As a result of it nutritional and rustic characteristics, cowpea has become an important source protein in the Northeast region of Brazil. Cowpea may benefit from biological nitrogen fixation and can receive part of the nitrogen needed for culture from symbiosis, which reduces the cost of production. An experiment in greenhouse conditions was carried out in order to assess the diversity of rhizobia isolates of the nodules of cowpea, in soils from Rio Grande do Norte State. The nodules were obtained from roots of Vigna unguiculata (L.) Walp., a species used as trap plant; 304 isolates with typical rhizobial features were obtained. Although all isolates showed rapid and acid growth in the medium, the isolates showed high morphological diversity, forming 18 clusters. No diversity differences of rhizobial isolates were observed among the different soil samples studied.
biological nitrogen fixation; Vigna unguiculata; semi-arid
