number per spike?GNS?and grain filling rate?GFR?,are the main breeding goals of yield improvement.They are controlled by multiple minor effect quantitative trait loci?QTL?and are affected by environment factors.Therefore,identification of stable QTL for grain related traits and development of user-friendly molecular markers are important for yield potential improvement in wheat breeding.Selective genotyping of individuals from the high and/or low tails of a phenotypic distribution provides a cost-effective alternative approach for genetic mapping.In the present study,266 recombinant inbred lines?RILs?derived from a cross between Zhongmai871?ZM871?and its sister line Zhongmai 895?ZM895?were evaluated for TGW,grain length?GL?,grain width?GW?and GNS in ten environments and for mean GFR in six environments.Sixty RILs,with30 higher and 30 lower TGW,respectively,were genotyped using the wheat 660K SNP array for preliminary QTL mapping.Four genetic regions on chromosomes 1AL,2BS,3AL and 5B were identified to have significant effects on TGW-related traits.A set of kompetitive allele specific PCR?KASP?markers were converted from the SNPs on the target chromosomes and were used to genotype all 266 RILs.The mapping results confirmed the QTL mentioned above and mapped a new QTL for GNS on chromosome5BS.Among the identified QTL,Qgw.caas-1AL,Qgl.caas-5BS and Qgns.caas-5BS are major stable loci that could explain 11.9%,14.7%and 10.2%of the phenotypic variances,respectively.These results indicate that selective genotyping is a simple,economic and effective approach for rapid QTL mapping and can be generally applied to genetic mapping studies for important agronomic traits.These QTL were further validated using 121 and 175 BC₁F₄ lines derived from backcrosses ZM871/ZM895//ZM871 and ZM871/ZM895//ZM895,and 186 advanced breeding lines.Among them,QTL for TGW,GW and GFR on chromosome 1AL showed constant effects on TGW and GW and negligible TGW-GNS tradeoffs in different genetic backgrounds,representing a valuable target for marker-assisted selection in wheat breeding.The availability of time-saving and cost-effective KASP markers could facilitate its use in wheat breeding.Short arm to the centromere region of chromosome 5B is an important but complex region that harboring major stable QTL for TGW,GL and GNS.A more precise delimitation of these QTL is a prerequisite for their utilization and gene cloning.Qgl.caas-5BS was confirmed using two sets of homozygous lines and seven F₂ segregating populations derived from two residual heterozygous lines.Obertained recombinated plants laid the foundation for furture fine-mapping and gene cloning.