Quantify the Requirements to Achieve Grain Zn Biofortification of High-yield Wheat on Calcareous Soils

Abstract

15The solution to address global human Zn deficiency is Zn biofortification of staple food crops, aimed 16 at high grain Zn concentration as well as high yield. However, the desired high grain Zn 17 concentration above 40 mg kg -1 is rarely observed for high-yield wheat on worldwide calcareous 18 soils, due to inadequate Zn uptake or Zn distribution to grain. The present study aims to investigate 19 how much Zn uptake or distribution is adequate to achieve the Zn.t of high-yield wheat on calcareous 20 soils with low available Zn (~ 0.5 mg kg -1 ). Of the 123 cultivars tested in a three-year field 21 experiment, 19 high-yield cultivars were identified with similar yields around 7.0 t ha -1 and various 22grain Zn concentrations from 9.3 to 26.7 mg kg -1 . The adequate Zn distribution to grain was defined 23 from the view of Zn biofortification, as the situation where the Zn distribution to grain (Zn harvest 24 index) increased to the observed maximum of ~ 91.0% and the Zn concentration of vegetative parts 25 (straw Zn concentration) decreased to the observed minimum of ~ 1.5 mg kg -1 (Zn.m). Under the 26 assumed condition of adequate Zn distribution to grain (~ 91.0%), all the extra Zn above Zn.m was 27 remobilized from straw to grain and the grain Zn concentration would be increased to its highest 28 attainable level, which was 14.5 ~ 31.3 mg kg -1 for the 19 high-yield cultivars but still lower than 40 29 mg kg -1 . Thus, even with the adequate Zn distribution to grain, the current Zn uptake is still not 30 adequate and needs to be increased to 308 g ha -1 or higher to achieve Zn.t for high-yield wheat (7.0 t 31 ha -1 ) on low-Zn calcareous soils. Besides, the established method here can also provide the priority 32 measures and quantitative guidelines to achieve Zn biofortification in other wheat production 33regions. 34