Field Testing Genetically Modified Organisms Framework for Decisions (1989) / Chapter Skim
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4 Enhanced Weediness: A Major Environmental Issue
4 Enhanced Weediness: A Major Environmental Issue
Pages 37-53
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From page 37... ...
This chapter discusses three aspects of the concern: whether the experience with the introduction of exotic plants into new environments (sometunes with the result that a weed problem is created) is a valid analogy for the introduction of genetically modified plants; the potential for domesticated crops to revert to a wild or weedy state; and the potential for hybridization between domesticated crops and wild relatives that might create or enhance weediness.
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From page 38... ...
Any added trait that enhances performance (such as frost resistance or drought tolerance) would also be analogous to providing the plant with an advantage sometimes gained by plants in a new environmental range.
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From page 39... ...
It illustrates the public's worst perceptions of errant organisms and s~multan~ ously exemplifies an exotic organism that ~ not analogous to any hypothetical genetically modified organism. Originally introduced into the United States from China and haps in the late nineteenth century for ornamental purposes, ku~zu was eventually touted as an excellent stabilizer of soil embankments and as a forage crop on unproductive land.
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From page 40... ...
Ecologically l~portant Changes that Result from Smog Genetic Alteratiom Even though exotic species such as ku~zu are not strongly analogous to genetically modified plants, circumstantial evidence suggests that a change in only a few characters can sometimes make a plant a successful invader. Within the large grass genus Bromus are several annual species that have become successfully naturalized In different temperate regions.
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From page 41... ...
. These examples illustrate that small genetic differences bet~veen closely related plants con produce phenotypes with different ecological properties that can increase or alter a plant's geographic range or enhance its aggressiveness in its normal range.
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From page 42... ...
The reassuring history for cultivated crops does not completely preclude a genetically modified crop from becoming weedy, but it suggests that the likelihood of that event is small. As new traits are inserted into cultivated crops, they might possibly change the crop in an ecologically significant way, but past experience with classical breeding h" shown this to be a manageable problem.
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From page 43... ...
The ability to revert to a weedy condition has never been attributable to traits deliberately retained in the domesticated crops-that is, traits that have been the object of an active breeding program. HYBRIDIZATION BETWEEN CROPS AND TH1:IR WILD RELATIVES Two closely related ecological questions that may be important to the introduction of genetically modified plants are (1)
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From page 44... ...
Fodder oats Hordeum ~ruI~are L. Barley Secale cereale L. Rye Triticum aestivum L. Bread wheat Pulses Cicer arietinum L. Chick-pea Lens esculenta Moench Lentil Pisum sativum L. Garden pea Vicia faba L. Broadbean Root and Beta vul~aris L tuber crops Brassica raPa L
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From page 45... ...
Drug plants Scoffed arabica L Cereals and Bermuda grass Pangolagrass Lovegrass Guineagrass Coffee CHINA Fazop~rum esculentum Moench Buckwheat pseudocereals Organza sativa L
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From page 46... ...
Fruits and nuts Anacardium accidentals L Rice Coconut Sesame Lime Sour orange Lemon Tangerine Grapefruit Sweet orange Banana (A genome)
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From page 47... ...
Furthermore, even if relatives are nearby, there Is no assurance that viable hybrids wid be produced, as there often are many formidable barriers to gene flow, such as differences in ploidy level, flowering time, tends breeding systems (Sirnmonds, 1979~. ~ fact, the deliberate introduction of genes from wild relatives into certain crop species by classical breeding techniques has been achieved only by manipulating the flowering tune and by repeated hand pollination (as in potatoes)
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From page 48... ...
~rtber plants w1D be produced. ~r a gene to p~s be~en rel~ tlve and crop ~nd be permanently lncorp grated luto eltber tbe crop or tbe rel~lve]
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From page 49... ...
identified many amaranth hybrids that resulted from crosses between crop add wild relatives. They maintained, without direct evidence, that under cultivation in the light, highly fertile organic soil in the region, hybrids could out-compete their weed parents (A.
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From page 50... ...
Even with ~sozyme studies there Is the possibility for an alternative interpretation; the crop and the wild relative may share aDeles derived from a common ancestor rather than through more recent introgression. Consequently, the best evidence for recent gene transfer arises in cases in which a wild relative possesses alleles in common with a crop, but only in those populations that have recently come into sexual contact with the crop.
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From page 51... ...
If these Johnson grass populations extend their already major ecological role outside agricultural fields, they will represent the most extreme category of known risk associated with gene flow from crop to weedy relative. Biotypes of S
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From page 52... ...
SUMMARY POINTS 1. The analogy between the introduction of an exotic species into a new environment and the introduction of a genetically modified crop plant is tenuous because introduced exotic plants that have caused problems bring with them many traits that enhance weediness, whereas genetically modified plants are modified in only a few characteristics.
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From page 53... ...
However, where cross-hybridiz~ng wild relatives do exist ~ close proximity (such as the sunflower) , precautions may be necessary to limit gene flow from the crop to the wild relative.
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