Genome-wide association study revealed the reason for the decrease in grain iron concentration during wheat breeding process in China

Iron (Fe) deficiency affects over two billion people worldwide. Developing high -yielding wheat (Triticum aestivum L.) cultivars with high grain Fe concentration (GFeC) is a key step toward alleviating malnutrition in humans. In this study, we used a diversity panel of 388 wheat accessions to examine the GFeC in four field environments. We found that the mean GFeC of the four environments decreased with the release year. And GFeC showed poor correlation with grain yield or the three yield factors in the four environments. Importantly, wheat cultivars in the major wheat -producing region of China showed the lowest GFeC. The GFeC phenotype was used for a genome-wide association study (GWAS) using a 660 K single -nucleotide polymorphism (SNP) chip, and 17 quantitative trait loci (QTLs) were identified on chromosomes 3B, 4 A, 5 A, 6B, 6D, 7 A, 7B, and 7D. However, no universal QTLs were detected among the 17 identified QTLs and 2280 yield -related QTLs. Through allelic analysis, two homologous genes, TraesCS7A01G197400 and TraesCS7D01G198900, were identified as potential candidate genes for GFeC, while the favourable alleles for GFeC were lost during the selection breeding process in China. The insights gained from this study showed that the yield dilution effect was not applied to the decrease in GFeC, which should be mainly caused by the loss of favourable alleles during the wheat breeding process in China. Therefore, wheat breeders should pay more attention to other traits to improve GFeC rather than the yield dilution effect.