Jan 7, 2005

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Fungus-resistant vines:

Vine trials abandoned

The first release experiment with genetically modified vines in Germany is being called off early. The Institut für Rebenzüchtung Geilweilerhof (Institute of Grapevine Breeding) has been testing different varieties of vine with a genetically engineered resistance to certain fungal diseases at two locations in Rhineland-Palatinate and Bavaria. However, they proved as susceptible to fungi as conventional vines. The trial also investigated biological safety issues.

Prof. Reinhard Töpfer, IRZ Geilweilerhof

Young genetically modified grapevines in the greenhouse. The genetically modified grapevines produce enzymes that attack the cell walls of fungi. In this way the plants should be able to defend themselves better against fungal diseases like the

Young genetically modified vines in the greenhouse

Transgenic vine pollen (blue) under the light microscope after application of saffron dye and GUS test.

Feeding experiments: The genetically modified grapevines produce chitinase, an enzyme that can dissolve fungal cell walls. To test to what extent the enzyme also attacks the intestinal wall of insects, grape-berry moth larvae are fed measured doses

A safety research project investigated whether the genetic modification had impacts on vine pests and beneficial organisms.

Photo: Grape-berry moth larvae are fed doses of chitinase in droplet form.

“With regard to fungal resistance, the genetically modified vines showed no advantages over the controls”, said Prof. Reinhard Töpfer, head of the Institut für Rebenzüchtung Geilweilerhof (IRZ) in Siebeldingen. The results obtained so far made a continuation of the trials appear unnecessary. They had been approved for ten years in 1999.

The genetically modified vines had been developed at the IRZ under Töpfer’s direction. To achieve increased resistance to fungal diseases like mildew and grey mould (botrytis), various barley genes were transferred to the trial plants. These genes cause the vines to produce the enzymes chitinase and glucanase as well as another protein (RIB), which inhibit cell wall development among many fungal pathogens or inhibit fungal growth.

In the past few years, conventionally bred fungus-tolerant vine varieties like Regent have become widespread, but there is a firm desire among farmers to make traditional vine varieties like the Riesling less susceptible to fungal diseases. The cultivation of fungus-resistant varieties can significantly reduce pesticide use.

The field experiments were designed to answer a range of questions:

  • In particular, they were supposed to determine whether the inserted gene constructs do actually result in increased resistance to fungal pathogens.
  • Since vines live a long time, it is important to know whether the introduced traits remain stable over several years under field conditions.
  • Experiments were carried out to investigate pollen spread and the outcrossing rates for vines.
  • And finally, the trials were supposed to answer an important question for wine consumers: whether the genetically modified vines produce the same wine quality.

Field test for fungal resistance

In July 1999, IRZ Geilweilerhof, part of the Federal Centre for Breeding Research on Cultivated Plants (BAZ), together with the Bayerischer Landesanstalt für Weinbau und Gartenbau in Würzburg planted genetically modified vines in the open. They contained various genes which, it was hoped, would produce significantly improved resistance to fungal diseases. At the Geilweilerhof site, plants were released with three different gene constructs. In Würzburg only one resistance concept was tested (see table below).

Three trial years have now been evaluated, showing that increased fungal resistance was not achieved. There therefore seems little point in continuing the trials.

Outcrossing

Possible pollen dispersal and outcrossing of transgenes from GM vines to other vines was investigated only at the Geilweilerhof trial site. Pollen traps were set up around 36 GM pollen donor plants at distances of 5, 10, 20 and 50 metres. The presence of the transgene in the pollen can be detected very quickly thanks to the blue colour produced by a marker gene inserted into the GM vines. At the same time, seeds were harvested at distances of 5, 10 and 20 metres from the pollen donor plants. Whether the seedlings that emerge from the seeds really are transgenic plants will be seen only after germination experiments. However, first indications of outcrossing have been found. Final data on the outcrossing experiments will not be available until sometime in 2005.

The wine quality question has, however, been answered. The Siebeldingen “GM Riesling” was tasted several times during the trial years. Prof. Töpfer says “The sensory test found no differences compared with the non-genetically modified control”.

Overview: Release of GM vines

Transformed variety Transformed genes Aim/effect Release site
Dornfelder ß-glucuronidase (GUS) from colibacillus GUS can be detected very easily because of its blue colouring and is used to determine the outcrossing rate Geilweilerhof
Seyval Blanc Chitinase and RIP (ribosome-inhibiting protein) from barley To increase fungal resistance Geilweilerhof
Riesling Chitinase and RIP from barley To increase fungal resistance Geilweilerhof and Würzburg
Riesling Chitinase and glucanase from barley To increase fungal resistance Geilweilerhof

The research project on fungus-resistant vines was sponsored by the Stiftung Rheinland-Pfalz für Innovation, Mainz (project no 543)

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