Dissecting the physiology of wild tomatoes under abiotic stress: Dynamic photosynthesis and metabolic adaptations to combined drought and salinity

Tomato (Solanum lycopersicum) is widely cultivated in open fields, being increasingly threatened by environmental constraints like drought and salinity, which disrupt water and nutrient uptake, photosynthesis, redox balance and growth. We examined how the wild relatives Solanum habrochaites LA1223 and Solanum galapagense LA1403 accessions respond to single and combined drought and salinity, in comparison to a modern cultivar. Growth, pigment content, dynamic photosynthesis, primary metabolism, and profiles of amino acids, polyamines, and phytohormones were evaluated to assess their natural resilience relative to the cultivated tomato. Wild tomato species sustained growth better under stress, with an enhanced nitrogen metabolism and osmotic adjustment. In particular, S. habrochaites exhibited higher pigment levels, superior photosynthetic performance, coupled with a rapid stomatal regulation, alongside the accumulation of osmoprotectants such as proline and sugars, leading to improved water use efficiency, likely mediated by salicylic acid. In contrast, S. galapagense showed a more conservative stomatal behavior and constitutively higher leaf spermine and root amino acid contents, being able to maintain biomass production and photosynthesis under water stress. Our results show that, despite their slower growth, wild tomato species display distinct and finely tuned physiological responses to abiotic stress, outperforming a commercial tomato cultivar. These findings emphasize wild species as valuable genetic resources for improving stress tolerance in cultivated tomato.