Mitigation of Abiotic Stress in Legume-Nodulating Rhizobia for Sustainable Crop Production

Abstract

Rhizobia form nitrogen-fixing nodules on leguminous plants and convert atmospheric nitrogen to plant-utilizable ammonia resulting into increased plant growth and crop yield. The growth of crops and rhizobia is adversely affected by various abiotic stresses including high temperature, soil salinity and drought. Under saprophytic phase in the soil, free-living rhizobial population usually declines due to abiotic stresses resulting to less nodulation in different legumes. Therefore, repeated inoculation is required every year for enhancing legume productivity. For effective nodulation, establishment and persistence of rhizobia in stressed environment is prerequisite, which depends mainly on their ability to tolerate, proliferate and survive under adverse environmental conditions. The major problem of abiotic stresses is faced in rainfed agro-ecosystems, which makes the survival of bio-inoculants a problematic issue. Moreover, a remarkable difference was observed in effectiveness of rhizobial bio-inoculants from laboratory to field conditions due to various abiotic stresses faced under field conditions. The survival of rhizobial inoculants and its limitations to enhance crop growth under field conditions may be overcome by screening the rhizobial isolates, which are tolerant to different types of stressed conditions. Stress-tolerant rhizobia could provide more beneficial effects under pot house and field trials leading to increased legume crop productivity in sustainable agriculture.