RESUMO
Aims@#Microbial cultures with multi-biological activities in increasing plant growth were developed to be an alternative way to reduce dependency on chemical fertilizer and to support plants productivity. The aims of this study were to characterize the potency of Tangerine var. Batu 55 diazotroph rhizobacteria as Plant Growth Promoting Rhizobacteria (PGPR) agents and to identify diazotroph rhizobacteria with multi-biological activities especially the activity of nitrogen fixation, ammonia (NH3) production, phosphate solubilizing, and Indole Acetic Acid (IAA) production.@*Methodology and results@#A total of 21 nitrogen-fixing bacteria (diazotroph) were isolated from Tangerine rhizosphere soil. Screening of PGPR isolates candidates were performed by in vitro assays consist of phytohormone Indole Acetic Acid (IAA) production, ammonia production, and phosphate-solubilizing assay. Candidates of PGPR isolates were identified based on 16S rDNA sequences. The result revealed that three isolates (Dbs 1, Dbs 2, and Dbm 3) had multibiological activities. Isolates of Dbs 1, Dbs 2, and Dbm 3 capable producing ammonia up to 10 μg/mL; 9.1 μg/mL; and 3.8 μg/mL, activity of IAA production were 30.08 μg/mL; 24.68 μg/mL; and 190.77 μg/mL, activity of phosphate solubilizing were 11.3 μg/mL; 8.6 μg/mL; and 2.2 μg/mL, respectively. Based on 16S rDNA, Dbs 1, Dbs 2, and Dbm 3 were identified as Acinetobacter schindleri, Pseudomonas syncyanea, and P. moraviensis, respectively. Based on our knowledge, this is the first report P. syncyanea was exhibited plant growth-promoting properties.@*Conclusion, significance and impact of study@#Candidates of PGPR isolates could be alternative PGPR agents, but still need to evaluate the effect of three PGPR isolates application on citrus plant growth.