Green-synthesized copper nanoparticles enhance drought tolerance in wheat for sustainable biomass and industrial applications

Drought stress severely limits the growth, physiological performance, and yield of Triticum aestivum L. (wheat), particularly under water-limited conditions relevant to industrial and bioenergy applications. This study evaluated the potential of green-synthesized copper nanoparticles (CuNPs), produced using Syzygium aromaticum (L.) Merr. & L.M.Perry) (clove) extract, to enhance drought tolerance in four wheat varieties—Dharab-11, Watan-94, Faisalabad-2008, and Faisalabad-2010—selected based on contrasting stress sensitivity and germination performance. Copper nanoparticles with an average crystalline size of 23.6 nm were applied as foliar sprays at 10, 20, and 30 ppm, while drought stress was imposed at the grain-filling stage by withholding irrigation for 15 days, reducing soil moisture to approximately 40 % of field capacity. CuNP supplementation, particularly at 30 ppm, significantly improved growth, physiological, and biochemical traits under drought. Dharab-11 exhibited the tallest plants (87 cm), Watan-94 maintained the largest leaf area (52 cm²), and Watan-94 also produced the longest spikes (22.5 cm). Relative water content increased up to 94 %, while proline accumulation reached 0.78 µmol g⁻¹ fresh weight, reflecting enhanced osmotic adjustment. Total soluble sugars increased up to 0.96 µmol g⁻¹ fresh weight, supporting cellular turgor and metabolic stability under stress. Yield components, including spikelet number and 1,000-grain weight, were also positively influenced. These findings demonstrate that clove-extract-mediated CuNPs provide a novel, eco-friendly approach to mitigate drought-induced morphological, physiological, and biochemical impairments in wheat. Future field trials are recommended to validate scalability, assess nanoparticle persistence in soil, and evaluate potential phytotoxicity at higher concentrations.