الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Two varieties of cowpea were gamma irradiated as a one method to create genetic variation resulting in new varieties with better characteristics in nodulation and nitrogen fixation processes. Conjugation is the second method used in this study, a cell contactdependent DNA transfer mechanism, which has served as elegant tool in the development of genetic engineering technology. The possibility of horizontal gene transfer to other rhizobia, revealed that it is necessary, in view of possibility of deliberate release of a variety of recombinant rhizobia into the environment for such agricultural purposes as improving nitrogen fixation. Cowpea rhizobia were first classified in an heterogeneous group of slowgrowing rhizobia nodulating promiscuous tropical and subtropical legume species known as cowpea cross inoculation group. They were later transferred to the genus Bradyrhizobium, an indigenous population of Bradyrhizobium nodulating cowpea cultivars under favourable and waterdeficient conditions. The main objective of this study was to explore and discuss the possibilities for enhancing N2 fixation by working on the plant host and the microbial symbiont that illustrate best practices and experiences for enhancing biological nitrogen fixation. The genetic contribution of the cowpea plants to establishment of a successful N2fixing symbiosis in the legumeRhizobium system has been clearly demonstrated through genetic variations induced in macro and microsymbiont using gamma irradiation and horizontal gene transfer, respectively.