Synergistic Effects of Cronobacter sp. BR4 and Date Palm Biochar on Salt-Stressed Tomato Physiology

Journal Article

2025

PurposeThis study aims to assess the combined effects of Cronobacter sp. BR4 and biochar on the morpho-physiological and biochemical responses of tomato plants under salt stress.MethodsThe 16 S rDNA sequencing analysis was employed to identify the bacterial strain BR4. Its plant growth-promoting potential was subsequently evaluated using in vitro tobacco seedlings. In addition, its antimicrobial susceptibility was assessed. Biochar (BC) was produced through pyrolysis at 340 degrees C and was later characterized. To investigate the effects of BR4 and BC on tomato plants under salt stress (100 mM NaCl), several parameters were measured, including growth traits, total chlorophyll and proline contents, activities of antioxidant enzymes, levels of non-enzymatic antioxidants, and the concentrations of potassium and sodium ions.ResultsThe rhizospheric bacterial isolate BR4 was identified as Cronobacter sp. based on 16 S rDNA sequencing analysis. This strain was selected for further study due to its notable plant growth-promoting traits, including indole acetic acid (IAA) production, phosphate solubilization, salt tolerance, antibiotic sensitivity, and non-hemolytic behavior. Its beneficial effects were first demonstrated in vitro, where BR4 significantly enhanced the growth of tobacco seedlings, as evidenced by increased leaf number, shoot and root lengths, and fresh biomass. Subsequent experiments on tomato plants showed that the combined application of BR4 and BC resulted in the most pronounced growth improvements under both non-saline and saline conditions. Under salt stress, this combination markedly improved key growth parameters such as plant height and total biomass. In addition, physiological and biochemical assessments revealed that BR4 + BC significantly elevated total chlorophyll and proline levels by 145% and 74%, respectively. Antioxidant activity also increased, with superoxide dismutase (SOD), catalase (CAT), phenolic compounds, and flavonoids rising by 1.11, 1.72, 1.12, and 1.13-fold, respectively. Furthermore, the treatment enhanced potassium (K+) accumulation by 19.6% in shoots and 100.1% in roots, while significantly reducing sodium (Na+) uptake by 47.8% in shoots and 50.8% in roots. This reduction in Na+ is likely associated with proline-mediated osmotic adjustment and enhanced antioxidant defenses. Additionally, combining BC with BR4 may further limit soil Na+ availability by enhancing the ion-exchange capacity of biochar and promoting PGPR-mediated plant adaptations.ConclusionsThis study highlights that the combined use of the plant growth-promoting Cronobacter sp. BR4 and biochar markedly improves tomato plant growth and physiological responses, especially under saline conditions. The synergistic effect of this treatment also promoted ion homeostasis by enhancing potassium uptake while limiting sodium accumulation in plant tissues. These results emphasize the potential of the BR4-BC combination as a sustainable and efficient biofertilizer approach to alleviate the detrimental impacts of salinity on crop performance. Therefore, this integrated method presents a viable and eco-friendly strategy to boost plant tolerance and improve soil quality in salt-affected agricultural environments.