The role of arbuscular mycorrhizal fungi in alleviating salt stress in Medicago sativa L. var. icon

Medicago sativa L. is the most important forage crop in arid and semi-arid areas, where increased salinity is a major factor limiting plant growth and crop productivity. The role of arbuscular mycorrhizal (AM) fungus Glomus viscosum H.T. Nicolson strain A6 in protecting alfalfa plants from salt stress, induced by sodium chloride (NaCl), was studied in two ways. Firstly, the root systems of 3-month old M. sativa plants, both mycorrhizal (AM+) and non-mycorrhizal (non-AM) (M. sativa L. var. icon), were placed in solutions of increasing salt concentrations (0, 50, 100, 150, 200 mM NaCl) to study the wilting response. G. viscosum improved the tolerance to salinity stress and the benefit was expressed in terms of the time required to reach the T4 stage in the wilting experiment. Secondly, to evaluate the ability of the Glomus-alfalfa symbiosis to tolerate salt, a pot experiment was set up in a glasshouse in which 3-month old alfalfa plants (M. sativa var. icon) were grown in a peat substratum at three salinity levels (0, 100, 150 mM NaCl). The AM symbiosis stimulated plant height, leaf area, root density, fresh and dry plant weight under saline conditions. Furthermore, proline accumulation was higher in mycorrhizal M. sativa plants than in non-mycorrhizal plants under conditions of salt stress. These and other results indicated that the micropropagated selected clone of M. sativa var. icon, when in symbiosis with G. viscosum H.T. Nicolson strain A6, exhibited better growth and physiological activities under saline conditions than non-AM plants. The AM+ plants also had lower sodium and chloride concentrations in tissues than non-AM plants.