Halotolerant Rhizobacteria from Phragmites Communis: A Controlled Proof-of-Concept for Crop Improvement in Degraded Sandy Soils

Halotolerant plant growth-promoting rhizobacteria (PGPR) represent a promising strategy for enhancing crop productivity in degraded soils. This study evaluated 51 bacterial strains isolated from the rhizosphere of the Saharan halophyte Phragmites communis L. for their capacity to improve the performance of wheat (Triticum aestivum L.) and pepper (Capsicum annuum L.) under nutrient-deficient sandy soil conditions. The selection of halotolerant isolates was based on their potential for cross-tolerance, assuming that their adaptive mechanisms against salinity could also mitigate the osmotic and nutritional constraints inherent to nutrient-poor sandy substrates. Two strains, XE-15 and XR-18, were selected based on in vitro screening and tentatively assigned to the genera Pseudomonas and Bacillus, respectively, using 16S rRNA sequencing and multilocus sequence analysis (MLSA). Greenhouse experiments demonstrated that bacterial inoculation significantly increased plant biomass (up to ~2-fold compared to control) and enhanced pepper fruit yield (0.68 g vs. 0.20 g in control). XR-18 notably increased Fe (up to 198.65 mg kg⁻¹) and P (7.98 mg kg⁻¹) accumulation in wheat, while XE-15 exhibited substantial concentrations of nitrogen (1.08%) and magnesium (4.11 mg kg⁻¹) and zinc (102.3 mg kg⁻¹). Soil properties were also improved, including increased water-holding capacity (~30%) and enhanced micronutrient availability. Zinc showed the most pronounced strain-specific response, increasing by 84% under XE-15 and by more than 160% under XR-18. However, taxonomic resolution remains tentative in the absence of genome-level analyses, and mechanistic insights are primarily inferred from in vitro traits. The simplified greenhouse system further limits ecological interpretation. These findings highlight the potential of halotolerant PGPR in degraded soils while emphasizing the need for genomic validation, mechanistic studies, and field-scale evaluation.