Tomato biodiversity reveals landrace enhanced drought-adaptive strategy.

Tomato (Solanum lycopersicum L.) is a major crop in the Mediterranean basin, vulnerable to drought at any crop stage. Landraces are traditional, locally adapted varieties with greater resilience to water scarcity than modern cultivars. This study compares the responses of Ciettaicale (CE), a tomato landrace, with Moneymaker (MM), a commercial variety, to controlled soil water deficit at early vegetative stage using biometric, physiological, biochemical, and molecular analyses. Our data highlighted that CE copes better with prolonged and severe drought stress, activating distinct response mechanism. CE sustained higher root water content, and root-to-shoot biomass ratio under drought compared to MM, which may be related to their phytohormones balance. Although pigment responses to drought did not differ markedly, the main ratios revealed different defense mechanisms. Both genotypes showed opposite trends in non-photochemical quenching (NPQ) and actual photon yield of PSII photochemistry under drought stress, with increasing NPQ while decreasing PSII electron transport rate and CO₂ uptake capacity. However, differences in substomatal CO₂ concentration indicated that drought mainly limits photosynthesis through diffusive resistances in CE and metabolic impairment in MM. Changes in antioxidant redox status and activities highlighted the CE ability to activate cellular processes to partially control oxidative stress and to induce a drought acclimation. Multicanonical analysis revealed clear genotype separation along the drought gradient, except for CE, which showed complex drought response and introgression of tolerance traits, particularly under moderate stress. Utilizing such genotypes can significantly improve horticultural production under drought conditions.