Jul 5, 2002

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Study under farm conditions in Australia

Oilseed rape pollen: flies a long way, rarely outcrosses

In commercial cultivation, oilseed rape rarely outcrosses, but does travel further than had previously been assumed. These were the findings of a comprehensive field study on herbicide-resistant oilseed rape plants in Australia. In most cases the proportion of seeds that became resistant as a result of pollen dispersal was less than 0.03 per cent.

Rape flowers: (Photo: Bayrisches Landesamt für Umweltschutz)

The study

The study covered 63 fields measuring between 25 and 100 hectares in three Australian states with different ecological conditions.

Seeds were collected on each of the fields examined following a set pattern – from the middle of the field and from the field margins closest and furthest from the field with herbicide-resistant rape.

In total, 100,000 rape seeds were collected and sown again to see whether they had taken on the herbicide resistance characteristic.

The Australian research team led by Mary Rieger at the University of Adelaide, studied pollen-mediated gene flow in more than 63 conventional oilseed rape fields. The scientists made use of the fact that herbicide-resistant oilseed rape was grown commercially in Australia for the first time in 2000. This oilseed rape had been developed using conventional breeding methods, so without genetic engineering. The fields with conventional and resistant rape were each between 25 hectares and 100 hectares in size.

The key findings of the Australian research group:

  • In almost two-thirds of the conventional rape fields individual plants were found that had taken on the herbicide resistance characteristic as a result of pollen flow.
  • Pollen was detected up to a distance of three kilometres. Beyond this distance no resistant oilseed rape plants were found, despite the large number of seeds examined.
  • The maximum proportion of resistant seeds in any one sample was nearly 0.2 per cent, but the maximum field average was 0.07 per cent.
  • On most of the conventional fields studied the amount of the harvest that was herbicide resistant was less than 0.03 per cent.

The Australian research also shows that pollen-mediated gene flow does not diminish to the same extent with distance from the source in large-scale cultivation as it does in small trial fields. Instead, herbicide resistance was found at a relatively constant level over different distances.

Thresholds for GMO presence: low, but not zero

The study by Mary Rieger’s group provides important indications about pollen flow and outcrossing rates if genetically modified rape were to be grown on a large scale.

  • A threshold of one per cent, or even 0.3 per cent, for adventitious GMO presence in conventional food and feed can be achieved under field conditions.
  • By contrast, zero tolerance is practically impossible once GM rape has been released.

The research findings were published on 28 June 2002 in Science Magazine (page 2386).