Nutritional, eco-physiological and symbiotic characteristics of rhizobia nodulating faba bean (<i>Vicia faba</i> L.) collected from acidic soils of Ethiopia

Abstract

Characterization of root nodule bacteria is used for selecting and using them as inoculants to improve legume production. To this end, faba bean (Vicia faba L.) rhizobia were isolated from nodules collected from acidic soils of Central and Southern-Western parts of Ethiopia. A total of hundred rhizobial isolates were collected and characterized based upon their nutritional, ecophysiological and symbiotic characteristics. The isolates produced low to copious amount of extracellular polysaccharides (EPS) and attain colony sizes ranging from 2 to 7 mm with generation time ranging 0.75 to 3.9 h. Most of the isolates were grown at different pH levels ranging 4.5 to 7.0 and temperatures between 4 and 45°C. They were also capable of growing on many carbon sources and most of the nitrogen sources, and showed significant variations in resisting different types of antibiotics and heavy metals. Based on symbiotic efficiency (SE), 56% of the isolates were found to be very effective when applied with both Degaga and Dosha varieties. All taken together, two isolates, HUGAVf1 and HUCDVf5 were nutritionally versatile, showed a wide range of tolerance to the stress in many of the ecophysiological characters and very effective symbiotic performance should be utilized in future faba bean inoculants production.

Key words: Rhizobium leguminosarum biovar. viceae, antibiotic tolerance, carbon utilization, fast growing, heavy metals, temperature tolerance.