Bt cotton planting does not affect the community characteristics of rhizosphere soil nematodes

Transgenic cotton plants expressing Cry1Ac proteins from the soil bacterium Bacillus thuringiensis (Bt) provide effective control of Lepidopteran pests and thus reduce pesticide application. However, whether Bt cotton exerts undesirable effects on soil nematodes is largely unknown. Here we report the seasonal variations of soil nematode populations and the associated community indices in the rhizosphere soil of Bt and non-Bt cotton fields in northern China. Soil samples were collected at the main growing stages of the cotton during 2009-2010. Nematodes were extracted and recovered from soil samples using a modified cotton-wool filter method and identified under a light microscope according to their morphological characteristics. In addition, the nematodes were also classified to trophic group according to their feeding habits. Two years of cultivating transgenic Bt cotton failed to affect the total abundance, community diversity index or functional index of soil nematodes in 0-15 cm layer of the rhizosphere soil. Bt cotton consistently exerted detectable effects on nematode community composition when measured as direct effects on the densities of nematode genera, while slight effects were found using the principal response curve (PRC) analysis of repeated sampling events. These results suggest that Bt cotton has no significant adverse impact on soil nematodes community. (C) 2013 Elsevier B.V. All rights reserved.