Green synthesis and characterization of selenium nanoparticles: preliminary compatibility assessment with beneficial rhizobacteria and their role in enhancing aggregatum onion (Allium cepa L. var. aggregatum) seed germination under salinity stress.

The era of nanotechnology has presented a new window of opportunity for sustainable agriculture, and the contribution of nanoparticles (NPs) to stress alleviation of abiotic stresses, with their exceptional physicochemical properties in the biological domain, has been the actual focus of researchers. Selenium nanoparticles (SeNPs) provide a promising nano-based solution to enhancing the delivery of selenium and the early development of plants in agriculture. In this work, the selenium nanoparticles were synthesized using the green synthesis technique with plant leaf extracts of guava and sapota, and thoroughly characterized to verify the physicochemical characteristics. The presence of selenium nanoparticles was confirmed by UV-Visible spectroscopy, and the role of plant-derived phytochemicals in the reduction and stabilization of nanoparticles was identified by FTIR. The amorphous form of the synthesized SeNPs was determined by X-ray diffraction analysis and scanning electron microscopy revealed that the nanoparticles were mostly spherical. Elemental analysis using EDAX confirmed the presence of selenium and thermogravimetric analysis revealed that the nanoparticles were thermally stable. One of the most important abiotic factors which severely limits development and production of aggregatum onion is salinity. However, the responses of plants to selenium nanoparticles under salt stress during seed germination have not been studied in detail. This study focuses on the effect of nanopriming on germination processes by using selenium nanoparticles (SeNPs) in different concentrations on salinity stress during the early seedling stage of germination of aggregatum onion. Nanopriming enhanced the final germination percentage, germination rate, speed of germination, seedling growth, seedling vigor, biomass accumulation, and antioxidant enzyme activity of aggregatum onion under salt stress. The highest germination percentage (93.3%) and superior seedling vigor were recorded at 50 ppm SeNP treatment. The results demonstrated that the use of SeNPs could be a new strategy and helpful approach to improve salinity tolerance in small onion crops.