Today's Topics in AgBioView Special Focus on Corn in Mexico.
* Rick Roush: Corn in Mexico and CIMMYT's response
* Transgenic Maize In Mexico: No Need For Concern
* Transgenic Crops: Cautionary Tale
* Transgenic Maize in Mexico - A Moratorium to Maintain Biodiversity or Underdevelopment?
* Gene Barrier In Corn May Boost Trade, Environment
* A Mexican Perspective On Biosafety
* Val Giddings: Teosinte and Gene Flow Threat
* Brian Johnson: Response to Giddgings
* Maize, Gift of The Gods or Slave of Mortals?
The issue of gene flow from transgenic crops to native land races of corn and its relative teosinte in Mexico, the center of origin of this crop, has been raised recently. I post the following letter from Rick Roush along with many relevant articles from earlier AgBioView, Agnet and Klaus Amman's 'Debate' to help provide information on this topic
From: "Rick Roush"
Subject: Corn in Mexico and CIMMYT's response
Although perhaps politically astute for its own position, CIMMYT's comment that the GM corn is "a serious development" is sure to be exploited by GM opponents and seems an over-reaction on the basis of what little information is now publicly available.
Greenpeace and other critics seem to have ignored a letter from Mexican scientists to the journal Science some 18 months ago that addressed the possible effects of GM corn in Mexico. Juan Pablo Ricardo Martinez-Soriano (from Unidad de Biotecnologia e Ingenieria Genetica de Plantas) and Dianna Sara Leal-Klevezas stated that the Bt gene (alledged to have been detected in Oaxaca) is not likely to spread as it conveys no selective advantage:
"[t]ransgenes cannot be established in a natural population of teosintes=fixation of a (trans)gene or allele in a teosinte population would be impossible if it did not confer an evolutionary advantage to the species. The bt gene, for example, would most likely not confer any advantage to teosinte because pests are not a natural selection factor in the wild." (Science, Vol 287, 25 Feb 2000, page 1399).
Further, Martinez-Soriano and Leal-Klevezas stated that we're not at risk of losing any unique reserve: "It seems paradoxical to argue that it is necessary to protect the genetic background of corn when, for 6000 years of traditional breeding, we have protected only alleles important for mankind." I would be happy to send a pdf file of the article in Science to anyone who is interested. (See Below for the Paper and responses to that.......CSP)
It is important to remember that the land-race corn is not the same as the ancestor species of corn - called "teosinte" - that would raise concern about preservation of ancestral genetic resources. The mere presence of biotech corn is no more of a concern than the presence of conventionally bred corn that is the product of 6,000 years of increasingly sophisticated selection and modification.
If there is "gene flow" is from corn brought to Mexico, there must surely be similar "contamination" from non-transgenic elite hybrid varieties from the US that have also been grown or used in Mexico (even if markers would more difficult to identify). What practices have been in place to protect against that, and what assessments have been made?
Transgenic Maize In Mexico: No Need For Concern
Science, February 25, 2000, Vol 287, No 5457, p 1399 ( Source: Agnet)
Juan Pablo Ricardo Martinez-Soriano of the Unidad de Biotecnologia eIngenieria Genetica de Plantas, Centro de Investigacion y Estudios Avanzados del Instituto Politecnico Nacional,Apartado Postal 629, 36500 Irapuato, Gto, Mexico,
According to pre-Hispanic traditions, gods gave native Mexicans the first maize seeds and from then on, and for thousands of years, maize has been a vital element to the Latin American cultures. Biologically, Martinez-Soriano says maize is an orphan plant and has only one relative, the annual teosinte (1). Morphologically the two are similar, but they differ strikingly in the pistillate inflorescence (what becomes the cob). For our discussion, the most notable difference is that the maize cob is solid, whereas the teosinte cob is brittle and comes apart at maturity. Molecular analysis, says Martinez-Soriano, has shown that maize was domesticated in the Balsas River drainage (Mexico) 6000 years ago (2). Primitive cobs found in caves and other archaeological sites share the same characteristics: they are of small size and are, invariably, solid.
This is of major importance--viable seeds can only be released by mechanical means (basically by humans). Maize does not disperse itself and therefore does not exist as a free species in nature.
