Unraveling the plant growth promotion potential of Pseudomonas species isolated from the rhizosphere of Lotus creticus grown in the Mediterranean coastal regions of Morocco

Abstract

Abstract. Rhizosphere-associated bacteria play a key role in improving plant performance in saline and nutrient-poor soils. In this study, the plant growth-promoting potential of rhizobacteria isolated from the rhizosphere of Lotus creticus naturally growing in Mediterranean coastal regions of northwestern Morocco was evaluated. Out of 30 isolates, five bacterial strains R125, P79, R8, R150, and R15 were selected based on their plant growth-promoting rhizobacteria (PGPR) traits. These strains were identified through 16S rRNA gene sequencing as Pseudomonas protegens, Pseudomonas sesami, Pseudomonas versuta, Pseudomonas helleri, and Pseudomonas trivialis, respectively. Phenotypic characteristics, including IAA production, phosphate solubilization capacity, cellulase and protease activities, and tolerance to salinity and temperature were evaluated. Additionally, a pot experiment was conducted to assess the impact of inoculation on the growth of Lotus creticus. Significant variation was observed among the selected strains. Pseudomonas protegens P79 stood out for its strong indole-3-acetic acid (IAA) production, high phosphate solubilization capacity (150.5 mg·L⁻¹), and notable cellulase and protease activities. It also demonstrated high tolerance to salinity (up to 13 % NaCl) and elevated temperatures (up to 45 °C). Conversely, Pseudomonas sesami R8 exhibited a broad spectrum of antifungal activity, including strong inhibition of Aspergillus ochraceus. The pot experiment revealed that inoculation with Pseudomonas versuta R15 and Pseudomonas helleri R125 significantly enhanced the aerial dry biomass and shoot length of Lotus creticus under controlled chamber conditions. This study highlights five Pseudomonas strains, particularly Pseudomonas protegens P79, as promising biostimulants for sustainable agriculture and the rehabilitation of saline marginal lands, due to their diverse plant growth-promoting traits.