Experts sound alarm over global spread of dangerous marijuana viroid

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Image of a cannabis plant infected with hop latent viroid next to a healthy plant

The cannabis plant on the left is infected with hop latent viroid; the plant on the right is healthy. (Photo courtesy of Zamir Punja)

The dangerous and infectious hop latent viroid that’s been on the radar of many marijuana growers since its discovery in 2018 has spread beyond North America and is threatening to spiral out of control and cause billions of dollars in industry losses, experts are warning.

Researchers are calling the viroid – which is surfacing across the world – “a hidden threat” and the “biggest concern for cannabis and hop growers worldwide.”

“It’s an all-out crisis,” said Av Singh, a Canadian cannabis cultivation adviser also working as the chief science officer of Green Gorilla, a Malibu, California-based manufacturer and online retailer of hemp-derived CBD oils, topicals and pet products.

“I think we’re not recognizing how big of a crisis it is.”

Zamir Punja, a professor of plant biology for Simon Fraser University in British Columbia, Canada, said hop latent viroid (HpLVd) is the No. 1 plant pathogen that the cannabis industry needs to be concerned about.

“You can’t adjust anything, such as environmental controls, to fight it,” Punja said. “It’s either there or it’s not.

“And once it’s there, and it’s not recognized, then you just automatically spread it.”

Growers can take preventive steps to curb the spread of the viroid, which can be transmitted from plant to plant through a variety of ways, according to experts.

But it’s hard to stop and might never be eliminated, experts said.

Oussama Badad, co-founder and chief scientific officer of Growmics, a plant research company in Carbondale, Illinois, said the viroid “remains a mystery.”

“The problem is the cannabis industry for the past 20 years at least was based on clones only,” Badad said.

“So everybody is shipping clones from here to there, and nobody was testing, or nobody was aware of any methodology to test for this virus.

“What we did was basically spread it all over the planet. Anybody receiving any plants from the United States, especially from California, has the viroid in their grow.”

Small and stealthy

Experts warned the viroid is stealthy. It’s also very small, asymptomatic and waiting for an opportunity to infect a plant.

The most likely form of transmission is from the everyday trim tools used for vegetative propagation and grafting or human hands.

When the viroid attacks, the plant pathogen moves quickly from the roots to the leaves to the flower in two to three weeks, Punja said.

It is most problematic in hydroponics – rather than outdoor grows – because the viroid can move through water and more easily infect roots that tend to be matted together.

Hop latent viroid doesn’t outright kill the plant.

But a grower can see an infected plant struggling to grow normally because the plant is shorter and the trichomes are underdeveloped or stunted.

The result: lower THC and CBD levels, which can drop as much as 40%.

“It’s almost like the plant just doesn’t have that energy to put into those trichomes,” Punja said.

It’s most noticeable when the plant flowers, Punja said.

He and other researchers suggest it’s that part of the growing cycle where the viroid might become more virulent, perhaps because of the stress the hydroponic plant is undergoing during the 12-hours-on, 12-hours-off lighting change that occurs during the flowering stage.

As a precaution, growers should have their plants tested, down to the roots, Punja said.

But even then, there are no assurances.

“Unfortunately, one test is not enough,” Punja said. “What we’re finding is that the first test will be negative.

“Three weeks later, again negative. Then three weeks later, positive.”

It’s unavoidable

The viroid is likely to be in the soil of grows, researchers said. It’s also in the water of a hydroponic grow. And it’s definitely in the roots.

In addition, the pathogen is in the seed, not on the seed. It also can spread to one’s hands as a grower handles plants, moves them, stacks them, hangs them.

Even one infected plant brushing up against another can transfer the viroid.

Any sort of sap-sucking insect that makes a hole in the plant, especially at the roots, can create a pathway to infection.

The insect itself does not carry the viroid from plant to plant, as far as researchers know now, Punja said.

The viroid also could be airborne. “Other viroids are,” Singh said. “So it may not be that big a stretch to say that it would be in the pollen.”

The viroid is likely to be present in most commercial licensed cannabis production facilities in the United States and Canada.

The frequency of infected plants is estimated to be in the range of 25%-50% in both countries, according to Punja.

Testing by clone cultivator Dark Heart Nursery on 100 cannabis growers in California from August 2018 to July 2021 found that one-third of plants in 90% of those grows were infected.

That finding supports projections that the viroid affects more than 30% of all cannabis plants in the United States.

“This translates into more than $4 billion in annual losses for U.S. growers who were expected to produce more than 7 million pounds of legal cannabis in 2021,” Jeremy Warren, director of plant science for Oakland-based Dark Heart, told MJBizDaily via email.

The viroid is believed to have been first identified at Glass House Farms, which has 5.5 million square feet of total cannabis greenhouse space in Ventura County, California.

Glass House cultivators noticed their plants looking stunted, with a lack of terpenes and cannabinoids, according to company President Graham Farrar, who said he began working with Phylos Bioscience, an Oregon-based cannabis biotech firm, and Dark Heart in 2017 to determine what was really going on.

“It’s actually hard to identify that it’s infected, because the plant looks fairly healthy,” Farrar said.

“If you have six plants and one of them is funky, you think it’s the plant.

“But when you have 10,000 plants, like in our facility, and they’re being fed the exact same nutrient recipe and it’s automated in the same greenhouse and it’s the same strain, then all of a sudden, 10% or 20% of your plants are not producing the way they should, you don’t just say, ‘That’s a bad plant.’

“You start kind of digging into it.”

An RNA sample from an infected plant from Farrar’s grow was examined in a lab, and sequenced, where the lab identified the genome matching the viroid.

“I’d be surprised if (the viroid) is something that ever is gone,” Farrar said. “I think it’s probably something that we’re going to have to live with.”

How to fight it

Help is on the way from multiple sources.

Dark Heart has developed a genetic test to differentiate infected plants from uninfected ones.

The company also helped develop a patent-pending cleaning process to eliminate the viroid from infected specimens.

The Dark Heart lab team has demonstrably eliminated the viroid in 31 strains so far, according to a news release.

In May 2021, Colorado-based Front Range Biosciences introduced a method of cleaning infected plants using tissue culture.

And last month, Biomerieux, a French diagnostics solutions company, developed a kit to test for the presence of the viroid.

“The solution is good biosecurity SOPs (standard operating procedures) and testing,” Farrar said.

“The viroid is tough, and it is persistent. The latent part is both a blessing and a curse,” he continued. “Right now, it’s nice that it doesn’t wipe out an entire greenhouse.

“But the latent part also makes it particularly hard for testing. If there’s a hope to get rid of it, that would be CRISPR genetic engineering or using selective breeding to breed plants that are resistant to it. So that’s a potential down the road.”

For now, so-called “living soil” can work as a sort of health insurance, Singh said.

“You are trying to optimize the health of the plant. You may not necessarily get as high a yield. You may not get high potency.

“But you have a more robust plant that can definitely keep some of these viruses and viroids more latent or asymptomatic.”

Glass House would like to assist growers in dealing with this viroid crisis.

“I definitely think we’d like to help people get to the point where they can test at a frequency and at a cost that’s affordable,” Farrar said.

“I don’t know if we’ll ever be able to eradicate the viroid, but at least we can keep it at a very low level so that it doesn’t have a negative impact.”