A multilevel trait-integration framework identifies key predictors of tomato salt tolerance

In this study, we investigate the integrative physiological basis of salt tolerance in tomato to support the identification of resilient germplasm for horticultural production under saline conditions and reduced freshwater availability. A greenhouse experiment compared one Solanum lycopersicum cultivar and five Solanum pimpinellifolium accessions under moderate and severe salinity stress, corresponding to 18% and 33% seawater in the nutrient solution, in a soilless cultivation system. These treatments were designed to simulate the prospective use of diluted seawater as an alternative irrigation source in coastal and water-scarce regions increasingly impacted by climate change. Morphological, physiological, biochemical and phenological traits were jointly analysed to identify key determinants of stress adaptation and their application for growth, reproductive development and fruit performance. An integrated multilevel analysis uncovered coordinated shifts across hormonal regulation, osmotic homeostasis, and phenological timing, suggesting a coordinated regulatory framework underlying adaptive responses. Osmolytes, flavonoids and hormones emerged as central physiological components associated with flowering dynamics and fruit set under salinity. Among the evaluated genotypes, WR10 showed the highest tolerance, maintaining shoot growth, membrane integrity and reproductive performance across the salinity stress. A predictive tolerance index based on plant height, electrolyte leakage, and stomatal conductance effectively ranked accessions and is based on simple, easily measurable traits suitable for practical screening in tomato breeding programs. These findings demonstrate that integrative physiological profiling of wild tomato species could facilitate the development of salt-resilient cultivars suited to protected and soilless horticultural systems.