Impact of harsh environmental conditions play an essential role in the control of legume-rhizobia
interactions. They can arrest the growth, multiplication and survival of rhizobia in soil
rhizosphere. The harsh environmental conditions may also have depressive effect on the
steps involved in legume-Rhizobium symbiosis such as molecular signaling, infection process,
nodule development and function, resulting in low nitrogen fixation and crop yield. Selection
of hosts and their nitrogen-fixing endosymbionts that are tolerant to a broad range of
environmental stresses is important for agriculture system. Understanding the key molecular
factors and steps in rhizobia-legume interaction is of crucial importance for the development
of Rhizobium strains and legume cultivars with high N2-fixation potential. Prevelence
and aboundance of rhizobia species vary in their tolerance to major environment factors;
consequently, the selection of resistant strains is an important option. Better N2 fixation can
be achieved by selecting tolerance or resistance rhizobia from soil subjected to environmental
stress. The selection and characterization of harsh conditions-tolerant strains with efficient
symbiotic performance may be a strategy to improve Rhizobium-legume symbiosis and
crop yield in adverse environments. Environmental stress severely affected on various metabolic
activities of legumes including, nod gene expression, photosynthesis, synthesis of proteins,
enzymes and carbohydrates. Therefore, understanding the environmental stress–
rhizobia–legume interactions is urgently required for growing legumes under harsh environmental
stress. Research into these areas is currently underway in several research groups
throughout the world and it is anticipated that this research will provide beneficial outcomes
resulting in improved sustainability and productivity in agricultural systems