Development of bio-herbicides is an emerging method to weed management in agricultural field. Very few studies were conducted on identification of microbial bio-herbicides to weed control. The present study was aimed to isolate and identify the effective bio-herbicide potential bacterium from soil and assess their role on plant growth inhibition. Three-hundred and one rhizobacteria were isolated from agriculture field soil samples collected from various parts of Republic of Korea. Two bacterial strains, I-4-5 and I-3 were significantly reduced the seedling growth of radish when compared to their controls. The highest rate of seedling growth inhibition was observed in I-3 bacterial isolate treatment in lettuce and radish. The mechanism of an effective bio-herbicide I-3 to plant growth inhibition was determined by analyzing IAA in their culture medium. IAA biosynthesis pathway of Enterobacter sp. I-3 was identified as tryptophan-dependent pathway and its production was increased due to addition of tryptophan in culture medium as quantified by using GC-MS SIM. In an in vitro study revealed that I-3 bacterial culture exudate combined with tryptophan significantly decreased leaf length, leaf width, root length and increased the number of lateral roots of lettuce. Indeed, the genomic DNA of I-3 bacterium was isolated and 16S rDNA was sequenced to find out the name of the bacterium. Based on phylogenetic analysis, I-3 isolate was identified and named into Enterobacter sp. I-3. The results of this study suggest that the utilization of Enterobacter sp. I-3 to crop field can be act as a potential bio-herbicide against weed growth.
Keywords: Enterobacter sp. I-3; Indole-3-acetic acid; Lettuce; Plant growth inhibition.