Recently, some biotechnology companies have requested authorization to plant and market transgenic maize in Mexico. Several ecological groups have raised concerns about the potential risks of introducing such plants to Mexico, where maize originated. The main concern regarding the possible effects on the native maizes and relatives has little if any scientific basis; it is more related to cultural factors rather than biological ones. Arguments stating that maize is genetically fragile are weak. It seems paradoxical to argue that it is necessary to protect the genetic background of corn when, for 6000 years of traditional breeding, Martinez-Soriano says we have protected only alleles important for humankind. Even if we decide to protect the actual genotypes, there should be no need for concern. Any transgene transferred inadvertently to native maizes can be removed from the progeny by selecting against the incorporated trait. Maize is always under strong artificial selection, and therefore natural selection
On the other hand, transgenes cannot be established in a natural population of teosintes. Any teosinte recipient of maize pollen is at risk of transmitting to its progeny the trait of not being able to release its seeds, just as in maize. The transference of an allele from teosinte to maize is, says Martinez-Soriano, a natural process. The opposite can only happen if the hybrid seeds are mechanically released. Still, fixation of a (trans)gene or allele in a teosinte population would be impossible if it did not confer an evolutionary advantage to the species. The bt gene, for example, would most likely not confer any advantage to teosinte because pests are not a natural selection factor in the wild. The transgene would be lost like the thousands that never conferred adaptative advantages to the recipient plants.
References1. W. C. Galinat, Maydica 30, 137 (1985) 2. R.-L. Wang et al., Nature 398, 236 (1999).
Transgenic Crops: Cautionary Tale
Science, March 17, 2000; Vol 287, No 5460 p927
Ronald Nigh, Centro de Investigaciones y Estudios Superiores en Antropologia Social del Sureste, Mexico, Charles Benbrook, Benbrook Consulting Services, USA, Stephen Brush Human and Community Development, University of California,Davis, CA, USA, Luis Garcia-Barrios Division de Sistemas de Produccion Alternativos, El Colegio de la Frontera Sur, Carretera Panamericana y Periferico Sur s/n, Mexico; Rafael Ortega-Paczka Direccion de Centros Regionales, Universidad Autonoma Chapingo, Mexico; and Hugo R. Perales, Departamento de Agroecologia, Mexico
Martinez-Soriano and Leal-Klevezas say that there "should be no need for concern" that the introduction of transgenic maize varieties in Mexico may pose a risk to landraces or wild relatives of maize in its ancestral home. However, the authors say it would be a mistake to dismiss such concerns given the limited state of our current knowledge. Indeed, what little evidence is available seems worrisome. Martinez-Soriano and Leal-Klevezas mention that there is only one wild relative of maize, annual teosinte, but there are several subspecies of teosinte (which is conspecific with maize itself) as well as a perennial teosinte, a separate species endemic to Jalisco, Mexico. Other less closely related species are found throughout Mexico and Central America.
The authors say that the possibility of gene flow from the teosintes to maize is well established and has been deliberately induced by Mexican farmers. The possibility of gene flow and introgression (incorporation of genes) from maize to teosintes is less studied, but the work of J. Doebley and M. Goodman and of B. Benz et al. confirm this possibility (1). Reviews on the issue (2) also make it clear that reciprocal gene flow between maize and the teosintes is possible. Thus, the available evidence does not support the authors' comment that "transgenes cannot be established in a natural population of teosinte." The concern expressed by some scientists that such gene flow could create aggressive strains of weeds cannot be dismissed on the basis of the reasoning presented in their letter.
The authors say that Martinez-Soriano and Leal-Klevezas also say, "Any transgene transferred inadvertently to native maizes can be removed from the progeny by selecting against the incorporated trait." But "gene" and "trait" are not synonymous; selection by farmers for a trait is not 100% efficient in eliminating a gene from a breeding population. Although perhaps technologically feasible, there is no practical way for farmers or breeders to select out genes for Bt or glyphosate resistance, for example, given the scale at which landraces are grown in Mexico. Furthermore, maize farmers actively increase infraspecific diversity by interplanting varieties to generate hybrids (3). Any transgenic trait that is introduced can therefore be expected to diffuse into other maize races -- especially if the trait is dominant. Martinez-Soriano and Leal-Klevezas say that transgenic maize is opposed because people think maize is "genetically fragile." However, the issue is not fragility, but the irreversible insertion of
The authors say they believe that the genetic and ecological risks of introducing transgenic crops into the centers of origin of agronomic crops are largely unknown. We must not get beyond the science. The effects may prove, in most cases, of little consequence, but we should not find out by default or accident. Regulatory decisions involving the introduction of transgenic plants should be based on thorough scientific research, which in the case of maize, at least, has not yet been conducted.
