Isolation And Molecular Characterization Of Indigenous Bradyrhizobium Species And Assessing Their Capability To Nodulate And Fix Nitrogen In Soybean (glycine Max)

This study was carried out to isolate, characterize and assess the capacity of indigenousBradyrhizobium spp. to nodulate and fix nitrogen in soybean (Glycine max). Six strains ofBradyrhizobium spp. were isolated from soil samples obtained from fields cultivated tosoybean and cowpea using the plant trap method. The six isolates were characterized basedon their colonial morphology, as well as biochemical and molecular characteristics.Similarity searches based on sequences on the genbank database showed that of the sixisolates confirmed to be strains of Bradyrhizobium spp, four were identified asBradyrhizobium elkanii with sequence similarity ranging from 93% to 99%, while theremaining two had no sequence similarities. All the six strains obtained were tested ininoculation trials in a screen house using soybean (TGx 1448-2E) as a test crop to assess thecapacity of the isolates to form nodules. Thus, the total number, percentage effective nodules,nodule fresh and dry weights, as well as the fresh and dry biomass yield and nitrogen contentwere assessed. It was observed that B. elkanii (B64) formed significantly higher number ofnodules per plant (70%) than all the other isolates tested and the standard inoculant. The samestrain was also found to fix higher biological nitrogen (25.12%) but it was not statisticallysignificant when compared with the standard inoculant (18.15%). There was a verysignificant positive correlation between the biological nitrogen fixed and the dry and freshweight of soybean crop (p<0.01). It was therefore concluded that soils from fields with recenthistory of soybean cultivation harbor strains of Bradyrhizobium species that could beconsidered as candidates for the development of inoculants for enhanced soybean productionin the Northern Guinea Savannah zone of Nigeria.

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