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Abstract
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Background Dracocephalum kotschyi Boiss., a perennial medicinal and aromatic plant endemic to Iran, is renowned for its diverse biological and medicinal properties. This study aimed to evaluate the influence of foliar application of selenium nanoparticles (SeNPs) and sodium selenite (SSe) on the growth, yield, physiological and biochemical characteristics, and essential oil (EO) of D. kotschyi. The experiment included seven treatments: a control (distilled water) and a foliar spray of 50, 100, and 200 mg L−1 of both SeNPs and SSe separately. Results SeNPs were more effective than SSe in improving plant growth and yield. Specifically, a 200 mg L−1 SeNPs treatment led to the highest plant height, fresh weight of the plant, dry weight of the leaf, and relative water content. Elevated Se concentrations were associated with a decrease in chlorophyll levels. Both SeNPs and SSe treatments increased hydrogen peroxide levels, and catalase and ascorbate peroxidase activity. The phenylalanine ammonia-lyase activity increased with SeNPs up to 50 mg L−1 and SSe up to 100 mg L−1. Application of 200 mg L−1 SSe resulted in the highest total phenol content and antioxidant activity. Although spraying 100 mg L−1 SeNPs led to the highest EO content, the EO yield peaked with 200 mg L−1 SeNPs. Notably, applying 200 mg L−1 SeNPs reduced the level of neral, while 200 mg L−1 SSe decreased both geranial and neral levels. Conversely, levels of α-pinene and geranyl acetate increased with Se application. Conclusions The results revealed that SeNPs were more effective than the SSe in improving plant growth and yield. Overall, the 200 mg L−1 SeNPs treatment was the most effective in improving the growth, yield attributes, and EO yield of D. kotschyi
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