Exploring plant growth-promoting bacteria from peanut (Arachis hypogaea L.) rhizosphere in Morocco's sandy soils: Potential for soil fertility improvement

Peanut (Arachis hypogaea L.) cultivation in Morocco’s sandy soils is limited by poor soil fertility and high permeability, which restricts nutrient and water retention. This study aims to isolate, identify, and investigate native plant growth-promoting rhizobacteria to improve the growth and resilience of peanut. Fifteen bacterial isolates were recovered from the peanut rhizosphere collected from the surface layer of the sandy soils in northwestern Morocco, characterized by low phosphorus and organic matter contents. Two isolates, JR62 and JR86, exhibiting high phosphate-solubilizing activity (238.651 and 196.111 mg/L, respectively), were chosen and identified based on 16S rRNA gene sequencing analysis as being closely related to Microbacterium oxydans (PQ758594) and Enterobacter asburiae (OM101034), respectively. These strains were initially characterized for soil-related biochemical activities phosphate solubilization, siderophore production, and lytic enzyme activities given their pivotal roles in driving soil nutrient cycling and improving nutrient bioavailability. Subsequently, they were examined for additional plant growth-promoting attributes, including IAA production, ACC deaminase activity, HCN and ammonia synthesis, antifungal activity, and tolerance to multiple abiotic stresses (salinity, pH and temperature variability, and PEG-induced drought). Collectively, these functional traits underscore the strains’ potential to substantially influence soil nutrient dynamics while promoting plant health. Inoculation of peanut plants with E. asburiae JR86 and M. oxydans JR62 significantly enhanced growth parameters. The JR86 strain demonstrated the highest increases in shoot (42%) lengths and biomass (180%), whereas JR62 resulted in increases of 24% and 62%, respectively. Such results are attributed to soil-mediated processes, including phosphate solubilization and iron chelation, which together enhance nutrient availability, promote soil nutrient cycling, and improve the fertility of sandy soils.