Dynamic Responses of Cherry Tomatoes to Salinity Stress: Growth, SPAD, Sap Ion Regulation and Leachate Chemical Composition Across Developmental Stages

Tomato production is highly affected by salt stress conditions, especially under protected cultivation systems using low-quality irrigation water. This study assessed the effects of increasing electrical conductivity (EC) levels of the nutrient solution (2, 4, 6, and 8 dS m−1) on growth, biomass distribution, RGB-based spectral indices, physiological traits, petiole sap composition, and leachate chemistry in tomato plants (Solanum lycopersicum cv. Tiny Tim) cultivated in containers within a bamboo nethouse under tropical conditions. The results obtained reported that increasing salinity significantly reduced fresh and dry biomass (61.72 and 61.55% respectively) across all plant organs, with fruits showing the highest sensitivity. Leaf area index (LAI), SPAD values, leaf nitrogen (N) concentration, leaf relative humidity (LRH), and water uptake also declined progressively under saline conditions. In contrast, root and leaf biomass allocation increased under the highest salinity level. Spectral analyses reported reductions in red and blue RGB components and normalized red and blue index values, while normalized green index increased under higher salinity levels. Petiole sap analysis showed a progressive accumulation of sodium (Na+) and chloride (Cl−) together with reductions in nitrate (NO3−-N) and potassium (K+) concentrations, particularly during the reproductive stage. In contrast, °Brix, calcium (Ca2+), and phosphorus (P) concentrations increased under salinity, particularly during the reproductive stage. Leachate analyses confirmed salt accumulation in the substrate and reduced plant water uptake. Overall, petiole sap analysis and RGB-based spectral indices provide a rapid, non-destructive, and cost-effective tool for the early detection of salinity stress in tomato, enabling timely irrigation and fertigation adjustments to improve crop performance and resource-use efficiency under saline conditions.