CHARACTERIZATION AND COMPARATIVE RESPONSE OF RHIZOBIA ISOLATES FROM ROOT NOODLES OF SELECTED WEED SPECIES AND SOYBEAN (Glycine max) TO ENVIRONMENTAL FACTORS

Screening and selecting the most effective strains of rhizobium is important for biological nitrogen fixation. To determine the effects of environmental factors on rhizobia strains associated with some selected leguminous weed species, rhizobia strains isolated from root nodules of five weed species (Mimosa pudica, Crotolaria retusa, Desmodium triflorum, Canavalina ensiformis, Stylosanthes spp.) were subjected to varying temperature, salinity, and pH in the laboratory. Results indicated better growths at temperatures of 30 and 370C compared to the temperature of 250C. Results further showed that microbial growth was optimal at 1.5% salt concentration. Optimum growth was also obtained at the pH range of 5 and 8. The study further revealed by a series of morphological and biochemical tests that all the strains were gram-negative, rod-shaped, and mucous producing. Rhizobia strains from leguminous weeds were found to exhibit faster growth than the strain nodulating soybean in all the conditions to which they were subjected. A cross inoculation study was therefore recommended to access the compatibility of these rhizobial strains from the wild with cultivated leguminous plant species.