Impact of Pesticides on PGPR Activity of Azotobacter sp. Isolated from Pesticide Flooded Paddy Soils

Abstract

Azotobacter strains were isolated from paddy soils by serial dilution agar plate method. The colonies were glistening; smooth, slimy, brown to black in morphology on Jenson’s N-free agar plates and the cells were Gram- negative bacteria. Biochemically, they were positive for indole production, citrate, catalase and Voges Proskauer test. Further, Nif gene sequence results revealed the presence of seven Azotobacter species. The effect of 1, 3 and 5% pesticides concentration viz., pendimethalin, chloropyrifos, glyphosate and phorate on nitrogen fixation, indole acetic acid, gibberllic acid, phosphate solubilization and bioassay of Azotobacter sp. were studied. Among all the species, GVT-1 strain was found to fix nitrogen at a maximum of 30µgN2 ml-1 day-1, produced highest quantity gibberllic acid (10µg25ml-1) and able to solubilize the phosphate at the rate of 9.8cm by forming the halo zone which was supplemented with 5% phorate. Similarly, GVT-1 strain produced a highest amount of indole acetic acid (31.8µgml-1) in 5% pendimethalin. Further bioassay activities of GVT-1 strain found efficient in increasing the root, shoot length and vigor of the plant. From these results it is clear that the Azotobacter sp. not only produces plant growth promoting substances but is also resistant to different pesticides and is not affected by the bacterial activity.