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

Seven stable QTLs for TGW, GW and GL were identified, and two major QTLs were stable in various genetic backgrounds and environments. 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 55 K 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-5 A.1 were novel, and QTgw/Gw.CK4-cib-6 A and QGl.CK4-cib-5 A.1 were major QTLs explaining more than 10% of the phenotypic variances. The effects of QTgw/Gw.CK4-cib-6 A and QGl.CK4-cib-5 A.1 on corresponding traits were further validated in different populations by developing the Kompetitive Allele-Specific PCR marker. QTgw/Gw.CK4-cib-6 A significantly increased TGW while reducing grain number per spike (GNS). Interestingly, the other QTLs for grain size, QGw.CK4-cib-2D, QGl.CK4-cib-5 A.1 and QGl.CK4-cib-5 A.2, showed a significant increase in TGW, but did not affect GNS. Moreover, the polymerization of QGw.CK4-cib-2D, QGl.CK4-cib-5 A.1 and QGl.CK4-cib-5 A.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-5 A.1. Taken together, the present results lay a foundation for subsequent map-based cloning of these QTL and their utilization in wheat breeding.