Potatoes were engineered for resistance to potato leaf roll virus and Potato virus Y in Poor sales led to their market withdrawal after three years. Yellow squash that were resistant to at first two, then three viruses were developed, beginning in the s. Squash was the second GM crop to be approved by US regulators. The trait was later added to zucchini. Many strains of corn have been developed in recent years to combat the spread of Maize dwarf mosaic virus , a costly virus that causes stunted growth which is carried in Johnson grass and spread by aphid insect vectors.
These strands are commercially available although the resistance is not standard among GM corn variants. In , the FDA approved the first plant-produced pharmaceutical , a treatment for Gaucher's Disease.
Biology of Transgenes
Algae is under development for use in biofuels. Lignin is the critical limiting factor when using wood to make bio-ethanol because lignin limits the accessibility of cellulose microfibrils to depolymerization by enzymes. Companies and labs are working on plants that can be used to make bioplastics. Scientists at the University of York developed a weed Arabidopsis thaliana that contains genes from bacteria that could clean TNT and RDX -explosive soil contaminants in However A. Genetically modified plants have been used for bioremediation of contaminated soils.
Mercury , selenium and organic pollutants such as polychlorinated biphenyls PCBs. Marine environments are especially vulnerable since pollution such as oil spills are not containable.
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In addition to anthropogenic pollution, millions of tons of petroleum annually enter the marine environment from natural seepages. Despite its toxicity, a considerable fraction of petroleum oil entering marine systems is eliminated by the hydrocarbon-degrading activities of microbial communities. Particularly successful is a recently discovered group of specialists, the so-called hydrocarbonoclastic bacteria HCCB that may offer useful genes.
Crops such as maize reproduce sexually each year. This randomizes which genes get propagated to the next generation, meaning that desirable traits can be lost.
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To maintain a high-quality crop, some farmers purchase seeds every year. Typically, the seed company maintains two inbred varieties and crosses them into a hybrid strain that is then sold. Related plants like sorghum and gamma grass are able to perform apomixis , a form of asexual reproduction that keeps the plant's DNA intact. This trait is apparently controlled by a single dominant gene, but traditional breeding has been unsuccessful in creating asexually-reproducing maize.
Genetic engineering offers another route to this goal. Successful modification would allow farmers to replant harvested seeds that retain desirable traits, rather than relying on purchased seed. Genetic modifications to some crops also exist, which make it easier to process the crop. Emulsifiers in packaged foods . Soybean oil . The number of USDA-approved field releases for testing grew from 4 in to 1, in and averaged around per year thereafter. Releases with agronomic properties such as drought resistance jumped from 1, in to 5, in As of September , about 7, releases had been approved for corn, more than 2, for soybeans, more than 1, for cotton, and about for potatoes.
Constant exposure to a toxin creates evolutionary pressure for pests resistant to that toxin. Over-reliance on glyphosate and a reduction in the diversity of weed management practices allowed the spread of glyphosate resistance in 14 weed species in the US,  and in soybeans. To reduce resistance to Bacillus thuringiensis Bt crops, the commercialization of transgenic cotton and maize came with a management strategy to prevent insects from becoming resistant.
Insect resistance management plans are mandatory for Bt crops. The aim is to encourage a large population of pests so that any recessive resistance genes are diluted within the population. Resistance lowers evolutionary fitness in the absence of the stressor, Bt. In refuges, non-resistant strains outcompete resistant ones. As a result, the resistance gene frequency in the population remains lower.
For example, if the temperature is not ideal, thermal stress can lower Bt toxin production and leave the plant more susceptible. More importantly, reduced late-season expression has been documented, possibly resulting from DNA methylation of the promoter. This success has depended on factors independent of management strategy, including low initial resistance allele frequencies, fitness costs associated with resistance, and the abundance of non-Bt host plants outside the refuges.
Companies that produce Bt seed are introducing strains with multiple Bt proteins. Monsanto did this with Bt cotton in India, where the product was rapidly adopted. Coined "Refuge-In-a-Bag" RIB , this practice is intended to increase farmer compliance with refuge requirements and reduce additional labor needed at planting from having separate Bt and refuge seed bags on hand. Increased concerns for resistance with seed mixtures include partially resistant larvae on a Bt plant being able to move to a susceptible plant to survive or cross pollination of refuge pollen on to Bt plants that can lower the amount of Bt expressed in kernels for ear feeding insects.
