Variability in Effectiveness of Rhizobia during Culture and in Nodules

Abstract

The ability of three strains of Bradyrhizobium sp. ( Vigna ) to fix dinitrogen in symbiotic association with siratro ( Macropitilium atropurpureum ) was measured after culture in broth and after isolation from nodules. Seven transfers were made between the initial broth culture and the final broth culture. A total of 40 single-colony isolates were obtained from cultures 1 and 7 to test effectiveness. Variation in dinitrogen-fixing effectiveness of the population of one strain did not change on culturing, whereas there was considerable variation in effectiveness of populations of the other two strains. Generally, single-colony isolates from individual nodules had similar levels of effectiveness, but some exceptions occurred. Isolates from different nodules formed by the same Bradyrhizobium strain often differed in their effectiveness.