Illinois Fertilizer
Conference Proceedings
January 21-23, 2002
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P. Stephan Baenzinger1
The Malthusian argument that population growth will outstrip agricultural production has yet to occur because agricultural science has continuously developed and implemented new technologies that have greatly enhanced agricultural productivity and quality. The dire predictions of massive worldwide famines due to the lack of agricultural production (Ehrlich, 1968) were averted by the Green Revolution in cereal productivity. The Green Revolution coupled improved genetics with great advances in fertilizer, irrigation, and pesticide technology. However, in the 21st century, we can expect continued, if slower, population growth and continued income growth, which will increase the demand for food with higher quality. We can also expect a greater emphasis on agriculture, as the greatest managed ecosystem, to become more environmentally sustainable and to play a greater role in the remediation of the detrimental effects of human activity.
The key question facing the future of agriculture is how it can meet this increased demand for its products. In advanced agricultural systems, increased use of fertilizer and pesticides may provide limited benefits, as they are already at near-optimum levels. Similarly, future productivity cannot rely upon increased irrigation of new lands because previously irrigated land is lost from production due to the build-up of salts-a zero-sum effect. Thus, agricultural productivity and enhanced end-use quality must continue to increase to meet humanity's needs, but it must also become less dependent upon fertilizer, pesticides, and possibly irrigation. The next "green" revolution will rely more on genetics coupled with environmentally sound cropping systems.
The next green revolution technology to greatly impact agricultural productivity and quality is biotechnology, which includes both genetic engineering and molecular mapping. From a plant breeder's perspective, genetic engineering (the ability to modify and transfer genes from one organism to another) will affect the first phase of a breeding program (the introduction of genetic variation). The extraordinary power of genetic engineering is that plant breeding is no longer limited by the ability to cross (hybridize) two plants of a common species or to induce mutations. The complete biosphere becomes a source of genes for crop improvement and end-use quality enhancement. While the initial products of genetic engineering were herbicide and pest tolerance, genetic engineering increasingly is being used to enhance intrinsic grain quality and to develop new uses or products from crops. In addition, food, feed, and fiber-harvested crops, which are pest tolerant, are more environmentally stable (more uniform) in the presence of pests. Uniformity is an important trait in many of the raw commodities processed in industry.
Genetic engineering is currently hindered by our limited understanding of how to regulate introduced genes, knowing which genes affect important traits (and hence should be transferred into crop genomes), and the fact that relatively few genes can be transferred at a time. It is also limited by consumer and environmental concerns.
Molecular mapping (the ability to locate and follow genes) will affect the second phase of plant breeding (selection of plants that have useful variation). Molecular mapping is important because it allows plant breeders to combine and select the numerous genes (the genotype) that are present in a successful cultivar.
The final phase (performance evaluations) of plant breeding requires extensive field and quality testing and will be less affected by biotechnology.
The promise of biotechnology is as great as is its need for the future of agriculture.
In this paper, five questions will be addressed:
Though this paper will attempt to cover most crops, many of the examples will
be from cereals and wheat (Triticum aestivum L.), as that is where the
author is most experienced.
Simply, biotechnology is derived from two words: "bios," meaning life or living beings (organisms), and "technology," meaning the application of scientific knowledge to practical purposes. Hence, biotechnology is the application of scientific knowledge of living organisms to practical purposes. In cereals, the expected products of biotechnology include value-added grains; more plentiful, consistent, and uniform supplies of grains; new ingredients for our food processes; and new diagnostic tools.
Our interest in biotechnology stems from our concerns about how to adequately feed our burgeoning human population. Currently, the world's population is estimated to be about 6.1 billion people (U.S. Bureau of the Census, 2001). Depending upon whose projections you use, in 2050, the population is expected to be between 9.1 (U.S. Census, 2001) and 9.3 billion (United Nations, 2000) people. Hence, in the next fifty years, the world's population will increase by 60 to 70 percent. Obviously, population estimates vary greatly (for example, the United Nations estimates go from a low estimate of 7.9 to a high estimate of 10.9 billion people in 2050), but even with the lowest estimate of population growth, an additional 1.8 billion people will need to be fed in 2050.
The first demand on our future food supply will be to simply meet the existing needs of this increasing population. The second demand on our future food supply will be to meet the needs of an increasingly prosperous world. In both cases, food production will need to greatly increase, as will the necessary transportation infrastructure, financial markets, and foodprocessing industries. This expansion must be beneficial to all segments.