1. B. Benz, L. Sanchez-Velasquez, F. Santana-Michel, Maydica 35, 85 (1990); J. Doebley, Bioscience 40, 443 (1990); J. F. Doebley, M. M. Goodman, C. W. Stuber, Syst. Bot. 9, 203 (1984); Econ. Bot. 41, 234 (1987).
2. J. A. Serratos, M. C. Wilcox, F. Castillo, Eds., Flujo Genetico Entre Maiz Criollo, Maiz Mejorado y Teocintle: Implicaciones para el Maiz Transgenico (Distrito Federal, Centro de Investigacion para el Mejoramiento del Maiz y Trigo, Mexico, 1996); N. C. Ellstand, C. H. Prentice and J. F. Hancock, Ann. Rev. Ecol. Syst. 30, 539 (1999).
3. M. R. Bellon, Econ. Bot. 50, 26 (1996); H. Perales, thesis, University of California, Davis, CA, 1998.
Shahal Abbo and Baruch Rubin of The Hebrew University of Jerusalem, Israel, writes that Martinez-Soriano and Leal-Klevezas say in their letter, "transgenes cannot be established in a natural population of teosintes. Any teosinte recipient of maize pollen is at risk of transmitting to its progeny the trait of not being able to release its seeds." They add that gene transfer is more likely to occur from (wild) teosinte to (cultivated) maize rather than vice versa.
However, the only alleles less likely to move from transgenic maize to teosinte are those linked to cob disarticulation loci. Other alleles will flow with no fitness reduction. Moreover, the amount of pollen released from cultivated fields relative to the amount of wild pollen would suggest that the direction of gene flow is more likely to occur from cultivars to the wild plants (1).
Indeed, the authors say, this seems to be the most frequent cross direction, as demonstrated in the cases of Indian red rice (1) and white-flowered lupines in Western Australia, to name just two examples. Such a process is bound to occur where and when wild progenitors grow adjacent to cultivated types. The general nature of the phenomenon would suggest that, before irreversible decisions are taken regarding transgenic maize, it would be wise to consider similar situations from other crops in other areas. In Israel and other Mediterranean countries, barley and Johnson grass grow wild. The six-row trait of cultivated barley has introgressed more than once into spontaneous forms and is maintained in many populations (1). Johnson grass without rhyzomes developed spontaneously after introgression of the pertinent genes from sorghum in Israel. If such morphological alleles could move into wild and weedy forms, what could prevent the introgression of a glyphosate resistance allele from (hypothetical) transgenic s
The authors conclude that transgenic crops are here to stay, but it is imperative to ensure that such crops are grown only outside the range of their wild progenitors. Otherwise, the most valuable gene pools for future food supplies will be at risk.
References 1. G. Ladizinsky, Plant Evolution Under Domestication (Kluwer Academic,
Dordrecht, Netherlands, 1998).
Transgenic Maize in Mexico - A Moratorium to Maintain Biodiversity or to Maintain Underdevelopment?
-ARIEL ALVAREZ-MORALES , Mexico (presented at the London 'Seeds of Opportunity' Meeting, June 1, 2001; http://www.seedsofopportunity.com)
In 1993 Mexico issued the first permit to conduct a field release of transgenic maize for experimental purposes. However, in 1999, the government decided to implement a "de facto" moratorium on this crop indicating that more information was needed on the possible impacts of these materials on biodiversity, and on teosinte and the maize landacres. Was that the reason behind this decision? In Mexico NGOs were very active on their campaign against transgenic crops, especially maize. There were public demonstrations on the streets and in front of the offices of the Secretary of Agriculture, as well as many notes in national newspapers condemning the use of these materials and stating that these were leading the country to the loss of traditional maize agriculture and thus of cultural and social values.
At that time Mexico was in the middle of a fierce political battle for the presidency, and for some politicians to be related to what was being portrayed as "frankenfood" or something coming out of the "X" files, was not something to be desired. The "moratorium" solved the immediate problem. The decision was taken without consulting the scientific consultative subcommittee of the General Directorate for Plant Health, which had been involved in the organization of two symposia, 1995 and 1997, to consult with experts about the potential risks involved with the release of transgenic maize in Mexico. The results from these events led to guidelines to test transgenic maize, and the identification of risk-free and intermediate-risk areas where transgenic maize could be released depending on the phenotype and other elements related to biosafety as well as high risk areas where no tests could take place.
