Biotechnological application of plant growth-promoting endophytic bacteria isolated from halophytic plants to ameliorate salinity tolerance of Vicia faba L.

Salinity is a major problem affecting crop production all over the world. A wide range of adaptation strategies are required to overcome this problem. Endophytic bacteria can build a symbiotic association with their host to improve host plant salt tolerance. In this study, eighteen bacterial endophyte strains were isolated from two native halophytic plants Arthrocnemum macrostachyum and Spergularia marina, and identified as Bacillus, Brevibacillus, Agrobacterium, and Paenibacillus. These endophytic strains exhibit plant growth-promoting activities including phosphate solubilizing, ammonia production, biocontrol of phytopathogen, extracellular enzymatic activities, and indole-3-acetic acid production under normal and salinity stress. A pot experiment was conducted under field conditions to alleviate the harmful effects of soil salinity on bean (Vicia faba L.) by inoculating their seeds with the most potent bacterial isolates Bacillus subtilis (AR5) and Bacillus thuringiensis (BR1). Salinity treatments induced a significant decrease in both growth parameters and metabolic activities, while the activity of antioxidant enzymes and proline content was significantly increased. However, salinity stress induced higher contents of Na and decreased contents of N, P, K, Ca, Mg, and K:Na, it was found that treatment with B. subtilis (AR5) and B. thuringiensis (BR1) individually or in a combination mitigated the effect of salt stress and improved the plant height, shoot dry weights, proline contents, enzymes activities as well enhanced the accumulation of mineral nutrients in shoot plants. Our results concluded that treatment with co-inoculation of B. subtilis (AR5) and B. thuringiensis (BR1) exerted the greatest effect in alleviating the harmful effect of soil salinity stress and can be used as a suitable bio-approach to reclaim salinity-stressed soils.