Existing Research on Pollen Movement


A considerable amount of research has already been conducted on the intricacies of out-crossing. Rather than carrying out new experiments, the aim of this Co-Extra project is to compile all information already known, and to learn from experience.


To take stock of existing knowledge on pollen movement, the results of completed research endeavours were evaluated and compiled into a review. One such research project is SIGMEA, which aimed  to set up a science-based framework and developed methods for assessing the ecological and economical impacts of GM crops and, among others, studied gene flow of several crops grown in the EU. The SIGMEA project was also funded by the European Commission’s 6th Framework Programme.

The review addresses specific topics including pollen production, emission dynamics, transport, and viability. Once finalised, the review will be published in a scientific journal.


Existing data on the spread of maize pollen shows that, although it is physically possible for maize pollen to pollinate plants several kilmometres away, the vast majority of pollen (95 to 99 percent) settles within about 30 metres from its source. Nearly all potential cross-pollination between maize fields occurs within 25 metres. Rare out-crossing "hotspots" can occur at distances of more than 600 metres when:

  • Convection from daytime heating lifts warm air above a field, carrying pollen with it
  • Steering winds carry the pollen to another maize field
  • The maize field downwind is receptive to pollen at the time of the long term dispersal

Research has also been conducted to see how out-crossing is affected when fields are surrounded by:

  • a buffer planting of maize
  • or a dividing row of trees

It was found that a buffer strip of maize significantly reduces the amount of gene flow both by intercepting GM pollen and by releasing competing pollen. It is suggested that four rows of maize can have the same buffering effect as six metres of open space. Trees also help disrupt pollen flow, but they do not release their own pollen that can compete with the undesired GM pollen. Recent observations suggest that after a ten to twenty metres buffer strip of maize, the 0,9 percent threshold for GM presence almost never was exceeded in the harvested grain.

It has also been shown that large conventional fields are less affected by out-crossing than small ones. This is because larger conventional fields have a greater number of plants distant from the GM planting that dilute the portion of the conventional field near the GM maize. Similarly, a rectangular field with its long edge along a GM maize field will be more likely to exceed the threshold for admixing than a field of the same size with its short edge abutting the GM maize.


Alexandra Huesken and Joachim Schiemann
Federal Biological Research Centre for Agriculture and Forestry, Germany
Email: info@coextra.eu