LAUSR

Abstract The growth and yield of plants, including halophytes, are widely affected by salinity. It is known that the rhizosphere and endorhiza of the plants growing in saline environments harbor salinity–tolerant bacteria with plant growth promoting (PGP) potential. However, information about PGP endophytic and rhizosphere bacteria colonizing in the halophytes is still scarce. This study was designed to isolate and characterize rhizosphere and endophytic bacterial isolates from salt–accumulating halophyte Salicornia sp. grown under extreme salinity and to evaluate the effect of effective rhizosphere and endophytic bacterial strains (no bacteria, B0; rhizosphere strain Staphylococcus sp., R; endophytic strain Staphylococcus sp., E; and combination of these strains, R + E) on Salicornia sp.–plant growth promotion under salinity stress (0, 200, 400, and 600 mM NaCl) in greenhouse conditions. A total of 214 rhizosphere and endophytic isolates were obtained from rhizosphere soil and the surface–sterilized roots of Salicornia sp. These isolates exhibited tolerance to NaCl and drought and had different PGP traits. The results of this study also showed that the growth of the halophyte Salicornia sp. was also affected by salinity. At level of 200 mM NaCl, salinity had a positive effect on plant growth, so that the highest growth indices of the plant were observed at this salinity level. However, at salinity levels higher than 200 mM NaCl (400 and 600 mM NaCl), the growth of the plant (5.8–42.9% decrease in growth indices) decreased compared to that of this plant at the concentration of 200 mM NaCl. Bacterial strains (R, E, and R + E) had a positive role in alleviating the negative effects of salinity on the plant growth (13.9–47.0% increase in growth indices) compared to control (B0) at all salinity levels. In the presence of the bacterial strains (R, E, and R + E), the highest plant growth (33.2–65.2% increase in growth indices) was obtained at a concentration of 200 mM NaCl. Among bacterial treatments, the combination of these strains (R + E) had the highest effect on the plant growth under salinity stress. In general, the results of this study show that salinity–tolerant rhizosphere and endophytic bacteria associated with the halophyte Salicornia sp. have an important role in enhancing growth and salt tolerance in the halophyte Salicornia sp. and can be used as bio–fertilizer for further improvement of the growth of this plant in saline environments.