The paddy rhizosphere soil sample was collected from 10 different locations and the Pseudomonas fluorescens & Bacillus subtilis isolates were characterized. The ten P. fluorescens & B. subtilis isolates were tested for their efficiency of IAA production, Gibberellic acid, Siderophore production and Phosphate solubilization. Among the various isolated of P. fluorescens & B. subtilis, the isolate PF-8 and BS-8 was selected as a more efficient strain and that strains were used for the Mutagenesis studies. The EMS mutated P. fluorescens & B. subtilis showed more plant growth promoting substances and phosphate solubilization when compared to the UV mutated P. fluorescens & B. subtilis. The antagonistic activity of wild and mutated of P. fluorescens & B. subtilis against Pyricularia oryzae was investigated. The mutated strains showed more zone of inhibition when compared to wild strain. The EMS mutated P. fluorescens showed maximum zone of inhibition than UV mutated isolates. The effect EMS mutated strains of P. fluorescens & B. subtilis on plant growth stimulation was studied. The seed treatment with combined application of EMS mutated P. fluorescens & B. subtilis was considered as best

Ms.S.Sivasakthi is a Project Fellow in UGC Major Research Project, Department of Microbiology, Annamalai University, Chidambaram, Tamilnadu, India. She completed her M.Sc in Annamalai University. She published 8 papers in reputed international journals & she participated in 11 seminars. Her area of specialization is PGPR & Spirulina based research.