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

Abstract

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.

Role of Phosphorus and Inoculation with Bradyrhizobium in Enhancing Soybean Production

“…Ohyama et al [32] reported that soybean yield could increase up to 4.6 t•ha −1 under prime environmental (climatic and soil) conditions. However, the USA and Japan have reported greater potential soybean yields of 10 and 8 t•ha −1 , respectively [32,33]. Hence, soybean productivity potential could be maximized than we have thought if proper soil and crop management practices are used [34].…”

Nodulation and Growth Promotion of Chickpea by Mesorhizobium Isolates from Diverse Sources

“…Another notable indirect mechanism involves the production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase that assists in alleviating the effects of stress (e.g., drought, salinity, heat, cold, and exposure to heavy metals) on plant growth, as it limits the formation of ethylene produced in response to stress (i.e., ACC, the immediate precursor of ethylene is degraded by ACC deaminase to alpha-ketobutyrate and ammonia) [31,33]. These abilities have been witnessed among Mesorhizobium whereby M. ciceri, M. loti, M. tianshanense, M. huakuii, M. mediterraneum, M. temperatum, and M. amorphae are capable of producing IAA to varying levels [34], and solubilize phosphate [33,35,36]. They are, however, unable to produce siderophores [27]; although, certain strains produce siderophores when exposed to particular pesticides and fungicides [37,38].…”