Antagonistic Activity of Plant Growth Promoting Rhizobacteria Isolated from Tomato Rhizosphere Against Soil Borne Fungal Plant Pathogens

The use of single strain inoculum with multiple plant growth promoting activities offers a new concept to address mode of action by combined use of multi-strain inoculum of plant growth promoting rhizobacteria (PGPR) each with specific capability and function. In the present work, bacterial isolates with plant growth promoting activities like P-solubilization, IAA production, siderophore production and broad spectrum antifungal activity against Fusarium oxysporum, Rhizoctonia solani and Sclerotinia sclerotiorum were isolated from the rhizosphere soil of tomato seedlings. In vitro antifungal antibiotic study revealed that among eleven isolates N₁₁ showed maximum inhibition against F. oxysporum (82.85%), R. solani (76.45%) and S. sclerotiorum (74.71%) after seven days of incubation. The per cent growth inhibition increased with increase in bacterial cell density from O.D 0.25 to 1.50. The novelty of the isolates is that the antibiotic production is induced only in the presence of fungal host and lack of antifungal activity in culture filtrate. Bacterial isolate N₁₁ showing maximum plant growth promoting activities and was identified to species level by biochemical characterization and 16S rRNA sequencing. Preliminary identification of bacterial isolate was made on the basis of morphological and biochemical characters and confirmed by partial 16S rRNA gene sequencing, which validated N₁₁ as Bacillus subtilis CKT1. Thus, the present study concludes that these bacterial isolate could serve as a proficient biocontrol PGPR inoculant in the integrated management of soil borne diseases of tomato.

The present study suggests that the use of single strain inoculum of CKT1 as a proficient biocontrol PGPR with multiple plant growth promoting activities offers a recent concept to address multiple mode of action by combined use of multistrain inoculum of PGPR with each having specific capability and function.