Feasibility of Nano-Urea and PGPR on Salt Stress Amelioration in Reshmi Amaranth (Amaranthus tricolor): Stress Markers and Enzymatic Response

Abstract

The present experiment aimed to examine the impact of nano urea (NU) and plant growth-promoting rhizobacteria (PGPR) on Reshmi amaranth (Amaranthus tricolor) growth under salt stress. Experiments were conducted using six different combinations of NaCl, NU, and PGPR for 35 days under greenhouse conditions. The results showed that salinity stress significantly (p < 0.05) reduced plant growth parameters, including shoot height, root length, fresh weight, and leaf area. However, the application of NU and PGPR, both individually and in combination, enhanced plant growth and physiological resilience under saline conditions. The NU + PGPR treatment yielded the best improvements, with a shoot height of 42.25 cm, root length of 34.79 cm, and fresh weight of 61.69 g, indicating a synergistic effect. Biochemical analysis showed that NaCl stress lowered chlorophyll (0.25 mg/g fwt.) and carotenoids (60.17 µg/100 g) and disrupted ionic homeostasis by increasing Na⁺ accumulation while reducing K+ and Ca2+ uptake. The combined NU and PGPR treatment restored ionic balance, with Na⁺ reduced to 58.12 mg and K⁺ and Ca2+ levels increasing to 115.25 mg and 78.70 mg, respectively. Stress markers such as malondialdehyde (MDA) and proline also showed significant reductions, while antioxidant enzyme activities stabilized under NU and PGPR application. Thus, this study indicated that NU and PGPR mitigate salt-induced stress by improving nutrient assimilation, promoting osmotic regulation, and enhancing antioxidative defenses in Reshmi amaranth.