Abundance and characterization of cowpea miscellany Rhizobium from sudanese soils

Abstract

Sudan is the fourth largest exporter of groundnuts in the world, yet little is known concerning the plant-rhizobial symbiosis. A study was made on the abundance of groundnut-nodulating rhizobia in the soils of Sudan as related to soil properties and the duration since groundnuts were last planted. Also, physiological, serological and nitrogen-fixing characteristics of Sudanese rhizobia are reported. All but one of 32 sites contained more than 300 rhizobia g −1 soil capable of forming nodules on siratro ( Macroptilium atropurpureum). Several of these soils had never been planted to groundnut. A correlation matrix indicated no relationship was present between soil rhizobial populations and any of the measured soil properties, or between soil rhizobial populations and the time since groundnuts were last planted in the rotation. Individual isolates of Rhizobium from six legumes: groundnut ( Arachis hypogaea), mung bean ( Vigna radiata), lubia ( Dolichos lablab), cowpea ( Vigna unguiculata), pigeonpea ( Cajanus cajan) and bambara groundnut ( Voandzeia subterranea) were obtained from four locations in Sudan. All isolates were able to nodulate each of the six legumes when grown in sterile vermiculite. The isolates grew in 0.1% NaCl-amended media, but growth was variable in 2.0% amended media. Most isolates grew after exposure to moist heat for 15 min at 50°C. Optimum pH for growth was, in general, between pH 6 and 8. Agglutination reactions indicated isolates from groundnuts, as well as isolates from other legumes, belonged to several serological groupings. Some isolates formed a large number of nodules on a Sudanese groundnut cultivar, whereas other isolates formed only few nodules.