At the present time, the Government is trying to set up the "Terms of Reference" which should orient in terms of the research needed biological, social, environmental, food safety, economy ˆ to provide data to properly assess the risks involved with the release of transgenic maize in Mexico. because there is a lack of knowledge in many of these areas. Nevertheless, there are many questions that need to be answered and lessons to be learned: Why is that no research was done before? Who should have done it? Who will pay for the research needed? How long will it take until we have the information required? These issues will be discussed in detail.
Gene Barrier In Corn May Boost Trade, Environment
October 12, 2000; University of Wisconsin, Madison
MADISON -- Working with teosinte, a wild cousin of maize, a University of Wisconsin-Madison scientist has found a molecular barrier that, bred into modern hybrid corn, is capable of completely locking out foreign genes, including those from genetically modified corn. The discovery is important because it means farmers will have access to a technology that can ensure the genetic integrity of their corn crop, making it easier to export to countries wary of recombinant DNA technology and providing a built-in buffer for potential environmental problems such as the threat to monarch butterflies from corn engineered to make its own biological insecticides.
"Governing the flow of genes between populations is what's at stake," says Jerry L. Kermicle, the UW-Madison professor of genetics who discovered teosinte's genetic barrier. Corn varieties of all kinds -- from organic to genetically engineered -- are prolific traffickers in genes. Cross-fertilization between strains occurs as gene-laden pollen is carried by bees or blown with the wind from one field to another. The resulting contamination, especially from genetically modified corn, can ruin organic crops or make traditional hybrid corn worthless for export to countries where consumers are wary of the new technology.
The new discovery, however, could permit American farmers to recapture those profitable markets in Europe and Asia by ensuring that organic or traditional hybrid corn is uncontaminated by genes from genetically modified crops. Moreover, the new technology can be used by farmers to plant buffers around fields of corn genetically modified to make their own insecticides and thereby limiting a highly-publicized threat to non-target species such as monarch butterflies. For thousands of years, teosinte has co-existed as a weed with the maize cultivated in Mexican fields. Like corn, teosinte is a grass and its genetic makeup is so similar to that of cultivated maize that scientists suspect the genetic differences between the two plants may be confined to a mere handful of genes. Teosinte, in fact, is corn's likely ancestor.
Despite this genetic affinity -- and the ease with which cultivated corn plants exchanges genes through cross pollination -- the teosinte strains that grow as weeds within Mexican corn fields only rarely acquire genes from cultivated corn. The reason, according to Kermicle, is that teosinte has a built-in barrier, governed by a single gene cluster, that keeps foreign maize genes out, enabling the plant to maintain its own unique genetic identity in an environment thick with gene-laden pollen. The ability to build a genetic barrier into hybrid corn is a significant technological advance, one that would permit farmers to assure buyers that the corn from their fields has not been contaminated by genes from neighboring fields. The technology, according to Steve Gerrish, an agronomist and licensing associate with the Wisconsin Alumni Research Foundation, would have instant appeal to organic farmers and farmers whose corn or corn products might be marketed to countries that now bar imports of genetically modified
"This technology can potentially solve the problem of contamination of regular hybrid corn and organic hybrid corn by any genetically modified organism (GMO) during the growing season," says Gerrish. "This technology could also allow a farmer to grow both types of maize crops and maintain a market segregated product." Today, about 22.6 percent of the corn grown in the United States is exported to other countries, 8 percent is used for sweeteners, 2.6 percent for starch, 5 percent is used in the manufacture of alcohol, and 1.2 percent is used in products for human consumption. A little more than 50 percent of the U.S. corn crop is used for animal feed. But even in the animal feed market, according to Gerrish, there is a growing interest in corn certified as a non-genetically modified organism, especially for organic livestock production which requires grain produced by plants that are not genetically engineered.
The reluctance of key foreign trading partners, including the European Union, Australia, Japan and other nations, to import genetically modified products has become a significant problem for American farmers as they compete in the international marketplace. In the United States, genetically modified crops, including corn and soybeans, are now planted on millions of acres of farmland. Using traditional breeding methods, the genetic barrier is being transferred to hybrid corn and testing quantities of seed should be available through seed companies in 2002, Gerrish says. Commercial quantities for planting by farmers are possible by the year 2003, he says. The new gene-barrier technology has been patented by WARF, a private, not-for-profit corporation that manages intellectual property in the interest of UW-Madison. It will be licensed non-exclusively for domestic and international use. Licensing terms will include a provision that GMO technology be kept out of maize varieties with the teosinte barrier. In add
Earlier Posting to Agbioview...
