Distribution, diversity and population composition of soybean-nodulating bradyrhizobia from different agro-climatic regions in Ethiopia

The genetic diversity and population composition of bradyrhizobial isolates collected from different parts of north-western and southern Ethiopia were studied. A total of 103 bacterial symbionts were trapped from the soils collected from Ethiopia. Genetic diversity and population composition of the bradyrhizobial isolates were assessed using restriction fragment length polymorphism (RFLP) of 16S-23S rRNA region. The results showed the presence of 30 distinct restriction pattern types in the population. The difference in bradyrhizobial communities between pairs of soil samples were estimated by alpha (H'(alpha)), beta (H'(beta)) and gamma (H'(gamma)) diversity. Southern Ethiopia showed the most diverse bradyrhizobial populations based on the many RFLP clusters occupied. The ratio of beta to gamma (H'(beta)/ H'(gamma)) diversity between the bradyrhizobial community compositions was greater in north-western than in the southern region of Ethiopia. The RFLP-based population composition suggested the frequent presence of individuals with admixture of ITS (16S-23S rDNA) region and showed the interlineage transfer of ITS genomic region. Phylogenetic analysis of 16S-23S rRNA sequences revealed the presence of a heterogenous group of Bradyrhizobium in Ethiopian soils. These results have provided new insight into the ecology of Bradyrhizobium nodulating soybean under different environmental conditions in Ethiopia.