BIODIVERSITAS ISSN: 1412-033X Volume 20, Number 9, September 2019 E-ISSN: 2085-4722 Pages: 2547-2553 DOI: 10.13057/biodiv/d200916 Streptomyces spp. from rhizosphere soil of maize with potential as plant growth promoter ARIS TRI WAHYUDI 1,♥ , JEPRI AGUNG PRIYANTO 1 , HANIFA NUR FIJRINA 1 , HIMA DEWI MARIASTUTI 1 , ABDJAD ASIH NAWANGSIH 2 1 Division of Microbiology, Department of Biology, Faculty of Mathematics and Natural Sciences, Institut Pertanian Bogor. Jl. Raya Dramaga, Bogor 16680, West Java, Indonesia. Tel./fax.: 62-251-8622833.  email: aristri2011@gmail.com. 2 Department of Plant Protection, Faculty of Agriculture, Institut Pertanian Bogor. Jl. Raya Dramaga, Bogor 16680, West Java, Indonesia, West Java, Indonesia Manuscript received: 7 July 2019. Revision accepted: 19 August 2019. Abstract. Wahyudi AT, Priyanto JA, Fijrina HN, Mariastuti HD, Nawangsih AA. 2019. Streptomyces spp. from rhizosphere soil of maize with potential as plant growth promoter. Biodiversitas 20: 2547-2553. Actinomycete is one group of rhizobacteria that plays an important role as a plant growth promoter. This study was aimed to evaluate the potential of Actinomycetes isolated from maize rhizosphere in promoting plant growth in vitro including their ability to produce IAA, promote maize sprout growth, solubilize phosphate, and grow in N-free medium. Thirty isolates have been isolated from maize rhizosphere using a spread plate method. All 30 isolates were probably not pathogenic to plants as tested by hypersensitivity reaction test on tobacco leaves. Based on the colorimetric assay, 30 isolates (100%) were able to produce IAA with concentrations ranging from 1.05 to 26.89 ppm. The highest concentration of IAA (26.89 ppm) produced by ARJ 21 and the lowest IAA concentration (1.05 ppm) produced by ARJ 12. By using the Ragdoll method, it showed that 9 isolates (30%) were able to promote maize sprout growth significantly on five growth parameters including primary root length, stem length, number of lateral roots, wet weight and dry weight. Twenty-one isolates (70%) were capable of solubilizing phosphate in Pikovskaya medium containing tricalcium phosphate. Also, 30 isolates (100%) were able to grow on N-free medium, suggesting their ability to fix nitrogen. Based on 16S-rRNA, five potential isolates with plant growth-promoting properties were highly similar to Streptomyces spp. Based on their potential characters, these Actinomycetes isolates have the potential to be further developed as a biofertilizer agent for sustainable maize farming. Keywords: IAA, nitrogen fixation, phosphate solubilization, plant growth, rhizosphere Actinomycetes INTRODUCTION Maize (Zea mays L) is one of the important food sources of carbohydrates, besides wheat, sorghum, and rice. As a source of carbohydrates, some people consume it as a staple food. Maize is also used as a source of vegetable oil, cornstarch, ethanol, organic acids, and animal feed. Maize farming currently depends on the use of chemical/ inorganic fertilizers. Kresnatita et al. (2013) reported that the use of inorganic fertilizers increased the growth and yield of sweet corn plants, by 114.8% compared to the treatment of organic fertilizers. However, the use of inorganic fertilizers extensively in agricultural cultivation will adversely affect the environment such as increased soil salinity, accumulation of heavy metals, eutrophication, and accumulation of nitrates in waters (Savci 2012). Therefore, other alternative fertilizers which environmentally friendly are needed for sustainable maize farming. Plant growth-promoting rhizobacteria (PGPR) is currently being the main topics of research for developing biofertilizer agents. Some beneficial microorganisms isolated from soil have the potential to be used as an alternative to inorganic fertilizers, especially rhizobacteria. Rhizobacteria are found around plant roots and can promote plant growth. PGPR could enhance plant growth through direct and indirect mechanisms. On the direct mechanism, PGPR is capable of producing phytohormones, fixing nitrogen, and solubilizing phosphate (Marques et al. 2010). Whereas in the indirect mechanism, PGPR increases plant growth by secreting phytopathogenic inhibitors, cell wall degrading enzymes, and siderophore (Sreevidya 2016). The exploration of indigenous Actinomycetes strains may lead to potential biological agents that are suitable for local conditions to enhance sustainable maize production. Among all bacterial groups, Actinomycetes, a filamentous Gram-positive bacteria, have some potential characters which could stimulate plant growth by producing Indole Acetic Acid (Jeon et al. 2003), siderophore and solubilizing phosphates (Patil et al. 2010). Streptomyces, one of the actinomycetes genus, have been considered as the most promising group for improving plant growth, soil fertility, and increasing plant biomass (Viaene et al. 2016). Isolation and screening of Actinomycetes isolated from maize rhizosphere were expected to obtain some promising isolates attributed to plant growth-promoting traits. In this present study, research focused on the isolation and screening of maize rhizosphere Actinomycetes as a plant growth promoter in vitro to obtain ideal candidates for developing natural fertilizer.