Zinc biofortification and yield enhancement in rice with nano- primed seeds and foliar sprays

Zinc deficiency in rice, a staple food consumed by more than half of the world's population, poses a major challenge to food safety and nutrition. In this study, the application of biosynthesized zinc oxide nanoparticles (ZnO NPs) was investigated as a sustainable strategy to solve this problem. The laboratory experiment on seed priming was conducted with four concentrations of ZnO nanoparticles (25, 50, 75 and 100 ppm) over three soaking times (12, 18 and 24 h). The priming of 25 ppm ZnO nanoparticles (NP) over a 24-hour period resulted in the highest germination and best growth of the rice seedlings, as evidenced by increased shoot and seedling length and improved overall seedling vigor. The optimized priming treatment (25 ppm ZnO NPs for 24 h), combined with a foliar spray of 100 ppm ZnO NPs applied at the panicle emergence and grain filling stage, was evaluated under field conditions for its effects on plant growth, yield and zinc content in rice. Field trials showed that this integrated approach significantly increased grain yield, straw yield and zinc accumulation in both the grains and straw compared to conventional methods. Biochemical analyzes showed an increase in chlorophyll content, total protein content and antioxidant enzyme activities (SOD, CAT and POX), all of which correlated with improved plant development. Phytohormone profiling showed increased levels of gibberellic acid (GA₃), indoleacetic acid (IAA) and salicylic acid (SA), which contributed to improved vegetative and reproductive performance. In addition, the expression of key zinc transporter genes (OsZIP1.1, OsZIP3, OsNAAT1 and OsYSL14) was significantly modulated in root and flag leaf tissue, indicating improved zinc uptake, translocation and accumulation in the grain. This study highlights the potential of biogenic ZnO NPs as a sustainable and cost-effective strategy for the biofortification of zinc in rice. It offers a novel solution to combat micronutrient deficiencies while improving plant productivity and nutritional quality.