Combining agronomic biofortification with a Zn-efficient wheat line synergistically increases grain Zn concentrations with varied effects on Cd in wheat grains

(Background and aims) Wheat grains are often too low in zinc (Zn) compared to human dietary needs, and are a major dietary source of highly toxic cadmium (Cd). Biofortification strategies can increase Zn in edible grain, but must not increase grain Cd. (Methods) We investigated the individual and combined effects of genetic and agronomic biofortification on Zn and Cd in wheat grains. Non-transgenic Bobwhite (BW-NT) and an OsNAS2-expressing line (BW-NAS) were grown in a pot experiment with isotope-labeled mineral Zn (70Zn) and green manure (70Zn, 106Cd). At flowering and maturity, Zn and Cd were quantified in wheat biomass. Wheat contents of Zn and Cd derived from inputs versus soil were determined using stable isotope analyses. (Results) Individually, the OsNAS2-expressing wheat and input application increased grain Zn. Combined OsNAS2 expression and input application led to grain concentrations of 76{+/-}4 mg kg-1 with mineral Zn application and 61{+/-}7 mg kg-1 with green manure. This was 154-217% higher than the 24{+/-}1 mg kg-1 observed in the BW-NT control and significantly higher than the additive effects of each strategy individually. The OsNAS2-expressing line increased grain Cd to 0.214{+/-}0.002 mg kg-1 under green manure, compared to 0.12{+/-}0.01 mg kg-1 in the BW-NT control. No other treatment increased grain Cd. (Conclusions) Our results encourage development of integrated genetic and agronomic biofortification strategies to increase grain Zn. They also underscore the need for careful monitoring of grain Cd concentrations when organic amendments are paired with genetic biofortification strategies.