Dynamics of microbial population size in rhizosphere soil of Monsanto's Cry1Ac cotton

Monsanto's Bt-cotton NC 33B, planted in northern China for more than one decade, effectively controls cotton bollworms; however the understanding of its potential effects on soil microorganisms is limited. The dynamics of eubacterial, fungal and actinomycetes population sizes in rhizosphere soil of the Bt cotton were analysed by real-time PCR (qPCR) at the different growth stages under field conditions during 2009 to 2011. Results showed that the population sizes (microbial rDNA gene copies) of eubacteria, fungi and actinomycetes in rhizosphere soil were markedly affected by natural variations in the environment related to the year, cotton growth and cultivar. However, there was no significant difference in eubacterial, fungal and actinomycetes population size in rhizosphere soil between the Bt-cotton NC 33B and its near-isogenic comparator DP 5415. In general, the Bt-cotton NC 33B did not show evident effects on the population sizes of eubacteria, fungi and actinomycetes in rhizosphere soil under field conditions after three-year cultivation.