From: Anatole F Krattiger
Since teosinte is threatened to be extinct, maybe insect resistance could be very useful a trait giving it a few more decades. In any case, there is one type of teosinte which grows mainly in the borders of agricultural fields. That is the most threatened. For that teosinte, herbicide tolerance might actually become the trait that saves it from total oblivion. Since nobody is transforming teosinte with that trait, outcrossing from maize could well be desirable rather than pose a threat. Just a thought.
A Mexican Perspective on Biosafety
From: Emily Spengler, Mexico City, Mexico
The biological diversity in Mexico is unique to the world's total biodiversity. A key factor is the genetic variation found within many single species, such as corn, tomatoes, hot peppers, and papaya, among others. For centuries, Mexico's peasants have domesticated dozens of species by selecting, nurturing, and maintaining them. Today, this biodiversity is enriched because of these efforts to keep the germplasm within its productive system. Several of these crops are essential, not only for Mexico's diet, but also for the growing world population's consumption of food and clothing. The challenge for Mexico will be balancing its participation in global agro-industrial complexes, while simultaneously conserving its unique germplasm.
Mexico presents a variety of social, environmental, economic, and cultural situations involving its one hundred million people and extremes of both climate and landscape. Except for the irrigated agricultural production in certain regions of the country (not more than 15% of the total cultivated area), agro-systems and production units in Mexico present a wide variety of environmental, social, economic and cultural situations. Different regimes of land ownership coexist not only for agricultural purposes, but also for forestry, fishing, and cattle raising.
In a country having such contrasts, as well as the center of origin and diversity of many species, the main ecological risk in the release of living modified organisms (LMOs) lies in the fact that through genetic engineering, transgenes are now available in nature, transgenes that had never been available before. Now, the possibility for genetic flux is opened to wild relatives and land races (native varieties), with a potential impact on the use and sustainable conservation of biodiversity in the specific site of the release. The potential problems in each region depend on the particular conditions of its environment, as well as the scale of use. Therefore, a proposed release or use must be evaluated case by case, in order to clarify the unanswered questions about the effects on the established equilibrium of species, as well as questions about how human health and other species will be affected.
To date, sixteen transgenic crops have been tested in experimental releases, and Mexico is center of the origin and/or diversity of at least six of them. The delayed ripening tomato has been deregulated in Mexico and Bacillus thuringiensis (B.t.)/herbicide tolerant cotton was cultivated in a pre-commercial test, reaching an accumulated area of 125,0000 hectares over the last three years.
B.t. cotton in the state of Tamaulipas illustrates the complexity of our agricultural system, since in the Northern region of the state the main pest, picudo del algodonero (Anthonomus grandis), is not susceptible to B.t. toxin. In the Southern region the transgenic crop by itself is unable to control the triple pest threat that also includes Heliothis virescens and Heliothis zea. Therefore, the use of chemical insecticides is still necessary, as well as other measures for pest control. The transgenic is just one more element in the equation to obtain commercial yields.
A central preoccupation for Mexico is transgenic maize. Several transgenic varieties have been deregulated and are freely grown in the USA. The specific worry in Mexico is the possibility that transgenic maize will outcross with local Mexican land races such as teosinte (a wild relative). In the case of maize, the worry is even more acute since open pollination is the common behavior in maize varieties, and more than 80% of our farmers keep seed for planting year after year. Even though Mexican imports of maize from the US are destined for food, feed or processing, deviation of grains for their use as seed remains a domestic problem.
In the short term, our main concern would be to use biosafety regulations for the enhancement of the agricultural situation in Mexico. The focus should be on achieving a balance between the sustainable use and conservation of our biodiversity, and appropriate technological development that normally would tend towards an open commercial market that does not consider the impacts on biodiversity.
Amanda Gálvez, Ph.D., mailto:firstname.lastname@example.org
Professor, Department of Food Science and Biotechnology, Faculty of Chemistry
National Autonomous University of Mexico (UNAM) <http://www.unam.mx/indexs.html>
Mexico City, Mexico
and Michelle Chauvet, Ph.D., mailto:email@example.com Professor, Department of Sociology,
Metropolitan Autonomous University (UAM) <http://www.uam.mx/cgi-bin/detecta.pl>
(From an earlier 'Debate' Posting by Klaus Ammann)
From: Klaus Ammann
Subject: Debate 2000'0321 a: Teosinte and gene flow threat again
Here is the voice of an experienced regulator in the US scene, I agree on the basic thoughts and would like to explicitly add that the genetic pressure through gene flow is an old phenomenon and has been studied before in many cases. And even more important: Gene flow is the driving force behind micro-evolution. Without natural gene flow, there would have been no crop development. And, most important (whether frightening or not): Evolution is irreversible....
