Mining Favorable Alleles of QTLs Conferring Thousand-Grain Weight from Synthetic Wheat

The aim of this study was to mine favorable alleles of QTLs conferring thousand-grain weight (TGW) from synthetic wheat using advanced backcross QTL analysis. A BC5 F2:3 population consisting of 85 lines were generated from a cross between Laizhou 953, a Chinese commercial wheat variety, and Am3, a synthetic hexaploid wheat, followed by backcrossing with Laizhou 953 as recurrent parent and then by selfing. A total of 348 polymorphic SSR markers were employed for genotyping. Using composite interval mapping (CIM), 3 major QTLs, QGw.caas-1A, QGw.caas-3D, and QGw.caas-4B, with alleles increasing TGW from Am3, were detected in at least 2 environments, explaining phenotypic variation ranging from 10.9% to 33.79%. The Am3 alleles at the 3 loci increased TGW by 2.3–4.8 g without decreasing grain number and spike number and, 2 of them, without increasing plant height. Using mixed-model composite interval mapping (MCIM), QTL QGw.caas-3D was detected and the QTL-by-environment interaction was not significant, indicating that QGw.caas-3D was insensitive to environmental factors. QGw.caas-3D might be a stable and major QTL for TGW.