High-CBD plants inherit approximately 90% of their genes from marijuana, according to a new cannabis genomics study by the University of Minnesota and hemp breeding company Sunrise Genetics.

The collaborators assembled a complete genome from a new cannabis variety and also examined several different cannabis varieties. They found that by breeding high-THC marijuana plants with lower-THC hemp varieties, breeders can develop new varieties that produce high levels of CBD.

But this breeding feat “poses a challenge” — and a big risk for farmers, according to study co-author CJ Schwartz of Sunrise Genetics.

“The genes that allow for the production of CBD are also a bit ‘leaky,’” Schwartz said in a statement.

“This can result in about 5% of the product ending up as THC instead of 100% CBD.”

Farmers who grow these high-CBD varieties to maturity have a much higher risk of their crops going hot, crossing the federal legal limit of 0.3% total THC.

“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,” said study co-author George Weiblen, a professor at the University of Minnesota.

“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.”

The full study is published in the New Phytologist, an online academic journal.

Weiblen and a team of researchers also developed a genetics test in late 2020 that can predict whether a cannabis plant will produce mostly CBD or THC molecules.