Salinity stress induced changes in onion genotypes: biochemical and physiological traits, ion homeostasis, and bulb formation

salinity levels at 0.5 and 0.85 dS m⁻¹ increased plant height, maintained leaf number, leaf area index, and dry matter accumulation of Bhima Shakti and Bhima Red, leading to a slight increase in bulb yield (1.3% ;1.8% respectively) at 0.5 dS m⁻¹, while a decline in yield (2.1% ;2.2% respectively) was observed at 0.85 dS m⁻¹. In contrast, Bhima Shweta and Bhima Kiran exhibited significant reductions in these parameters, resulting in 11.4% and 19.0% lower bulb yields respectively compared to the control. In addition, higher salinity levels at 1.85, 3.55, and 5.0 dS m⁻¹ significantly declined plant growth, chlorophyll content, membrane stability index, relative water content, protein levels, and nutrient concentrations, with reductions of over 30% at 1.85 dS m⁻¹ for all the parameters. Additionally, increased Na⁺ and Cl⁻ accumulation disturbed nutrient balance both in bulbs and leaves, raising Na⁺/K⁺, Na⁺/Ca²⁺, Na⁺/Mg²⁺, Cl⁻/N, Cl⁻/P, and Cl⁻/SO₄ ratios. Antioxidant activity, total phenolics, and pyruvic acid concentrations increased with salinity up to 5.0 dS m⁻¹ across all genotypes, while protein concentrations decreased at higher salinity levels. The study indicated that Bhima Shakti and Bhima Red showed better growth and yield under mild salinity conditions (0.5-0.85 dS m⁻¹), while Bhima Shweta and Bhima Kiran were highly sensitive to salinity stress in clay loam soils. Overall, identifying genotypes that can tolerate salinity up to 1.85 dS m⁻¹ could help expand onion cultivation in saline regions, boosting agricultural productivity in marginal lands.