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High-CBD Hemp Crops Are Mostly Marijuana, Genetic Study Finds

By Leo Bear-McGuinness

Published: Feb 26, 2021   
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Hemp crops may have more in common with recreational, “drug-type” varieties of cannabis than previously thought, according to new research.

Published in New Phytologist, the study found that a high-CBD cultivar of cannabis shared 89 percent of its ancestry with marijuana and only 11 percent with hemp.

As marijuana remains federally illegal in the US, the researchers behind the study warn that farmers of such high-CBD crops could be at risk from legal action if their plants are tested and, on a genetic basis, found to be marijuana.

Hidden genes

To reach their conclusions, the researchers from the University of Minnesota and the company Sunrise Genetics first sequenced the genes found in a high-CBD variety of cannabis, known as CBDRx. Once assembled, this genome was compared with the genomes of a marijuana cultivar and a pure hemp variety.

While only 97.4 percent complete, the CBDRx genome was found to overlap with 89 percent of the marijuana genome and just 11 percent of the hemp genome. The researchers attribute this similarity with marijuana to CBDRx’s strong cannabis ancestry. The plant’s hemp-like qualities, they say, have only recently been introduced into the crop’s history, following the increasing popularity of CBD.

“We suggest that breeders have responded to recent interest in CBD with targeted introgression to produce marijuana cultivars with exceptionally high levels of CBD,” the researchers write in their study.

On a genetic level, this cross breeding with hemp appears to have knocked out the genes that code THCA synthase, the enzyme that helps produce THC. When investigating the plant’s seventh chromosome – where one might expect to find a THCA synthase gene – the researchers instead found genes that code for CBDA synthase, the enzyme that helps produce CBD.

“This poses a challenge, though,” CJ Schwartz, CEO at Sunrise Genetics and study co-author, said in a statement. “The genes that allow for the production of CBD are also a bit ‘leaky.’ This can result in about 5% of the product ending up as THC instead of 100% CBD.”

According to Schwartz and his colleagues, these “leaky” genes could pose a legal threat to US hemp farmers, who are required to keep their crops’ THC content below 0.3 percent by federal law.

“These high-CBD plants are genetically marijuana for the most part and they can’t be expected to meet the legal definition of industrial hemp in every situation,” George Weiblen, a professor at the University of Minnesota and co-author of the paper, said in a statement.

“This means that CBD products – such as flowers, extracts and edibles – that are labeled ‘hemp’ could be incorrectly labeled and falsely branded. Fiber hemp and products made from hemp seeds, however, are drug-free.”

Hope for hemp

Hemp farming has been legal across the US since December 2018, when President Trump signed the Agricultural Improvement Act, commonly known as the Farm Bill. But farmers can still fall foul of the law if their crops breach the legal 0.3 percent threshold of THC.

Last year in Arizona, the Department of Agriculture announced that 41 percent of 130 hemp lots tested for THC in the state had breached the legal limit. Even by some conservative estimates, these noncompliant acres could have totaled a loss of $13.4 million for the farmers.  

The reasons underlying such THC surges are still unclear. The findings from the University of Minnesota and Sunrise Genetics study indicate that hemp’s “leaky” genes could be to blame. But which factors could help coax out these hidden marijuana traits? Rain? Sunlight? Certain soul nutrients? Several studies have been launched in recent years to find out, including one at West Virginia University.

“We want to test the effect of different individual abiotic and biotic stressors on the accumulation of terpenes and cannabinoids in hemp. Thus, it is absolutely essential to grow the hemp plants under controlled environment conditions,” Michael Gutensohn, an assistant professor of horticulture at West Virginia University and author of that study, told Analytical Cannabis last July.

“Once we understand how individual factors affect the terpene and cannabinoid metabolism and its genetic regulation in hemp, then we can start to study the effect of combining several factors, which will be closer to the scenario a plant faces when grown under field conditions.”

It may take some more time – and a lot of overwatered, overheated hemp – for Gutensohn and other researchers to locate these factors that really make a difference to THC production. But when they are found, there's hope that such discoveries could help develop genetically divergent, hardier crops that can keep their THC content low even under extreme conditions.

“We hope that the knowledge gained in our research project will help and guide in the development of new improved hemp varieties,” Gutensohn said.

“The proposed genetic engineering is a common approach in plant science to study how metabolic and genetic networks respond to the inactivation or activation of individual genes in the network. Here we will, for example, inactivate individual cannabinoid/THC biosynthetic gene(s) to study how the terpene and cannabinoid metabolic network in hemp responds to such a modification.”


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