Though often overlooked, demand for food increases as real income increases. For example, the growth in wheat utilization can be divided into two-thirds being caused by population growth and one-third by increased income (Rejesus, 1985). Currently, 800 million people (14 percent of the world's population) are undernourished because they cannot afford to purchase adequate quantities of food. As real income increases, more food will be purchased. For example, for each 1 percent increase in real income, it is expected that the demand for wheat will increase 0.5 percent (CIMMYT, 1985). In addition, as incomes rise, the demand for meat will increase, which will increase the demand for feed grains. Already, 35 percent of the world grain supplies are used for livestock production (CAST, 1999). Hence, even when the world's population stabilizes, the demand for food will increase with the rising income.
The fundamental question facing our food system and humanity is this: Will the dire predictions of overpopulation and mass starvation made by Thomas Malthus (population increases geometrically and food production increases arithmetically) and later reiterated by Paul Ehrlich ("The battle to feed humanity is over. In the 1970s, the world will undergo famines-hundreds of millions of people are going to starve to death in spite of any crash programs embarked upon now…" [Ehrlich, 1968]) finally come true? It should be noted that there is no historical precedent for their predictions (Eberstadt, 1995).
The reason that mass famine has been averted is that new technologies have allowed greatly increased food production. The most recent major advance in agriculture has been the Green Revolution, which was the coupling of semi-dwarfing cultivars with increased farm inputs (fertilizer, pesticides, and water). Before the Green Revolution (1955 to 1964), wheat production increased 1.7 percent per year, which was very similar to the increases (1.5 percent per year) in wheat production after the Green Revolution (1984 to 1994). In the latter period, governmental policies to reduce overproduction and inclement weather may have affected the rate of annual increase. During 1978 to 1984, the implementation period of the Green Revolution, wheat production increased 3.4 percent per year (Rejesus, 1995). As population and income increases, increases in annual production similar to those of the Green Revolution will be needed.
One final demand will be placed on future agricultural systems-namely, how to enhance our environment. Though intensive agriculture, with its reliance on fertilizer and pesticides, is often viewed as an enemy of the environment, it must be understood that only by increased productivity has non-agricultural land been maintained. Programs to remove environmentally sensitive land from production (such as the U.S. conservation reserve program) are only possible because of productivity increases in other agriculture. The benefits of productivity, as well as enhanced transportation, can be seen in the land usage trends in the northeastern U.S. (New England). In 1880, 31 million hectares of land were in agricultural production. By 1990, the same region had only 10 million hectares in agricultural production. Wildlife habitat greatly increased (Avery, 1995).
Similarly, agriculture, being a managed ecosystem, is the most flexible ecosystem and can respond to human needs. One way to reduce atmospheric CO2 is to increase soil organic matter or to harvest lumber. Livestock wastes are routinely used to fertilize soils. Agriculture will increasingly become the most important remediation mechanism for environmentally detrimental aspects of human activity.
While population growth is perceived to be geometric and food production is perceived to be arithmetic, knowledge growth is also geometric. The application of new knowledge, especially that provided by biotechnology, will lead to the next green revolution. This next green revolution must also enhance our environment. This dual need for increased production with less environmental impact will require a greater emphasis on genetic improvement and less emphasis on chemical inputs (fertilizer, pesticides, and water). It is precisely for these reasons that agricultural, environmental, and food scientists are interested in biotechnology.
In the past, genetic improvements were made primarily by plant breeding. In the future, plant breeding will be augmented by the new tools and capabilities of biotechnology. To understand how biotechnology will augment plant breeding, one first needs to understand the three phases of plant breeding. The first phase is the introduction of genetic variation. The second phase is the selection of useful variants (which may involve inbreeding or population improvement). The third phase is extensive testing of the selected variants to insure that they have commercial value (Baenziger and Peterson, 1992). Biotechnology will impact the first two phases. The third phase relies upon testing selected lines in a sufficient number of environments to estimate the commercial worth of a line. Nothing can or will replace adequate testing.
Historically, genetic variation was introduced by sexual hybridization (by far the most common method) or mutations. However, sexual hybridization only allowed genes to be introduced from plants that were highly related (one of the definitions of a specie is that the plants are cross compatible). Furthermore, mutations only changed genes that were already present within a species. Hence, both methods have limited genetic variation.
Genetic engineering allows the transfer of gene(s) from one organism to another organism and does not rely upon sexual hybridization or mutation. In theory, the complete biosphere and synthetic genes become the genetic resources (syn. gene pool) for every organism that can be transformed. Though some plant breeders initially thought they had adequate genetic resources, they are increasingly becoming aware of the limitations of naturally occurring genetic variation and their ability to induce useful mutations. For example, little improvement in the winterhardiness of winter wheat has occurred in the past 70 years (Jaglo-Ottosen et al., 1998). Similarly, for many diseases, insects, and abiotic stresses, there are inadequate genetic resources using traditional plant breeding methods.
