Effect of Bt Cotton on Enzymes Activity and Microorganisms in Rhizosphere

For three consecutive years Bacillus thuringiensis (Bt) transgenic cotton (var. Mech 162) and its isogenic non Btcounterpart were assessed for the risks of transgenic crop on the soil ecosystem under Indian subtropicalconditions. To observe effect of Bt cotton on soil biochemical properties, activities of dehydrogenase, alkalinephosphatase, nitrate reductase and urease soil enzymes were assayed at its different growth stages i.e., seedling,vegetative, flowering, bolling and harvesting stages. To observe effect of Bt cotton on soil microorganisms,number of nematodes, collembola and ants representing micro, meso and macrofauna, respectively wereobserved in Bt and non- Bt cotton plants rhizosphere at different growth stages.Results showed no significant difference (P<0.05) in alkaline phosphatase, nitrate reductase and urease activitybetween Bt and non- Bt cotton rhizosphere during crop growth period. However, dehydrogenase activity wassignificantly high (P<0.05) in the Bt cotton rhizosphere as compared to non Bt cotton rhizosphere through outthe observation period. At most of the growth stages numbers of micro, meso and macro fauna were more in Btcotton rhizosphere as compared to non Bt cotton rhizosphere. The temporal and spatial variations observed innumber of nematodes, collembola and ants between Bt and non Bt cotton plants rhizosphere were significant.The present study shows that the Mech 162 variety of Bt cotton was not posing any risk to soil microorganismsand soil biochemical properties.