Zinc biofortification of hydroponic mustard microgreens grown under different red and blue LED lighting ratios

Zinc (Zn) is important for different metabolic processes of the human body and controls different enzymatic processes, which are responsible for good human health. Zn deficiency in soil and plants and its low nutritional status in the population encourage studies on enrichment of agricultural products. Thus, the objective of this study was to evaluate the Zn doses applied to the hydroponic solution and to increase the concentration of this element in the microgreen of mustard (Brassica juncea ‘Red Lace’), depending on different blue–red (B:R) light ratios in light-emitting diode (LED) lighting. Mustards were grown hydroponically in controlled environment growth chambers under different B:R light ratios - 10%B:90%R, 75%B:25%R 10 days after sowing. A 220 µmol m^-2 s^-1 total photon flux density (TPFD), 18 h photoperiod, 21/17 ± 2 ºC temperature and 60% ± 5% relative humidity in the growth chamber were maintained during cultivation. The results showed that the Zn content in mustard increased with increasing Zn dose in hydroponic solution. The B:R ratio at 75%:25% resulted in higher Zn content in mustard compared to 10%B:90%R. Also, there was a tendency for higher Zn translocation factor at a higher percentage of B LED lighting. However, the higher percentage of B light and the increasing concentration of Zn in the solution, reduced the hypocotyl length and leaf area of mustard microgreens. The opposite results were obtained for mustards grown under 10%B:90%R lighting and increasing Zn in solution. The results suggest that the addition of Zn in a hydroponic solution and adapted LED lighting could be a suitable way for the cultivation of Zn-biofortified mustard microgreens. Acknowledgements: This project has received funding from the Research Council of Lithuania (LMTLT), agreement No. S-MIP-19-2.