Methods for Isolation and Characterization of Nitrogen-Fixing Legume-Nodulating Bacteria

Symbiotic nitrogen fixation (SNF) is a characteristic feature of nodulating legumes. The wild legumes are comparatively less explored for their SNF ability; hence, it is essential to study nodulation and identify the microsymbiont diversity associated with them. This chapter aims to describe the methodology for nodule hunting; trapping, isolation, and characterization of root nodule bacteria (RNB) at phenotypic, genotypic, and symbiotic levels. The documentation of nodulating native legume species and the rhizobial diversity associated with them in various parts of world has gained attention as this symbiotic association provides fixed nitrogen, improves productivity of plants in an ecofriendly manner. Before field-based applications the symbiotic bacteria need to be assessed for their N fixing ability as well as characterized at molecular level. The phylogeny based on symbiosis-essential genes supplemented with the host-range studies helps in better understanding of the symbiotaxonomy of rhizobia. More efficient symbiotic couples need to be screened by cross-nodulation studies for their application in agricultural practices.