Best management practices BMPs to control weeds may help delay resistance. BMPs include applying multiple herbicides with different modes of action, rotating crops, planting weed-free seed, scouting fields routinely, cleaning equipment to reduce the transmission of weeds to other fields, and maintaining field borders. By some weed populations had evolved to tolerate some of the same herbicides. Palmer amaranth is a weed that competes with cotton. A native of the southwestern US, it traveled east and was first found resistant to glyphosate in , less than 10 years after GM cotton was introduced.
Farmers generally use less insecticide when they plant Bt-resistant crops. Insecticide use on corn farms declined from 0. This is consistent with the decline in European corn borer populations as a direct result of Bt corn and cotton. The establishment of minimum refuge requirements helped delay the evolution of Bt resistance. However, resistance appears to be developing to some Bt traits in some areas. In addition, conservation tillage reduces the carbon footprint of agriculture. The regulation of genetic engineering concerns the approaches taken by governments to assess and manage the risks associated with the development and release of genetically modified crops.
Gene Flow from GM Plants - Google книги
There are differences in the regulation of GM crops between countries, with some of the most marked differences occurring between the US and Europe. Regulation varies in a given country depending on the intended use of each product. For example, a crop not intended for food use is generally not reviewed by authorities responsible for food safety. In , GM crops were planted in 27 countries; 19 were developing countries and 8 were developed countries. Farmers have widely adopted GM technology see figure. For example, the system of planting glyphosate-resistant seed and then applying glyphosate once plants emerged provided farmers with the opportunity to dramatically increase the yield from a given plot of land, since this allowed them to plant rows closer together.
Without it, farmers had to plant rows far enough apart to control post-emergent weeds with mechanical tillage. However critics have disputed whether yields are higher and whether chemical use is less, with GM crops. See Genetically modified food controversies article for information. Europe grows relatively few genetically engineered crops  with the exception of Spain, where one fifth of maize is genetically engineered,  and smaller amounts in five other countries.
In recent years GM crops expanded rapidly in developing countries. Japan has the largest number , followed by the U. Maize has the largest number events in 27 countries , followed by cotton 49 events in 22 countries , potato 31 events in 10 countries , canola 30 events in 12 countries and soybean 27 events in 26 countries.
Direct genetic engineering has been controversial since its introduction. Most, but not all of the controversies are over GM foods rather than crops per se. GM foods are the subject of protests, vandalism, referenda, legislation, court action  and scientific disputes. The controversies involve consumers, biotechnology companies, governmental regulators, non-governmental organizations and scientists. Opponents have objected to GM crops on multiple grounds including environmental impacts, food safety, whether GM crops are needed to address food needs, whether they are sufficiently accessible to farmers in developing countries  and concerns over subjecting crops to intellectual property law.
Secondary issues include labeling, the behavior of government regulators, the effects of pesticide use and pesticide tolerance. A significant environmental concern about using genetically modified crops is possible cross-breeding with related crops, giving them advantages over naturally occurring varieties. One example is a glyphosate-resistant rice crop that crossbreeds with a weedy relative, giving the weed a competitive advantage.
The transgenic hybrid had higher rates of photosynthesis, more shoots and flowers, and more seeds than the non-transgenic hybrids. No reports of ill effects from GM food have been documented in the human population. It allows indirect disclosure such as with a phone number, bar code, or web site.
Advocacy groups such as Center for Food Safety , Union of Concerned Scientists , Greenpeace and the World Wildlife Fund claim that risks related to GM food have not been adequately examined and managed, that GM crops are not sufficiently tested and should be labelled, and that regulatory authorities and scientific bodies are too closely tied to industry. Environment International. In spite of this, the number of studies specifically focused on safety assessment of GM plants is still limited.
However, it is important to remark that for the first time, a certain equilibrium in the number of research groups suggesting, on the basis of their studies, that a number of varieties of GM products mainly maize and soybeans are as safe and nutritious as the respective conventional non-GM plant, and those raising still serious concerns, was observed. Moreover, it is worth mentioning that most of the studies demonstrating that GM foods are as nutritional and safe as those obtained by conventional breeding, have been performed by biotechnology companies or associates, which are also responsible of commercializing these GM plants.
