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Update on Bt Cotton and Transgenic Crops

Crop and Soil Environmental News, December 1996

Charles Hagedorn,
Extension Biotechnology Specialist

Bt Cotton Performance - Success in Alabama

In the August update, the Bt cotton situation in Texas and the Mississippi Delta was examined as intense weevil pressure had resulted in insecticide applications to substantial acreage of Bt cotton. On a more positive note, two major advances in cotton production - boll weevil eradication and Bt cotton - came together in Alabama this year to reverse what appeared to be a hopeless cotton production situation. The boll weevil eradication program is finally working and 75 percent of the statešs cotton was planted in Bollgard cotton in 1996. These two advances have provided a near-perfect environment for growing cotton at a significant level of profit.

Alabama producers went from a worst-case scenario in 1995 to the best of times in 1996. Some growers went from 13 insecticide applications last year to zero this year and a significant portion of the cotton in Alabama was not sprayed at all. In 1995, Bt cotton was not available and weevils still were being cleaned up. This year, insecticides to control weevils were applied on a very small percentage of the acreage (about five percent). The Boll Weevil Eradication Program is finally taking out a pest that's been in the cotton production system for approximately 80 years. This occurred in the same year that more than 70 percent of the state's cotton acreage was planted in Bollgard varieties - varieties that are resistant, in most cases, to budworms and bollworms. Alabama's weevil eradication program began in September of 1987, in the southern region of the state, and has now expanded to all of the cotton producing areas.

The weevil eradication program fits in well with the new Bt cotton varieties. In contrast, growers in the Delta still face serious insect control problems because they have to over-spray Bt cotton every five days for boll weevils. This takes out beneficial insects, and beneficials play a vital role in Bt cotton. The full benefits of Bollgard cotton will never be felt in those areas that still have boll weevils. The remainder of the Cotton Belt will have to proceed with eradication programs before growers can get the full benefit of Bt cotton. The Boll Weevil Eradication Program, combined with Bt cotton, has revitalized Alabama's agricultural economy. Cotton estimates for 1996 are 700-pounds-per acre statewide average yield. This is a tremendous contrast to 1995, where the cotton crop in Alabama was described as a failure, and points out in graphic terms the importance of protecting the Bt mechanism to prevent insect resistance to Bt.

Concerns over Engineered Crops and Superweeds: The Transgenic Squash

The Freedom2 Squash and its cousins look like any other plump yellow squash, but actually they represent significant improvements. These squash varieties have been genetically engineered by the Asgrow Seed Co. of Kalamazoo, Michigan, to resist two common plant viruses. In large-scale field trials in Texas over the last two years, Freedom2 has significantly out-produced lesser squash. Yet despite Freedom2's virtues, a debate has begun swirling about this and other transgenic crops. The public's original fears about genetically engineered crops have subsided, but now some biologists are raising a new concern: that advantageous genes, such as those that make Freedom2 resist viruses, may escape from transgenic crops to their weedy relatives and thus create a hardy new race of weeds.

New ecological crop data appears to show that genes can move from transgenic crops to wild relatives more often than once thought. As more and more transgenic varieties are planted, some plant geneticists worry that it is only a matter of time before the transfer of an engineered gene creates a new weed or invigorates an old one. This year alone, eight new transgenic crops have been approved for wide-scale field tests, including a cousin of Freedom2 that resists even more viruses. Even rare genetic transfers to wild plants could have the potential for devastating effects. Agricultural officials say that they already assume that gene flow may occur to wild populations, and that they approve field trials only when they are convinced that there is no hazard. And they note that the dangers of creating a "superweed" are at the moment hypothetical. After all, the Freedom2 Squash, which was approved 2 years ago, and its weedy relative, the Texas gourd, haven't taken over Texas yet. Agriculture experts also say that any risk has to be weighed against the benefits of transgenic crops--especially in developing countries, where nonprofit agencies are trying to introduce the new varieties to nations that need them most.

First-generation hybrids between crops and wild plants are often sterile, so researchers once thought that gene flow from transgenic crops to weeds would be minimal. However, a new report has documented unusually high rates of such gene flow by studying 12 marker genes in cultivated and wild sunflowers. For example, near fields where sunflowers had been growing for 10 years, the frequencies of the marker genes in wild sunflowers averaged about 28%; in a 35-year-old system, the figure was 38%. Another report showed that, in a population of wild strawberries growing within 50 meters of a strawberry field, more than 50% of the wild plants contained marker genes from the cultivated strawberries. Lastly, a third report from Denmark, showed, not surprisingly, that the same thing can happen with genes from transgenic crops. In a study of hybrids of transgenic oilseed rape, which carried a gene for herbicide resistance, and a weedy relative in the canola family, Brassica campestris, or field mustard, the results showed that first-generation crosses resisted herbicides, and so apparently had retained the transgene, and had highly fertile pollen.

Even so, ecologists say, there is no need to worry about most transgenic crops. Many transgenes, such as those that make tomatoes ripen more slowly, wouldn't give wild plants an advantage. And many crops don't have native relatives that could hybridize with transgenic strains. Freedom2 was the first U. S. transgenic crop with a weedy relative to be approved, and USDA officials say they took special care in the case. After looking at data from Asgrow and outside reviewers for over two years, APHIS decided to deregulate because the virus doesn't infect the Texas gourd in the wild, so the transgene wouldn't confer any special advantage.

But some plant taxonomists are not convinced and feel that more evidence is needed to establish that the viruses don't affect the wild Texas gourd, noting that the crucial data came only from Asgrow and were not an exhaustive survey of wild populations. These scientists say they don't want to stop transgenic crops cold, but they fear that the Freedom2 has established a precedent and that ecological concerns will be swept aside as more and more crops are approved. Federal officials counter that there should be limits to regulation, and that in many cases, it's the company's responsibility to protect their investments by making sure that transgenic crops don't lend their genetic strengths to weeds. Herbicide-resistant crops are usually developed by the herbicide marketers themselves, so if the transgene escapes into a wild population and eventually renders the herbicide obsolete, the company will lose a portion of its herbicide market.

As ecologists and regulators debate these issues, the stakes surrounding transgenic crops are rising. Developing nations, where crops may have more native relatives, are beginning to test and adopt the new varieties. For example, a potato genetically engineered for virus resistance has been in field trials in Mexico since 1992. If this year's large-scale trials go well, the potato could come up for deregulation in mid-1997. The introduction of transgenic crops to regions where many crops originated raises another concern. One of the centers of diversity for the potato is central Mexico, for example, and many wild potatoes still grow there. Traditional breeders and transgenic crop critics worry that transgenic varieties could introduce a potentially dominant genotype into the wild. Such a takeover would reduce the genetic pool available to breeders who currently tap these diverse populations to develop new crop strains.

It is hoped that existing rules for selling seed crops would prevent such a takeover by guarding against hybridization. Most widely grown crops go through a rigorous certification process in which fields are monitored for signs of hybridization. Many feel it is important for developing nations to get the benefits of new technologies, and say that careful seed certification in these countries can prevent the shadowy dangers of gene flow. Most developing nations posses limited arable land and burgeoning populations, and are going to need some infusion of technology in order to meet their food needs.

Whether or not transgenic crops spawn superweeds, they are likely to generate continued debate, as the opinions of officials sometimes clash with those of research ecologists. The official U.S. position is that transgenic crops should be deregulated on a case by case basis that adequately reviews the issues of gene flow to weedy relatives. How well this position protects the centers of diversity of important crops remains to be seen.

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