Involvement of bacterial and organic biostimulants in osmoprotection and promotion of growth and development of tomato (solanum lycopersicum l.) Against salt stress

Abstract

Salinity stress poses a significant threat to global food security by compromising crop quality and yield. To address this challenge, eco-friendly approaches were explored in this thesis, focusing particularly on mitigating salinity stress in tomato (Solanum lycopersicum L.) plants. The investigation centered on the efficacy of a selected PGPR strain, Bacillus cereus MR64, identified via 16S rRNA gene sequencing, alongside an aqueous extract from brown seaweed Cystoseira compressa, used as biostimulants. The assessment included the individual and combined effects of these biostimulants on plant growth, physiological parameters, biochemical markers, development and production responses. FT-IR analysis of C. compressa confirmed the presence of various compounds, aligning with prior studies and showcasing the diverse organic components within the seaweed. LC-MS/MS analysis of the seaweed indicated a prevalence of essential amino acids such as L-alanine, L-glutamic acid, and L-aspartic acid. Furthermore, HPLC analysis revealed key phytohormones, particularly zeatin, and substantial quantities of essential sugars, including monosaccharides and disaccharides. Bacterial characterization demonstrated that B. cereus MR64 exhibited tolerance to elevated salt concentrations and displayed plant growth-promoting traits, including indole acetic acid (IAA) production. The results indicated that the interactive treatments T7 (CLE at 10% + BT) and T8 (CLE at 15% + BT) significantly enhanced shoot and root lengths, biomass, and chlorophyll content, while also reducing electrolyte leakage. Additionally, biochemical analyses revealed a reduction in Na+ levels and an increase in K+ and proline concentrations, contributing to improved osmotic regulation and salt tolerance. FT-IR spectroscopy revealed significant spectral changes in treated plants, highlighting the presence of unique compounds characterized by functional groups such as O-H and C-H. The seaweed extract treatments, particularly T5 (CLE at 15%) were more effective than the bacterial strain alone in enhancing shoot growth, photosynthetic pigments, membrane integrity, and proline content. When applied individually, the bacterial strain increased root length and biomass compared to the seaweed extract treatments and the control. The combined application of PGPR and algae extracts showed a synergistic effect, resulting in superior plant growth and enhanced physio-biochemical parameters. This synergy likely arose from the complementary actions of microbial and organic biostimulants. The findings underscored the potential of integrating PGPR and algae extracts as a sustainable, eco-friendly and cost-effective strategy to enhance tomato resilience and growth in saline environments.