The research team, led by Imane Achkouk of Abdelmalek Essaadi University in Tangier, collected plants and rhizosphere soil from wild populations of L. creticus growing on mobile dunes in March 2024. The site receives roughly 525 millimeters of rain a year under a Mediterranean climate, but the soil itself is unforgiving. Laboratory analysis classified it as a sandy Arenosol with a pH of 8.4, moderate salinity of 4.2 millisiemens per centimeter, and alarmingly low fertility: organic matter made up just 0.48 percent of the soil, available phosphorus sat at a mere 3 parts per million, and total nitrogen was only 0.08 percent. These are precisely the conditions that immobilize phosphorus into insoluble calcium complexes and leave iron locked away as insoluble oxides, starving plants of essential nutrients.

Despite the hostile chemistry, the plants themselves were in excellent condition. The researchers documented strong nodulation, with large pink nodules signaling an active nitrogen-fixing symbiosis, and the wild stands produced up to 781.25 kilograms of dry matter per hectare with a crude protein content of 12.60 percent. That combination of vigor and nutrition is what makes L. creticus such an attractive candidate for stabilizing and rehabilitating degraded coastal ecosystems, and it suggested to the team that its rhizosphere might harbor bacteria with equally valuable talents.

From the soil clinging to the roots, the researchers cultured thirty bacterial isolates on King B medium and, based on growth characteristics, selected five for deeper investigation. Molecular identification using nearly full-length 16S rRNA gene sequencing revealed that all five belonged to the genus Pseudomonas: Pseudomonas protegens strain P79, Pseudomonas sesami strain R8, Pseudomonas versuta strain R15, Pseudomonas helleri strain R125, and Pseudomonas trivialis strain R150. The sequences, deposited in GenBank, showed greater than 98 percent similarity to known type strains, and a phylogenetic tree built with the neighbor-joining method confirmed their placement within the Pseudomonas radiation.

Each strain brought a distinct toolkit to the table. Pseudomonas protegens P79 emerged as the standout generalist: it solubilized tricalcium phosphate at the highest rate measured, 150.5 milligrams per liter, produced strong indole-3-acetic acid, the auxin-type phytohormone that stimulates root development, and secreted cellulase and protease at high levels, enzymes that decompose organic matter and release nutrients in nutrient-starved sands. It also produced siderophores, iron-chelating compounds that convert insoluble ferric oxides into bioavailable forms. Pseudomonas sesami R8, by contrast, was the team’s biocontrol specialist, producing abundant hydrogen cyanide and ammonia and showing the broadest antifungal activity, including a striking 50.37 percent inhibition of the mycotoxigenic mold Aspergillus ochraceus. The remaining strains showed moderate phosphate solubilization, ammonia production, and siderophore secretion, painting a picture of complementary rather than redundant functions.

The stress tolerance results were equally compelling. P79 grew in the presence of up to 13 percent sodium chloride, survived temperatures of 45 degrees Celsius, and tolerated an alkaline pH of 11, an extraordinary range that mirrors the punishing conditions of its native habitat. Pseudomonas helleri R125 and Pseudomonas versuta R15 managed 12 and 11 percent salt respectively, while R150 and R8 were the most salt-sensitive, tolerating 9 percent. For strains intended to function in saline coastal soils, the ability to remain metabolically active under osmotic stress is not a luxury but a prerequisite, and the local isolates clearly carry that adaptation in their biology.

The decisive test came in the greenhouse. The researchers surface-sterilized L. creticus seeds, germinated them, and planted seedlings in pots of sterilized soil from the original collection site, inoculating each seed with roughly one hundred million colony-forming units of a given strain. After growth under controlled conditions, the differences were dramatic. Inoculation with Pseudomonas helleri R125 and Pseudomonas trivialis R150 significantly increased the aerial dry biomass of the plants by 300 percent compared with uninoculated controls, a result the authors attribute to their nutrient-mobilizing activities, particularly phosphorus solubilization and iron chelation. Pseudomonas protegens P79, meanwhile, proved the best root promoter, boosting root elongation by 8 percent, consistent with its high auxin production, and Pseudomonas versuta R15 preferentially drove shoot elongation over biomass accumulation.

The mechanistic story that emerges is one of division of labor in the rhizosphere. Direct effects operate at the plant level: bacterial auxin stimulates root branching and soil exploration, while ACC deaminase activity lowers stress ethylene and cushions plants against salinity shock. Soil-mediated effects operate at the interface: phosphate solubilization frees phosphorus precipitated by calcium in alkaline sands, siderophores unlock iron, and ammonia production shifts rhizosphere pH in ways that improve nutrient solubility. Add to this the biocontrol dimension, in which hydrogen cyanide, ammonia, and lytic enzymes suppress pathogens such as Fusarium oxysporum, against which P79 achieved 55.56 percent inhibition, and the case for these strains as multifunctional biostimulants becomes difficult to ignore.

The authors are careful to note the limits of the study. Most of the plant growth-promoting traits were assessed in vitro, which may not fully reproduce natural soil conditions, the underlying mechanisms were inferred from functional assays rather than genomic analyses, and the long-term persistence of the strains in the field remains unknown. Future work, they argue, should include field trials across diverse coastal soils, larger sample sizes, and genomic approaches, as well as tests of single and co-inoculation formulations. Even so, the implications are broad. As climate change, overgrazing, and human pressure continue to degrade Mediterranean coastal ecosystems, strategies that harness native plant-microbe partnerships could restore fertility without synthetic fertilizers. The bacteria that help a wild legume survive on Moroccan dunes may one day help farmers coax life back into the world’s salt-stressed marginal lands.

Subject of Research: Plant growth-promoting Pseudomonas rhizobacteria associated with Lotus creticus in Moroccan Mediterranean coastal soils

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

Article References: Unraveling the plant growth promotion potential of Pseudomonas species isolated from the rhizosphere of Lotus creticus grown in the Mediterranean coastal regions of Morocco. (n.d.). https://doi.org/10.5194/soil-12-947-2026

Image Credits: AI Generated

DOI: 10.5194/soil-12-947-2026

Keywords: Pseudomonas, plant growth-promoting rhizobacteria, Lotus creticus, rhizosphere, saline soils, phosphate solubilization, siderophores, biocontrol, coastal soil restoration, Morocco, sustainable agriculture, biostimulants