Physiological and Biochemical Mechanisms in Two Alfalfa (Medicago sativa L.) Cultivars with Contrasting Salinity Tolerance

Salinity stress has been accepted as an abiotic stress factor that decreases agricultural productivity. Earlier studies have showed that salinity stress has a negative impact on plant growth, development, and yield, while also leading to quality losses. Among forage crops, alfalfa is one of the species that exhibits sensitivity to salinity stress. Thus, gaining insights into the physiological and biochemical mechanisms of alfalfa under salinity stress is essential for formulating effective strategies to improve its tolerance. This study aimed to reveal the physiological and biochemical mechanisms of two alfalfa cultivars showing different sensitivity to salinity stress when exposed to salt stress. Preliminary petri dish experiments conducted before the study revealed that the two alfalfa cultivars exhibited different sensitivities to salinity stress, with the 'Diane' being more tolerant compared to 'Bilensoy-80'. In the study, the effects of varying salinity levels (0, 50, 100, 150, 200 mM NaCl) were tested in alfalfa cultivars by performing growth parameters, physiological and biochemical status. The results indicated that the cultivar 'Diane' showed maintained root development, physiological and biochemical status, compared to control under salinity stress, except for 150 and 200 mM NaCl. In contrast, salinity stress in the 'Bilensoy-80' caused a significant reduction in growth parameters and severe impairments in physiological and biochemical traits, compared to control. The results collectively revealed that higher salinity tolerance in 'Diane' could be attributed to its increased free proline content and antioxidative defense mechanism, including total phenolic content, APX, CAT and GR enzyme biosynthesis. The findings of this study can be used in breeding strategies that aimed to develop salt-tolerant alfalfa plants. Additionally, it is recommended that the 'Diane' cultivar, which has been identified as more tolerant to salinity stress, be tested through field trials to evaluate its yield and adaptation capacity under saline conditions.