The quality of wheat grain was an important factor affecting the processing quality and nutritional. Mining loci and candidate genes significantly associated with wheat grain quality traits provided a basis for broadening the understanding of the genetic mechanism of quality traits and molecular marker-assisted quality.

By measuring five quality traits, including protein content (GPC), wet gluten content (WGC), starch content (GSC), settling value (SV) and grain hardness (GH), in 259 winter wheat varieties (lines) from domestic and abroad, and conducting genome-wide association analysis in combination with 90K SNP chip, the significant association loci located were subjected to haplotype analysis.

All five traits conformed to normal distribution and showed rich variation among different environments, and the coefficient of variation of sedimentation value was the largest (20.11%-24.42%). All traits have shown highly significant differences (P<0.001) among genotype, environment, and genotype×environment, with a broad-sense heritability of 0.77-0.84. A total of 44 loci significantly associated (P<0.001) with five traits were detected by genome-wide association analysis, distributed in 19 linkage groups other than chromosomes 1D and 3D. Eighteen loci were stable in two or more environments, involving all five traits including protein content (12), wet gluten content (9), starch content (11), sedimentation value (12) and grain hardness (7), explaining 4.27%-10.98% of the genetic variation. Thirteen of them were multi-effect loci, with the largest number of multi-effect loci (7) associated with traits such as protein content, wet gluten content, settling value and starch content. The GENE-0762_631, IAAV7742 and RAC875_c66845_466 loci located on 2B, 2D and 3A chromosomes were detected simultaneously at two environmental and BLUP values with a range of 4.32%-7.07% phenotypic contribution. Through haplotype analysis of multi-effect loci present in multiple environments with high phenotypic contribution, four different haplotypes, Hap1, Hap2, Hap3 and Hap4, which were significantly associated with traits such as protein content, sedimentation value and starch content, were uncovered at the D_GDS7LZN02F4FP5_176 locus of chromosome 5D, among them Hap1 was a high starch content haplotype (P<0.001), while Hap2 and Hap3 were both haplotypes with high protein content and sedimentation value (P<0.05), and the four haplotypes accounted for 74.22%, 16.21%, 6.92% and 2.65%, respectively. The distribution frequencies of haplotypes from different sources of winter wheat were analyzed, in which the distribution frequencies of haplotype Hap2 with high protein content and sedimentation value were from high to low in the Huanghuai winter wheat regions>northern winter wheat region>abroad varieties>middle and lower reaches of the Yangtze River winter wheat region>southwest winter wheat region. Candidate genes were mined for stable genetic loci, and 10 candidate genes that might be related to wheat grain quality were screened.

In the study, 18 stable loci significantly associated with grain quality traits were detected, 4 different haplotypes were identified, and 10 candidate genes related to grain quality were screened.