Zhou 8425B is one of the most important founder parents in China and Xiaoyan 81 is an elite cultivar with high yield and good quality. Thousand-grain weight (TGW) is an important factor that affects wheat yield. Identification of QTL associated with grain related traits from Zhou 8425B and Xiaoyan 81, and haplotype analysis of these QTL in wheat cultivars from different ecological regions would be beneficial for yield improvement by molecular marker-assisted selection.

In this study, a RIL population (F₈) derived from Zhou 8425B × Xiaoyan 81 was planted in Yangling during 2015 and 2016 cropping seasons to evaluate grain related traits. Using a high-density genetic map constructed by 90K SNP markers, QTL mapping of thousand-grain weight, grain length, grain width and thickness was performed under three environments. Simultaneously, the KASP markers linked to the identified QTL were developed and molecular detection was carried out among 479 wheat accessions worldwide. Moreover, haplotype analysis of target QTL was performed in 106 current wheat commercial cultivars from Yellow and Huai River Valley Winter Wheat Region selected from 479 wheat accessions.

A total of 22 QTL on 8 chromosomes were detected, and the phenotypic variation explanation (PVE) ranged from 4.77% to 19.95%. Among them, 12 QTL are major QTL (PVE>10%) and Qkgw.nwafu-6B is a new QTL. QTL on chromosomes 4A, 6A, 6B, and 7D were detected in multiple environments, of which, the QTL on chromosomes 4A and 7D are same as previously reported ones. Compared to TaGW2-6A using molecular detection, both Zhou 8425B and Xiaoyan 81 carried the same allele of TaGW2. Based on haplotype result of Qkgw.nwafu-6A, Zhou 8425B and Xiaoyan 81 were placed in different groups. Therefore, Qkgw.nwafu-6A tends to be a new one. Haplotype analysis showed that there were five haplotypes for Qkgw.nwafu-6A and there were eight haplotypes for Qkgw.nwafu-6B. 6A_h1 and 6B_h6 accounted for over 20% in different ecological regions. In addition, a co-segregated KASP marker was developed for Qkgw.nwafu-6B and was significantly associated with the grain weight in the 479 wheat accessions.

Qkgw.nwafu-6A and Qkgw.nwafu-6B are possible new QTL associated with thousand-grain-weight, and 6A_h1 and 6B_h6 are likely favorable haplotypes. A molecular marker KASP_IWA349 co-segregated with Qkgw.nwafu-6B was developed and will be useful for marker assisted selection.