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

backgroundSoil salinity disrupts several physiological, biochemical, and metabolic processes essential for onion growth and development. MATERIALS AND

methodsA pot experiment was conducted to examine the effect of salinity (0.12, 0.5, 0.85, 1.85, 3.55, and 5.0 dS m⁻¹) on plant growth, physiological traits, biochemical properties, ionic balance, and bulb formation of four onion genotypes grown in clay loam soils during the winter season at ICAR-DOGR, Pune.

resultssalinity 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.