Abstract
The selection of superior strains of Rhizobium is one of the key steps in improving the nitrogen fixation capacity of legume plants. A major source of variability which can be exploited in strain evaluation programmes is the genetic heterogeneity among wild strains of rhizobia which have evolved in the centres of diversity of the host plant. The collection of nodules, isolation of strains and their evaluation in symbiosis with groundnuts are described. Some of the variability in response to temperature and host genotypes is discussed to demonstrate the wealth of potential variability available among these strains.
