Int.J.Curr.Microbiol.App.Sci (2014) 3(8) 158-171 158 Original Research Article Optimization for production of Indole acetic acid (IAA) by plant growth promoting Streptomyces sp VSMGT1014 isolated from rice rhizosphere Hariharan Harikrishnan 1 , Vellasamy Shanmugaiah 1 *, and Natesan Balasubramanian 2 1 Department of Microbial Technology, School of Biological Sciences, Madurai Kamaraj University, Madurai - 625 021, Tamil Nadu, India 2 CREM and Department of Life Sciences, Faculty of Science and Technology, University of New Lisbon, 2829-516 Caparica, Portugal *Corresponding author ABSTRACT Introduction Rhizosphere is a wealthy location of microbes, ecological niche and should be explored for potential plant growth promoting rhizobacteria (PGPR), which developing as bio- inoculants for interact with plant roots and enhancement of yield of crop plants. There are several plant growth promoting rhizobacterial (PGPR) inoculants that seems to promote plant growth through different mechanism such as ISSN: 2319-7706 Volume 3 Number 8 (2014) pp. 158-171 http://www.ijcmas.com Keywords Rice rhizosphere, Streptomyces sp, Indole acetic acid, plant growth promotion The present study focused on the the characterization of Indole acetic acid (IAA) production under in vitro condition. A total of 90 actinomycetes was isolated from rice rhizosphere, which was collected from rice fields in the southern districts of Tamil Nadu, India. All isolates were screened for antagonism towards phytofungal pathogens such as Rhizoctonia solani, Macrophomina phaseolina, Fusarium oxysporum, Fusarium udum and Alternaria alternata. Out of 95 isolates, 65 were found to be producing IAA was confirmed by colorimetric method. Isolate VSMGT1014 produced IAA in the ISP-2 medium supplemented with 0.5% L - tryptophan in the amount of 15.96 μg/ml. The ISP-2 medium was recorded as the best medium for production of IAA, where the maximum IAA production was recorded at 30 °C and pH 8 for the production of 4.76 μg/ml and 26.63 μg/ml respectively. The specific spot was found from the extracted IAA has similarity to authentic IAA with the same Rf value of 0.92. High performance liquid chromatography (HPLC) was carried out compared with authentic IAA at 17.5 min retention time was recorded. The selected strain VSMGT1014 could significantly enhance the growth of rice plants compared with that of non- inoculated plants. The results showed that an increase in root and shoot length 52% and 54.55% respectively compared to control. Overall, the results of this study indicate that potential of VSMGT1014 as a significant plant growth substance producer and good inoculants for the growth of rice seedlings.