Soybean [Glycine max (L) Merr.] is a nutritious crop used as food, feed and a raw material forrnmanufacturing various products. Soybean improves soil fertility due to its association withrnsymbiotic bacterial groups known as Bradyrhizobium, Rhizobium/Sinorhizobium andrnAgrobacterium species. It is also associated with diverse plant growth promoting rhizobacteriarn(PGPR) that enhance its health, growth and productivity. Soybean is widely grown in thernlowlands regions of Ethiopia with average yield of about 2.0 tons ha-1 compared to 2.70 tons ha-1rnof world average. The low yield of soybean in the country is predominantly attributed to low soilrnfertility associated with the absence of effective indigenous rhizobia that nodulate and fix enoughrnnitrogen to the host. Attempts to inoculate the crop with exotic rhizobia showed inconsistent andrnunsatisfactory results that necessitated the search for effective local rhizobia adapted tornecological conditions of the country. To this end, 140 soil samples were collected from variousrnsites of Ethiopia to screen for symbiotically effective soybean rhizobia, and plant growthrnpromoting rhizobacteria (PGPR). The rhzobial isolates were trapped, authenticated and tested forrntheir symbiotic effectiveness using three soybean varieties (Cheri, Ethio-Yugoslavia and Jalele)rnunder greenhouse conditions. The PGPR were screened in vitro for their multiple plant growth promoting traits and potential ecological adaptations. The diversity of the selected rhizobia andrnPGPR was studied using their phenotypic (numerical taxonomy), and genotypic characters viarnsequence analysis of 16S rRNA (and some other genes of rhizobia). The most effective rhizobiarnand the most versatile PGP Achromobacter were inoculated on a soybean cultivar (Jalele) tornevaluate their effect on nodulation, growth and yield of the crop against a standard soybeanrninoculant Bradyrhizobium japonicum SBTAL379 under field conditions. The result showed thatrnonly 18 soil samples (13%) induced nodulation on the host variety from which 21 bacterialrnisolates were authenticated as soybean rhizobia. The isolates were equally distributed into fastrngrowing (11) and slow growing (10), and grouped under the genus Rhizobium andrnBradyrhizobium, respectively as classified previously. Based on genetic characters, a fastrngrowing isolate (SNB 41) was identified as Rhizobium/Agrobacterium sp. whereas three slowrngrowing isolates (SNB57B, SNB70 and SNB120A) were identified as Bradyrhizobium spp.rnLikewise, the representative PGPR isolates were also classified into seven genera; six underrnProteobacteria (Gram negative): Achromobacter, Acinetobacter, Enterobacter, Microbacterium,rnPseudomonas and Stenotrophomonas; and one under the Firmicutes (Gram positive): Bacillus.rnThe isolates under the genera Pseudomonas and Stenotrophomonas were the most diverse grouprnamong the PGPR. With regard to their plausible ecological adaptations tested under in vitro, thernfast growing soybean rhizobia were more tolerant to pesticides, higher temperature and higherrnNaCl concentrations and more versatile to utilize different carbon and nitrogen sources than thernslow growing isolates which were better in their inherent antibiotic resistance (IAR). Thernmajority of the rhizobacteria were grown at 40oC, 4% NaCl and showed multiple antibiotic andrnheavy metal resistance. Some of the soybean rhizobia and rhizobacteria also demonstratedrnmultiple PGP traits (2 to 9). The data also showed the overall better performance of gram negative rhizobacteria and fast growing rhizobia in terms of the number of PGP traits andrntolerated stresses. The nodulation and symbiotic effectiveness tests of the rhizobia showed thatrnSNB57B, SNB120A, SNB120C, SNB125A, SNB125B and SNB140 nodulated all the threernsoybean varieties with prolific nodulation (54-173 nodules plant-1; 1.76-2.33 mg of nodule dryrnweight plant-1) and shoot dry weight (1.10-2.27 g plant-1) showing highly effective symbiosisrn(80-100%) in relation to the nitrogen-fertilized control plants under greenhouse experiment. Thernisolates showed similar pattern of relatively high nodulation parameters and symbioticrnperformance on Jalele and Cheri varieties compared to the Ethio-Yugoslavia variety. Thernfindings also showed co-inoculation of rhizobia and the PGP Achromobacterium significantlyrnincreased more growth and yield parameters of soybean at Dembi station of DebrezeitrnAgricultural Research Center (DDARC) field site with low population of indigenous soybeanrnrhizobia and where maximum nodule number (168 plant-1) and dry matter (1.96 g plant-1), shootrndry matter (25 g plant-1) and total nitrogen (4 %), number of pods (114 plant-1) and seeds (214rnplant-1) and grain yield (4.01 tons ha-1) were recorded. There were highly significant (pâ‰¤0.05)rneffects of the rhizobial isolates on most growth, nodulation and yield parameters. Indigenousrnsoybean rhizobia performed much better than the exotic Bradyrhizobium japonicum SBTAL379rnand control treatments under greenhouse and field conditions so that they can be furtherrnvalidated and recommended as inoculant (together with the PGP bacterium) to improve growthrnand productivity of the crop in the country.rnKey words: soybean, rhizobia, PGPR, diversity, nodulation, yield