Thanks, Val Giddings for this important contribution (firstname.lastname@example.org).
Its just the 'bad luck' of GT that now we have some marker genes to follow up properly the dynamics of gene flow and we should not fall into the trap of seeing everything very negatively, for sure. I agree fully with Val that many biologists (and astonishingly enough many ecologists) have too conservative a view on ecosystems and population genetics, it is, as if Darwin would not have changed our view on the evolution of biodiversity.
On the other hand, the hazard evaluation depends on the nature of the transgenes and soon we will have transformed crops at hand where some ecological characteristics will have changed, in order to adapt to arid conditions or salty soils -- what an achievement this will be, let alone in the Sahel zone, where millions of people die of starvation, according to Amnesty International the worst of all the kinds of torture.
ETHICS WILL ALSO HAVE TO BE TAKEN INTO ACCOUNT WHEN EVALUATING THE GOOD AND THE BAD OF NEW TRAITS. EVERYBODY IS CRYING AFTER ETHICS TO BE CONSIDERED IN TECHNOLOGY RISK ASSESSMENT, BUT WHEN IT COMES TO POSITIVE ETHICAL CONSIDERATIONS, THEY ARE TOO OFTEN JUST FORGOTTEN.
These above statements on ethics have nothing to do with the naive slogan: GT will feed the world, its just a call for a holistic approach when integrating ethics.
This is also nothing new basically, but GT gives us the chance to do better in the future, when it comes to the risk assessment of releasing new crop traits. I am also convinced that we MUST do better in the future, since the new GT traits will be much better - this means also more efficient and consequently they could have more impact on the agro- and ecosystems.
Another field of new concern will be the traits producing some pharmaceutical compounds, as Val rightly points out. There are many cases of genetic pressure known today, which have nothing to do with GT, just one example: Medicago falcata, a rare dry meadow species is seriously threatened by modern traits of Medicago varia in Switzerland.
A follow up on the Dutch-Swiss biogeographical assay will be given in the next Debates to come. And for sure, it will be put into the framework Val Giddings is describing here. - Klaus
From: Val Giddings
Klaus -- if the issue here is properly not genetic "fragility [of teosinte populations] but the irreversible introduction of a new trait that may become common in Mexican maize landraces or wild relatives" then perhaps those who are worried about such a threat should focus as well on other sources of threat, such as cosmic rays and the huge panoply of naturally occurring transposable elements in maize. Banning corn varieties improved through modern biotechnology will not significantly reduce the threats of new genetic variation in populations of maize ancestors and relatives.
The notion that novel genetic material is, ipso facto, risky and dangerous is rooted in the platonic notion of species that Darwin overturned in 1859. If, as H.J. Muller wrote in 1959 "One hundred years without Darwin is enough" then surely 141 years without an understanding of genetics, variability in natural populations, and the sources of environmental threats is over the top.
As a regulator working for the US Department of Agriculture for 8 years evaluating proposals for field trials, I always assumed that if the probability of gene flow between a transgenic and a wild relative was not zero, then it was taken for risk assessment purposes to be 1. Then and only then can one really focus on the relevant question, which is not "will there be gene flow" but rather "what consequences might be expected in the event of gene flow." For the vast majority of gene constructs being inserted into agricultural cultivars, this is easy. In most cases it is difficult or impossible to imagine a selective advantage imparted to the wild relative that would create a new environmental problem, or exacerbate an existing problem, as weediness.
In the worst case one might see a trait imparted that might provide the wild relative with a measure of protection against, say, an herbicide that might otherwise be a threat. But herbicides are not a threat outside agricultural or other controlled areas, and most of us concerned about conservation would be delighted if a wild cultivar could thus be given a measure of protection against a potential threat. There are some weediness examples where this general rule doesn't hold true, as perhaps with sunflowers. The solution however is not trying to eliminate gene flow (see the example of Canute and the tides for a useful parallel) but appropriate agronomic management and stewardship.
