Abstract
Soil salinity is a major constraint to crop productivity, particularly in arid and semi-arid regions. This study aimed to evaluate the salinity stress responses of diverse lettuce (Lactuca sativa L.) cultivars at two key developmental stages: early seedling and vegetative growth. A two-stage experimental approach was employed. In the first stage, 24 cultivars were screened under increasing NaCl concentrations using a high-throughput seedling phenotyping protocol. Seedling length was identified as a reliable marker for salt sensitivity, allowing for the identification of cultivars with varying degrees of tolerance. Five contrasting cultivars were selected for the second stage, which assessed physiological and biochemical responses to salt stress in a controlled glasshouse environment. Measurements included biomass accumulation, chlorophyll content (SPAD index), photosynthetic efficiency (Fv/Fm and PIabs), oxidative damage, and antioxidants. The results revealed that while early seedling performance provided a useful initial indication of salt sensitivity, three of the five cultivars exhibited notable discrepancies in tolerance between developmental stages. These findings support the use of high- throughput seedling screening as a preliminary tool for cultivar selection but also highlight the importance of additional assessments across developmental stages.