Characterization of Indigenous Rhizobia Strains Associated to Soybean [Glycine max (L.) Merrill] in Benin

Legumes such as soybean establish symbiotic relation with nitrogen fixing bacteria such as Rhizobia. Nitrogen fixation via legume-rhizobium symbiosis is the most important source of Nitrogen in agro-ecosystems. But environmental stresses are important limiting factors for this process. Hence, the aim of this study is to evaluate the physiological characteristics and Plant Growth Promoting (PGP) properties of soybean rhizobia. A total of 28 Rhizobia strains obtained from soybean root nodules collected in from three Agro-Ecological Zones (zones 3, 4 and 5) producers of soybean in Benin were used. The physiological characteristics include utilization of carbon source, tolerance to temperature, salinity and pH, resistance to antibiotics and heavy metals. The PGP properties were relative to production of indole, hydrogen cyanide and ammonia and catalase test. The results revealed that, irrespective of their geographical regions, the 28 isolates were grouped into five Clusters. Most of them tolerated neutral to alkaline pH and high salt stress and 17% of them could grow at 40°C. Most of them showed resistance to heavy metal and antibiotics. These isolates tested were able to use a broad range of carbohydrates as sole source of carbon. Production of indole, hydrogen cyanide and ammoniac were respectively found on 56%, 41% and 44% of isolates but all isolates gave positive reaction to catalase test. These rhizobial isolates showing best physiological and PGP properties could be good candidates to establish a successful symbiosis with soybean under the variation of environmental conditions that prevail in Benin.