Bacterial consortia enhance nutrient uptakes and molecular response in tomato seedlings under alkaline soil stress: a comparative study

Nutrient deficiencies in alkaline soils (pH 7.9-8.5) frequently limit plant growth due to insufficient nutrient availability and uptake. This study investigated the effects of two bacterial strains, VITK-1 (<i>Pseudomonas</i> sp.) and VITK-3 (<i>Burkholderia</i> sp.), on nutrient absorption, growth, and gene expression in tomato (<i>Solanum lycopersicum</i>) seedlings grown in alkaline soil. Bacterial treatments were applied individually and as a consortium, and their ability to promote plant growth and nutrient solubility was evaluated. <i>In vitro</i> studies demonstrated the strains' ability to solubilize essential nutrients, generate extracellular enzymes, and exhibit a variety of Plant Growth-Promoting Rhizobacteria (PGPR) characteristics, with strong antagonistic activity against <i>Fusarium oxysporum f.</i>sp. <i>lycopersici</i> and <i>Ralstonia solanacearum</i> (35.7%-76.5%). <i>In vivo</i> investigations revealed notable improvements in germination (73.3%), root and shoot development, and overall seedling vigor when compared to untreated controls. The bacterial consortium significantly improved protein (54.5%) and proline (69.5%) levels, antioxidant activity (50.7%), phenolic (60.9%), and flavonoid content (52.5%), and decreased carbohydrate accumulation. Furthermore, treated plants exhibited activation of nutrient-regulating genes (<i>NRT2</i>, <i>PR-1</i>, and <i>AMT-1</i>) associated with better root metabolism (improved 1.58-1.70 mg) and resilience to stress (<i>GR-1</i> and <i>DREB3</i>). These results show the potential of PGPR inoculants, particularly consortia, as a promising strategy for improving nutrient uptake, biochemical characteristics, and stress tolerance in crops grown in alkaline soils.