Scientists Identify Viroid-Resistant Purple Cannabis Strain

A strain of cannabis appears to be resistant to HLVd, and turns purple as it fights the viroid.

While humans battle COVID, cannabis plants face an equally devastating threat: Hop latent viroid (HLVd), a viroid that occurs worldwide in hops, but in recent years jumped to cannabis, destroying THC yields in infected plants.

SFGate reports that scientists from Massachusetts-based Medicinal Genomics observed a cannabis variety, Jamaican Lion, that appears to be partially resistant to HLVd, and it turns purple as it fights the viroid. 

Chief Science Officer for Medicinal Genomics Kevin McKernan presented “Hop Latent Viroid Shares a 19 Nucleotide Sequence with Cannabis sativa COG7” at CannMed23 at the Marriott Resort at Marco Island, Florida. The late Raphael Mechoulam was originally scheduled to speak at the event alongside other cannabis science leaders such as Ethan Russo, MD; Bonnie Goldstein, MD; Debra Kimless; and others. 

The strain Jamaican Lion appeared to be resistant to the viroid, and also continued to turn purple as it fought the viroid. Jamaican Lion is an award-winning strain rich in CBD.

Viroids can be spread by biological avenues, or it can be spread by growers via touch or from tools. Sterilizing with a 10% bleach solution can reduce infection. Scientists rubbed the viroid directly onto cut leaves of the plant to infect them, then injected a plant with the viroid. Six weeks later, the plant variety was still not infected after repeating the test 57 times. While the researchers were able to detect HLVd in the plant’s roots, the leaf and flower tissue tested negative up until harvest time.

“We don’t know why [this is happening]. This could be an immune response, but we’re not seeing this [purple coloring] as heavily increased in the control that’s not infected,” McKernan said.

What HLVd viroid Does to Plants

HLVd causes plants to produce smaller flowers and significantly less THC. Upon observation with an electron microscope, it causes mature trichomes—where most of the THC is located—to look like a deflated balloon instead of their normal ball shape.  A study shows that as many as 90% of California cannabis is infected with HLVd, and that it could cost up to $4 billion in lost yields. While the viroid is bad news for cannabis, viroids only infect plants, therefore it’s not a physical danger to humans.

It’s not immediately clear why the plant was resistant to the viroid. McKernan said it turned purple as the production of anthocyanin, a chemical that can turn plants purple, was increased. The team believes that scientists should set out to determine if there are more purple plants that are resistant to HLVd, because anthocyanin production is already linked to fighting viroids.

The cannabis variety could help save pot farms. “There is literature that links anthocyanin production with viroid infection. This is in different plants and with different viroids but these anthocyanins are a known immune response for plants,” McKernan told SFGate.

McKernan turned to cannabis to help combat his father’s stage-4 prostate cancer. He used professional guidance from Mechoulam, Goldstein, Kimless, and others to maximize the health benefits of cannabinoids.

Zamir K. Punja said at the conference that HLVd should be considered  a “major threat” to cannabis farms. Punja calls HLVd the “COVID of the cannabis world.” Findings suggest that THC yields from infected plants can drop as much as 40%, which is bad news to a cannabis farm.

Medicinal Genomics’ long-term solution in the battle against HLVd is to help guide breeders to develop resistant cultivars—perhaps some purple varieties—that do not experience yield or potency loss.

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