Characterization of Acid and Salt Tolerant Rhizobial Strains Isolated from Faba Bean Fields of Wollo, Northern Ethiopia

Density of Rhizobium population in faba bean (Vicia faba L.) fields of Wollo area (Asketema, Gashana, Kotem, Major and Sekota) northern Ethiopia was studied. The highest population of rhizobia was found at Major and the least at Sekota regions. The native rhizobial strains isolated from the northern parts of the country tolerated a higher salt concentration (5% NaCl) than the exotic rhizobial strains (Tall 1402 and Tall 1397). Both native and exotic strains failed to grow at pH 4 and 4.5 levels in the laboratory conditions. In the soil adjusted to pH 4-7, all the native rhizobial strains persisted while those of the exotic strain failed to survive at pHs below 5.5. The native strains were more versatile than the exotic ones in utilizing different carbohydrates as a sole carbon source and were found to be more resistant to many antibiotics (streptomycin, chloramphenicol, rimfampenicillin, oxytetracycline, penicillin and tetracycline) than the exotic strains which are found resistant to chloaramphenicol only. Percentage of nitrogen fixation is also higher for native rhizobial strains these isolates being found to be superior to the exotic strains in stimulating growth, dry matter yield, nodulation and nodule wet weight of faba bean in pouch culture.