Evaluation of Salt Tolerance in Four Self-Rooted Almond Genotypes for Super-High-Density Orchards Under Varying Salinity Levels

Increasing soil salinity threatens almond production globally, driving the need for the development of salt-tolerant cultivars. This study investigated the salt tolerance mechanisms of four self-rooted almond genotypes (Vialfas, Guara, Penta, and Avijor) under controlled conditions. Young plants were exposed to four salinity levels (0, 25, 50, and 75 mM NaCl) for 5 months. Growth parameters (trunk diameter, shoot length, fresh and dry weights), physiological responses (chlorophyll fluorescence, gas exchange, Soil–Plant Analysis Development (SPAD)), and mineral content were analyzed. Results show significant genotype-specific responses at the critical salinity threshold of 50 mM NaCl. Under these conditions, Guara and Vialfas maintained higher stem fresh weights (31.4 g and 37 g, respectively), while Avijor showed significant declines. Trunk diameter measurements revealed Vialfas’ superior performance (7 mm) compared to Guara and Penta (both around 6 mm), while Avijor exhibited the most significant reduction (5 mm). Chlorophyll fluorescence parameters indicated stress impact, with F v /F m values decreasing to 0.84 compared to control values of 0.87. Guara maintained higher K + /Na + ratios in leaves (3.05) compared to Avijor (1.95), while Penta showed better Na + exclusion ability with the lowest leaf Na + content (0.57%). Cl − accumulation patterns also differed among genotypes, with Avijor and Vialfas showing higher leaf Cl − concentrations (0.74% and 0.73%, respectively) compared to Penta (0.44%). Genotype responses across all salinity levels revealed distinct tolerance patterns: Guara maintained growth and physiological functions across treatments, while Penta showed remarkable stability under high salinity. Vialfas exhibited vigor at low salinity but declined sharply at 75 mM NaCl. Avijor demonstrated the highest salt sensitivity. These findings highlight the genetic variability in salt tolerance among almond cultivars and identify potential sources of salt-tolerant traits for breeding programs. The study also provides insights for optimizing genotype selection and management strategies in salt-affected orchards, contributing to more sustainable almond production in challenging environments.