<i>Haematococcus pluvialis</i> bionanoparticles boost maize seedling health, serving as a sustainable seed priming agent and biostimulant for agriculture

The rising frequency of extreme climate events requires sustainable strategies to secure food production. Environmental stress impacts seed germination and seedling development, posing a significant agricultural challenge. To address this, we developed and applied iron-based nanoparticles (Bio-NPs) synthesized through green biosynthesis from Haematococcus pluvialis, a microalga rich in antioxidants like astaxanthin. These Bio-NPs, approximately 21 nm in diameter and characterized by a negative surface charge, were used as priming agents for maize seeds. Their effects on physiological traits were analyzed with multispectral imaging, showing enhanced normalized difference vegetation index (NDVI) and chlorophyll levels in maize seedlings, highlighting Bio-NPs as effective biostimulants. Among the tested concentrations, 6 mM Bio-NPs yielded the most substantial improvements in seedling health compared to unprimed and hydro-primed groups. Importantly, in vitro studies confirmed that Bio-NPs had no harmful effects on beneficial bacteria and fungi of agronomic importance, underscoring their safety. Although the exact biological pathways responsible for these enhancements are yet to be fully understood, further research into plant responses to Bio-NPs could yield new insights into plant biostimulation. Bio-NPs thus hold promises for strengthening seedling resilience under extreme environmental scenarios, currently observed due to global climate change, offering a safe, sustainable approach to agricultural enhancement. By leveraging microalgae-based biostimulants, this work advances seed priming technology, fostering crop resilience and supporting environmentally friendly agricultural practices.