Oct 30, 2002

Research Projects

Send

Creating a model for gene transfer and feral tendency among transgenic sugar beet

(1998 – 2000) Justus Liebig University Giessen, Biometry and Population Genetics

Topic

The task of the project is to develop a mathematical model that can be used to answer various questions linked to the possible large-scale cultivation of genetically modified sugar beet.

• How do transgenes spread in sugar beet populations or among other crossing partners? (vertical gene transfer)
• How quickly does dispersal take place? (population dynamics)

The idea is that the model should help assess the gene flow for large-scale cultivation of transgenic sugar beet, but also for other plants.

Summary

The model that was developed simulates the outcrossing frequencies that can be expected. It produces results that are closely in line with experimental data.

• The model can be used to take safety aspects into account when planning test facilities. For outcrossing experiments the model provides data on the necessary number of sampling tests.
• The model can be used on a small scale in connection with individual plants and populations. But it can also simulate the gene flow and its impacts on larger regions (max. 30 x 30 km²). The results can be used to help design a future monitoring programme.

Experiment description

No separate experiments were carried out in order to obtain the data necessary to develop the model. The model is based on data from other experiments and from the literature.

The model takes the following parameters into account: genotype, bolter frequency, pollen and seed count, distance of seed dispersal, germinability, overwintering and crop rotation.

The model consists of two modules in order to depict the gene flow both in the temporal and spatial dimension.

Module: Vertical gene transfer

In the vertical gene transfer module, the outcrossing of transgenic pollen to other populations (wild and cultivated species) is assessed as a function of distance and wind.

Module: Internal population dynamics

This module describes the consequences for a beet population in which the transgene may be retained, setting off a process of change within the population (population dynamics). Depending on the overwintering, germination and competitive strength of the seedlings, the model calculates how the distribution of the various plant individuals will change in the next vegetation period. This data is fed back into the module for vertical gene transfer.

The model is linked to the Geographic Information System (GIS). This means that maps showing land use and distribution of wild beet can be incorporated.

Results

The model developed on the example of sugar beet is suitable for assessing the possible gene flow for transgenic crop plants in wild populations in specific individual cases.

Vertical gene transfer module

This module was checked using experimental data. For greater distances it corresponds closely to the observed values. For distances of less than 20 metres, however, the model calculates outcrossing probabilities that are too high.

The module can also be used to improve sampling in outcrossing experiments. Depending on the distance, it will calculate the number of random samples necessary to detect at least one outcrossing event.

Internal population dynamics

There is currently insufficient data available on the population dynamics of sugar beet. The module could therefore only be checked using theoretical considerations.

The model is suitable for simulating various processes. It does, however, need to be developed further and “calibrated” using concrete data. Only then will it be possible to make sound statements under suitably selected conditions.

Example: Impact of a cultivated variety on neighbouring wild populations

The model is used to simulate the effect of a certain cultivated sugar beet variety on neighbouring wild beet under different cultivation methods.

• With one-off cultivation of sugar beet, a few hybrid plants (crosses between wild beet and sugar beet) occur outside the cultivated areas, as do isolated sugar beet plants, but they disappear again after six years (top).
• Under permanent cultivation, the sugar beet totally supplants the wild beet (middle).
• With a crop rotation in which sugar beet is planted every three years, over 50 per cent will be hybrids. Wild and cultivated beet are about evenly balanced (bottom).