ISOLATION AND MOLECULAR CHARACTERIZATION OF INDIGENOUS BRADYRHIZOBIUM SPECIES AND ASSESSING THEIR CAPABILITY TO NODULATE AND FIX NITROGEN IN SOYBEAN (GLYCINE MAX)

Abstract
This study was carried out to isolate, characterize and assess the capacity of indigenous Bradyrhizobium spp. to nodulate and fix nitrogen in soybean (Glycine max). Six strains of Bradyrhizobium spp. were isolated from soil samples obtained from fields cultivated to soybean and cowpea using the plant trap method. The six isolates were characterized based on their colonial morphology, as well as biochemical and molecular characteristics. Similarity searches based on sequences on the genbank database showed that of the six isolates confirmed to be strains of Bradyrhizobium spp, four were identified as Bradyrhizobium elkanii with sequence similarity ranging from 93% to 99%, while the remaining two had no sequence similarities. All the six strains obtained were tested in inoculation trials in a screen house using soybean (TGx 1448-2E) as a test crop to assess the capacity 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 content were assessed. It was observed that B. elkanii (B64) formed significantly higher number of nodules per plant (70%) than all the other isolates tested and the standard inoculant. The same strain was also found to fix higher biological nitrogen (25.12%) but it was not statistically significant when compared with the standard inoculant (18.15%). There was a very significant positive correlation between the biological nitrogen fixed and the dry and fresh weight of soybean crop (p<0.01). It was therefore concluded that soils from fields with recent history of soybean cultivation harbor strains of Bradyrhizobium species that could be considered as candidates for the development of inoculants for enhanced soybean production in the Northern Guinea Savannah zone of Nigeria.
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE DEGREE IN MICROBIOLOGY DEPARTMENT OF MICROBIOLOGY, FACULTY OF LIFE SCIENCES, AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA
Keywords
ISOLATION,, MOLECULAR CHARACTERIZATION,, INDIGENOUS BRADYRHIZOBIUM SPECIES,, ASSESSING., CAPABILITY,, NODULATE ,, FIX NITROGEN,, SOYBEAN
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