Selenium nanoparticles from Dermacoccus abyssi MT1.1ᵀ improve water status, biomass, and antioxidant defense in tomato under salt stress

Salt stress severely limits plant growth and agricultural productivity. Nanoparticles have emerged as a promising strategy to alleviate salinity stress. This study investigated the biogenic synthesis of selenium nanoparticles (SeNPs) using the culture supernatant of Dermacoccus abyssi MT1.1 T and evaluated their effects on tomato germination and seedling growth under salt stress. Successfully synthesized SeNPs were spherical, nanoscale, negatively charged, and moderately stable. Application of SeNPs at 5 mg mL −1 showed no phytotoxic effects on tomato germination under 50, 100, and 150 mM NaCl. Under 150 mM NaCl, SeNP-treated seedlings exhibited increased fresh and dry weights and enhanced accumulation of proline and total soluble sugars, leading to improved relative water content. Furthermore, SeNPs alleviated salt-induced oxidative stress by reducing hydrogen peroxide levels and enhancing antioxidant enzymes, including catalase and guaiacol peroxidase. These findings highlight biogenic SeNPs from D. abyssi MT1.1 T as a potential eco-friendly nanobiostimulant for improving tomato salt tolerance.