Genetic identification and characterization of quantitative trait loci for wheat grain size-related traits independent of grain number per spike

Thousand-grain weight (TGW), mainly determined by grain length (GL) and width (GW), is an important yield component of wheat. In the study, combined with phenotyping in four field trials and a high-quality genetic map constructed with the Wheat 55K SNP array, a total of seven stable QTLs for TGW, GW and GL were identified in a doubled haploid (DH) population derived from the cross between Chuanmai 42 (CM42) and Kechengmai 4 (K4), in which QTgw.CK4-cib-3D , QGw.CK4-cib-2D and QGl.CK4-cib-5A.1 were novel, and QTgw/Gw.CK4-cib-6A and QGl.CK4-cib-5A.1 were major QTLs explaining more than 10% of the phenotypic variances. The effects of QTgw/Gw.CK4-cib-6A and QGl.CK4-cib-5A.1 on corresponding traitswere further validated in different populations by developing the Kompetitive Allele Specific PCR marker. QTgw/Gw.CK4-cib-6A significantly increased TGW while reducing GNS . Interestingly, the other QTLs for grain size, QGw.CK4-cib-2D , QGl.CK4-cib-5A.1 and QGl.CK4-cib-5A.2 , showed a significant increase in TGW, but did not affect GNS. Moreover, the polymerization of QGw.CK4-cib-2D , QGl.CK4-cib-5A.1 and QGl.CK4-cib-5A.2 had a significant addition effect on TGW without reducing GNS, suggesting that these QTLs can work together as an excellent molecular module to break the trade-off between GNS and TGW in wheat high-yield breeding. By analysis of expression, sequence and function annotation TraesCS5A02G001400, TraesCS5A02G002700 and TraesCS5A02G003400 were predicted as the candidate genes for QGl.CK4-cib-5A.1 . Taken together, the present results lay a foundation for subsequent map-based cloning of these QTL and their utilization in wheat breeding.