Field Testing Genetically Modified Organisms Framework for Decisions (1989) / Chapter Skim
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5 Past Experience with the Introduction of Modified Plants: Molecular Genetic Techniques
5 Past Experience with the Introduction of Modified Plants: Molecular Genetic Techniques
Pages 54-64
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From page 54... ...
The directed transformation of commercial varieties and hybrids should significantly shorten the time to commercial release. The rapid progress that has been made in gene identification and isolation methods, plant tissue culture, and gene transfer techniques has now permitted the extension of specific genetic change (for example, by recombinant DNA methods)
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From page 55... ...
By deleting the genes that modify normal cells into tumorigenic cells and leaving hit act those genes that are responsible for transferring DNA from the bacterium to the plant cell nucleus, modified A tumefaciens cells can vector desirable genes into appropriate plants cells.
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From page 56... ...
In addition, no evidence suggests that gene insertion with Agrobacterium-based vectors imparts any plant pest characteristics to the recipient plant. The vast majority of plant modifications target nuclear chromosomes; however, attempts are being made to modify organelIar genomes, those of chIoroplasts and m~tochondria.
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From page 57... ...
Multiple transformation of a single Individual could produce a plant with many introduced genes, as does sexual hybridization of individuals that carry genes at distinct alleles. Whereas genes are commonly introduced to add new traits, it has not been possible to inactivate or remove a specific gene by homologous recombination or msertional activation.
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From page 58... ...
compositions are altered (Beachy et al., 1985; Sengupta-Gopalan et al., 1985~. The rapidly expanding knowledge base in plant biology makes it likely that future targets for plant improvement via molecular genetic techniques wiD include resistance to environmental pressures that can affect plant productivity.
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From page 59... ...
The key consideration in approval of each test has been a scientific evaluation of its risk and environmental impact. The major issues that have emerged from these discussions are stability of the inserted genes, undesirable alteration in crop phenotype, environmental impact on nontarget species, potential for weediness of genetically modified crops, and ability to maintain the gene within the test site.
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From page 60... ...
All the evidence indicates that genes or traits introduced by molecular methods behave similarly to those introduced by classical techniques such as cell selection, mutagenesis, or sexuad hybridization that is, regular inheritance patterns ~ generations (Eraley et al., 1986; KuhIemeier et al., 1987~. Undesirable Alteration of Plant Phenotype Since gene insertion ~ random, inactivation of an important plant gene or genes could possibly result from the insertion process.
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From page 61... ...
Plant field tests to date have used removal of reproductive structures, the lack of non-cross-pollinating weedy relatives, and distance from related cross-poBinating varieties to prevent new genes or gene combinations from escaping beyond the control of the experiment. Established conditions for confinement of cIassicaBy modified plants in field tests are being used to limit movement of genes outside the test site, thereby minimizing effects on natural and managed ecosystem.
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From page 62... ...
Several crops such as tobacco, tomato, and oilseed rape that have been modified to resist active ingredients of herbicides, such as glyphosate, bromozynil, sulfonylureas, and phosphinothricm, have been tested In the field. The benefit of such research will be increased flexibility ~ weed control, including benefits such as unproved weed control efficacy, reduced costs to farmers, the opportunity to replace currently used chemicals with more environmentally friendly chemicals, and the reduction of overall herbicide usage (Boyce Thompson Institute, 19873.
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From page 63... ...
In addition to the confinement afforded by the lack of crosspollination and the absence of sexually compatible weed species, it was possible to physically contain plants at the test site by fencing to discourage seed dispersal by predators. Also, tilIage Ad chemical means were used to destroy volunteer tomatoes.
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From page 64... ...
thuringiens~ endotox~n and coat-protein grew normally; there were no indications of any adverse phenotypes such as plants with increased susceptibility to other viral or fun gel diseases. Although much field research is needed to evaluate the performance of insect-tolerant and virus-res~st~t tomato varieties under different conditions, the preliminary data confirm the predictable behavior of plants modified by molecular methods and tested in lam oratory and greenhouse.
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