Anyhow, this represents a notable advance in comparison with the lack of studies published in recent years in scientific journals by those companies. Krimsky, Sheldon Archived from the original PDF on 7 February Retrieved 9 February I began this article with the testimonials from respected scientists that there is literally no scientific controversy over the health effects of GMOs.
My investigation into the scientific literature tells another story. Panchin, Alexander Y. Critical Reviews in Biotechnology. Here, we show that a number of articles some of which have strongly and negatively influenced the public opinion on GM crops and even provoked political actions, such as GMO embargo, share common flaws in the statistical evaluation of the data.
Having accounted for these flaws, we conclude that the data presented in these articles does not provide any substantial evidence of GMO harm. The presented articles suggesting possible harm of GMOs received high public attention. However, despite their claims, they actually weaken the evidence for the harm and lack of substantial equivalency of studied GMOs. We emphasize that with over published articles on GMOs over the last 10 years it is expected that some of them should have reported undesired differences between GMOs and conventional crops even if no such differences exist in reality.
Yang, Y. Journal of the Science of Food and Agriculture. It is therefore not surprising that efforts to require labeling and to ban GMOs have been a growing political issue in the USA citing Domingo and Bordonaba, Overall, a broad scientific consensus holds that currently marketed GM food poses no greater risk than conventional food Major national and international science and medical associations have stated that no adverse human health effects related to GM food have been reported or substantiated in peer-reviewed literature to date.
Despite various concerns, today, the American Association for the Advancement of Science, the World Health Organization, and many independent international science organizations agree that GMOs are just as safe as other foods. Compared with conventional breeding techniques, genetic engineering is far more precise and, in most cases, less likely to create an unexpected outcome. Pinholster, Ginger 25 October American Association for the Advancement of Science. Retrieved 8 February American Medical Association.
Archived from the original on 7 September Retrieved 19 March CS1 maint: BOT: original-url status unknown link. GM foods currently available on the international market have passed safety assessments and are not likely to present risks for human health. In addition, no effects on human health have been shown as a result of the consumption of such foods by the general population in the countries where they have been approved. Continuous application of safety assessments based on the Codex Alimentarius principles and, where appropriate, adequate post market monitoring, should form the basis for ensuring the safety of GM foods.
British Medical Association. March Retrieved 21 March In our view, the potential for GM foods to cause harmful health effects is very small and many of the concerns expressed apply with equal vigour to conventionally derived foods.
What can plants reveal about gene flow? That it's an important evolutionary force
However, safety concerns cannot, as yet, be dismissed completely on the basis of information currently available. When seeking to optimise the balance between benefits and risks, it is prudent to err on the side of caution and, above all, learn from accumulating knowledge and experience. Any new technology such as genetic modification must be examined for possible benefits and risks to human health and the environment. As with all novel foods, safety assessments in relation to GM foods must be made on a case-by-case basis.
Members of the GM jury project were briefed on various aspects of genetic modification by a diverse group of acknowledged experts in the relevant subjects. The GM jury reached the conclusion that the sale of GM foods currently available should be halted and the moratorium on commercial growth of GM crops should be continued. These conclusions were based on the precautionary principle and lack of evidence of any benefit. The Jury expressed concern over the impact of GM crops on farming, the environment, food safety and other potential health effects.
The Royal Society review concluded that the risks to human health associated with the use of specific viral DNA sequences in GM plants are negligible, and while calling for caution in the introduction of potential allergens into food crops, stressed the absence of evidence that commercially available GM foods cause clinical allergic manifestations. The BMA shares the view that that there is no robust evidence to prove that GM foods are unsafe but we endorse the call for further research and surveillance to provide convincing evidence of safety and benefit.
From Wikipedia, the free encyclopedia. Main article: History of genetic engineering. Main article: Genetic engineering techniques. The neutrality of this section is disputed. Relevant discussion may be found on the talk page.
