Morpho-Physiological Responses of Sunflower Seedlings to Salinity Stress under Hydroponic Conditions

Abstract Salinity stress is a major constraint limiting crop productivity by disrupting plant growth, physiological processes, and ionic balance, particularly at the seedling stage. Limited information is available on the integrated morpho-physiological and ionic responses of sunflower genotypes under controlled hydroponic salinity conditions. This study evaluated the growth, biomass, physiological, and ionic responses of ten sunflower (Helianthus annuus L.) genotypes exposed to four salinity levels (T1: control, T2: 3 dS m–1, T3: 4.5 dS m–1, and T4: 6 dS m–1) under hydroponic conditions. A completely randomized design with factorial arrangement and three replications was used. Seedlings were grown in half-strength Hoagland solution, and salinity stress was applied gradually using NaCl. Growth traits (root and shoot length, root-to-shoot ratio), biomass attributes (fresh and dry weights), physiological parameters (photosynthesis, transpiration, stomatal conductance, and relative water content), and ionic traits (Na+, K+, and Na+/K+ ratio) were recorded. A composite stress–performance index was also calculated to rank genotypes. Salinity significantly reduced growth, biomass, physiological traits, and K+ concentration, while Na+ accumulation and Na+/K+ ratio increased progressively with increasing salinity, with significant genotype × treatment interactions. ORP-7 showed superior root and shoot growth under control conditions, while ARMONI maintained higher root length, relative water content, and K+ levels under severe stress. PARSUN-3 exhibited comparatively higher photosynthetic rate and root-to-shoot ratio under stress, whereas T-40318 maintained higher shoot length and biomass under higher salinity levels. A-67 showed relatively stable stomatal conductance across treatments. In contrast, ORP-5 and A-415 exhibited greater reductions in growth, biomass, and K+ content along with higher Na+/K+ ratios under stress conditions. The composite index identified ARMONI, A-67, and ORP-7 as the most tolerant genotypes, whereas ORP-5 was the most susceptible. These findings demonstrate substantial genotypic variation in salinity tolerance associated with growth performance, physiological stability, and ionic regulation, and highlight the effectiveness of hydroponic screening for identifying resilient sunflower germplasm for breeding programs.