Though genetic engineering is the addition of gene(s), by making "anti-sense" gene constructs, existing genes that are not wanted can be effectively eliminated (Shimada et al., 1993). This strategy is being used to eliminate the naturally occurring anti-quality traits (e.g., proteinase inhibitors) and to modify protein, starch, and oil components.
In the second phase of plant breeding (selection), selectable or molecular markers can be extremely helpful (Lee, 1995). The two most common markers are selectable and molecular markers. A selectable marker allows a researcher to select transgenic plants, usually on the basis of herbicide or antibiotic tolerance (Casas et al., 1995; Weeks et al., 2000). The value to a plant breeder is that if the selectable marker is linked to the gene of interest (either through co-insertion or having the selectable marker and gene of interest on the same plasmid), he or she can select for the gene of interest by selecting for the selectable marker. It is much easier to spray a field of segregating plants with a herbicide that kills the non-transgenic progeny than to do DNA preparations on individual plants to determine if the gene of interest is present.
A molecular marker allows a researcher to select for traits on the basis of closely linked DNA (e.g., restriction length fragment polymorphisms or simple sequence repeats, etc.) or gene products (e.g., isozyme polymorphisms; Summers et al., 1988; Koebner and Martin, 1990). Molecular markers are part of the field of genomics and are much less controversial than genetic engineering; hence, they will be briefly discussed. Some of the traits that have been linked with molecular markers include high grain protein (Khan et al., 2000), milling yield (Parker et al., 1999), starch and noodle quality (Briney et al. 1998), flour viscosity (Udall et al., 1999), breadmaking quality (Manifesto et al, 1998), and kernel hardness (Sourdille et al., 1996; the genes controlling kernel hardness have since been identified, Giroux et al., 2000). The difficulty with using linked markers is that crossing-over can occur, and the gene for the trait of interest might be lost. This problem is largely avoided by using flanking molecular markers and by identifying markers that are more tightly linked (i.e., that have less crossing-over potential). Eventually, the gene itself may be known and can be used as the marker.
Genetic engineering requires three things: a reliable transformation system that includes both putting the gene into the plant and a way to find the transgenic plant; a gene(s) of interest; and a promoter to regulate the gene once put into the crop. Fortunately, cereals are immensely important crops and methods have been developed to transform most of the commercially important cereals. Barley (Hordeum vulgare L.), maize (Zea mays L.), oat (Avena sativa L.), pearl millet (Pennisetum americanum L.), sorghum (Sorghum bicolor L.), and wheat have published transformation systems (Casas et al., 1995). All of these systems are reliable and are being used routinely in a number of laboratories, with the possible exception of sorghum. Many legumes also have reliable transformation systems.
As for promoters, most of the early studies used constitutive promoters (promoters that expressed the gene all of the time). For some traits, this was not a problem in that it was useful or at least not harmful to have the gene of interest expressed in every tissue and all the time (for example, disease or insect resistance). However, for other traits, it is critical to have the gene expressed in specific organelles or tissues (e.g., male sterility genes expressed in the anther [de Block et al., 1997] or glutenin genes expressed in the endosperm [Altpeter et al., 1996; Blechl and Anderson, 1996]). For other traits, inducible promoters (promoters that can turn on a gene by an external stimulus) are important (Caddick et al. 1998). Obviously, many plant processes are complex and require a set of genes to be activated to affect the process. Recently, a regulatory gene for freezing tolerance was cloned and inserted into a model plant. This gene is able to turn on a family of genes induced by cold acclimation (Jaglo-Ottosen, 1998). It appears that genetic engineers now are able to manipulate, however crudely, the complex genetic systems that determine plant characteristics. Developing useful promoters continues to be an important area of research.
No discussion of genetic engineering would be useful without a brief mention of its commercial adoption (Vasil, 1998). In 1996, approximately 3 million hectares were planted to transgenic crops. In 1997, over 13 million hectares were planted to transgenic crops. In 1997 in the U.S., 18 percent of the cotton (Gossypium hirsutum L.), 13 percent of the soybean (Glycine max (L.) Merrill), and 9 percent of the maize was transgenic. In Canada, over 25 percent of the canola (Brassica napus L.) was transgenic. In many cases, the technology adoption was limited by seed availability. As seed became available, transgenic crops had a greater role. The adoption of this technology continues, as now over 25 percent of corn and over 50 percent of soybeans and cotton in the U.S. are transgenic.
