FACTORS INFLUENCING NODULE OCCUPANCY BY INOCULANT RHIZOBIA

Inoculation of legumes under field conditions with superior nitrogen-f ixing rhizobia does not always result in the desired yield increase. O ften it is observed that the inoculum strain fails to occupy a signifi cant proportion of the nodules. The introduced inoculant strains have to compete with the indigenous, often ineffective, nitrogen-fixing rhi zobial population at different levels. The success of inoculation depe nds to a large extent on the ratio of the inoculant cells to indigenou s rhizobia. However, intrinsic characteristics of the inoculant and in digenous rhizobia, and their responses to abiotic and biotic environme ntal variables, also influence the outcome of inoculation. In this rev iew, the genetic basis for ''efficient host-bacteria interaction'' is reviewed. In addition, environmental factors that influence competitio n and saprophytic competence of rhizobia are discussed.