Effectiveness of Grafting in Enhancing Salinity Tolerance of Tomato (Solanum lycopersicum L.) Using Novel and Commercial Rootstocks in Soilless Systems

The scarcity of high-quality water in arid regions like Saudi Arabia necessitates saline water use in irrigation. Sustainable techniques, such as grafting and soilless cultivation, enhance crop resilience and optimize resource use, ensuring long-term agricultural and water sustainability to meet rising food demand. So, this study evaluated grafting’s effectiveness in enhancing the salt tolerance of tomato (Solanum lycopersicum L.) under soilless culture. The experiment tested two salinity levels, two growing media (volcanic rock and sand), and six grafting treatments: the scion ‘Tone Guitar F1’ was cultivated through non-grafting (G1), self-grafted onto itself (G2), and grafted onto the commercial rootstock ‘Maxifort F1’ (G3), which was grafted onto three newly developed rootstocks, namely X-218 (G4), X-238 (G5), and Alawamiya365 (G6). The results indicated that plants performed better at 2 dS m−1, while higher salinity (4 dS m−1) negatively impacted growth. However, grafting under saline stress improved most of the measured traits, excluding fruit quality (vitamin C, titratable acidity, and total soluble sugars). Grafted plants (G2–G6), particularly those grown in volcanic rock at 2 dS m−1, exhibited superior fruit characteristics, yield, water productivity, and leaf calcium (Ca2+) and potassium (K+) content compared to the non-grafted controls (G1). The sand medium generally produced lower values for all the traits, regardless of salinity or grafting. Moreover, grafting under 2 and 4 dS m−1 reduced leaf sodium (Na+) and chloride (Cl−). The best overall performance was provided by the rootstocks X-218 and X-238. Grafting onto salt-tolerant rootstocks is a promising strategy for improving tomato yield and water productivity under saline irrigation in arid and semi-arid regions.