While some of those tools are controversial today (e.g., transformation), it should be understood that biotechnology has had an enormous impact and, with its appropriate use, can continue to have a major role in developing new and useful cultivars. (For more information, visit the websites http://www.nbiap.vt.edu/, http://www.aphis.usda.gov/biotech/, and http://www.ers.usda.gov/Briefing/biotechnology/, which includes databases of both field-testing permits and commercialized crops.)
The two main concerns with transgenic crops are whether the food is safe to consume (specifically, have allergens or toxins been incorporated into our foods?) and whether transgenic crops are beneficial (or at least not harmful) to the environment. Numerous reports have discussed these issues (e.g., National Research Council, 2000; Barton and Dracup, 2000; Kaeppler, 2000; McHughen, 2000).
As for food safety, most Americans are consuming transgenic foods and byproducts with no obvious side effects. In many parts of the world, the concern is over whether consumers have the right to know what is in their food; however, labeling laws are notoriously uninformative (McHughen, 2000) and often provide information of little value. Philosophically, the greatest question relates to allergenicity and our familiarity with our foods. For example, if oats are transformed with a gene from corn, is it possible that a person who is allergic to corn but not to oats will no longer be able to eat oats? These are important questions, and the regulatory approach (e.g., having to prove complete safety before release, or proving safety within acceptable limits coupled with monitoring for unforeseen consequences after release) will play an important role. It should be understood that many "natural" foods contain allergens and that these foods were introduced with far less regulations than transgenic crops.
As for environmental concerns, the main one seems to be the possible creation of super weeds by gene flow from crops to weedy relatives. Transgenic herbicide resistance flowing into noxious weed populations is a concern; however, weeds have become resistant to herbicides by spontaneous mutation. Similarly, the concern about super weeds that couldbe created by disease-resistance transgenes overlooks the fact that disease and pest resistance are key targets for conventional plant breeding and that these conventional genes would have the same ability to flow into weedy relative populations. The potential to reduce the reservoir of diseases in weedy relatives by having resistance genes in those populations is also commonly overlooked. The reduction in pesticide use in the crop by having less disease in the alternate host would be an environmental benefit.
Hence, while the concerns are real, the regulatory and scientific understanding is often limited, and it remains to be determined how these crops will affect our environment and food system. It is clear, however, that transgenic crops face a regulatory scrutiny far greater than do conventionally developed crops.
As for the genes of interest, it must be understood that plant genomes are large and contain thousands of genes, most of which have no known function. As genomics and our genetic understanding evolve, it is likely that we will know many (most) of the genes that affect a trait. The goal of many functional genomics programs is to know the identity and function of every (or most) expressed gene(s) in a crop (Somerville and Somerville, 1999). Based on our then-limited understanding, early transgenic work concentrated on well-characterized genes of commercial importance.
For example, cereals, being major food crops, supply much of the world with protein and calories (carbohydrates and oils), and these genes are the ones that have been characterized. In wheat, considerable effort has been made to modify protein composition to enhance end-use quality (Altpeter et al., 1996; Blechl and Anderson, 1996; Vasil and Anderson, 1996; Caddick et al., 1998; Alvarez et al., 2000). In corn, efforts have often tried to enhance protein quality. In rice and wheat, genetic engineering has been used to complement naturally occurring starch mutants to develop waxy starch lines (e.g., Shimada et al., 1993). Much of the work on modifying oils (Ohlrogge, 1994) is being done in oil seed crops but in principle can also affect the oils of cereals. These efforts have direct commercial importance and are well described by others.
However, three areas generally receive less attention as possibly important aspects of future genetic engineering: considering truly novel uses for plants, improving product consistency or uniformity, and regulating whole sets of genes.
In considering truly novel uses for plants, the use of food as a delivery mechanism for medicines is becoming more important. Recently, transgenic potatoes (Solanum tuberosum L.) were shown to be a viable way of delivering an oral cholera vaccine (Arakawa et al., 1998). In the future, it is possible that many oral vaccines will be delivered through foods. Though food-based vaccines will be niche markets, their potential importance-especially to those who historically have not been able to afford vaccines-may be great.
