Role of bioinoculants in development of salt-tolerance of Vicia faba plants under salinity stress

Through biological inoculation technology, the bacterial-mycorrhizal-legume tripartite symbiosis in saline conditions was documented and the effects of dual inoculation with Azospirillum brasilense (NFB) and Arbuscular mycorrhizal ( Am) fungus Glomus clarum on the host plants ( Vicia faba) in pot cultures were investigated at five NaCl levels (0.0 - 6.0 dSm(-1)) in irrigating water. Am faba plants showed decreases in salinity tolerance, \% of mycorrhizal infection and higher accumulation of proline with increasing levels of salinity. Am infection significantly increased tolerance of salinity, mycorrhizal dependency, phosphorus level, phosphatases enzymes, nodule number, nitrogen level, protein content and nitrogenase enzymes of all salinized faba plants in comparison with control and non-Am plants either in the absence and presence of NFB. In shoot system of non-Am plants, Na+ concentration was increased while the concentrations of K+, Mg+ and Ca+ were decreased with raising salinity stress. In Am plants, K+/Na+, Mg+/Na+ and Ca+/Na+ ratios were higher than that of non-Am plants at all salinity levels. The Na+ level in shoots of Am plants showed slight increase with raising salinity meanwhile, K+ and Ca+ concentrations showed noticeable increases especially at higher salinity levels. The results clearly showed that the inoculation of NFB to Am plants had potentiality to increase the effects of Am fungi under salinity stress. This study provides evidence for benefits of NFB to Am fungus in the protection of host plants against the detrimental effects of salt. If so, bacterial-Am-legume tripartite symbioses could be a new approach to increase the salinity tolerance of legumes plants under salinity conditions.