Diversity of rhizobiuns capahle of forming nodules tropical legumes

Abstract

Tropical legume species are generally capable of forming nodules with a broad rhizobium range, which contributes significantly to biological nitrogen fixation activity. This work had the objective of studying the host range of Rhizobium group generally referred as tropical rhizobia or miscellanea cowpea group and design strategies for obtaining an efficient inoculant for peanut. Seven species within the Aeschynomeneae tribe were used as host plant for rhizobia present in soil samples from Pernambuco State located in the North-east region of Brazil. Rhizobia were isolated from nodules of Arachis hipoaea, A. villosulicarpa, Stylosanthes guyanensis, S. scabra, Aeschynomene americana, A. paniculata and A. histrix and characterized regarding growth ratio, pH change of culture medium and colony morphology parameters: size, appearance, color, elevation, transparency, form and mucous type and quantity. The fenotipical characterization resulted in the identification of 44 groups. These data were used for estimating diversity indices related to the Rhizobium population present in soil samples under different vegetation and/or management. Shanon and Weaver diversity index and Margalef index indicated that soil covered by native vegetation (caatinga) showed a more diverse rhizobia population than the soil under peanut cultivation.