African Journal of Basic & Applied Sciences 5 (2): 95-101, 2013 ISSN 2079-2034 © IDOSI Publications, 2013 DOI: 10.5829/idosi.ajbas.2013.5.2.2934 Corresponding Author: P. Saranraj, Department of Microbiology, Annamalai University, Annamalai Nagar, Chidambaram-608 002, Tamil Nadu, India. 95 Prevalence and Production of Plant Growth Promoting Substance by Pseudomonas fluorescens Isolates from Paddy Rhizosphere Soil of Cuddalore District, Tamil Nadu, India P. Saranraj, P. Sivasakthivelan and S. Siva Sakthi Department of Microbiology, Annamalai University, Annamalai Nagar, Chidambaram-608 002, Tamil Nadu, India Abstract: Pseudomonas species are important plant growth promoting rhizobacteria (PGPR) used to enhance crop yield by direct and indirect mechanisms. Several researchers have shown that fluorescent Pseudomonas is abundant in the rhizosphere of different crops. The paddy rhizosphere soil sample was collected from ten different locations in Cuddalore district of Tamil Nadu. The population of bacteria, fungi and actinomycetes in the rhizosphere soil sample of paddy was estimated by Serial dilution and Pour plating method. The total bacterial population ranged from 15.8 to 24.3 × 10 cfu gG of soil and the highest population of 24.3 × 10 cfu 6 1 6 gG was observed in soil of Sivapuri. The total fungal and actinomycetes population were ranged between 1 8.9 to 13.3 × 10 cfu gG and 10.5 to 19.3 × 10 cfu gG of soil respectively. The occurrence of Pseudomonas 3 1 5 1 fluorescens also examined and the population ranged between 7.71 × 10 cfu gG and 7.21 x 10 cfu gG of soil. 6 1 6 1 The Pseudomonas fluorescens was isolated by Pour plate method. The isolate Pseudomonas fluorescens were characterized by Gram staining, motility test, plating on King’s B medium and bio-chemical tests. The ten Pseudomonas fluorescens isolates obtained from the rhizosphere of paddy were tested for their efficiency of IAA production. The maximum IAA production was recorded by the isolate PF-8. The minimum production of IAA was found in PF-4 isolates. The isolate Pseudomonas fluorescens (PS-8) showed maximum Siderophore production and the least Siderophore production was showed by the Pseudomonas fluorescens isolate PS-4. Key words: PGPR %Pseudomonas fluorescens %Indole acetic acid and Siderophores INTRODUCTION growth directly by providing nutrients or growth factors Plants are exposed to diverse species of microbes through secondary metabolites [1, 2]. Many of the that are present in soil. Plants are the prime source of studies with PGPR show plant growth promotion but nutrients for microbes and provide nutrients indirectly only under gnotobiotic condition [3, 4] or in potting from root exudates and dead plant matter. In some cases, media [5, 6] where these bacteria do not compete with the nutrients are provided directly to microbes that form normal array of soil microorganisms. close relationship with plants. Plant microbes lead to Plant growth-promoting rhizobacteria (PGPR) are many harmful and beneficial sequences. During recent free-living, soil-borne bacteria, which enhance the years, studies on beneficial aspects of plant-microbe growth of the plant either directly or indirectly [7]. interactions, metabolites mediating microbial plant The direct mechanisms involve nitrogen fixation, communication and plant strategies to manage nutrient phosphorus solubilization, HCN production, production fluxes and nutrient acquisition have gained great of phytohormones such as auxins, cytokinins and importance. gibberellins and lowering of ethylene concentration The potential of variety of soil microorganisms to [8-10]. Bacteria belonging to the genera Azospirillum, exert beneficial effects on various crops is now well Pseudomonas, Xanthomonas and Rhizobium as well as established. Rhizosphere bacteria may promote plant Alcaligenes faecalis, Enterobacter cloacae, Acetobacter or indirectly by antagonizing soil borne phytopathogens