of gene dispersal from plants produced by recombinant DNA technology
Genetic modifications (manipulation or engineering) and the introduction
of new characters into crop plants has considerable potential for European
agriculture. It is already possible to introduce genes which make crops
resistant to certain pests and diseases and to improve the quality of
the plant product, and many other new opportunities are emerging. Because
genes from a wide variety of organisms and even synthetic genes produced
in the laboratory can be introduced into crop plants, it is important
to study their function in the modified plant. Most importantly, the biosafety
aspects of any release into the environment must be carefully considered.
The likelihood and consequences of the genes, and thus the traits, being
transferred to other crop plants or related weed species is of particular
Approach and methodology
The aim was to study the frequency and extent of cross-pollination between
modified crop plants containing introduced marker genes, and other plants
of either the same species or other related species, and particularly
those that are common weeds. Three major crop species were used: potato,
alfalfa and oilseed rape. Powerful techniques for transformation of these
species are already available, and each illustrate specific safety aspects
as concerns introduction into an open environment. Two major issues were
addressed. First, the extent and distance of cross-pollination between
modified plants and non-modified plants growing around them in an adjacent
crop was examined. Oilseed rape was used for these experiments. Second,
the ability of crop plants to transfer introduced genes to related species
was considered. This also involved analysing the likelihood of the affected
plants (especially weeds) becoming established in wild populations. Potato,
alfalfa and oilseed rape were used. This study involved both natural outcrossing
and the application of sophisticated technology to generate hybrids for
findings and outcome
A marker gene, the gene for resistance to a particular herbicide, was
introduced into alfalfa. The gene was transferred from the modified plants
to other alfalfa plants and also to various related plants: M. sativa
spp. falcata, M. sativa spp coerulea, M. sativa spp glutinosa,
M. saxatilis and M. cancellata. The marker gene was inherited
and expressed in the hybrid plants in accordance with standard genetic
theory. In contrast, potato could not be crossed with local weed relatives
black nightshade and bittersweet. Using appropriate sophisticated techniques,
oilseed rape could be crossed with related wild species. Initial characterisation
suggested that the hybrids expressed the transgene in a normal way. However,
due to the hybrid nature of these plants, there were specific effects
interfering with normal propagation (for example partial or complete sterility).
Even under optimal conditions for interaction between oilseed rape and
related weeds (mixed stands of the two plant species) the frequencies
of outcrossing were very low. Indeed, no outcrossing was detected after
screening many millions of individual plants. Field trials were used to
estimate the distance of biologically relevant gene dispersal. At a distance
of 4 metres from the pollen source, the frequency of outcrossing dropped
to below 1 in 1000.
Gene transfer may occur between alfalfa and certain non-cultivated relatives
growing nearby. In the conditions studied, the dispersal of transgenes
by potato pollen is not possible and there is therefore no biosafety problem.
Gene transfer from oilseed rape to certain non-cultivated relatives is
possible by specific experimental techniques, but extremely unlikely in
natural conditions. Furthermore, such hybrids do not persist in the environment.
The range for biologically relevant dispersal of pollen from oilseed rape
is short where suitable biological containment measures are used (for
example guard rows of cultivated plants).
Scheffler J.A., Parkinson R. & Dale P.J., "Frequency and
distance of pollen dispersal from transgenic oilseed rape (Brassica
Transgenic Research, 2, 1993, pp. 356-364.
P.J., Irwin J.A. & Scheffler J.A., "The experimental
and commercial release of transgenic crop plants".
Plant Breeding, 111, 1993, pp. 1-22.
P.J., "The impact of transgenes in hybids between genetically
modified crop plants and their related species - general considerations".
Molecular Ecology, 3, 1994, pp. 31-36.
H.C. & Dale P.J., "An assessment of gene transfer by
pollen from field-grown transgenic potatoes to non-transgenic
potatoes and related species".
Transgenic Research, 3, 1994, pp. 216-225.
J.A. & Dale P.J., "Opportunities for gene transfer from
transgenic oilseed rape (Brassica napus) to related species".
Transgenic Research, 3, 1994, pp. 263-278.
February 1989 December 1990
John Innes Centre of Plant Science Research
W. De Greef
PGS Plant Genetic Systems N.V.
Le Rheu (FR)
Centre for Plant Breeding Research