Comparative Studies On Structural And Functional Diversities Of Bacterial Communities Associated With Transgenic Bt And Non Bt Cotton

The potential risk of genetically modified plants to environment and human health has great concern due to their worldwide release and replacement of traditional crops by genetically modified crops.One of the most widely transformed gene is the cry1AB from Bacillus thuringiensis (Bt).The expression of this gene in plants produces an insecticidal toxin to kill Lepidopteran pests.Transgenic Bt plants release Bt toxins from plant biomass and root exudates in the soil. Therefore, soil may retain larvicidal activity for a long time even after crop harvest. It has been claimed after different studies that Bt toxins have no adverse effects on human, nontargeted microorganisms or to the environment. But it is important to keep in mind that whether one uses Bt, or any other method to control pests and if the pest population is reduced, there must be some impact on biological community.Therefore, it is important to address these changes in biological community. In the present study, total bacterial population, N2 fixers, Azospirillum spp. phytohormone producing bacteria and phosphate solubilizers were higher in the rhizosphere (soil & root) of non-Bt cotton as compared to Bt cotton. Bacterial population plays an important role in maintaining soil health status of an ecosystem.There was a partial shift in microbial communities in rhizosphere of Bt cotton as compared to non-Bt cotton.Microbial activities in the rhizosphere of non-Bt were either higher or equal to the microbial activities of Bt cotton rhizosphere and were highest at crop peak growth stage.A rich population of Azospirillum spp. was found in the wheat rhizosphere. Sixteen Azospirillum spp.were isolated and identified from wheat rhizosphere by BOX-PCR and 16S rRNA genes sequence analysis.They have shown potential to improve the growth of cotton plants.