Effects of different carbon and nitrogen sources in Broth culture on the growth of Rhizobium leguminosarum bv. phaseoli and symbiotic effectiveness of haricot bean (Phaseoulus vulgaris L.) in Eastern Hararghe soils of Ethiopia

An experiment was conducted to test the growth efficiency of Rhizobium leguminosarum bv. phaseoli strain no. 46 on different nutrient media in laboratory and consecutively test the performance of the Phaseoli on nitrogen fixation and growth performance of the bean. Various treatment combinations were made for the Rhizobium growth study by replacing mannitol with sucrose, starch, and molasses as carbon (C) sources and yeast extract by baker’s yeast as nitrogen (N) source, respectively, in the standard yeast extract medium (YEM) medium; where mannitol as C and yeast extract as N sources, respectively, were used. The growth of the Rhizobium was highest (322.8 CFU/ml x 10 2 ) in the medium where molasses was used as carbon and baker’s yeast was used as nitrogen sources, respectively, as compared to the standard YEM medium. When we compared the effect of the Rhizobium grown on different media on the growth performance and nitrogen fixation of the bean, highest nodule number (66 per plant) was obtained in bean plants inoculated with the Rhizobium grown on the medium where molasses as carbon and baker’s yeast as nitrogen sources, respectively, were used and higher shoot dry matter (2.85 g per plant) was obtained for the bean plants inoculated with the Rhizobium grown on the medium where molasses as carbon and yeast extract as nitrogen sources, respectively, were used. Highest N fixation (42.7%) was also observed in the bean plant tissues inoculated with the Rhizobium grown on medium where molasses as carbon and baker’s yeast as nitrogen sources were respectively used.