Environmental advantages from plant genetic engineering

Dr. Maurice M. Moloney, Professor and Chair of Plant Biotechnology

University of Calgary, 2500 University Dr. NW, Alberta, T2N 1N4

This article first appeared in "Environment Network News" Sept/Oct Issue 1995

Introduction
Agricultural biotechnology and the specific phenomenon of transgenic crop plants has, not surprisingly, received much scrutiny in recent years. It is normal to greet any new technology with a critical, analytical gaze. From the earliest times any technology which represents a paradigm-shift has elicited a knee-jerk reaction of suspicion and concern. It is the job of those involved in such science not only to generate the technology, but also to provide factual information which will enable society to make rational decisions about its desirability. Rationality has not always been the hallmark of the biotechnology debate. Much effort has been wasted on the criticism of biotechnology using arguments that come from narrow philosophical belief systems such as creationism, left or right-wing politics or aesthetic rather than rational views of nature. It is not the purpose of this article to discount that side of the debate. It is real, although not always helpful. However, I should like to explore agricultural biotechnology in a different way.

In principle, I shall focus this discussion on the facts of the technology. I shall, however, provide an interpretation of these facts which argues that we would be foolish not to promote cautious use of biotechnology. My reasons for taking this stance are the strong environmental, societal and economic advantages inherent to judicious practice of the technology. As an expert in agricultural plant biotechnology, I shall concentrate on that sector. In fact, much of the discussion will be pertinent to other sectors of biotechnology.

Since about 1983, it has been possible to introduce genes from any organism into plants. The early work was performed with members of the solanaceous plant family such as tobacco and petunias. As techniques became more sophisticated, it became possible to transform{1} a wide range of broad-leaved crop plants such as tomato, canola, potato, alfalfa, etc. Later, beginning in about 1990, a number of narrow leaved crops (cereal grains) such as corn, rice and recently wheat proved amenable to one of a number of gene transfer techniques developed in the late '80s. Today, it is correct to say that virtually all the world's major food crops are capable of being genetically modified through gene-transfer technology.

Gene Transfer: A Natural Process

Gene transfer between species that do not normally undergo sexual crossing sounds unnatural to the layperson. However, the development of gene transfer techniques is mainly based on copying systems already present in nature that have been moving genes around for hundreds of millions of years. While not many people have heard about the bacterium, Agrobacterium tumefaciens, a common soil bacterium which acts in nature as a "gene taxi," most have heard of retro-viruses through publicity about herpes and AIDS. Such viruses act as gene transfer agents to the cells they infect. Gene transfer between diverse organisms is a common phenomenon and has probably acted as an important catalyst to certain types of evolution.

Taking a natural phenomenon and turning it into a "technology" is an important step. The "technology" label implies that there is purpose and choice behind its use, rather than the random way it occurs in nature. It is, therefore, not unreasonable to focus on issues of purpose and choice in order to determine the value of the technology. What are we really trying to achieve with plant biotechnology? Do we want it? Do we need it? Who would it benefit? In fact, the major objectives of plant biotechnology are no different than more traditional plant breeding. Plant breeding was one of the earliest rational actions of human civilization. Without any knowledge of genes or DNA, it was noticed that certain plants gave better yields, survived drought conditions or were unpalatable to insects or pests, and that those properties were heritable. This led to selection of plant seeds with unusually good agronomic characteristics. These activities were certainly taking place 10,000 years ago in the Persian Gulf area as the excavations in Jarm-- and Tepe Sarab have shown.

Advantages of Precise Genetics

If the goals of modern plant biotechnology are not truly novel, the effects of the technology are.Whereas all classical plant breeding has depended on selecting a trait (or "phenotype"), biotechnology seeks to create that trait through producing a modified genetic make-up (or "genotype"). The plant breeder has no idea initially what other genetic baggage is dragged along with a new phenotype. However, the biotechnologist knows exactly how the genotype differs from the original starting material. This rather fundamental idea is the first advantage of plant biotechnology. The modified plant is a precisely-defined entity which presents less unknowns than the traditionally bred plant variety and is therefore inherently more predictable.

Herbicide Resistance: Cleaner Chemicals, Better Soil, Purer Food

Precision and predictability are by no means the only environmental or social advantages to cautious utilization of plant genetic manipulation. A common target for criticism of plant genetic engineering has been the use of herbicide resistance. The technical successes which gave rise to plant varieties resistant to herbicides have become a lightening rod for highly polarized criticism. A document typifying this polarized negativity is "Biotechnology's Bitter Harvest" (Goldburg et al., 1990, Report of the Biotechnology Working Group). This document is replete with misleading sentences with dark overtones such as, "Herbicides are toxic chemicals intended to be poisonous to plants. They are best known to the US public as agents used to defoliate forests in the Vietnam War and more recently to eradicate marijuana and coca plants."

