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EC-sponsored Research on Safety of Genetically Modified Organisms - A Review of Results
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image Safety assessment of the release of transgenic crops: spread of herbicide resistance genes from wheat and foxtail millet to weedy species

Background and objectives

The need for herbicide resistant wheat in developing countries is immense. If biotechnologically derived resistant varieties are released, a major biosafety issue that needs to be investigated, is the ability of any local weeds to acquire resistance genes from wheat, creating a situation which would jeopardise herbicide use. Although crosses of wheat with wild relatives are reputed to be unlikely and to produce sterile hybrids, a recent report described fertile spontaneous hybrids between wheat and Aegilops cylindrica, a pernicious weed found in the United States. Wheat has three different genomes, A, B, and D. Only D is common with Aegilops cylindrica, but other wild relatives have genomes with partial homologies to A, B or D, which can make gene flow easier. However, nothing is known about the behaviour of hybrid descendants in the field. In contrast, the experimental study of the frequency of resistance genes in weed field populations can be studied with foxtail millet, which is as self-fertile a cereal as wheat. Descendants of hybrids between millet and wild relatives have already been described by botanists and three independent herbicide resistances have been bred using classical techniques. The main objective of this project is to provide scientific information on the possibility and probability of transgene escape from biotechnologically-derived, herbicide-resistant wheat, to wild plants, via spontaneous interspecific hybridisation. This includes studies in different regions where different wild relatives are indigenous (including China, France, Israel, Spain and Switzerland), studies on different wheat transformants, and different modes of inheritance of transgenes that could be less prone to transferring the gene. The impact of the transfer of herbicide resistance genes into a wild population is also addressed using millet as a model for cereals.

Wheat Wheat.

Approach and methodology

Four key approaches are being undertaken. The first involves the development of genetically different types of herbicide-resistant wheat from a large number of transformations and their characterisation using introgression-substitution lines and DNA tools to identify on which genome the resistance gene was located. Herbicide resistance is both a very desired trait in agronomy and a good marker to detect gene escape and exert a clear-cut selection pressure.

The second approach involves the identification of grasses that can breed with wheat in specified ecological conditions and countries. This includes field study of flowering time and weed characteristics of wheat-related grass species, the estimate of the possibility of the intercrossing of wheat and the wild relatives by hand-crossing and embryo rescue techniques, and spontaneous interspecific hybridisations in the greenhouse and the garden. The rate of spontaneous mutations in cell culture of wild plants will be compared to gene escape from transgenic wheat.

The third approach involves a comparison of the growth, developmental fitness and natural reproduction of the different hybrids to those of the parents. This is followed by monitoring the introgression between wheat and wild relatives by means of chromosome identifying tools and DNA markers among hybrid progeny and further generations.

The fourth approach examines the collection of data on the spread of resistance genes after a large scale release of a resistant crop and the behaviour of resistance genes when inherited in different ways and under different regimes of selection pressure. This applies to herbicide-resistant millet used as an advanced model because resistant varieties are already available.

Main findings and outcome

Several experimental approaches and laboratory techniques have been established including the development of wheat lines which are resistant to an inexpensive, environmentally safe herbicide, and a quick test for screening and evaluating Dalapon resistance. The first interspecific hybrids between wheat and one of its wild relatives have also been produced. Wild relatives of wheat, and conditions leading to increased risks in fields, have been identified. Other techniques which have been established are a suitable and quick test to identify on which wheat genome (A, B or D) the transgene is located, cell culture conditions for several wild grass species, and the identification of molecular and cytogenetic markers specific for millet and wild relatives.


This project will help provide genetic engineering recommendations to wheat breeders to prevent uncontrolled gene escape by hybridisation between wheat and related grass weeds in the field. It will determine the likelihood of the spread of resistance genes into a weed population, the biosafety implications of such movements, and the extent (if any) of negative impact on farming activity and on the environment. It aims to propose guidelines about actual gene flow and its management, providing more information on the risk/benefit balance, and minimising the risks as far as is possible.


Major publications

Gressel J., "Molecular biology of weed control".
Transgenic Research, 9, 2000, pp. 355-382.

Gressel J., "Potential failsafe mechanisms against the spread and introgression of transgenic hypervirulent biocontrol fungi".
TRENDS in Biotechnology, 19, 2001, pp. 149-154.

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Contract number

February 1999 - January 2002

H. Darmency
Dijon (FR)



J. Gressel
The Weizmann Institute of Science
Rehovot (IL)

M-C. Chueca
Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria
Madrid (ES)

H. Wang
Hebei Academy of Agricultural and Forestry Sciences
Shijiazhuang (CN)

T. Wang
Chinese Academy of Agricultural Sciences
Beijing (CN)

K. Ammann
University of Bern (CH)

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