Isolation and evaluation of Qatari soil rhizobacteria for antagonistic potential against phytopathogens and growth promotion in tomato plants

Plant growth promoting rhizobacteria are a diverse group of microorganisms that enhance the growth of plants under various conditions. In this study, 55 isolates of endogenous rhizobacteria were collected from the rhizosphere of Avicennia marina, Suaeda vermiculata, Salsola soda, Anabasis setifera, Salicornia europaea, Arthrocnemum macrostachyum, Limonium axillare, Tetraena qatarensis, Aeluropus lagopoides, and Prosopis juliflora. The isolates were evaluated in-vitro for their antagonist potential against Fusarium oxysporum and Botrytis cinerea using the dual culture technique, where the maximum growth inhibition reached 49% and 57%, respectively. In-vivo evaluation was accomplished to determine the growth-promoting potential of the rhizobacteria under greenhouse conditions where the strain ANABR3 (Bacillus subtilis) showed the strongest growth-promoting effects. Further in-vivo testing regarding the effectiveness of rhizobacteria in the presence of the phytopathogen was also completed using the Hoagland medium. LEMR3 and SALIR5 (both identified as two strains of B. subtilis) supported the tomato seedlings to overcome the disease and significantly (p ≤ 0.05) increased above and belowground biomass compared to the control. Additionally, several characterizing tests were carried out on the selected strains, these strains were found to possess numerous features that promote plant growth directly and indirectly such as the production of IAA, HCN, hydrolytic enzymes, ACC deaminase, NH3, and some rhizobacteria were capable of phosphate solubilization. In conclusion, this study showed that local rhizobacterial isolates collected from arid lands possess valuable traits, making them promising bio-control agents and bio-fertilizers for agricultural purposes.