Canola pollen travels... but doesn't do much when it arrives

Pollen from a herbicide-tolerant canola crop spreads to neighbouring fields, according to Australian study published in the June 28th issue of Science, but only a very low percentage of plants are fertilised there.

During the 2000-01 growing season, Dr Mary Rieger, from the University of Adelaide and the CRC for Australian Weed Management, and her colleagues used a newly introduced variety of canola with herbicide resistance as a source and collected canola seeds from fields up to 5km away from the source crops to monitor the spread of the resistance.

Fields were sampled at the front, in the middle and at the back and results averaged over the field. Seeds were screened by planting and spraying with herbicide. Over 48 million seeds were screened, Rieger said.

Although the varieties used were all conventionally bred, the herbicide resistant crop was newly introduced to Australia and was a good model for the introduction of a GM canola crop.

Herbicide-resistant plants were found almost 3km from the source crop, demonstrating that the herbicide-resistance trait did spread. However, the highest percentage of herbicide-resistant plants in a single non-resistant field was 0.07 per cent, Rieger said, and overall only 0.03 per cent of the plants were resistant.

"It basically means that we can plant GM and non-GM together, and exclusion zones will work," she said.

"It won't be zero tolerance, but it will be workable. We need to set realistic limits."

Australia is considering 1 per cent GM contamination as the limit for labelling non-GM crops GM-free.

Rieger said the surprising result from the study was the random nature of the spread. Canola pollen is relatively large and while it mostly self-fertilises, can cross-pollinate as well.

"People knew it was going to travel, knew that it would be low, but it is more random than expected. It doesn't follow a mathematical model," she said.

She said that it was difficult to explain why the spread was so random, but suggested that environmental variation including topographical differences, climate and other factors might all play a part.

Rieger said that she did not intend to continue the research as the CRC had decided to discontinue the project.

"After six years it's a bit disappointing, but I'm being philosophical about it," she said.

For more information:

Pollen-Mediated Movement of Herbicide Resistance Between Commercial Canola Fields. Mary A Rieger, Michael Lamond, Christopher Preston, Stephen B Powles, and Richard T Roush. Science 2002 296: 2386-2388.