Rhizosphere nitrogenase and Azospirillum sp. association with wild, trisomic and cultivated rice

The nitrogenase activity of rice rhizosphere and root associated Azospirillum sp. was evaluated in wild, trisomic and cultivated rices grown unde uniform field conditions. Wide variations in rhizosphere nitrogenase were noticed among the wild species of rice. The nitrogenase activity associated with rhizosphere was initially low and reached the maximum during the heading and reproductive phases of the rice plant. Oryza latifolia exhibited low nitrogenase compared to the six other wild species. The trisomic rices exhibited higher associative rhizosphere nitrogenase activity in comparison to normal cultivated rices. Similarly, Azospirillum sp. isolated from the trisomics exhibited higher nitrogenase activity compared with the isolates from normal ric roots. Although O. latifolia showed low rhizosphere nitrogenase, the Azospirillum sp. isolated from this had highest nitrogenase activity. In general, cultivated and trisomic rices supported considerable nitrogenase activity in the rhizosphere and as well harboured efficient Azospirillum sp. compared to wild rices.