International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Index Copernicus Value (2013): 6.14 | Impact Factor (2013): 4.438 Volume 4 Issue 8, August 2015 www.ijsr.net Licensed Under Creative Commons Attribution CC BY Comparative Study of Phosphate Solubilizing Bacteria from Paddy Field Padmshree Patel 1 , Pratibha Desai 2 , Sharda Patil 3 1, 2, 3 Department of Microbiology, Shree Ramkrishna Institute of Computer Education and Applied Sciences, Veer Narmad South Gujarat University, Surat-395 001. Gujarat. India Abstract: Rice (Oryza sativa) is important grain providing one-fifth of caloric requirement of humans globally. Phosphorus is one of the major macronutrients required by plants. But, most of phosphorus present in soil is in insoluble forms and un-utilizable by the plants. Phosphate solubilizing bacteria (PSB) existing in rhizosphere solubilizes insoluble, in-organic and organic phosphorous forms thereby making soluble phosphate retrieved by the plant root from the soil environment. The present work is comparative study on phosphate solubilizing bacteria isolated from rhizosphere of rice plant and from non-rhizospheric soil (bulk soil) of the paddy field during flowering and harvest stage. Total number of PSB isolates obtained from rhizospheric soil is more as compared to bulk soil; 21 and 17 in flowering stage and 14 and 13 from harvest stage samples respectively. Out of total 38 isolates from flowering stage and 27 from harvest stage all have phosphate solubilizing ability in qualitative detection which was then quantified. It has been observed that potential for phosphate solubilization was higher among the isolates from harvest stage (282 μg/ml to 705 μg/ml) with reference to isolates from flowering stage (186 μg/ml to 645 μg/ml). Other traits of isolates aiding in nutrient acquisition by plant viz. nitrogen fixing ability and potassium solubilization were also determined. Keywords: Phosphate solubilizing bacteria, Rhizosphere, Flowering stage, Harvest stage, Nutrient acquisition 1.Introduction Phosphorus, potassium and nitrogen are three major macronutrients required by plants. A large amount phosphorus existing in soil is insoluble type and not exploitable by the plants [1]. Additionally, phosphorus is applied to the soil in the form of phosphatic manure; a large portion of it is rapidly immobilized and thus become unavailable to plants [2]. The soil microbes, referred to as phosphate solubilizing microbes, having solubilizing ability dissociate these forms and make it available to the plants. Mineral phosphorus solubilization in the soil is probably due to secretion of organic acids, such as gluconic acid, 2- ketogluconic acid [3]. Rice (Oryza sativa) is the most important grain satisfying more than one-fifth of the caloric requirement of humans globally [4]. Cultivation of rice crop needs external application of fertilizers. At present, to increase rice production, chemical fertilizers and pesticides are applied in abundance in the paddy fields. This led to several environmental problems viz., deterioration of quality of soil and water and their health, resistant pathogens emergence and elimination of useful flora implicated in growth of paddy [5]. Thus, sustainable agriculture demands replacement of agrochemicals with the eco-friendly soil microbiota. In the same context, agricultural microbiologists are now a days interested in identifying soil bacteria that can solubilize mineral phosphate, thus aiding plant growth. Ashrafuzzaman M. et al., 2009 [6] have reported that ability to solubilize precipitated phosphates in soil and making it available to the plant can be one of the possible mechanisms of plant growth promotion by rhizobacteria under field conditions. Previous reports suggest that PSB are the most promising bacteria among the PGPR and thus can be used as biofertilizers for nutrient use efficiency and plant growth promotion [7]. 2. Materials and Method Sample Collection: Soil and rice plants were collected from Paddy fields at Vyara, District-Tapi, Gujarat, India, in Kharif season during flowering and harvest stage. The five rice plants were uprooted from the irrigated plot along with surrounding soil adherent to the roots from the four corners and one from the centre of the plot. The rice plants were kept in sterile polythene bags and taken to the laboratory and processed as composite sample. Processing of Sample for isolation of Phosphate Solubilizing Bacteria: Using 1 ml supernatant from bulk/rhizospheric soil suspension, serial dilution was made up to 10 -6 . 0.1ml of aliquot from last three dilutions were transferred and spread on Pikovskaya's agar medium. The plates were incubated at room temperature (30+ 2°C) for 48- 72 hr. The isolated colonies were studied for their growth characteristics and sub-cultured on the respective media for acquiring pure culture of the isolates. Qualitative Determination of Plant Growth Promoting Traits: Phosphate solubilization: All isolates were screened for phosphate solubilization. A bacterial culture was inoculated as a line on Pikovskaya Agar medium [8] containing inorganic phosphate. The plates were then incubated at room temperature for 48-72 hrs and examined for zone of clearance. Nitrogen fixing ability: It was checked as per method described by Gothwal et al., 2002 [9] using Nitrogen free malate medium containing bromothymol blue as an indicator. Change of colour of the medium surrounding the colony to blue indicates nitrogen fixing ability of bacteria. Potassium solubilization: Using Aleksandrove agar medium, potassium solubilization of the isolates was Paper ID: SUB157246 400