Drought Stress and Tolerance Mechanisms in Alfalfa (Medicago sativa L.)

Drought is one of the major abiotic stresses threatening agricultural productivity all around the world. Alfalfa (Medicago sativa L.) is the most important forage crop in temperate regions whose importance may further increase because of its positive contribution to sustainable agriculture and its productivity on animal feeding. Although 3-4 years old alfalfa is relatively drought tolerant, it is very vulnerable to drought stress at germination and early seedling growth stages as well as at regrowth stage right after grazing. On the other hand, development of drought tolerant alfalfa varieties by selection or classical crossing is very difficult to due to low heritability of drought tolerance traits and longtime requirement. Introduction of foreign drought tolerant varieties comes along with adaptation and royalty payment problems. Although it is possible to develop relatively drought tolerant transgenic varieties by applying biotechnological approaches, the acceptance of such crops are still controversial and planting of those crops is not allowed in our country. Therefore, success for development of drought tolerant new plant genotypes will depend on understanding of stress related morphological, physiological and molecular mechanisms, and collective use of such new breeding approaches. The aim of this study is to help the understanding of drought stress and tolerant mechanisms of plants, specifically alfalfa, under the light of current literature.