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Hemp or marijuana?

Is it or isn't it? Only University researchers know for sure.

A new way to tell rope from dope

University researchers have developed a new technique to distinguish hemp from its illegal relative, marijuana

April 7, 2006

Several years ago, a group assembled by Gov. Jesse Ventura recommended research on the potential of hemp as a Minnesota crop. A natural for northern climates, the hardy plant matures in three months, needs no pesticides and only moderate fertilizer, and has potential for use in paper, textiles, building materials, food, medicine, paint, detergent, varnish, oil, ink, and fuel. It would be a real boon for Minnesota farmers, as it has been for their Canadian counterparts.

There's one little problem though: Hemp belongs to the same species, Cannabis sativa, as marijuana, and although the plants differ in levels of the psychoactive drug tetrahydrocannabinol (THC), they are otherwise difficult to tell apart. Or they were, until two University researchers found a way.

"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."

Enter George Weiblen, a University assistant professor of plant biology. When he heard about the Ventura-era recommendation, he decided to investigate the genetics of hemp and its marijuana twin. Weiblen saw in his work not only economic benefits for the state, but an easy-to-grow model plant that could help illuminate the genetics of tropical figs and other trees he regularly studied.

"Most of my research is rather esoteric," says Weiblen. "I thought, 'What an opportunity to jump into a new area that people might care about.' It has implications for economics, drug enforcement, medical marijuana, and hemp advocacy."

Now, using a new DNA "fingerprinting" technique (called AFLP for "amplified fragment length polymorphism"), Weiblen and a colleague have become the first to unequivocally separate hemp plants from marijuana plants with genetic markers. The technique holds promise for distinguishing different cultivars (domesticated plant lines) in U.S. criminal cases. It may also prove useful in countries where the cultivation of hemp is permitted but marijuana is illegal, as in Canada and Europe. The work appears in the March issue (volume 51, No. 2) of the Journal of Forensic Science.

The new technique is an improvement on previous means of separating the two types of Cannabis, says Weiblen, an assistant professor in the College of Biological Sciences and College of Food, Agricultural and Natural Resource Sciences. For decades it has been possible to identify THC chemically, but the drug is not present in all plant tissues or throughout a plant's life cycle. And other researchers have found that genetic markers known as "short tandem repeats," which are used to identify individuals in paternity and criminal cases, lack the power to distinguish Cannabis cultivars unequivocally.

In tests with three different cultivars of hemp and one of marijuana, the DNA fingerprints of all the cultivars were distinct and nonoverlapping. Weiblen and Shannon L. Datwyler, a postdoctoral associate who is now on the faculty of California State University, Sacramento, found that the AFLP technique generated hundreds of genetic markers that together established separate identities for each of the four cultivars.

"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."

Weiblen wants 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 one day be possible to produce an entirely drug-free hemp plant that looks different from marijuana. Currently, all hemp products are imported into the United States. Developing a new variety that could be cultivated in the United States would reduce American dependence on foreign products while creating a new alternative crop for American farmers.