Genetic test can predict THC vs. CBD levels in plants

Validation of a predictive model of cannabinoid inheritance

Farmers are often left with the uncertainty of never knowing whether their next harvest will be good or not. For industrial hemp growers there are additional complications. These difficulties lie in the levels of THC present in the crop throughout the production season. If the harvest exceeds federal THC levels, growers must destroy the harvest. New research from the University of Minnesota could be a solution for these growers and could save a lot of time, money and effort: a genetic test that can predict the levels of THC versus CBD in plants of cannabis.

Descriptive classification of THC, intermediate and CBD type plants

Industrial hemp growers monitor their plants and send in samples for chemical analysis, but THC levels peak as the plant matures and can catch growers off guard. How genetic variation within a species affects phytochemical makeup is a fundamental question in botany. 

As a result, a team of researchers studied three varieties of cannabis plants from industrial hemp growers, wild cannabis and samples of marijuana from the National Institute on Drug Abuse. They compared their genetic markers with the THC / CBD ratio, then verified that genetics were a good predictor of this ratio.

The ratio of the two most abundant cannabinoids, tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA), which become THC and CBD, is represented by three main classes:

  • Plants THC type with THC: CBD ≥ 10,
  • Plants intermediate type with THC: CBD ≈ 1
  • Plants CBD type with THC: CBD ≤ 0,1
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The study tested a genetic model associating these three groups with functional and non-functional alleles of the gene. cannabidiolic acid (CBDAS).

Notes : The descriptive terms also avoid the confusion associated with recent statutory definitions of Cannabis sativa L which vary widely across political jurisdictions (eg, "industrial hemp" "medical marijuana" "recreational weed"). The results suggest that patterns of cannabinoid inheritance render some of these popular definitions inaccurate, at least from a botanical perspective.

“We have validated a simple genetic test that can predict whether a plant will primarily produce the CBD or THC molecule, using a variety of Cannabis sativa plants,” said George Weiblen, who is a professor at the College of Biological Sciences and the scientific director and curator of plants at the Bell Museum.

Determine if the plant belongs to the category of "hemp" or "marijuana"

Depending on the amount of THC present in the plant, it will be possible to determine whether it belongs to the category of hemp or marijuana. However, researchers say that a definition based solely on THC does not match biology. Instead, they suggest using the THC / CBD ratio to separate THC-like plants from CBD-like plants.

During their study, they were surprised to find that the ditch grass contained both CBD-like and THC-like plants. The populations are mixed and the mixture of plant types extends beyond the grass of the ditches (ditch weed). Weiblen said that finding THC-like plants in a field of ''wild grass Is rare, a one in 100 chance. THC levels are also much lower than what marijuana users are looking for.

predict THC levels compared to CBD, hemp genetic test
Cannabinoid biosynthesis occurs in glandular trichomes borne mainly on pistillate inflorescences consisting of leaves, bracts and florets. 
  • (A) Pistillate inflorescence with receptive white stigmas before pollination. 
  • Scale bar = 1 cm. 
  • Photo credit: George Weiblen. 
  • (B) Scanning electron micrograph of an immature pistillate floret surrounded by a pair of interlocking bracts (br1 and br2) bearing multicellular hairs. 
  • Scale bar = 0,1 mm. 
  • Photo credit: David Marks. 
  • (C) Scanning electron micrograph of stalked glandular trichomes (gt), sessile glands (sg) and cystoliths (cy). 
  • Cystoliths are sharp hairs containing calcium carbonate crystals. 
  • Scale bar = 100 µm. 
  • Photo credit: David Marks. 
  • (D) Biosynthesis of the main cannabinoid compounds. 
  • CBDA and THCA are produced enzymatically from a common CBGA precursor by different enzymes.
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Genotyping CBDAS can predict the ratio of cannabinoid profiles

Upon further examination, the team discovered impurities in the seeds of plants imported from Canada. Some strains turned out to be 100% pure CBD-like, but a few had too much THC to meet the legal definition of industrial hemp. As for CBD products that claim to be 100% industrial hemp, Weiblen is also skeptical.

Understanding the genetic basis of CBD-like and THC-like plants has implications for the US Department of Agriculture and state industrial hemp programs. The possibility of knowing that the seeds are of the CBD type before planting is important and the seeds could be certified to ensure consistency and quality.

“We hope this new test can contribute to the new certification of seeds for the hemp industry,” said Weiblen. "For hemp to take off in Minnesota and elsewhere, there must be ways to assure growers that they won't have to destroy their crops at the end of the season."

The research team, led by the Weiblen laboratory, published their findings in theAmerican Journal of Botany.

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Tags : Agriculture / GrowGeneticTechnology

The author Weed-master

Weed media broadcaster and communications manager specializing in legal cannabis. Do you know what they say? knowledge is power. Understand the science behind cannabis medicine, while staying up to date with the latest health related research, treatments and products. Stay up to date with the latest news and ideas on legalization, laws, political movements. Discover tips, tricks and how-to guides from the most seasoned growers on the planet as well as the latest research and findings from the scientific community on the medical qualities of cannabis.