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Please do not remove this message until conditions to do so are met. December Learn how and when to remove this template message. See also: List of genetically modified crops. This section needs expansion with: examples and additional citations of how farmers' use of GM crops changes their practices. You can help by adding to it. September Main articles: Regulation of genetic engineering and Regulation of the release of genetic modified organisms.
Main article: Genetically modified food controversies. Food portal. Scientific Reports. Bibcode : NatSR Bibcode : PLoSO D; Ciliberto, F; Hennessy, D. A; Moschini, G Maize and soybeans". Science Advances.
Archived from the original PDF on 17 September Retrieved 8 July We have reviewed the scientific literature on GE crop safety for the last 10 years that catches the scientific consensus matured since GE plants became widely cultivated worldwide, and we can conclude that the scientific research conducted so far has not detected any significant hazard directly connected with the use of GM crops.
Such debate, even if positive and part of the natural process of review by the scientific community, has frequently been distorted by the media and often used politically and inappropriately in anti-GE crops campaigns. Agricultural Biotechnology: Meeting the Needs of the Poor.
Health and environmental impacts of transgenic crops". Despite the fact that the gene transfer from crops to their wild relatives is widely studied, there are no detailed data available on what happens with these genes, which have been introduced into wild populations after a longer period of time. Namely, the majority of this research concludes with the first generation of hybrids. However, genes originating from the cultivated sunflower can persist in wild populations over the five-year period, following the hybridization [ 43 ].
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Some authors [ 74 ] have also studied the effects of a year long gene transfer from the cultivated to the wild sunflower populations. Importance of crop-weed hybrids produced as result of gene flow from HR crops to wild or weedy relatives for future crop production can be different depending on traits introduced into progeny.
Therefore, assessment of gene flow occurrence requires not only estimating the degree of gene flow, but also evaluating the relative fitness of hybrids. It long dominated the view that crop-wild hybrids have a lower fitness than their wild parent [ 75 , 76 ]. But, many studies confirmed that some hybrids display increased [ 47 ], while the other display reduced [ 77 ] fitness in comparison with their parents.
Displayed fitness depends not only on the crop traits introduced to wild relatives, but also on environmental conditions. Namely, fitness of hybrids between crop and wild sunflower increases in stressful conditions common to conventional agroecosystem like competition and herbicide application [ 77 ]. The role of seeds in the transfer of HR genes from crops to their wild relatives is evident in their spread into new areas where volunteer populations are formed.
After that HR genes can be transferred from these volunteer populations to their wild relatives through the pollen. Also, hybrids resulting from spontaneous crosses of HR crops and their wild relatives through seeds can be carried into new areas, where they subsequently present a source of pollen, which carries the resistance genes. Unlike pollen, the seeds usually remain in the close proximity of the plants from which they have originated. But, as seeds are more persistent than pollen, movement of seeds is possible to further distances by human activities then pollen movement [ 59 ].
In general, seed dispersal of HR crops or progeny created through their spontaneous crossing with wild relatives, depends on the biological properties of the crop, the ecological conditions, crop production technology and the agrotechnical measures applied on these fields, following with harvest. Nevertheless, it is possible to monitor the dispersal of these seeds in space and time. Some authors [ 78 ] have confirmed the gene transfer of sugar beet to their wild relatives through the seeds whose dispersal resulted from soil transport. Namely, although spontaneous spatial dispersal is often considered as irrelevant since the seeds of a majority of crop cultures have lost this ability, seed dispersal is also possible as a result of spillage during the harvest and their transport and storage operations, which enables the spread to great distances.
Also, it should be considered that, in addition to pollen and seeds, soil seedbank has an important role in the plant dispersal [ 79 ]. Namely, when considering different life forms of sugar beet cultivated, wild, and weedy , it is well known that they form long-term seedbanks [ 80 ], which, over a longer period of time, can provide the plants which are then a source of HR genes. Gene flow by the vegetative propagules stolons, rhizomes, roots, crowns, and bulbs is possible on short distance via natural means or on equipment moved between fields, while long-distance movement could be possible only with human activities or through the waterways [ 58 ].
