Wheat breeding in China over the past 80 years has increased grain zinc but decreased grain iron concentration

Abstract Breeding wheat with enhanced zinc (Zn) and iron (Fe) concentrations in the grain is a promising strategy for alleviating micronutrient malnutrition in humans. Elucidating trends of grain Zn and Fe concentrations with the breeding period may help to evaluate the progress in wheat breeding to date. A total of 292 wheat accessions, including 154 cultivars and 138 landraces, were used in this two-year field study to elucidate trends of grain Zn and Fe concentrations with the year of variety release from 1933 to 2017, and to identify grain Zn and Fe concentrations of wheat cultivars in comparison with Chinese landraces. Across all the data, mean grain Zn and Fe concentrations were 42.08 mg kg−1 with a range of 28.96–63.25 mg kg−1 and 39.73 mg kg−1 with a range of 25.53–66.98 mg kg−1, respectively. Chinese landraces and cultivars had similar grain Zn concentration, but grain Fe concentration was significantly higher in landraces than cultivars. Grain Zn and Fe concentrations in wheat cultivars released from 1933 to 2017 showed different trends with year of variety release. Grain Zn concentration increased through the breeding period, while grain Fe concentration decreased. Therefore we hypothesize that, beyond the yield dilution effect associated with increasing yield, intentional and directional selection for increased grain yield indirectly contributed to the differing trends for grain Fe and Zn concentrations. Consistent with this, the correlation was significantly negative between grain Fe concentration and harvest index, kernel weight, grain yield and biomass, while grain Zn concentration showed weak association with these traits. In this regard, our study highlights that wheat breeding in China over the past eighty years has increased grain Zn concentration, but at the same time, it has decreased grain Fe concentration.