Impacts of Rhizobium Strain Ar02 on the Nodulation, Growth, Nitrogen (N₂) Fixation Rate and ion Accumulation in Phaseolus vulgaris L. under Salt Stress

Background: Phaseolus vulgaris L. -rhizobia symbiosis has effectively enhanced common bean productivity via multiple biological mechanisms. This study aims to assess the impacts of the strain of Rhizobium on the nodulation, growth, nitrogen (N₂) fixation rate and ion accumulation within Phaseolus vulgaris L. under salt stress.
Methods: The Coco Blanc cultivar of the common bean was inoculated with the Ar02 rhizobia strain at 15 days after germination. Bean plants were inoculated in perlite culture to which salt was added in concentrations of 0, 25, 50 and 75 mmol L^-1 NaCl. 
Result: Inoculation with the Ar02 rhizobia strain led to infective and effective symbiosis with the common bean plants exposed to saline solutions and non-saline solutions, respectively. Nodule biomass and nitrogen content declined under salt stress but maintained a higher number of nodules and nodule biomass at 75 mM NaCl. Plant root and shoot length increased with higher biomass under saline conditions, significantly more than the non-inoculated plant without salt. However, the progressive addition of NaCl reduced the growth of the root and shoot and the biomass within the inoculated plant. Salinity led to increased Na⁺ within the plant’s shoot, along with a reduction in Ca⁺² and K⁺ concentrations. The shoot’s Ca⁺², Na⁺ and K⁺ content were higher in the inoculated plant than the non-inoculated. The salt tolerance in common bean plants inoculated with Ar02 rhizobia was linked with the plant’s capability to sustain nodulation and enhance Na⁺ concentration in the shoot. Furthermore, salt tolerance within the same variety inoculated with Rhizobium was linked to a decline in the Ca⁺ and K⁺ concentrations in the shoot region of salt-exposed plants.