Eco-physiological and physiological characterization of cowpea nodulating native rhizobia isolated from major production areas of Ethiopia

Abstract Eco-physiological and physiological characteristics are used to study native rhizobial species for their ecological and physiological adaptability to different conditions. This study aimed to assess the eco-physiological and physiological characteristics of cowpea-nodulating rhizobia isolated from major production areas of Ethiopia. Twenty-eight isolates were isolated from cowpea root nodules and evaluated for different eco-physiological and physiological characteristics. All tested isolates grew within a temperature range of 20°C and 35°C. All isolates were able to grow at pH values of between 6.0 and 8.5, with optimal growth at pH around neutral. All isolates were tolerant of NaCl concentration ranging from 0.1% to 1%. The growth of isolates decreased as the salt concentration increased. The tested isolates were able to grow on different carbon sources, such as glucose (100%), fructose (100%) glycerol (100%), mannose (96.43%), lactose (96.43%), galactose (85.71%), arabinose (60.71%) and maltose (46.43%) showing that the majority of tested rhizobia were able to use a broad range of carbohydrates as sole carbon sources. Similarly, the isolates were able to grow on L-lysine (89.29%), L-arginine (92.86%), tyrosine (82.14%), L-tryptophan (89.29%), L-asparagine (78.57%), methionine (75%) and glutamate (85.71%) as a source of amino acids. The tested isolates showed a wide diversity for their tolerance to different eco-physiological conditions (temperature, pH and salt concentration) and had the ability to utilize a large variety of carbon and nitrogen sources. The variation and diversity of tolerance to different ecological conditions and utilization of different nutrients would provide them an ecological advantage and enhance their chance for survival.