Pollen flow from engineered crops-problems for growers

Herbicide-Resistant Canola-A Grower's Dream or Nightmare?

Canola, a valuable oil crop widely grown in western Canada, has been genetically engineered so that it won't be killed by several common herbicides. The Canadian government has thus far approved varieties resistant to three weed killers- -glyphosate, glufosinate, and imidazolinone.

Herbicide-resistant canola would appear to be a grower's dream come true. For example, farmers have only to plant canola seeds immune to glyphosate (sold under the trade name Roundup) or glufosinate (sold as Liberty). When weeds come up, they simply spray the field with Roundup or Liberty weed killer. The weeds wither and die; the canola keeps on growing.

Unfortunately, the dream one season can become a nightmare the next because the new genes do not stay put. Natural pollen transfer can create new weed-control problems.

As an example, suppose Sally, a Canadian farmer, had planted and harvested Roundup-resistant canola last year. Her neighbor, Scott, unbeknownst to Sally, had planted Liberty- resistant canola. Now, the following spring, she is planning to rotate flax into the canola fields.

Expecting that any volunteer canola in her field would be Roundup-resistant, Sally sprays Liberty herbicide to kill weeds before planting flax. To her surprise, lots of canola survived the spray. She sprays again with Liberty, but the volunteer canola keeps growing. She buys another herbicide, which finally works. Meanwhile, the weed problem has forced her to miss the optimal planting date for flax.

What happened? The probable explanation is that last season insects or wind carried pollen from Scott's Liberty- resistant canola into Sally's field-creating a small percentage of seeds resistant to Liberty. During harvest, some of those seeds were left behind-ready to germinate and grow this spring, causing Sally extra expenses for weed control.

This is not the only difficulty that herbicide-resistant canola may cause. The crop, which is a member of the mustard family, may easily pass the herbicide-resistance gene to its close relatives--wild, weedy mustards--which abound along roadsides and in fence rows and fields. Just like the engineered crop, these weeds may not be killed by the herbicide. Over a number of seasons, some weeds may become immune to all the herbicides which canola is engineered to resist. As a result, a farmer might have to run through several different herbicides before all her weeds are killed.

In the new world of engineered canola, farmers will be able to decide what herbicides to buy only after they know their neighbors' recent crop history.

Sources: T.R. Mikkelsen, et al., "The risk of crop transgene spread," Nature 380:31, March 7, 1996; Status of Plants with Novel Trait Approvals, Canadian Food Inspection Agency, Plant Biotechnology Office, web site:www.cfia- cia.agr.ca/english/plant/pbo/okays.html.

Engineered Crops-A Menace to Organic Growers

Another instance where farmers need to know what their neighbors are planting occurs with organic growers.

Consumers expect organic food to be free of engineered genes--whether the genes are deliberately put into crops in a biotech lab or move inadvertently via pollen from engineered plants into nearby organic fields. Most worrisome for organic growers are crops like corn which readily cross breed. Corn pollen is easily carried by wind from a corn variety in one field to another variety in another field- producing kernels with genes of both varieties. Other crops, like soybeans, are far less of a problem because they are self-pollinating and not wind pollinated. Pollen from a soybean plant typically fertilizes the same plant or close- by plants--resulting in little pollen flow between different varieties unless they are planted very close together.

To avoid contaminated crops, organic growers must plant only nongenetically engineered seeds and be sure that cross breeding will not occur with neighbors' engineered crops. Preventing cross breeding in corn and other interbreeding crops by planting the organic field so far from engineered ones that pollen cannot be carried between the two is not always feasible.

With millions of acres of US cropland planted to genetically engineered crops, avoiding contamination from a neighbor's engineered crop could become a major challenge.

Aware of the cross-breeding threat to organic growers, the Swiss government recently denied permission for a field trial of genetically engineered corn. The Swiss department for environment, forestry, and agriculture reportedly rejected an application from a biotechnology company, AgrEvo, to test herbicide-resistant corn because organic crops might be contaminated.

Source: A. Abbott, "Swiss reject GM trial to protect organics," Nature 398:736, April 29, 1999.