Effects of Salt-Tolerant PGPR on Tomato Growth under Salinity Stress

Abstract

Aims: The study aims to evaluate the effectiveness of Pseudomonas lactis OYAS35 and Bacillus thuringiensis OYAS36 in enhancing tomato (Solanum lycopersicum L.) growth and yield under salinity stress. Study Design: The study comprised in vitro screening of two rhizobacterial isolates for plant growth-promoting traits and salt tolerance, followed by a greenhouse experiment involving bacterial inoculation and different salinity treatments. Place and Duration of Study: The study was conducted at the Microbiology Laboratory and greenhouse of the Federal University Oye-Ekiti, Ekiti State, Nigeria. The greenhouse experiment lasted eight weeks. Methodology: The isolates were screened for indole-3-acetic acid production, phosphate solubilisation, siderophore production, and ammonia production. Salt tolerance was evaluated in vitro at 0%, 0.5%, 1.0%, and 1.5% NaCl. Both isolates were subsequently evaluated in the greenhouse at the same salinity levels using inoculated and uninoculated tomato plants. Plant height, leaf number, stem diameter, and fruit yield were measured. Data were analysed using two-way analysis of variance followed by Tukey’s honestly significant difference test at P < 0.05. Results: Both isolates exhibited multiple plant growth-promoting traits, including phosphate and potassium solubilisation and production of ammonia, amylase, and protease. In vitro, Pseudomonas lactis OYAS35 showed greater salt tolerance at 1.5% NaCl, with a mean OD₆₀₀ of 0.48 ± 0.02, compared with 0.24 ± 0.02 for Bacillus thuringiensis OYAS36. Under greenhouse conditions, both inoculated treatments maintained higher plant height than the corresponding uninoculated controls at 1.5% NaCl, with mean heights of 15.66 ± 0.28 cm and 15.99 ± 0.28 cm for P. lactis OYAS35 and B. thuringiensis OYAS36, respectively, compared with 12.88 ± 0.23 cm in the control. Mean fruit production was also higher in inoculated plants, with 0.60 and 0.40 fruits per plant for P. lactis OYAS35 and B. thuringiensis OYAS36, respectively, compared with a mean of 0.30 fruits per plant in the uninoculated control at 1.5% NaCl. Conclusion: Both isolates possessed multiple plant growth-promoting traits and sufficient salt tolerance to enhance tomato performance under saline conditions, indicating their potential as bio-inoculants for sustainable tomato production in salt-affected soils.