As HR crops are mainly annual species, gene flow via vegetative propagules can be interesting only for perennials like glyphosate-resistant alfalfa commercially available and creeping bentgrass Agrostis stolonifera , under consideration [ 58 ]. Gene flow risk assessment is a procedure, which helps determine whether the transfer will occur, and if it will, in which degree, with a goal to reduce such a risk to the minimal possible level. Furthermore, such estimates are also significant due to the possibility that the transfer of genes responsible for HR will lead to an increase in the survival and adaptability of the introduced weed species.
Also, it is considered that certain plants can attain the traits of invasive species as a result of introduced genes, making the assessments of long-term consequences of gene transfer from crops to their wild relatives a necessity. There is no same potential for gene flow for all HR crops. For example gene flow from maize is theoretically possible to teosinte, but these species only exist in Mexico and Central America and not yet been reported for contamination with transgenes [ 81 ].
On the other hand, there is good potential for introgression from sunflower [ 74 ], sugarbeet [ 82 ] and rice [ 83 ] to wild relatives. Namely, the dangers of the transfer of genes responsible for HR and the ecological consequences of this must be evaluated individually for each specific case herbicide, plant, wild relatives, etc. Crucial steps in the rational assessment of ecological consequences of this phenomenon include the understanding of the following: 1 gene transfer from crops to wild relatives; 2 gene expression and inheritance in hybrids, which have resulted from the gene transfer from crops to wild relatives; 3 changes in fitness in wild relatives caused by the introduction of genes; and 4 the dynamics of the gene transfer from crops to wild populations.
The invasibility of crop-weed hybrids, which have originated as a result of gene transfer from HR crops to wild relatives, is dependent on all of these aspects. The likelihood of gene transfer from crops to their wild relatives depends on the genetic characteristics of crops and their wild relatives, as well as the homology of their genomes [ 62 ]. Additionally, the introduction of genes is dependent on the part of the genome, in which the gene is positioned. Some authors [ 30 ] found a possibility of gene introduction from 13 most important crops into wild relatives and determined that 12 of the studied crops can hybridize with their wild relatives.
Of the 12 listed crops, cases of introduction have been confirmed for 7, while in the remaining five there is a possibility that the introduction will occur. A similar categorization pertaining to the risk assessment was also applied by other authors [ 84 , 85 ]. The risk level of the introgression of genes from crops to their wild relatives [ 86 ] made based on data reviewed by [ 76 ].
In order to prevent or reduce the unwanted transfer of pollen from HR crops onto their relatives, different barriers can be used, although there is no absolute guarantee that the gene transfer can be prevented in this manner. The most often used barriers are isolation in space or time, protective vegetation barriers made up of one or more different species, male sterility as a genetic mechanism for the prevention of gene transfer, etc. Spatial distance isolation means increasing the distance between fields sown by HR crops and populations of its relatives.
Also, spatial isolation is applied as preventive measure in production of GM and non-GM crops in coexistence with the aim to avoid contamination products of non-GM crops. It has been known that by increasing the distance between crops and its relatives, the dispersal of pollen is reduced, i. Thus, the frequency of pollen originating from a transgene oilseed rape decrease from 1.
Also, frequency of crop-wild relative hybrid decreased from 0. Distances between pollen source and gene occurrence can be very valuable in the planning of spatial isolation of HR varieties, in order to prevent the gene flow to their relatives. This distance depends on many factors such as the presence of local barriers, the local climate, and the topography of the area. In the case of sunflower, the isolation distance should be greater than m [ 89 ].
Also, maize pollen can be detected at distances greater than m from the pollen source [ 90 ]. But, pollen of maize has short flight range [ 91 ], after which it settles to the ground rapidly [ 92 ] due to relatively heavy and large grains. Due to that cross-fertilization mainly occurs within 50 m of the pollen source [ 93 ]. Therefore, measure for keeping seed purity of non-GM maize, which coexists with GM maize, suggests isolation distance between 10 and 50 m to achieve EU admissible threshold of 0.
Temporal isolation is a measure, which should prevent overlapping flowering times of crop and wild relatives with the aim to avoid gene flow. About 5 days lag in flowering of imazamox-resistant in comparison with tribenuron-methyl resistant sunflower resulted in lack of gene flow to weedy sunflower probably due to the short period of overlapping flowering time between the resistant hybrid and the weedy sunflower [ 42 ].
