Bulb-Priming Followed by Foliar Magnetite Nanoparticle Applications Improve Growth, Bulb Yield, Antioxidant...

Shallot (Allium hirtifolium Boiss.) is of considerable nutritional and medical significance due to its strong antioxidant properties; however, no nanophytotoxicity studies have assessed whether the use of nanofertilizers would improve shallot performance, micronutrient iron (Fe) enrichment, and yield in semi-arid regions. Herein, we evaluated the effects of magnetite nanoparticles (nFe₃O₄) on shallot grown for a full lifecycle in two semi-arid regions through bulb-priming followed by foliar application and compared them with conventional ferrous sulfate (FeSO₄) fertilizer and untreated control. Our results showed remarkable cellular adaptations to semi-arid climate upon nFe₃O₄ treatment as leaves displayed thickened cell walls, distinct chloroplasts featuring organized thylakoid grana and stroma, normal mitochondria, abundant starch grains, and plastoglobuli around chloroplasts compared to FeSO₄ or untreated control. At 900 mg/L nFe₃O₄, chlorophyll-a, chlorophyll-b, and carotenoid increased by 27-55%, 108-126%, and 77-97%, respectively, compared to FeSO₄ applied at recommended field rate (1800 mg/L). Significant increments in bulb diameter (38-39%) and sister bulb number (300-500%) were observed upon 900 mg/L nFe₃O₄ treatment compared to FeSO₄ (1800 mg/L) and control. Furthermore, with 900 mg/L nFe₃O₄ treatment, total phenol, flavonoids, and Fe in bulbs increased by 27-46%, 29-73%, and 486-549%, respectively, compared to FeSO₄ (1800 mg/L). These findings demonstrate that bulb-priming followed by foliar application of 900 mg/L of nFe₃O₄ could significantly promote cellular adaptation, thereby improving photosynthetic efficiency, bulb yield, antioxidant activities, and Fe biofortification in shallot, and may serve as a novel approach for improving shallot production in semi-arid regions.