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EC-sponsored Research on Safety of Genetically Modified Organisms - A Review of Results
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image Virus-resistant transgenic plants: ecological impact of gene flow

Background and objectives

Virus resistance was among the very first agronomically useful traits to be introduced into transgenic plants, and several virus-resistant transgenic cultivars have already been commercially released in the US and China. In order to provide the necessary science-based risk assessment of such plants before contemplating commercial release in Europe, it is essential to clarify several points concerning potential ecological impact.

The most important potential impacts could result from two forms of gene flow, either from plant to virus by recombination, or from plant to plant by sexual outcrossing. At the end of this three year project, it is expected that the results will clarify whether the currently developed types of virus-resistant cultivars can be released with acceptable risk due to either of these two forms of gene flow.

Turnip mosaic virus infection of oilseed rape.
The infected transgenic plant shown on the left is resistant, while the sensitive control on the right shows severe symptoms (leaf decolouration) of virus infection.

Approach and methodology

VRTP IMPACT will address the two outstanding questions concerning the potential ecological impact of virus-resistant transgenic plants: will recombination with an infecting virus lead to the creation of novel virus genomes, and will transmission of a virus resistance gene to wild relatives of the modified crop species confer a fitness advantage on the wild plants? These questions will be answered through both laboratory and field studies. In the studies of recombinational plant to virus gene flow, the particular targets will be two groups of important plant viruses, the cucumoviruses and the potyviruses. The plant to plant gene flow studies will focus on two major crop plants that are known to be able to outcross with wild relatives, beet and oilseed rape. Since it is known that gene flow between the crop and wild relatives can occur with these species, the work will focus, not on the incidence of gene flow, but on its outcome. In all cases, potential impact will be assessed relative to studies of these two forms of gene flow in the absence of transgenic plants.

Main findings and outcome

The participants have already at their disposal a considerable number of the tools and biological materials required for this programme, including numerous transgenic plant lines expressing sequences derived from viral genomes of several virus groups.

In the plant to virus gene flow studies, parallel experiments are being carried out with plants expressing sequences from cucumoviral or potyviral genomes. Some, but not all of these plants display some level of resistance to the viral strain from which the transgene was derived. In both systems, baseline information on the occurrence of recombinant viral genomes in doubly-infected non-transgenic plants is being obtained and compared to the occurrence of recombinant viruses in singly-infected transgenic plants. The biological properties, including relative fitness, of the recombinant viruses created will be tested. The comparison of these two data sets will make it possible to determine if the transgenic plants can promote the appearance of recombinant viral genomes that would not occur in non-transgenic plants.

In a complementary approach, a baseline study of the prevalence of recombinant viral genomes in natural cucumoviral and potyviral populations is underway. This will fill a significant gap in current knowledge, and will provide the natural biological context against which previous laboratory studies can be assessed.

In the plant to plant gene flow studies, the prevalence of the viruses studied in the wild plant populations will be determined, and the effects of virus infection on the fitness of the wild species evaluated, in particular whether introgression of a virus resistance gene from a transgenic crop relative can confer a fitness advantage on the wild plant species.


This project compares transgenic and non-transgenic plants to show whether recombination in the former could lead to the appearance of novel recombinant viral genomes not found in the latter. The field studies of naturally-occurring recombinants virus will tell us whether the recombinants occurring under laboratory conditions correspond to those observed in the field. The gene flow studies in beet and oilseed rape and their wild relatives will allow prediction of whether the passage of a virus resistance gene into the wild species will affect their fitness.

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Contract number

December 2000 - March 2004

M. Tepfer
INRA - Versailles (FR)

Project website address



E. Maiss
Hannover University (DE)

M. Jacquemond
Montfavet (FR)

D. Bartsch
Aachen University of Technology RWTH (DE)

R. Delon
Institut du Tabac
Bergerac (FR)

F. García-Arenal
ETSI Agronomos
Madrid (ES)

E. Balázs
Agricultural Biotechnology Center
Gödöllö (HU)

P. Palukaitis
Dundee (UK)

A. Raybould
Centre for Ecology and Hydrology
Dorchester (UK)

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