This article is reproduced with permission of California Rare Fruit Growers, Inc., a non-profit organization that promotes growing "rare" fruits and vegetables. The article originally appeared in their magazine, Fruit Gardener, July/August 1998, vol. 30, no. 4, pp. 15-18.

The ringspot virus is the single largest threat to Hawaii's papaya industry. It destroys leaves, diminishing the quality of the fruit, and eventually kills the entire tree. There are no chemicals available to combat the disease. Quarantine programs and rouging efforts by the Hawaii Department of Agriculture have failed to arrest the problem. There is, however, new hope as scientists at the University of Hawaii and Cornell University have developed a papaya resistant to this dreaded disease.

Nearby, at the University of Hawaii's Plant and Molecular Physiology Department, scientists are working on a coffee plant that produces caffeine-free beans. Success means elimination of the harsh process of decaffeination that affects the taste and aroma of the final brew.

Both these crops are products of the latest in plant breeding: transgenics. Here genes from some organisms are introduced into others with the hope of improving succeeding generations. Through transgenics, a number of crops, including corn, potatoes, cotton and ornamentals, have been developed for pest control and for greater marketability.

Compatibility

A professor of mine, a vegetable breeder, used to speak for hours of his experiences in crossing wild species of vegetables with domestic cultivars to produce the desired effects. His challenge was getting plants from the wild with the desired genes for pest control and hardiness to breed with domestic plants with genes for the proper size, shape and taste acceptable to consumers. They were often of different species and not genetically compatible. He used then-innovative techniques to overcome the hurdles--physical and chemical--that prevent fertilization and subsequent seed formation.

Traditional techniques to overcome these barriers include surgical alteration of flower parts, bud pollination, use of mentor pollen, use of immunosuppressants, in-vitro fertilization, manipulation of chromosome numbers, and ovary culture.

These techniques have led to an ever-increasing utilization of the available gene pool. Still, there are limitations as the crosses must be between two genetically related parents, usually within the same genus. This limits the gene pool to only those traits available in that particular group, leaving no available characteristics for such attributes as decaffeinated coffee and papaya resistance to the ringspot virus.

New Techniques for New Times

Transgenics, the latest technology, allows the transfer of genetic material between totally sexually incompatible species. The genes for papaya ringspot resistance and decaffeinated coffee come from a virus and a bacterium respectively. This exchange has augmented the gene pools of a species to limits previously unheard of.

Methods of transferring genetic material include a "gene gun," where genetic material from one organism is coated on pellets and shot into the tissue of another. The result is then cultured and grown for further breeding and analysis. The most recent techniques use fungi, bacteria and viruses that transport the gene as they infect the plant.

A Brief History of Transgenics

The toxin produced by the bacterium Bacillus thuringiensis has been an effective insecticide against feeding Lepidoptera caterpillars. Its safety to humans makes it even more attractive. First-generation Bacillus insecticides are cultures mixed with water that are sprayed onto crops.

About ten years ago, the second-generation products came on the market. By placing the toxin-producing gene into another bacterium, Pseudomonas, scientists found a stronger, faster-acting, longer-lasting but still safe product. This insecticide is formulated and sold as Bacillus toxin encapsulated in dead Pseudomonas. Although an improvement, repeat treatments to the crop are still necessary.

Transgenics puts the toxin-producing gene into plants such as corn and cotton, giving them continuous protection. It also eliminates the process of mixing and applying an insecticide, a process that takes hours or even days.

Also using transgenics, scientists have bred several varieties of crops resistant to various herbicides, enabling growers to broadcast a herbicide over an entire field without killing the crop.

Benefits

Of the many benefits, one of the most significant is health. Xerophthalmia is an eye disease that affects five million children and eventually blinds a quarter of a million each year. A diet adequate in Vitamin A could prevent this and also prevent two million infant deaths each year. Scientists are developing transgenic rice high in the vitamin [note 2] with hopes of mitigating this disease. This rice is a product of material from a bacterium and daffodil.

Other current health-related research is aimed at developing oral vaccines in plants to protect humans against a multitude of diseases, a more convenient vehicle than being given shots at a clinic.

As you read this, research is going on to genetically engineer over a hundred different crops to provide an environmentally safe alternative to the use of chemicals. As an example, cotton resistant to Lepidoptera has reduced chemical use by 6 million pounds of insecticides so far. Bioengineered plants may provide a safer alternative to synthetic pesticides but will not completely replace them.

Pest Resistance

The development of bioengineered plants is not entirely without risk. One scientific concern is related to the well-documented ability of pests to adapt and become "resistant" to many pesticides including Bacillus. There are several modes of resistance, some morphological, other physiological. In all cases, this is natural selection at work where the strong survive and pass on traits to their progeny. For a species with a high reproductive rate such as insects, there could be a significant rise in the resistant population in a very short time.

The adaptation of pests depends heavily on the amount of the substance applied. The more of the substance in the environment, the faster resistant strains develop. In the case of transgenic plants, we are speaking of potentially massive acreages of resistant crops being planted. The result: a large amount of toxin to hasten the resistance-forming process.

Runaway Genes

Another concern with respect to transgenic plants is the escape of the protective gene into other plant populations. There can be movement of genetic material through pollen transfer, seed dispersal, and vegetative reproduction. Consequently, it is possible for the transgenic plant to cross with its relatives in the wild and for their progeny to pick up engineered characteristics. Concern is especially great for those species whose pollen can be transported over long distances. Ultimately, beneficial organisms may be jeopardized.

