Genetic Diversity of Rhizobia in Ethiopian Soils: Their Potential to Enhance Biological Nitrogen Fixation (BNF) and Soil Fertility for Sustainable Agriculture

Nitrogen is one of the most limiting nutrients to plant growth. It has to be fixed in the form of NH4 through chemical (fertilizer production) and biological (bacterial) processes (BNF) in the soil. The endosymbiotic associations of root nodule bacteria (rhizobia) with leguminous plants fix 200-500kg N ha-1 yr-1. Consequently, the legumes are integrated into different agro-ecosystems for plant production and soil protection. In view of the ever-increasing demand for food and feed for the burgeoning population in the country, the search for cheaper ways of enhancing soil fertility is very important. To that end, many research activities have been undertaken for the last 20 years to realize the full potential of the legume-rhizobia symbiosis in crop production and agro forestry systems. Although the pioneer research works were focused on the agronomic relationship of resident rhizobia with food legumes, recent studies encompassed rhizobial diversity and effectiveness on different pulse crops and other woody shrub and tree legumes. Some of the polyphasic studies on the rhizobia from Southern Ethiopia revealed that Ethiopian soils harbour diverse groups of rhizobia that are very distinct (more than 80%) from the hitherto known taxa of the Family Rhizobiaceae. This suggests that the country has enormous rhizobial resources for more phylogenetic studies and for the selection of elite strains to enhance effective Rhizobium-legume symbiosis in its agro ecosystems. In this review, the challenges and prospects associated with the exploitation of BNF in the country, in general, and the potential to develop and promote broad-host range inoculants to small-scale farmers, in particular, will be discussed. Keywords : Genetic diversity; Indigenous rhizobia; Legume-Rhizobium symbiosis; Nitrogen fixation Ethiopian Journal of Biological Sciences Vol. 6 (1) 2007: pp.77-95