Browsing by Author "Menzel, Ralph"

Before pest-resistant genetically modified maize can be grown commercially, the risks for soil-beneficial, nontarget organisms must be determined. Here, a tiered approach was used to assess the risk to free-living soil nematodes posed by maize genetically modified to express the insecticidal Cry3Bb1 protein (event Mon88017), which confers resistance towards western corn rootworm (Diabrotica virgifera; Coleoptera). The toxicity of purified Cry3Bb1 for the nematode Caenorhabditis elegans was determined using a bioassay and gene expression analysis. In addition, a soil toxicity test was used to assess the effects on C. elegans of rhizosphere soil obtained from plots of an experimental field grown with Mon88017, the near-isogenic cultivar, or either of two conventional cultivars. Finally, the indigenous nematode communities from the experimental field site with Mon88017 and from the control cultivars were analyzed. The results showed a dose-dependent inhibitory effect of Cry3Bb1 on the growth and reproduction of C. elegans, with EC50 values of 22.3 mg l(-1) and 7.9 mg l(-1), respectively. Moreover. Cry-protein-specific defense genes were found to be up-regulated in the presence of either Cry1Ab or Cry3Bb1. However, C elegans was not affected by rhizosphere soils from Mon88017 compared to the control plots, due to the very low Cry3Bb1 concentrations, as indicated by quantitative analyses (<1 ng g(-1) soil). Nematode abundance and diversity were essentially the same between the various maize cultivars. At the last sampling date, nematode genus composition in Bt-maize plots differed significantly from that in two of the three non-Bt cultivars, including the near-isogenic maize, but the shift in genus composition did not influence the composition of functional guilds within the nematode communities. In conclusion, the risk to free-living soil nematodes posed by Mon88017 cultivation can be regarded as low, as long as Cry3Bb1 concentrations in soil remain four orders of magnitude below the toxicity threshold. (C) 2011 Elsevier B.V. All rights reserved.

The genetically modified maize MON89034 x MON88017 expresses different crystal (Cry) proteins with pesticidal activity against the European corn borer (Cry1.105; Cry2Ab2) and the Western corn root worm (Cry3Bb1). Non-target organisms, such as soil nematodes, might be exposed to the Cry proteins that enter the soil in course of crop growing. Therefore, the risk of those proteins for nematodes was assessed by testing their toxic effects on Caenorhabditis elegans. All three insecticidal Cry proteins showed dose-dependent inhibitory effects on C elegans reproduction (EC50: 0.12-0.38 mu mol L-1), however, at concentrations that were far above the expected soil concentrations. Moreover, a reduced toxicity was observed when Cry proteins were added jointly. A C elegans mutant strain deficient for receptors for the nematicidal Cry5B was also resistant against Cry1.105 and Cry2Ab2, suggesting that these Cry proteins bound to the same or similar receptors as nematicidal Cry proteins and thereby affect the reproduction of C elegans. (C) 2013 Elsevier Ltd. All rights reserved.