In those cases where one would really want to eliminate the potential for gene flow, as in some (but not all) pharmaceutical producing plants, two things are important to note: 1) no one proposes to grow such plants outside containment and 2) pharmaceutical companies would have major economic incentives to eliminate potential for such gene flow through various gene switching techniques as well as physical security, to protect their massive R&D investments, whether or not there is any safety issue.
One must keep in mind the first step in risk assessment, which is hazard identification. Abundant data and massive experience demonstrate that gene flow is not per se hazardous. Then one must also keep in mind that for the extraordinarily rare circumstances in which gene flow which might lead to a hazard, it is important to determine if there is differential risk if the introgression takes place from traditional cultivars as opposed to from modern transgenics and landraces. And then all this must be factored in to a consideration of the global risks and benefits relating to agriculture and the environment.
As Jim Watson said 20 years ago, "In considering the risks of recombinant DNA, we shy at kittens and cuddle tigers."
Val Giddings is absolutely right about our need to be able to predict the impacts of gene introgression and he is also right when he says that for many (not the vast majority, Val!) traits the impact on native plant populations is likely to be zero. But equally there are of course many traits, especially those for pest/disease resistance and tolerance to abiotic factors, where increased fitness of crop/native hybrids and backcrosses could have serious effects on the population dynamics of ecosystems. This is the same problem we have with introduction of aliens and it can cost a lot to deal with! The real problem is that we do not have the time, or maybe even the science, to be able to predict the likely magnitude of such hazards, so Val's view about our ability to assess risk is a little optimistic. In fact I have yet to see a rigorous (ie information-based) assessment of hazard from this direction, probably because there are no data to enable rigour.
I don't share all Val's views on evolution. The introduction of novel genetic material to native plants is surely not equivalent to mutational events or transposition! We risk giving some native plants traits (sometimes from other phyla) which could enable them to move into ecological 'niches' which would normally be inaccessible because the genes they need to do this are not, and could not ever be, present in the 'species complex' gene pool. I agree that evolution relies on new genetic raw material, but within a species this is usually derived from a limited gene pool. Most 'new' genes are removed pronto by sex and selection, but may, rarely, enable a species to make a quantum leap into new territory. I would argue that gene flow from transgenics may increase the chance of these rare events. Humans have so altered the ecology of vast areas of the planet (especially in the developed world) that there will be opportunities wide open for plants with new traits.
Because gene flow between sexually compatibles is inevitable, Val says that we should rely on farmers to ensure that these hazards are not realised. I don't believe it! I have worked with farmers for the past 20 years and even with the best intentions, my view is that they will never be able to deliver effective containment. As I said in Bern, ironically the solution may be found in genetics. Engineering genetic isolation should be relatively straightforward (eg Terminator sequences, pollen incompatibility etc) and the highest priority. Genetic isolation can also be delivered by choosing the right (sexually incompatible with natives) crop to transform, especially for pharmed crops. These are the ingredients we need not only to deal with potentially risky transformations, but also to boost public confidence in our abilities to protect agricultural, natural and semi-natural ecosystems.
Maize, Gift of The Gods or Slave of Mortals?
Juan Pablo Ricardo Martínez-Soriano1* Diana Sara Leal-Klevezas2
1Unidad de Biotecnología e Ingeniería Genética de Plantas Centro de Investigación y Estudios Avanzados, IPN 2Centro de Investigación Biomédica de Occidente
Instituto Mexicano del Seguro Social, Meixco
(Translated from a Mexican Spanish-language newspaper in 2000; I forgot which one......CSP)
In the aztec language (náhuatl), maize means "seed of humans". According to prehispanic traditions, Gods gave native Mexicans the first maize seeds and from then on and for thousands of years, maize has been vital element for the Latin American cultures. In Mexico, it is still considered a "pure" and mystical plant.
Biologically, maize is an orphan plant and has only one relative: teosinte, náhuatl name for "seed of the Gods". This is puzzling name because maize should be the "seed of the Gods", should it not?. Why is a weed, a wild plant the "chosen one"? Probably because the answer (which we still have not completely discovered), was known by the ancient natives: how teosinte was transformed into maize. Maize is the only plant with but a single existing wild relative that can reasonably be considered its immediate ancestor: the annual teosinte.
The relationship between corn and its closest wild relative has no close counterpart in other plants. Both have the same chromosome number and they hybridize readily. The fertility of the hybrids is high because their chromosome pairing is regular and virtually complete; crossing over between their chromosomes is of the same order as it is in maize itself. Morphologically, teosinte is similar to maize; and indeed when both grow together in the maize fields of the Valley of México, distinguishing one from the other before they flower is not an easy task, even for the keen eyes of the Mexican farmers. Even after flowering, there is a marked similarity in the staminate inflorescences, the tassels.
