Seed- and Foliar-Applied Iron Chelate Improves Performance, Physiological, and Biochemical Aspects of Black Cumin (Nigella sativa) under Semi-Arid Conditions

The cultivation of medicinal plants plays a crucial role in promoting human health benefits. However, the production of these plants can be affected by drought conditions. This research aimed to investigate the impact of differing water status (non-drought and drought during the flowering to harvest stage) and various iron treatments on the performance of black cumin. The iron treatments included no iron as the control (nFe), no iron with seed hydro-priming (nFe + P), seed iron priming (pFe), seed iron priming with iron foliar spraying (pFe + sFe), and double iron foliar spraying (sFe + sFe). The purpose of these treatments was to assess the effect of iron application methods on plant response under different water conditions. The findings revealed that drought significantly reduced the levels of Chla (15%) and RWC (5.9%), plant height (7%), follicle number (16.7%), seed number (4.6%), 1000-seed weight (3.2%), and seed yield (30.1%). Additionally, drought increased the proline content (90.9%), electrolyte leakage (9.2%), and MDA levels (23.9%). Interestingly, applying iron amendments reduced electrolyte leakage and increased seed yield under both water conditions. The drought-induced increase in proline content was more pronounced in the nFe treatment than in the other treatments. The amount of MDA in the nFe and nFe + P treatments was significantly higher under drought conditions compared to non-drought conditions. In conclusion, the addition of iron amendments helps black cumin plants recover from the effects of drought and reduces damage to seed growth. This means that using both seed iron priming and iron foliar spraying can significantly improve yields. Alternatively, focusing on either seed iron priming or double iron foliar spraying can also boost black cumin production compared to not using iron amendments.