Ecological research into possible environmental risks of genetically modified virus-resistant sugar beet (Main focus: Environmental behaviour of different transgenic cross hybrids of cultivated and wild beet or mangold

(1992 - 2000) RWTH Aachen University; Chair of Biology V

Topic

Three successive projects investigated whether genetically modified sugar beet resistant to rizomania , a disease triggered by viruses, behaves differently in the environment to conventional beet.

The project focussed on three key topics.

Key topic (2):
Environmental behaviour of different hybrids of cultivated, wild and volunteer beet and mangold

When genetically modified sugar beet is cultivated, outcrossing to related species such as mangold or wild beet can occur. It is conceivable that the resulting cross hybrids will behave differently in the environment to conventional reference plants.

Do cross hybrids of transgenic sugar beet (rizomania resistance) and wild beet or mangold differ from conventional reference plants in terms of their naturalisation and dispersal behaviour?
Do the integrated genes confer a fitness advantage on the transgenic hybrids, which manifests itself in terms of increased competitiveness, overwintering and persistence ability?

Summary

Competitive behaviour. The genetically engineered viral resistance does not lead to increased competitive behaviour in the transgenic hybrids. During a viral attack, transgenic hybrids show slightly increased competitiveness compared with the non-transgenic reference plants.
Overwintering behaviour. It was not possible to detect a difference in overwintering ability between transgenic and non-transgenic hybrids in either cold or mild winters.

Experiment description

Release trials were conducted over a period of several years – in one location with the rizomania virus (Mainz) and one without (Aachen).

The studies comprised:

transgenic virus-resistant varieties of sugar beet (with a herbicide resistance marker gene)
various hybrids of transgenic sugar beet and wild beet or mangold. These were produced artificially using hand-pollination.
the respective isogenic non-GM reference lines.

Results

Competitive behaviour

To simulate competitive behaviour, a typical weed (Chenopodium album) is planted in varying densities (high, low, without) together with the hybrids under investigation. Biomass production is measured as an indicator of competitiveness.

The studies were conducted at locations with and without the virus.

Transgenic hybrids only produce increased biomass when there is no competition from weeds and virus infection is present. In these circumstances the virus resistance confers a competitive advantage.
In all other conditions no significant differences in biomass production were found between the transgenic and the non-transgenic hybrids.
Competitive pressure from the weed Chenopodium results in reduced biomass production in all hybrid types and in transgenic sugar beet.
Viral infection – irrespective of competitive pressure – causes a reduction in biomass.

Overwintering behaviour of the plants

Sugar beet is a biennial plant. In the first year the beet itself is formed. In order to flower in the second year, the plant must survive a winter. In Central Europe this only occurs during mild climatic conditions.

The overwintering behaviour of mangold and wild beet hybrids was studied at different locations with and without the virus. In the autumn the fields were not harvested and in the spring surviving plants were examined. The surviving plants, the seed that had been produced and the fertile offspring were recorded.

The findings were correlated with climatic data (snowy days, cold spells).

In general, the survival rate decreased dramatically when temperatures frequently fell below -4°C.
The studies with transgenic mangold hybrids and the associated control plants could only be conducted in winter 1996/97 due to limited seed material. In all locations – with and without the virus – the number of surviving plants was very low due to the severe winter. No significant differences between the transgenic and non-transgenic plants were identified.
In winter 1997/98 various hybrids showed an increased overwintering ability compared to the parent strains at the virus-free location. An increase in hybrid vigour can be explained by the heterosis effect .
No significant differences were found between the transgenic hybrids and their respective non-transgenic control plants.