Halotolerant Nodule Rhizobial and Passenger Endophytes Alleviates Salinity Stress in Groundnut (Arachis hypogaea L.)

The ability of endophytes to confer plant stress resistance opens a new avenue for mitigating the negative impact of various stresses on crop production. Consequently, the purpose of this study was to investigate plant growth-promoting nodule endophytes for alleviating salt stress in groundnut. Under salt-stressed conditions, rhizobial isolates (Rhizobium phaseoli S18 and Rhizobium pusense S6R2) and passenger endophytes (Pantoea dispersa YBB19B and Bacillus tequilensis NBB13) exhibited multiple plant growth-promoting traits, including IAA, siderophore production, nutrient solubilisation, and ACC deaminase, and compared to the control, the co-inoculation of Rhizobium pusense S6R2 and Bacillus tequilensis NBB13 produced the highest number of nodules (18 per plant) in saline soil. Analysis of root exudates revealed the presence of acetic acid, phenol, and succinic acid compounds in groundnut treated with Rhizobium pusense S6R2 + Pantoea dispersa YBB19B might have resulted in an enhanced stress tolerance mechanism in groundnut. In a pot culture experiment, the combined application of Rhizobium pusense S6R2 and Pantoea dispersa YBB19B or Bacillus tequilensis NBB13 increased plant growth, pod yield, production of anti-oxidant enzymes such as catalase and ascorbate peroxidase, and resulted in accumulation of osmolytes. Similarly, in the field experiment, the co-inoculation of Rhizobium pusense S6R2 and Pantoea dispersa YBB19B resulted in the highest groundnut yield in comparison to the other treatments. This study demonstrated that plants co-inoculated with Rhizobium pusense S6R2 and Pantoea dispersa YBB19B alleviated salt stress; consequently, they may be recommended as a bio-inoculant for salt stress alleviation in groundnut following field evaluation at multi locations.