Clearly, this is not a good definition of a herbicide and belief in this definition would add unwarranted sinister dimensions to the idea of herbicide resistance. Herbicide resistance in plants using genetic manipulation is, in fact, a much more optimistic story. The first thing to note is that herbicide resistance in plants is permitting us to abandon older herbicides which were chosen from a narrower group of "selective molecules." The requirement for selectivity (i.e. that a chemical could differentially inhibit growth of weeds, rather than crops) placed a constraint on companies who had to make compromises between selectivity, residual half-life and possible side effects. By creating resistance in the plant, genetic engineering has removed these chemical constraints and enabled companies to match resistance to their most benign herbicides. Herbicides such as glyphosate (Monsanto's Roundup) can now be used with crop plants which are engineered for resistance. Given that glyphosate's active ingredient is less toxic to mammals than table salt (Merck Index, 1986, 10th edition), use of this chemical is much more desirable in many circumstances than older selective herbicides. The residual effects of glyphosate are also attractive. Roundup is virtually undetectable in soil just days after use. Thus, a second advantage of such genetic engineering is that it permits the use of much more benign agricultural chemicals.

Effective weed control such as this can have a number of beneficial spin-offs. For example, it is widely believed that plants are rather benign entities. This is an aesthetic rather than a rational viewpoint. In fact, plants are the sources of some of the nastiest chemicals available. Consider the castor bean which produces ricin, the favourite molecule of developers of chemical warfare; Belladonna (Nightshade), the natural source of the potent drug atropine; Cassava which produces cyanides as "natural herbicides" to limit competition and even mustards and horseradish whose flavour comes from organic thiocyanates which, when produced industrially, are regarded as dangerous chemicals. Weeds, which are simply plants growing in the wrong place, frequently produce undesirable molecules of this nature. Nightshade can grow alongside tomatoes as they are close relatives, hemlock and hogweed can grow in fields of carrots. Such weed contamination in food crops is neither desirable for quality nor for safety. Similarly, the judicious use of herbicides may obviate frequent tillage which leads to soil erosion. In many parts of the world, particularly in more arid climates, soil conservation may require chemical rather than mechanical tillage and will lead to widespread acceptance of herbicide resistant crops.

One spurious argument frequently heard is that herbicide resistance is sponsored by agricultural chemical companies and will promote increased herbicide use. This idea is false. In fact, the majority of herbicides used on field crops today act to insure against an eventual weed problem. In many cases, point application is impossible once the crop is established. With herbicide resistance, it will be possible to react to weed problems and this is likely to decrease overall use of chemicals. The major benefit to the chemical companies will be improved market share, but this says nothing about total amounts of chemicals needed. In fact, most forecasts predict a reduction in overall use.

Reducing Pesticide Usage

Plant genetic engineering will also provide environmental benefits in crop production through studies on pest resistance. Recently, in the US, Ciba-Geigy obtained clearance to market seed for corn resistant to corn borers. Once in the plant, these insects are very difficult to control with chemicals. Soil sterilants are frequently used to eradicate these pernicious larvae. The resistant seeds were produced by engineering them to make an insecticidal protein which has no known toxicity effects in mammals. The use of insecticidal proteins will allow elimination of a number of potent insecticides which are quite poisonous to mammals. Furthermore, population dynamics studies have yielded programs which appear to avoid the selection of insect mutants resistant to the protein. Recent advances in disease resistance in plants will also lead to strategies to eliminate the use of powerful fungicides by copying fungal resistance mechanisms in naturally occurring plant populations.

Summary

Despite our sophistication as a society, we live in an illogical world. Plant genetic engineering has been targeted by some as being generally undesirable without any real attention to its possible effects. Yet we do not question the sale of naturally-occurring plants or plant products. Mustard and horseradish with thiocyanates, cassava which produces cyanides and even rhubarb which makes toxic oxalates could never have been registered as food crops in today's regulatory climate. In forming judgements about the utility of genetically engineered crops, we certainly require a rigorous regulatory system. However, we must recognize that new technology may offer advantages which go counter to our preconceived notions. In a climate of calm, deliberate and rational analysis, we shall discover that it would be foolish to deny ourselves or our environment the advantages which may be offered by plant genetic engineering and allied technologies.

In summary, plant genetic engineering may offer major advantages when compared to current agricultural practice. Many of these advantages have positive environmental impacts. These include predictability through precise genetics, use of much more benign chemicals in agriculture, efficient weed removal and reduced contamination of food products, reduced use of herbicides, insecticides and fungicides and sustainable management systems to combat soil erosion. While economics will always play a role in the establishment of new technologies, it is quite likely that the manifest environmental advantages of plant genetic engineering will also act as a strong incentive for its widespread use.

FOOTNOTES********************************


{1}1 The word "transform" is used throughout to describe gene insertion into a target plant.