author(s)
Sivaji Mathivanan and Sridar Raghupathi

abstract
The present study was undertaken to evaluate the effects of root exudates of transgenic cotton (Bt cotton) plants on selected plant growth promoting microbes. Root exudates were collected from the Rhizosphere soil of Bt and non Bt cotton (RCH BG II and RCH respectively) at 30 days after sowing (DAS) and 60 days after sowing (DAS) under in vitro condition and incorporated in to the respective broth of selected beneficial microbes (Azospirillum brasilense, Bacillus megaterium, Pseudomonas fluorescens and Trichoderma viride). Presence of Cry 1 Ac and Cry 2 Ab (endo-toxins) in Bt cotton root exudates was confirmed with qualitative Desi-Gen ELISA Kit assay. The population count results revealed that no population variation on any of the microbes which were tested in both the root exudates taken from 30 and 60 DAS of the Bt and non Bt cotton. Among four microbes A. brasilense was found in high numbers and the least was T. viride. At 30 DAS A. brasilense and P. fluorescens were higher in Bt cotton where as B. megaterium and T. viride were found to be high in non Bt cotton. On 60 DAS A. brasilense and T. viride was more in Bt cotton, P. fluorescens was more in non Bt cotton. The population of B. megaterium was on par in both Bt and non Bt cotton. However there were no significant differences observed between cultivar in both the stages (30 and 60 DAS) on functional microbes.