The discovery of Rhizobium leguminosarum bv. trifolii and photosynthetic Bradyrhizobium as rice endophytes from Egypt and Africa has added a new paradigm in beneficial plant-microbe association with their role in plant growth promotion (Yanni et al 1997, Chaintreuil et al 2000).
These bacteria were capableof colonizing rice root interiors endophytically (in intercellular space) while promoting plant growth of certain rice cultivars. Earlier, other bacteria such as Azospirillum and Herbaspirillum were isolated from rice and they showed colonization and growth promotion (Okon and Labandera-Gonzales 1994, James et al 2002).
In India, where rice has been under cultivation for many decades, we looked at the possibility of such natural rhizobial endophytes occurring in Indian soils.