ACRE Advice

A Report on a Paper Concerning the Diversity of Bacterial Communities Associated with Conventional and Genetically Modified Herbicide Tolerant Oilseed Rape

Advice of the Advisory Committee on Releases to the Environment under Section 124 of the Environmental Protection Act 1990

June 2002

ACRE was asked to review the study by K.E. Dunfield and J.J. Germida (2001) ¹ concerning the microbial communities associated with the roots of field sown oilseed rape in Canada over a period of two years.

The study compared seven varieties of oilseed rape (Brassica napus): four were genetically modified for herbicide tolerance, one was herbicide tolerant but not genetically modified and two were conventional varieties; in addition to these there was one variety of the wild relative, wild turnip rape (Brassica rapa). The varieties were grown on four soil types at different locations in Saskatchewan, Canada. Three of the GM herbicide tolerant varieties were tolerant to glufosinate ammonium and one variety was tolerant to glyphosate.

In the study, microbial communities were isolated from the rhizosphere (root surface) and endorhizosphere (root interior) of the rape plants and were subjected to two types of analysis; Fatty Acid Methyl Ester (FAME) analysis and carbon substrate utilisation profiling (also known as BIOLOG). The authors concluded that the composition and functional diversity of the microbial community were influenced by plant variety and soil type.

ACRE considered the study and its implications for the release and marketing in the UK of rape crops genetically modified (GM) to express tolerance to either one of the herbicides glufosinate ammonium or glyphosate.

ACRE's advice:

ACRE emphasised that although soil ecology is a complex and difficult subject to investigate, there remains a need for investigation using rigorous scientific technique and methodology where the varied components can be analysed fully in order to produce an integrated picture. Further, there is acknowledged difficulty in pursuing scientific investigations of this kind on soil ecology, with a lack of consensus within the scientific community on suitable methodology.

ACRE considered the report and noted that the samples used for both FAME and BIOLOG analyses would have contained whole microbial communities and hence mixed samples of bacteria. While these methods can provide useful information they were being used to analyse a complex picture and the data obtained by these methods would not necessarily provide a detailed or sensitive picture of the extent of changes in diversity.

ACRE was also critical of the statistical analysis, noting that the Authors had used the method of principal component analysis and had not produced a robust analysis of the data, but nevertheless had superimposed a bold interpretation onto the results. The data also appeared to have been presented in a selective manner. ACRE highlighted that it is important to practice caution in interpretation of the results of these kinds of statistical methods. In addition, previous work has indicated that plant variety can be expected to have subtle effects on microbial communities and investigations must be able to pick up these small changes. ACRE questioned whether these experiments would be sensitive enough to do this.

It is known that bacterial populations associated with different crop types grown over the seasons differ and that climate and soil type can have a large effect on this variation. Many hundreds of years of agricultural experience has involved rotation of crops and deliberate changes of crop type where each crop has effects on the ecology of soil associated with it. The changing dynamic of the soil, its reversibility and plasticity, are desirable and beneficial qualities which, for example, can contribute to, controlling plant pathogens.

Given this, it is not unexpected that this paper appears to show some small effects of crop variety on microbial communities. However, the results of this study did not indicate that this variation bore any relation either to genetic modification or herbicide tolerance. Nor does the study appear to have taken account directly of any application of the herbicide to the plants during the period of the field growth of the plants. There is no clear link to causal effects for genetic modification or herbicide tolerance and these changes are consistent with the expected changes which could be found in the context of normal agriculture.

In conclusion, ACRE had no safety concerns arising as a result of this study and the results were within the bounds of variance in microbial populations as it is understood to occur in agricultural environments. No further information has come to light as a result of this study which affects the risk assessment of release of GM herbicide tolerant oilseed rape in the UK.

1 Dunfield, K. E. & Germida, J. J. (2001) Diversity of bacterial communities in the rhizosphere and root interior of field-grown genetically modified Brassica napus. FEMS Microbiology Ecology 38 p1-9