Effects of transgenic glufosinate-tolerant oilseed rape (Brassica napus) and the associated herbicide application on eubacterial and Pseudomonas communities in the rhizosphere

Abstract

A containment experiment was carried out in order to evaluate possibleshifts in eubacterial and Pseudomonas rhizosphere community structuresdue to the release of genetically modified Basta-tolerant oilseed rapeand the associated herbicide application. Treatments includedcultivation of the transgenic plant as well as of the wild-type cultivarin combination with mechanical removal of weeds and the application ofthe herbicides Basta (active ingredient: glufosinate) and Butisan S(active ingredient: metazachlor). Rhizosphere soil was sampled fromearly and late flowering plants as well as from senescent plants. Aculture-independent approach was chosen to characterize microbialcommunities based on denaturing gradient gel electrophoresis of 16S rRNAgene fragments amplified from rhizosphere DNA using eubacterial andPseudomonas-specific PCR primers. Dominant pseudomonads in therhizosphere were analyzed by sequence analysis. Whole community andPseudomonas electrophoresis fingerprints revealed slightly alteredmicrobial communities in the rhizosphere of transgenic plants; however,effects were minor as compared to the plant developmentalstage-dependent shifts. Both herbicides caused transient changes in theeubacterial and Pseudomonas population structure, whereas differencesdue to the genetic modification were still detected at the senescentgrowth stage. The observed differences between transgenic and wild-typelines were most likely due to unintentionally modified plantcharacteristics such as altered root exudation. (C) 2002 Federation ofEuropean Microbiological Societies. Published by Elsevier Science B.V.All rights reserved.