Spatial diversity of free living rhizobia present in Rhizosphere soils of six different physiographic regions of Maharashtra, India

A total of 76 free living Rhizobia isolates were recovered from the rhizosphere soils of six different physiographic regions of Maharashtra. The distinct variation was observed in colony and cell morphology among different isolates. A significant variation was observed in the nitrogenase activity from 1.9 to 119.7 nmol C₂H₄ mg protein⁻¹ hr⁻¹ among the 76 Rhizobium isolates. Among six physiographic regions of Maharashtra, Rhizobium isolates from Western Maharashtra exhibited a higher average nitrogenase activity (33.1 nmol C₂H₄ mg protein⁻¹ hr⁻¹). Based on UPGMA clustering analysis, Rhizobium isolates were classified into three broad clusters and the genetic variation observed among Rhizobium isolates was due to domestication of the isolates in different agro-ecological regions as well as their nitrogenase activity. Based on nitrogen-fixing ability, highly efficient Rhizobium isolates may be further exploited in biofertilizer production.