Temporal isolation is very suitable to prevent non-GM crop contamination with GM when grow in coexistence. Also, temporal separation in sowing days improves the coexistence of maize [ 96 ]. Contrary to that, temporal isolation based on selection of hybrid varieties in which flowering noncoincide achieves the same results although sowing date was the same [ 97 ]. Temporal separation and isolation distance together can be a good solution to minimize unwanted gene flow. Protective vegetation barriers , made up of one or more different species, can prevent the gene flow by physically stopping pollen in the case of wind pollination.
The sowing of conventional crops of the same species, also known as pollen traps, in the vicinity of HR hybrids is an efficient measure, as their role is to attract pollinating insects in order to leave pollen on these pollen traps. This type of barrier can be much more effective than isolation distance. Namely, the sowing of pollen traps between GM and conventional crops is the most efficient measure for the prevention of gene flow [ 98 ].
Also, gene flow through pollen from the HR oilseed rape decreases rapidly with the increase of pollen source distance, with the added necessity of a protective vegetation barrier or pollen traps [ 99 ]. Some authors [ 95 ] studied pollen-mediated gene flow between GM and non-GM maize and concluded that effect of two maize rows surrounding the recipient field in reduction of cross-fertilization is the same like effect of 12 maize rows surrounding the pollen donor.
The use of biological barriers achieves the best results in the prevention of gene flow, and so far the barriers based on cytoplasmatic male sterility, maternal inheritance, and seed sterility have mostly been used. Cytoplasmic male sterility is based on the inability of plants to produce viable pollen. This type of barrier is suitable option to reduce gene flow in sunflower and maize [ 43 , 66 , ]. Maternal inheritance is successfully used in the prevention of gene flow across the pollen, in the case of several species, including tobacco and tomato [ , ].
However, this strategy is seen as the most controversial control measure for limiting genes flow. None of these strategies can be applied in all crops, therefore using combinations of different approaches for the prevention of unwanted gene flow is recommended. All mentioned measures for prevention and reduction of gene flow are important separately, but their integration and combination with stewardship production system could be the best solution.
Options for chemical control of broadleaf weed species, especially weeds belonging to Asteraceae family, without injuring the crop are quite limited in sunflower compared to most other row crops [ ]. Due to that, sunflower hybrids resistant to ALS-inhibiting herbicides, including imidazolinone IMI and sulfonylurea SU , was developed by conventional breeding methods, with the aim to improve weed control. For development of those hybrids were used for subsequent crossings between cultivated sunflower and wild resistant sunflower [ ] or seed mutagenesis [ ]. Also, ExpresSun system has been developed as result of mutagenesis breeding [ ] with the aim to grow sunflower hybrids resistant to tribenuron-methyl [ 17 ].
The breeding of sunflower hybrids resistant to herbicides belonging to IMI and SU groups in Serbia was started in , and since , this technology has been applied in the production. As a donor of imazamox-resistance gene, the wild sunflower originating from the USA was used, in which the resistance to herbicides of the imidazolinone group was developed following a seven-year consecutive application of imazethapyr [ ].
The produced hybrid has shown a high level of resistance toward imazethapyr [ ] and imazamox [ ], not only regarding different vegetative parameters, but also considering the activity of ALS enzymes in vivo , and in vitro. Source populations SURES-1 and SURES-2 were used as a source of genes responsible for the resistance to tribenuron-methyl [ 1 , ], producing also a hybrid with a highly distinguished resistance for this herbicide [ , ].
The introduction of such crops in the production in Serbian fields has enabled a more efficient control of economic harmful weed species, such as Sorghum halepense , A. Although the presence of four species from the genus Helianthus H. The origin of these populations is not known, but it is possible to determine. These three traits are already stacked into a single maize hybrid prepared for the African continent South Africa. Such hybrids might have a positive fitness and may thus spread and expand in agricultural systems that reuse their seeds. The vulnerability of a field for gene introgression due to pollen flow is inversely proportional to the size relation of the receiving field to the surrounding donor fields 33 , Some authors have claimed that fields larger than 5 ha do not need any isolation distance This situation is similar to most communities in Zambia in terms of size and isolation distances of fields for small-scale farmers smaller than 5 ha.
