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[SANET-MG] ready for Dicamba
ISIS Press Release 20/06/07
Ready for Dicamba Ready GM crops?
Turning an environmental disaster into a real catastrophe Prof. Joe Cummins
A fully referenced version of this article is posted on ISIS members’
website.http://www.i-sis.org.uk
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full references, can be sent to you via e-mail for a donation of £3.50.
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Herbicide tolerant GM crops near obsolete
It has become all too clear that genetically modified (GM)
herbicide-tolerant crops are not sustainable, as herbicide resistant
weeds soon appear, rendering the GM crops obsolete [1, 2] ( Roundup
Ready Sudden Death, Superweeds, Allergens... , SiS 28) . In addition,
herbicide-tolerant crops may themselves become ‘volunteer' weeds.
Monsanto Company had recognized the problem, and created patented
herbicide mixtures as early as 2001 to combat weeds resistant to its
formulation of glyphosate (Roundup) and volunteer ‘Roundup Ready' GM
crops [3]. Herbicide-resistant weeds arise either by mutation or by gene
flow from the transgenic crops [4]. The herbicide-tolerance gene from GM
crops has been found to transfer to weedy relatives [5]. In short, the
useful life of the original GM herbicide-tolerant crops is rapidly
nearing its end.
So, crops resistant to the phenoxy herbicide Dicamba have been developed
as a replacement for the near-obsolete tolerance to glyphosate, as well
as glufosinate or bromoxynil. Dicamba is produced by BASF chemical
corporation and marketed as Banvel, the dimethylamine salt, or as
Vanquish the diglycolamine salt [6]. “Inert” ingredients in the
formulations include 3,6-dichlorosalysilic acid, dimethylnitosamine, and
ethylene glycol and 2,7-dichlorodibenzo-p-dioxin.
Dicamba an old companion of “agent orange”
Dicamba is actually an old herbicide that served alongside “agent
orange” in Vietnam [7], and has been resurrected as an environmentally
friendly chemical through the magic of public relations.
Dicamba degradation was characterized in the bacterium Psuedomonas
maltophilia , which can utilize the herbicide as a sole carbon source.
Three separate enzymes, an oxygenase, a ferredoxin and a reductase act
sequentially to convert Dicamba to its first degradation product
3,6-dichlorsalyicylic acid [8]. The primary patent for Dicamba degrading
organisms including transgenic crops was assigned to the University of
Nebraska. The genes for the Dicamba oxygenase, ferridoxin and reductase
were used to transform crop plants. No selectable markers were required
because the transformants could be identified by the fluorescence of
3,6-dichlorsalyicylic acid [9]. Success has been reported in
transforming the soybean with only the dicamba monooxygenase gene driven
by a promoter from peanut chlorotic streak virus and enhancer from the
tobacco etch virus, a chloroplast transit peptide gene from pea for
localization to the chloroplast and a transcription terminator from pea.
In this transformation, which localized the Dicamba monooxygenase to the
chloroplast, the ferridixin and reductase genes were not required to
maintain active Dicamba degradation [10].
Between 2004 and 2007 over 40 field-test releases of Dicamba resistant
corn, cotton or soybean were approved in the United States; all
undertaken by Monsanto Corporation, except for one test each from the
University of Kansas and BASF Corporation. Several field test releases
included crops stacked with transgenes for glyphosate tolerance, or for
yield, or oil composition. With the exception of the University of
Kansas release, the donors of the Dicamba resistance transgenes were
designated confidential business information (CBI), though CBI
constructs are unlikely to be much different from the Psuedomonas
maltophilia genes used in the Kansas release [11]. However, the use of
CBI designations in field releases where the public may be exposed to
toxic products is both unwise and unwarranted. Environmental impact
studies do not appear to be available for the numerous field tests
releases of Dicamba resistant GM crops or GM crops with stacked traits,
and the locations of the tests are withheld from those who may be exposed.
Dicamba not safe nor environmentally friendly
The toxicity of the Dicamba herbicide is worth reviewing. Both pure
Dicamba and Banvel proved to increase sister-chromatid exchange in human
lymphocytes. The study concluded that Dicamba is a DNA damage agent and
potentially hazardous to human [12]. Dicamba proved genotoxic in
mutation tests using transgenic Arabidopsis thaliana plants [13].
Dicamba was found to be a peroxisome proliferator in rats, an activity
associated with liver cancer in rodents [14]. Dicamba is certainly not
safe or environmentally friendly, and its increased deployment must be
resisted.
Dicamba is relatively persistent in the environment and it is only
slowly degraded in turf grass [15]. In Saskatchewan, Dicamba was found
to leach into the South Saskatchewan river, a source of drinking water
for urban populations [16]. High levels of Dicamba were observed in
rivers draining two prairie watersheds, Manitoba streams draining
agricultural lands were elevated during the herbicide application period
in May and June [17].
Predictably, the overuse of herbicides in GM crops has resulted in the
GM crops becoming obsolete as weeds become herbicide resistant.
Introducing GM crops resistant to an old polluting phenoxy herbicide
seems like a measure of sheer desperation, turning an environmental
disaster into a real catastrophe.
The only way to deal with the problem of herbicide resistant weeds and
volunteers is to return to sustainable, organic agriculture, free of
polluting herbicides.
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