Genetic insights into the synergistic effects of nano-iron on yield, quality, and antioxidant defense in barley under salt stress.

Salt stress adversely impacts crop growth and development, resulting in stunted growth and diminished grain yield. Therefore, this study explores the synergetic effects of seed priming with iron nanoparticles (FeNPs) integrated with a genome-wide association study (GWAS) on the phenotypic, biochemical, and agronomic traits of 138 barley accessions under control, salinity stress, and seed iron priming treatments. A normal phenotypic distribution was observed across all accessions under the tested conditions, with significant natural phenotypic variation in response to the treatments. Remarkably, seed priming with FeNPs showed a significant enhancement in superoxide dismutase (SOD) activity and selective modulation of catalase (CAT) and glutathione reductase (GR) activities, indicating a targeted oxidative stress response. Compared to control and salinity stress conditions, priming with FeNPs showed substantial increases in all agronomic traits, including spike length (SL), number of spikelets per spike (NSS), number of grains per spike (NGS), weight of grains per spike (WGS), and thousand kernel weight (TKW), suggesting its potential to mitigate the adverse effects of salinity and promote better crop performance. Based on GWAS analysis, sixteen highly significant marker associations/candidate genes were detected to be associated with antioxidant components. Using quantitative real-time PCR analysis (RT-qPCR), FeNPs seed priming effectively modulates the plant's transcriptional response to salinity stress by balancing rapid gene activation with sustained stress adaptation. This approach mitigates excessive defense responses while promoting long-term stability through controlled upregulation of key genes, such as PP2C, Phosphotransferase, Terpene Synthase Putative, and RWP-RK. The findings support the potential of FeNPs as a biotechnological tool to enhance crop resilience and optimize agronomic performance under adverse environmental conditions.