For example, the average farm size in Uganda is 1. The timing in flowering between the relevant maize populations will determine the potential pollen cross-hybridisation. If the environment and cultural practices permit, this can be used as a measure to avoid pollen flow In the studied Zambian communities, where farmers plant maize under rain-fed conditions, maize is typically planted after the first rain following a longer period of cool dry and hot dry seasons from May to July and August to October, respectively.
Therefore, many farmers plant more or less at the same time when the rainy season starts in November. Thus, maize cultivation is regionally largely synchronized. With the limited possibility of adapting planting dates under the practice of rain-fed agriculture, planting varieties with different time to flowering might be an alternative way to minimize cross-pollination, although the possibilities to implement and control this in practice would need to be further studied. The option might however not be sustainable since the differences between the varieties would be reduced by cross-hybridisation and exchange of seed among farmers.
The vital role of seeds as an additional vehicle for gene flow must not be underestimated In particular, the human-driven gene flow through intentional and unintentional seed movement is relevant. Other publications confirm the importance of sharing and re-using seed in other resource-constrained smallholder communities in particular 35 , 62 , 66 , 67 , The practice of re-using seed was an important part of the local food security and independence, according to the interviewed farmers.
Both local maize varieties and commercial hybrid maize varieties were re-used. This latter practice constitutes a link between the informal and the formal seed system, as also documented elsewhere 16 , 71 , 72 , In South Africa, GM maize is grown both in large and small scale, and seeds from formal and informal sectors are frequently mixed in smallholder systems.
Thus, specific hypotheses on cross-hybridisation and introgression of transgenes could be tested there. Transgenic seeds were also kept for recycling by smallholder farmers This illustrates how transgenes may enter into subsistence maize locally adapted genepools and stay there over time. To estimate outcrossing rates require an understanding of the mechanisms that influence gene flow quantitatively. This can be done with modelling and is of interest scientifically as well as for policy and regulation.
For example, in case a transgenic maize plant expressing Bt-toxin is hybridizing with a non-Bt plant, and recycled, the outcome would likely be a plant that expresses Bt-toxin at a low level. Notably, once a transgenic gene or trait is out, it is almost impossible to eliminate it from the regional seed pool. The task of removing transgenes from a subsistence farming system like the one in Eastern Cape would be highly difficult, as it would require control of innumerable informal seed storages A clean-up process might also lead to a loss of locally selected genes and traits.
Given that smallholders often recycle and share seed, genes will not only diffuse locally but also regionally since sharing of seed also happens over longer distances compared to the range of pollen flow. One illustrative case in the community of Chongwe showed that sharing of seeds within a family, from mother to daughter, moved seeds over a distance of about kilometers, after the daughter moved to another village. A recent modeling study showed that seed flow between farmers contributes to a much wider diffusion of genes transgenes in Mexico than expected from pollen flow only The practices of re-use and sharing of hybrid as well as OPV seed documented in the present case is not limited to the studied communities, or to Zambia alone, but widespread across Africa 16 , Most African countries, including Zambia, have not adopted GM maize.
Therefore, apart from a scientific contribution to the understanding of gene-flow in small-scale farming in general, this study also contributes relevant information at a Zambian or wider African policy-level: the physical arrangements and sizes of fields, as well as farmer seed saving and sharing, will significantly affect the rate of gene flow.
Country specific evaluations should take into account the efficiency of containment measures, pest resistance management applicability, as well as transboundary movement regulation compliance in a crop variety admission context. In conclusion, we show through modelling that smallholder Zambian farmers work in a system where high rates of pollen flow leads to extensive cross-hybridisation of maize varieties used in the field. In addition, farmers recycle and share maize seeds. This increases gene flow locally, but also increase the distance that genes travel.
More data is needed to evaluate how representative the studied communities are for other small-scale farming areas in Zambia and other African countries. Future studies should address the combinatory effect of ecological e. Seed saving and sharing needs to be co-analyzed and integrated into models of gene flow to understand what happens at different scales: from local to regional, national and transnational levels, over time. Pollen-mediated gene flow and seed exchange in small-scale Zambian maize farming, implications for biosafety assessment.
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