Genetic Diversity Of Soybean Root Nodulating Bacteria

Soybean (Glycine max L. Merrill), is a summer annual herb grown extensively in China, Argentina, Brazil and USA. It was thought to be very selective for its symbiotic partner. Earlier, only Bradyrhizobium japonicum was reported to nodulate soybean. It now is reported to be nodulated by a number of rhizobial genera and species; Rhizobium, Bradyrhizobium, Mesorhizobium and Sinorhizobium. Sinorhizobial species (fredii) nodulating soybean shows broad host range, where as the slow growing Bradyrhizobium is more selective. Slow growing B. japonicum, B. elkanii, B. liaoningense and B. yuanmingense are more effective nodulaters of soybean. Fast growers Rhizobium tropici, Rhizobium sp., Rhizobium oryzae and Mesorhizobium tianshanense have also been reported to form nodules on soybean. A large genetic diversity exists within the slow growing Bradyrhizobium isolates nodulating soybean. Due to the ecological and economic importance, the Bradyrhizobia species and their diversity have been extensively investigated in the last few years. The diversity and the size of indigenous population in soil can vary with the presence of the host legume and the history of the land use pattern at the sampling site. This review focuses on the genetic diversity existing in the bacteria nodulating soybean with special reference to Indian work.