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George Weiblen
College of Biological Sciences and College of Food, Agricultural
and Natural Resource Sciences
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Both classified
under the species Cannabis sativa, Hemp, a crop grown for
centuries for its durable fibers and nutritious seeds, and marijuana,
the most abundant illegal drug of abuse in the United States are
historically difficult to tell apart. Marijuana and hemp contain
differing levels of the psychoactive drug tetrahydrocannabinol (THC)
and scientists have been able to identify THC chemically for decades.
However, THC is not present in all plant tissues or throughout the
life cycle of any given plant. Genetic markers known as “short tandem
repeats,” used to identify individuals in paternity and criminal
cases, have been considered by some in the scientific community
to lack the power to explicitly distinguish Cannabis cultivars (domesticated
plant lines).
Using new DNA “fingerprinting” techniques, two University of Minnesota
researchers have become the first to unequivocally separate hemp
plants from marijuana plants with genetic markers, publishing their
findings in the March 2006 issue of the Journal of Forensic
Science. The new technique is an improvement on previous means
of separating the two types of Cannabis and hold promise for distinguishing
different cultivars in U.S. criminal cases, said author George Weiblen,
an assistant professor of plant biology in the university's College
of Biological Sciences, College of Food, Agricultural and Natural
Resource Sciences, and curator of the Bell Museum. It may also prove
useful in countries where the cultivation of hemp is permitted but
marijuana is illegal, as in Canada and Europe.
Through work funded by the University of Minnesota and the David
and Lucille Packard Foundation, Weiblen and Shannon L. Datwyler,
a postdoctoral associate now on the faculty of California State
University, Sacramento, found that the AFLP (amplified fragment
length polymorphism) technique was successful in generating hundreds
of genetic markers that together established separate identities
for each of tested cultivars—three different cultivars of hemp and
one of marijuana.
Weiblen and Datwyler discovered this to be true in their tests as
well--the DNA fingerprints of all the cultivars were distinct and
non overlapping. The AFLP technique chops up DNA and generates numerous
fragments of DNA, each defined by particular “marker” DNA sequences
that act like bookends. The lengths of the fragments within the
bookends were found to vary according to the cultivars. Thus, the
pattern of fragment lengths adds up to a composite picture of each
cultivar. “With this technique, we find hundreds of markers scattered
across the genome; the larger number of markers gives us the power
to separate the cultivars” said Weiblen.
The Cannabis plant has been cultivated for millennia and is important
in the global economy as both a licit and an illicit crop, said
Weiblen. “We think this technique has the potential to distinguish
marijuana varieties as well,” said Weiblen. “It has implications
not just for separating hemp from marijuana in countries where hemp
cultivation is permitted, but in establishing origins of seized
drugs and, therefore, conspiracy in drug distribution networks.
It also could be used in criminal defenses against claims of conspiracy
and identifying geographic sources of seized drugs.”
Hemp is a source of durable fiber that provides an alternative to
cotton fabric, and it is capable of producing paper, textiles, building
materials, food, medicine, paint, cooking oil, ink and bio fuel.
Unlike cotton, hemp does not require pesticide application or a
hot climate to cultivate in, which makes it ideal for local Minnesota
agriculture. Currently, all hemp products are imported into the
United States, as cultivation of the plant is suppressed by laws
supported by drug enforcement agencies dating back to the 1930s.
In many ways, it is a legitimate concern that high THC plants could
potentially be grown amidst the low THC plants used for hemp production,
despite nation-wide drug-enforcement efforts, marijuana trafficking
is still a booming, billion dollar industry.
Weiblen seeks to screen a wider range of Cannabis cultivars to refine
the technique, and is also working to identify regions of the Cannabis
genome responsible for drug content in marijuana. If enough can
be learned about the genome, it may be possible to produce an entirely
drug-free hemp plant that looks different from marijuana. That gives
Weiblen's work a broader scope—beyond mere forensics. The development
of a new hemp variety for cultivation in the U.S. would reduce American
dependence on foreign products and create a new alternative crop
for American farmers—giving them the opportunity to compete in the
growing market for hemp-based products.
By Andria Peters
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