Another area where truly novel uses for plants may occur is in our ability to modify plants so they are more easily processed. An example of this research is the development of a transgenic barley line that expressed a heat stabile (1,3-1,4)-â-glucanase (Jensen et al., 1996). The â-glucanase was a hybrid gene from a fusion of the barley á-amylase promoter and signal peptide with a hybrid â-glucanase gene from two Bacillus spp. that had been modified to use codons more similar to the usage in barley â-glucanases. This example truly illustrates the power of genetic engineering. A partially synthetic gene derived from the fusion of two different bacterial species genes was regulated by different barley gene promoters. The rationale for this research was "to produce barley plants that during steeping and germination express a (1,3-1,4)-â-glucanase that survives the high temperatures used for kiln drying of green malt." Hence, the transgenic barley plant would have enzymes used in malting that were not inactivated by the high temperatures used in kiln drying.
Finally, no discussion of the future products of genetic engineering would be complete without making reference to the work of Prof. Potrykus, who has developed rice with elevated levels of iron and provitamin A that has the potential to greatly foster human health and well being among the poor (Lucca et al., 2000; Ye et al. 2000; Potrykus, 2001). In creating these lines, he used diverse gene sources (plants to fungi to bacteria) to create improved rice. These examples illustrate how the complete biosphere and what can be synthesized has become the source of genes for crop improvement.
Organisms often live in extreme conditions. For example, the Archaea (formerly archaebacteria) live in conditions of extreme salinity, heat (as high as 113° C), and anaerobic conditions (Delong, 1998). Most crops have enzymes that function from 0° to 45° C, with an optimal temperature range that is much smaller. Proteins derived from archaeal genes can be used in innumerable food and feed products that involve high levels of salt, high temperatures, or anaerobic conditions. For example, thermostable proteins can be used in malting, baking, and boiling. A key question is whether the food and feed processing provides conditions that will allow the enzyme to be active. For example, during bread baking, the internal loaf temperature may reach 100° C, but will there be sufficient water in a loaf of bread to allow a waterbased enzyme to function, or will the enzyme only be useful in soups or boiled noodles?
Though much of the discussion on genetic engineering as it relates to food and feed emphasizes value-added products, one area where genetic engineering may have an important effect is in product availability, uniformity, and consistency. Consistency will become more important as populations become more urban. The market for food products may well separate into two overlapping entities. Convenience foods, such as bread with extended shelf life and instant fried noodles, may predominate in everyday life. High-speed technologies will be used to produce large quantities of low-priced products. Uniformity in inputs will be required to insure consistent products. The other segment may include celebration foods, which will be produced by crafts people and command a premium price in the marketplace. The cost of inputs for these items, while important, will be less significant. Biotechnology may play a role in the production of grains with uniform kernel size and characteristics, which will assist the high-speed production of low-cost goods and allow the artist to focus more time on creating and less time on procuring suitable inputs.
Stresses can greatly reduce yield and change kernel characteristics (e.g., grain volume weight, kernel weight and size) and cereal quality (e.g., dough strength and kernel composition; Blumenthal et al., 1998). Crops that are resistant to insects (Shuler et al. 1998), diseases (Grumet, 1995), and abiotic stress such as freeze damage (Jaglo-Ottosen, 1998) or rain at maturity leading to sprouting should have greater yield and quality stability. Similarly, controlling weeds using herbicide-resistant crops (Daneill et al., 1998) may increase grain production and uniformity and reduce foreign matter. It is estimated that 42 percent of crop productivity is lost due to weeds, insects, and disease. Kernel size should be more uniform and kernel composition more consistent. Of course, there will still be genetic differences among cultivars, but the effect of the environment and how the environment interacts with the cultivar will diminish. Hence, purchasing cereal grains should become easier, and processors should need to make fewer adjustments and add fewer amendments with each new shipment of grain.
Finally, while plants are important constituents in food and feed, they are not the only components derived from living organisms that can be modified by biotechnology. One of the most studied organisms is bakers or budding yeast (Saccharomyces cerevisiae), which is very important for many baked products. There is tremendous progress in understanding its genome (e.g., http://genome-www.stanford.edu/Saccharomyces/). For aspects of wheat utilization that can occur by modifying yeast or wheat, it would be simpler to modify yeast. The latter approach has the advantage that the modified yeast strain can be used within any wheat cultivar, thus eliminating the need to put the transgene into numerous cultivars.
Genetic engineering and biotechnology are needed to provide the food required
for an increasing population that, as it becomes wealthier, will demand more
food per capita and food of better quality. Agriculture will increasingly be
called upon to remediate the detrimental aspects of human activities. While
agricultural productivity tends to increase arithmetically, knowledge, like
population, can increase geometrically. It is the application of new knowledge
that has consistently prevented the famines predicted by Malthus and his followers.
Biotechnology and genetic engineering appear to be the next major influx of
knowledge that will enhance agricultural productivity.
1 P. Stephan Baenzinger works for the Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE 68583-0915, U.S.A.
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