Effect of root inoculation of two alfalfa cultivars with strains of Bacillus and Sinorhizobium species on growth, chlorophyll content and cell membrane stability under salinity stress

In this research، seeds and seedlings of two alfalfa cultivars (Yazdi and Hamedani) were inoculated singly or in combination by strains of Sinorhizobium and Bacillus species and grown at 2 levels (0 and 100 mM NaCl) of salinity. Rhizobium strains were isolated from nodules of alfalfa plants and Bacillus was isolated from rhizosphere soils of fields in Isfahan-Dolatabad. Salt tolerant strains were detected by drop plate method on YMA and PVK culture medium containing 100 mM NaCl. Salinity increased electrolyte leakage and reduced fresh and dry weight of plants، chlorophyll a، b content، in both cultivars. Cultivar ''Hamedani'' was more sensitive to salinity compared to cultivar ''Yazdi''. Inoculation with Sinorhizobium and Bacillus improved plants growth، chlorophyll content and membrane stability under both non-saline and saline conditions compared with the non-inoculated control plants. Two bacterial strains acted synergistically، so that، co-inoculation was often more effective than single inoculation with Rhizobium or Bacillus. Our results suggest that inoculation by strains of these two bacterial species could help to alleviate salinity stress in alfalfa plant.