Rhizobia: A Potent Tool for Amelioration of Drought Stress in Legumes

Rhizobia in association with legumes form an effective symbiosis and fix atmospheric nitrogen for uptake by plants. Nitrogen fixation in leguminous crops contributes significantly in maintaining fertility of soil. For the growth of rhizobia and legume-rhizobial association, drought stress is one of the limiting factors, among different stress factors in the environment. Under the arid/semi-arid conditions, establishment of an effective rhizobium-legume interaction is very sensitive. Drought conditions affect root development, nodulation, chlorophyll content, changes in cell volume and concentration of solutes and other properties which are important for biological nitrogen fixation. Thus, interactions of rhizobia and legumes to drought are very sensitive in maximizing the benefits of nitrogen fixation. Various studies have been conducted on different aspects to overcome the shortcomings of drought stress on biological nitrogen fixation. These strategies include screening of germplasms, genetic multiplication of drought-tolerant genotypes, tissue culture, biological approach and biotechnological interventions. Rhizobia play vital role in the production of plant’s metabolites, molecular responses, adjustment of hormones and dissolution and utilization of nutrients, to evade moisture stress conditions. Present chapter elaborates the detailed studies on the impact of drought stress on rhizobia and legumes grown in different moisture levels. Different strategies and techniques to overcome the shortcomings of drought stress on biological nitrogen fixation are also presented and discussed in logical manner.