Contrary to claims that environmental or biological stress causes an increase in THC production in hemp, a new study from Cornell University finds no evidence that stress increases THC levels or the ratio of CBD to THC in hemp plants.
Growing hemp for CBD (cannabidiol) is an emerging industry, but when hemp contains more than the legal THC limit, the plants can test “hot”. State and federal regulations classify hemp as containing 0.3% or less THC; If the crops exceed this amount, farmers can lose their entire harvest.
“One of our goals in our research and in fulfilling our expansion mission is to reduce the risks to farmers as much as possible,” said Larry Smart, lead author of the study and professor in the horticultural division of the School of Integrative Plant Science in the College of Agriculture and Life Sciences. “With this research, breeders should feel reassured that stress doesn’t appear to have a major impact on changing the CBD to THC ratio.”
In the study, lead author Jacob Toth, a PhD student in Smart’s laboratory, created a series of plots in Geneva, New York that included control plots and five stress treatments applied to three genetically unrelated high-CBD cannabis strains. Stress treatments included flood conditions; Exposure to a plant growth regulator called ethephon, which is used to promote fruit ripeness; Mildew; Herbicide; and physical injuries. They then tested the THC and CBD levels over a four week period as the flowers matured.
“What we found over the weeks that we sampled is that the levels of CBD and THC in all of these different strains increased proportionally for all of these different stresses,” said Toth.
By the fourth week, at harvest time, they found that almost every plant (except for those treated with herbicide, which were almost dead) produced the expected ratio of CBD to THC, with high levels of CBD and THC levels above 0 , 3% matched the threshold.
The study further proves that genetics, not the environment, determine the THC content and CBD to THC ratio in hemp, Smart said.
More research and breeding is needed to select appropriate genetics that result in high CBD but low THC levels, and regulatory testing may be needed earlier, before harvest and before the plants reach high levels of THC, Toth said .
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Materials provided by Cornell University. Originally written by Krishna Ramanujan. Note: The content can be edited in terms of style and length.