Dark Heart Nursery Research Finds 90% of California Facilities Test Positive for Hop Latent Viroid

cannabis plant.

Earlier this summer, the team at Dark Heart Nursery announced the findings of a formal survey of growers across California: After some 200,000 tissue tests, 90% of California facilities researched were testing positive for hop latent viroid (HpLVD).

All told, the presence of that pathogen—to that degree—could account for a $4-billion loss in crops, according to the Dark Heart team.

The tests ran across more than 100 licensed cannabis facilities, from August 2018 to July 2021. This endeavor began during the research phase that saw Dark Heart connect HpLVd to a suite of worrying symptoms known as “dudders” or “dudding” at the time. This included stunted plants, low trichome production, weak stems and so on. 

“Very early on, we knew there was this problem in the industry where plants wouldn’t produce: low yields, low trichomes. We took the time to do the science, to do some RNA sequencing and figure out what was the actual cause of that. Hop latent viroid was only in the infected [plants], not in the healthy ones.” But simply identifying the pathogen was not enough. Once it was found, the Dark Heart team removed the pathogen, isolated it in a pure culture and then infected an otherwise healthy plant with it. Quickly, they noticed the familiar symptoms.

READ MORE: The ‘Dudders’ Case or: How Legalization Opened the Door for Cultivators to Embrace Science 

From there, the question became: How widespread is this issue? Cannabis forums were already lighting up with anecdotal stories of dudding plants.

Dark Heart NurseryA cannabis plant infected with HpLVd. Same strain, age and inputs as in the first photo.

Warren took the scientific approach used to connect HpLVd with the disease and began to tour licensed cannabis facilities in California, going to the places where reports of 20% crop loss were coming through loud and clear. The work focused on nursery stock that would eventually become a business’s mother plants and involved PCR (polymerase chain reaction)testing in a clean environment to detect the presence of the virus. (PCR testing will sound familiar to anyone who’s been exposed to the COVID-19 virus in the past year or so.)

Once the present of HpLVd is confirmed (or even before then), what’s a grower to do?

“You’ve got to get team buy-in,” Warren says. “There are growers who have their own mother blocks, and they run their own genetics. No. 1 for everything for this viroid is sanitation. It’s spread by people, usually pruners, cutting an infected plant and then taking [scissors] to a healthy plant, infecting it.” (Warren said that Dark Heart has forthcoming research that will get into the infection rate with more specificity, as well as differences in infection rates among varying grow environments.)

From there, ongoing testing of mother plants is critical. Three to four tests per nursery plant is key, Warren says, due to the aforementioned latent nature of the virus.

WATCH: Future Cannabis Project’s Interview with Dark Heart Nursery and Glass House Farms on Hop Latent Viroid 

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