Salt Stress Effects on Physiological Responses of the Sensitive and Tolerant Varieties of Alfalfa (Medicago sativa L.)

To investigate salt stress effects on physiological responses of alfalfa cultivars, a factorial experiment based on completely randomized block design was carried out using two (Yazdi and Diabolourde) cultivars in three levels of salt along with the control group. In this study, plants were grown in Hoagland half strength solution as control. Three levels of salt solution containing 100, 150, and 200 mM salt were obtained by adding appropriate amounts of NaCl as saline treatments to the Hoagland half strength solution. The effects of varying salinity levels on root length; shoot length; root to shoot ratio; relative water content (RWC); chlorophyll content; the sodium, potassium and chloride ions contents of roots and leaves; and Na to K ratio of leaves were investigated. The results showed that root and shoot lengths decreased in both cultivars under salt stress while root to shoot ratio did not make significant change (p≤0.05). The amounts of sodium and chloride ion contents of roots and leaves increased while their potassium content decreased under salt stress condition. The sodium to potassium ratio of leaves increased while their relative water contents reduced in both cultivars. The changes of mentioned factors differed between sensitive and tolerant cultivars (p≤0.05). According to results, Yazdi cultivar can uptake potassium in a more efficient manner compared to Diabolourde cultivar, which means Yazdi cultivar can keep the Na to K ratio of leaves at significantly lower levels. This ability helps Yazdi cultivar to maintain water content and makes it more tolerant against salinity.