Some researchers fear a wider ecological impact with transgenic trees. In forests, damage to non-target organisms is a big concern, for we try to preserve the pristine forest ecosystem. Lepidoptera and parasitic wasps are host-specific and may be in danger if their host trees develop resistance. If these beneficials are destroyed, the results could devastate the forests because these beneficials are needed for pollination and for maintaining the balance of the forest's ecosystem.

Yet another potential result of an escaping gene is the development of a super race of weeds with resistant qualities. If so, these weeds will be able to resist moderate applications of herbicides resulting in the application of even more synthetic herbicides [note 3].

Food Safety

The public tends to view food safety in terms of synthetic chemicals in our food and drinking water. We establish tolerable limits for some pesticides. For others, we disallow even the slightest trace to remain on anything consumed. Let's look at pesticides from another angle, however.

Plants have their own built-in defenses, and under the stress of a pest attack, will activate these defense mechanisms, many of them chemical in nature. A good number of these are known carcinogens such as those found in peppers and celery. With transgenics, synthetic pesticides use may decline, but will there be a corresponding increase in the levels of natural toxins? If so, at what level will these natural defenses be considered unacceptable?

Bacillus is considered "safe." What about materials from other organisms? Can transgenic food bring on allergic reaction in humans?

Managing the Risks

Once the risks have been identified and characterized, the task of managing them comes into play. Strategies may include not releasing the product or restricting it to certain geographic areas.

Resistance management is a buzzword among plant breeders as they strive to slow, if not eliminate, this process of pest adaptation. In truth, efforts against pest resistance are not new. The foundation of a resistance management program is to put less of the toxin in the field, thereby decreasing chances of adaptation. There are several methods for dealing with Bacillus resistance--specifically, interspersing transgenic plants among non-transgenic plants or confining the toxin to only those parts of the plants needing protection, such as the buds of cotton and the ears of corn.

A number of protocols are used to keep pollen, seed, and vegetative materials from spreading and escaping. Test plots must be isolated by distance.

In corn, tassels and ears are bagged to prevent escape. After tests are completed, tassels are removed and the surrounding areas treated with a herbicide and then disked to kill any remaining plants that may have germinated.

The United States Department of Agriculture (USDA) is at the forefront for testing and release of these organisms. They decide if field testing is permitted and if materials may be released to the growing public. During testing the USDA requires protocols to prevent environmental damage and will assess possible dangers before final release.

Also involved in the risk-assessment process are the Food and Drug Administration (FDA) and the United States Environmental Protection Agency (EPA). The FDA's function is to assure food safety of these products. They work hand in hand with the EPA, which regulates pesticides under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). Traditionally the EPA has not regulated plant material as pesticides. However, with the advances made in biotechnology, they have expanded the definition of pesticides to include transgenic plants.

As pesticides, transgenic plants must be placed under the same scrutiny for human and environmental safety as other pesticides before gaining approval. Then they must be labeled according to law, each label coming with caveats and specific directions for use to prevent environmental contamination and human illness. Each label will be a legal document that must be adhered to by the user.

Front-line regulators, used to dealing with pesticides packaged in bottles, bags and test tubes, will find interesting challenges as these products enter mainstream agriculture.

Some Ongoing Transgenic Projects

A predatory virus. Scientists have been given permission to field test a virus engineered to express the insect control properties of a scorpion. Tests are against the tobacco bud worm and cabbage looper on cotton, tomato, and leafy vegetables.

A Mighty Mite. The USDA has granted a permit for testing a transgenic predatory mite to control the spider mite in a variety of crops.

Heat-resistant nematode. Scientists at Rutgers University were given permission to test a genetically engineered nematode for insect control. This nematode is designed to withstand heat shock and higher temperatures than its naturally occurring relative.

No more mushy fruit? Ethylene gas is a ripening agent that can also spoil fruit over time. Italian scientists have found that an Arabidopsis [note 4] ethylene receptor gene extends the shelf life of fruits by making them ethylene insensitive.

A greater variety of seedless fruit. Italian and German scientists produced transgenic eggplant and tobacco plants that set seedless fruit by engineering them to produce auxin in the unfertilized ovary. They used two genes, one from a bacterium and the other from snapdragons.

--G. Y. K.

About the author:
Gerald Y. Kinro grows fruit and writes agricultural how-to articles "for fun." His article on the Indian mulberry appeared in the July/August 1997 issue of Fruit Gardener magazine.

Note: we do not have an email contact for Gerald Kinro.

Beyond Veg editorial notes:

1. The article above has been edited for use on Beyond Veg. The original magazine article includes photos, which we have chosen to not include here.

2. Nutritionally savvy readers will note that plant foods do not contain vitamin A, but instead contain carotenoids that are converted to vitamin A in the human digestive system. Thus, the effort to provide vitamin A via transgenic rice is (more precisely) an effort to produce rice that contains carotenoids (i.e., beta-carotene) and not pre-formed vitamin A.

3. The article originally read: "...able to resist moderate applications of herbicides resulting in the application of even more synthetic pesticides." The last word in the preceding, "pesticides," in context clearly should read as "herbicides" and we have changed it here.

4. Arabidopsis (thaliana) is a plant that is frequently used as a model for genetic research in plant biology. A web search using the google search engine shows extensive data resources on the plant.

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