Exploration of root and shoot physiological traits for selecting drought tolerance in alfalfa (Medicago sativa L.)

Alfalfa has developed different physiological mechanisms in response to drought stress. Therefore, ten alfalfa cultivars (Qomi, Isfahani, Hamedani, Bami, Ordobadi, Gharayonje, Nikshahri, Yazdi, Baghdadi and Cody) were evaluated under four irrigation regimes (55, 65, 75 and 85% depletion of available soil water) to determine their physiological mechanisms under drought stress. Leaf and root proline, soluble sugars contents and dry matter, leaf chlorophyll, carotenoid and relative water contents were measured during 2012 and 2013. Drought increased leaf and root proline contents, leaf soluble sugars and carotenoid contents, while, decreased other traits, however, the effects were drought level-cultivars-specific and discriminated the cultivars based on their drought tolerance. Based on cluster analyses of measured traits at the highest drought level, Baghdadi ranked as the most drought tolerant followed by Qomi, Bami, Nikshahri, Yazdi, Gharayonje, Cody, Isfahani, Ordobadi and Hamedani, respectively. In addition, relative water content had the highest and positive correlation with drought tolerance (r= 0.97) followed by root proline content (r= 0.96), carotenoid content (r= 0.95), leaf soluble sugars (r= 0.94), chlorophyll (with root soluble sugars) (r= 0.93), and root dry weight (r= 0.92), respectively. The results showed that Baghdadi was the superior cultivar under drought stress and relative water content was the most important marker for alfalfa cultivar selection under drought.

Keywords:

Alfalfa , Drought tolerance , Proline , Soluble sugars , Physiological marker