Effect of grafting on different rootstocks on yield, quality and biochemical content of eggplant under salt stress and alkaline conditions

This study was conducted in a greenhouse under soilless conditions between April 15 and December 1, 2025, to determine the effects of grafting on eggplant under salt and alkaline stress conditions. Eight different eggplant rootstocks (AG38R F₁, AGR 703 F₁, Boğaç F₁, Kingkong F₁, Hercules, Hikyaku F₁, Yula F₁, and Hawk) and the commercial cultivar Anamur RZ F₁ were used as plant material in the experiment. Non-grafted and self-grafted plants were evaluated as control groups. In the salt stress experiment, 25 and 50 mM NaCl doses were used in addition to the control treatment (0 mM NaCl). In the alkaline stress experiment, a pH level of 8.1 was tested alongside the control treatment (pH 6.5). NaCl (99% purity) and NaHCO₃ (99% purity) were used to induce salt and alkaline conditions, respectively. Both trial were established in a randomized split-plot design with three replications. During the experiment, plants were supplied with a modified Hoagland nutrient solution. Parameters assessed included such as plant height, stem diameter, biomass, leaf chlorophyl index (SPAD), physiological disorders, macro and micronutrient contents, antioxidant enzyme activities (SOD, CAT, APX), MDA, H₂O₂, and proline levels. Salt stress significantly reduced marketable yield, decreasing from 192.16 t/ha under control conditions to 130.67 and 95.69 t/ha under 25 and 50 mM NaCl, respectively. A similar trend was observed in early yield. Fruit weight, stem diameter, plant height, and biomass also decreased due to salt stress with plant biomass declining from 34.48 kg/plant (control) to 20.07 kg/plant under 50 mM NaCl. Additionally, some rootstocks better maintained chlorophyll content and quality parameters. Plant height decreased from 4.66 m to 3.32 m under salt stress, and the SPAD values ranged between 53.97 and 55.54. Salt stress significantly increased antioxidant enzyme activities in eggplant leaves: SOD rose from 130.35 U/g to 365.35 U/g (180% increase), CAT from 278.91 µM to 537.73 µM (92.7% increase), and APX from 3.62 µM/min/mg to 6.68 µM/min/mg (84.6% increase). MDA increased from 4.34 µM/g to 10.69 µM/g. While salt stress significantly reduced the uptake of macro and micronutrients, grafting largely mitigated this effect. Sodium accumulation increased under salt stress, but was restricted in grafted plants. Stress conditions also led to notable physiological disorders, resulting in significant quality losses and yield reductions. Alkaline stress also caused substantial reductions in marketable yield, decreasing from 215.21 t/ha (control) to an average of 158.22 t/ha under alkaline conditions (a 26% reduction). A 54% decline in early yield, 28% reduction in fruit number, and 9.6% decrease in fruit weight were recorded. Plant height decreased by 16.5% to 4.03 m, and stem diameter and biomass decreased by 14.2% and 26.5%, respectively. Biomass declined from 33.30 kg/plant (control) to 24.49 kg/plant under alkaline conditions. Alkaline stress activated antioxidant defense systems in eggplant leaves, increasing SOD activity by 119.1%, CAT by 67.4%, and APX by over 70%. MDA content increased by 79.7%, proline by 127.2%, and H₂O₂ by 71.2%, indicating elevated oxidative stress. The uptake of macro nutrients (P, K, Ca, Mg) and micronutrients (Fe, Cu, Zn, B, Mn) was significantly reduced under alkaline stress. However, grafting mitigated these reductions, reduced Na accumulation in leaves, and stabilized K/Na and Ca/Na ratios. Alkaline stress also increased physiological disorders such as skin discoloration, blistering, seeded fruit formation, and blossom-end rot, with incidence rising from 4–5% to 9–12%. Grafting was effective in reducing the severity of these disorders and limiting quality losses. The study showed that salt and alkaline stresses significantly reduced growth parameters of rootstocks Under salt stress, plant height, stem diameter, and biomass decreased by 30%, 25%, and 35%, respectively, while similar suppressive effects were observed under alkaline stress. Some rootstocks experienced 15–20% fewer losses under stress, while sensitive rootstocks exhibited losses up to 40%. Potassium and phosphorus uptake decreased by 20–30%, whereas tolerant rootstocks limited these losses to 10–15%. A similar trend was observed for micronutrients; under salt stress, Fe content decreased by 35.1%, Cu by 27.8%, Zn by 39.8%, and B by 27.3%. Alkaline stress caused similar reductions. Under stress conditions, proline content in rootstock leaves increased by 142% (salt) and 105% (alkaline). Similarly, H₂O₂ levels increased by 157% and MDA accumulation by 171%. Antioxidant defense systems were activated under stress, with increases of 213% in SOD, 85% in CAT, and 100% in APX activities. While salt and alkaline stresses caused losses in all evaluated parameters, these losses were significantly reduced by grafting. In particular, rootstocks derived from S. torvum, such as Hawk and Hercules, as well as Boğaç F₁ and AG38R F₁, provided substantial protection against salt and alkaline stress. The tomato rootstock KingKong F₁ was ineffective due to graft incompatibility, and Yula F₁ was identified as the weakest rootstock. Non-grafted and self-grafted plants, as well as KingKong F₁ and Yula F₁, were among the least effective treatments. In conclusion, this study demonstrated that salt and alkaline stress cause significant reductions in growth, yield, physiological, and biochemical parameters in eggplant. However, grafting onto tolerant rootstocks was found to be an effective strategy to mitigate these negative effects and enhance tolerance to salt and alkaline stress.