The most striking differences between maize and teosinte are found in the pistillate inflorescence. In maize, individual feminine spikes are many ranked, in teosinte they are two ranked; the maize ear is solid, the teosinte spike is brittle and comes apart at maturity; the seeds of maize are not enclosed, while those of teosinte are encapsulated in fruit cases. The process of maize domestication is controversial and remains obscure. There is no evidence of any kind (genetic, archaeological, linguistic, ethnobotanical, etc.) that could support a slow and gradual transformation from the teosinte ear into the corn ear. Any theory supporting this faces the problem of deriving the maize ear from a female spike of teosinte, and the fact that the ears of maize are themselves terminal branches like the male tassels of teosinte (and not lateral like teosinte ears).
According to archaeological records, maize was domesticated in the Balsas river drainage (Mexico) 6000 years ago. Corn appears suddenly in the archaeological record, giving almost no clues as to its ancestor. The latter disappeared when maize emerged. Wherever primitive cobs have been found, they are of small size, and invariably, indehiscents. This is of major importance: only humans can release them, allowing the plant to multiply and preserve its species.
Maize does not exist as a free species in nature. Of all cultivated plants it is the only one that humans have completely enslaved and yet it is the one that possesses the highest degree of diversity. This may seem a paradox. Indeed, this enormous diversity can be clearly detected by looking at the native maizes of Mexico.
This richness has been "created" by humans and only by humans, for only one purpose: to use it as food. Maize does not disperse itself and therefore it is not selected by Nature. Yes, maize has been our disfunctional slave for 6,000 years.
Recently, several biotech companies have requested authorization to plant and market transgenic corns in Mexico. Several ecological groups have raised concerns about the potential risks of introducing such plants to Mexico, where maize originated. Two main concerns are that a) the genetic background of maize and its relatives will be affected and b) the ecological impact on other plant and insect species.
The concern regarding the possible effects on the native maizes and relatives has little if any scientific and practical background. It is more related to cultural factors rather than biological ones. The arguments stating that maize is genetically fragile are weak. The maize genome has been molded over thousands of years and only the useful genetic background has been maintained by humans. The plant has survived the selection process only because we have helped it. It seems like a paradox to argue at this point that it is necessary to protect the genetic background of corn when for 6000 years of traditional breeding we have protected only the alelles we have needed. However, for the sake of argument let us imagine that we need to protect the actual genotypes. Here there is no need for concern, because any transgene transferred by accident to native maizes can easily be removed from the progeny by simply selecting against the incorporated trait. Maize is always under strong artificial selection and therefor
Also, the concern about the effect of transgenes on the wild relatives, teosintes, is also unjustified. We humans have bred maize, without thinking that by doing this we could be affecting teosintes, sometimes irreversibly. Any "unlucky" teosinte recipient of maize pollen is at risk of transmitting to its progeny the "unfortunate" trait of not being able to release its seed (just as in maize). Again, the domestication and later breeding of corn has lasted 6000 years and even when the teosintes are affected (see figure 1), their populations have been maintained in the wild. No doubt our cultivation of maize has eliminated an uncountable number of generations; nonetheless teosinte is still out there. Why are we suddenly concerned about teosintes when nobody has cried for them in the past 6000 years ?
The transference of a (trans)gene or alelle from maize to teosinte is a natural process (the opposite is also true). Nevertheless, its fixation in a teosinte population would be impossible if it did not confer an evolutionary advantage to the species. A transgene will be lost by natural selection or neutral evolution like the thousands that never conferred adaptative advantages to the recipient plants If the human species become extinct at this moment, only corn and the silkworm, the "loyal slaves" will disappear with us. Every other domesticated species may go back to nature and eventually reestablish its ecological niche. The extinction of species during human "domination" has occurred basically because of the comfort and prosperity we desire. This has asphyxiated natural ecosystems and eliminated species that have not been "genetically fit". We have to keep educating our society and promote the respect and care for nature.
In Mexico we adore maize and its "divine origin". The reality is different: maize is a slave, far from the gods and too close to us.
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Wang, R.-L., A. Stec, J. Hey, L. Lukens y J. Doebley 1999. "The limits of selection during maize domestication." Nature 398: 236-239.