Unlocking the diversity and plant-growth promoting potential of the bulk soil bacteria associated with the Saharan tree Vachellia tortilis subsp. raddiana

Abstract

In this study, we investigated the bacterial diversity and plant growth-promoting (PGP) properties of bulk soil bacteria of Vachellia tortilis subsp. raddiana collected from the Taidalt and Amazloug nature preserves area in southern Morocco. Using repetitive extragenic palindromic polymerase chain reaction fingerprinting and 16S rDNA sequencing, 93 strains were identified. They belonged mainly to the genera Bacillus and Peribacillus. In vitro tests for PGP traits showed high levels of activity for strains belonging to the genera Bacillus and Pseudomonas. It was relevant that several Bacillus strains produced auxin (maximum amount 262.61 µg mL⁻¹ for Bacillus sp. LMR1097), solubilized phosphate (maximum amount 22.10 µg mL⁻¹), or produced siderophores, while three strains were able to fix atmospheric nitrogen (LMR1145, LMR1013, and LMR1015). Inoculation of V. tortilis subsp. raddiana plants with selected bacterial strains (LMR881 and LMR1097) increased shoot and root growth parameters. The strain Pantoea sp. LMR881 had the highest mean values for shoot and root length (24.60–14.80 cm) and shoot dry weight (1.31 g), whereas Bacillus sp. LMR1097 showed the lowest mean shoot dry weight. Overall, these results highlight the potential of using selected native bacterial inoculants for improving growth of candidate tree plants to be used in restoration programs of arid degraded areas.