| Summary: | Abstract The fitness of microbes and their colonization efficiency in plants is significant for promotion of plant growth, but the mechanism between plants and bacteria in rhizospheric region is not clearly explained. This study focused on identification and characterization of some plant growth promoting biocontrol bacteria. A total of 94 bacteria strains were isolated and tested for different plant growth promotion activities and their antagonistic behaviors towards different pathogenic fungi. The isolated bacteria were categorized into 23 bacterial genera, using 16S rRNA. The most predominant genera of bacterial isolates were Pseudomonas (4 species) and Bacillus (6 species). The isolates (Qassim University Saudi Arabia (QUSA) 52 and 45) and their transposon mutagenesis mutants inhibited mycelium growth of Rhizoctonia solani, Alternria sp., and Colletotrichum sp. Isolates 52 and 45 of P. fluorescens and their mutants’ 52-M12, 45-M19, and 45-M20 yielded the highest dry weight and shoot, and root length in alfalfa plants. Furthermore, the efficiency of these bacterial isolates and mutants against R. solani was considerably higher than the control treatment. Therefore, application of biocontrol agents can significantly control the soil-born fungal pathogen in alfalfa plants.
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