# Bulb-Priming Followed by Foliar Magnetite Nanoparticle Applications Improve Growth, Bulb Yield, Antioxidant Activities, and Iron Fortification in Shallot in Semi-Arid Regions

## TL;DR

Using magnetite nanoparticles on shallots improves growth, yield, and iron content in semi-arid regions.

## Contribution

Demonstrates that magnetite nanoparticle treatment enhances shallot performance and iron fortification in semi-arid climates.

## Key findings

- nFe3O4 treatment increased chlorophyll and carotenoid levels significantly compared to conventional FeSO4.
- Bulb diameter and sister bulb number increased by 38–39% and 300–500%, respectively, with nFe3O4 treatment.
- Total phenol, flavonoids, and iron in bulbs increased by up to 73% and 549% with nFe3O4 compared to FeSO4.

## Abstract

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.