Identification and in vitro Characterization of Plant Growth-promoting Pseudomonas spp. Isolated from the Rhizosphere of Tomato (Lycopersicum esculentum) Plants in Kenya

Abstract

The rhizosphere is a rich environment for microbial communities and plays a crucial role in many plant-microbe interactions. This research aimed to isolate, identify, and in vitro characterize plant growth-promoting Pseudomonas species from the rhizosphere of field-grown tomato plants. Twenty-five soil samples were taken from tomato plants grown under various management conditions, isolated with population densities greater than 104 cells g-1 and obtained from N-free semisolid media. Important plant growth-promoting processes in vitro were identified and defined in the ten bacterial strains, which were then phylogenetically classed. Screening for their PGP properties revealed that seven (18%) isolates exhibited nitrogen-fixing ability in solid medium, nine (24%) isolates were able to solubilize phosphate, and five (13%) isolates were able to produce hydrogen cyanide. Only one isolate (3%) was capable of synthesizing IAA. The maximum potassium solubilization was achieved in KCl (16%) and K₂SO₄ (13%). The isolates showed more comprehensive levels of tolerance to pH (5 to 9), temperature (20℃ to 40℃), and salt (0% to 15%). Based on this, rhizobacterial isolates with numerous plant growth-promoting potentials were discovered based on their 16S rRNA gene sequencing, and the phylogenetic analysis of the isolates was evaluated, and all selected isolates as being similar to members of the genus Pseudomonas spp. Therefore, based on the plant growth-promoting properties assessed in vitro, the selected bacterial isolates have the potential to boost plant growth and biofertilizer production.