Isolation and Characterization of Rhizobium Strains from Root Nodules of Faba Bean (Vicia faba L.)

Abstract

Rhizobia are Gram-negative bacteria able to form nodules and fix nitrogen through legumes. Root nodules were collected from young and healthy plants of faba bean (Vicia faba L.) at the flowering stage from five different districts of Bangladesh to isolate effective rhizobial strains with beneficial characters for bio-fertilizer production. Thirteen rhizobial strains were isolated from root nodules of faba bean and characterized by different morpho-physiological tests. The colony size of the strains was ranged from 1.2 to 2.0 mm. All strains showed a positive result in nodulation test and also showed acid-producing fast-growing nature in bromothymol blue test suggesting that they are first growing rhizobia. Four strains (Faba-1, Faba-2, FM-4c, and FM-4f) survive at 1.7% NaCl and six strains (Faba -1, Faba -2, Faba -6, Faba -10, FM-1a, and FM-4c) were able to grow at pH 5.7. Two strains (Faba- 1 and Faba- 2) were able to sustain at high temperature (400C), survive at a wide range of pH (5.7-11), and showed high phosphate solubilization index. The strain Faba-2 seems to be promising for future bio-fertilizer production since it had nodulation capacity, high-temperature tolerance as well as high phosphate solubilizing capacity and therefore could be used for enhancing the growth and yield of faba bean in stress-prone areas of Bangladesh with reduced chemical fertilizers.