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Genetics, not environmental stress, increases THC in hemp

It has long been assumed that THC in hemp can increase due to environmental stress on the plant. But now, a new study from Cornell University points to genetics as the cause for greater or lesser THC production. 

The research has very real world consequences. Government regulators closely monitor levels of THC in hemp. If plants contain 0.3% THC or less, they’re classified as hemp, if they contain more, they’re said to test “hot.” When plants test hot, farmers can lose entire crops.  

“One of our goals in our research and in fulfilling our extension mission is to reduce the risks to growers as much as possible,” explained study senior author Larry Smart.

“With this research, growers should feel some comfort that stresses do not seem to have a strong effect on changing the ratio of CBD to THC.”

To test whether or not environmental stress caused an increase in THC, researchers created five test plots of hemp. The plants were each exposed to a different stressor, such as physical damage, flooding, powdery mildew, or an herbicide. 

The plants were then tested for THC levels throughout a four week trial period as their flowers matured. 

“What we found over the weeks that we were sampling, the amounts of CBD and THC went up proportionately in all of these different cultivars for all of these different stresses,” said study lead author Jacob Toth.

The study further proves that genetics, rather than environment, determine the THC content and CBD to THC ratios in hemp, said Smart.

According to the experts, further research is now needed to discover the specific genetic components that make up plants with low and high THC content. This could lead to methods of regulatory testing earlier in a plant’s life, before it actually reaches a high level of THC content.  

The study is published in the journal GCB Bioenergy.

By Zach Fitzner, Staff Writer


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