Hop Latent Viroid (HLVd) & Cannabis

Successful cannabis cultivation depends on many variables, including plant genetics, environmental control, pest and plant disease management, and that’s only to name a few. Ultimately, any factor that can negatively impact the health of cannabis plants is something that cultivators should be aware of and should be taking action to prevent that factor from causing harm to their plants.

Plant pathogens are one of the most critical variables to consider when cultivating cannabis, particularly when growing at a large scale. Plant pathogens are infectious organisms that cause disease in plants; common pathogens found in cannabis include fungi (e.g., powdery mildew), bacteria (e.g., E. coli, Pseudomonas), viruses (e.g., beet curly top virus), and viroids (e.g., Hop Latent Viroid). As of recent, one plant pathogen that is becoming more prominent in cannabis cultivation dialogue and more prevalent in the analytical testing of cannabis is Hop Latent Viroid (HLVd). This lesser-known plant pathogen has now been detected in several geographies across North America, and an increase in positive test results seems to indicate the pathogen is spreading. Subsequently, the negative impact of the viroid is growing.

What is Hop Latent Viroid?

HLVd is an infectious plant pathogen that can cause disease within cannabis plants. Much simpler than a virus, HLVd consists of only 256 nucleotides of RNA and is unable to survive on its own without a host (Warren et al., 2019). Often, plants infected with HLVd do not show symptoms of HLVd, and it can stay latent within the plant depending on environmental and biological conditions. Therefore, it can be difficult to detect and confirm its presence within a growing facility without proper analytical testing. Despite its simplicity or common latency, this viroid can have major impacts on cannabis cultivation and plant health and should be taken seriously by those growing cannabis commercially.

How does Hop Latent Viroid affect cannabis?

Sometimes referred to as “Dudding” or “Dudding disease,” HLVd expresses symptoms in the form of stunting the growth performance of cannabis plants (Wilson, 2021). While symptoms are not always obvious, confirmed cases of HLVd have been reported to cause plants to grow shorter, with smaller leaves during their vegetative cycle, and produce smaller, looser buds with lower trichome coverage during flowering cycles. Cannabinoid concentrations have been reported to be reduced by as much as 50% and overall yield by as much as 30% (Medical Genomics, 2022). Anyone who grows and sells cannabis understands that economic success in growing is typically highly correlated with cannabinoid concentration (mainly THC or CBD) and crop yield.

When should I test my cannabis plants for Hop Latent Viroid?

When it comes to testing cannabis plants for HLVd, it is not economically practical to test every plant in a growing facility. Therefore, cultivators should employ a strategical approach to monitoring and testing for HLVd. If, during regular plant-monitoring activities, it is determined that a plant is not healthy, it should be removed from the grow in almost all cases. If it is suspected that the plant is infected with HLVd, a sample should be submitted from the plant in question, as well as a sample from the mother plant it was cloned from for testing. If test results do not indicate the presence of HLVd, then it narrows down the list of potential pathogen culprits affecting the health of this plant. If test results confirm the presence of HLVd in the progeny plant but not the mother plant, then there is likely another source of contamination in the grow facility which should be investigated. If test results indicate infection at the level of your mother stock, this can be problematic, and although there are solutions available for remedying your mother stock, it can be very time-consuming and expensive. Therefore, upfront prevention should always be of utmost priority for cannabis growers.

How can Hop Latent Viroid be prevented and properly mitigated?

“Unlike humans, plants are rarely cured of disease. Instead, plant pathologists try to prevent plants from getting sick in the first place, and work to control the symptoms and spread of diseases” (University of Florida, Emerging Pathogens Institute, 2022)

To best avoid the damaging effects that accompany HLVd infection, prevention is key. Good sanitation practices should be developed, implemented, and adhered to in every facility that is used for growing cannabis. The most common cause for the spread of HLVd is infected tools and equipment, which is why strict sanitation protocols should always be followed. Another common way for HLVd to spread is through cloning from mother plants. When bringing new genetics and mother stock into a growing facility, it is good practice to either request a COA showing the stock is not infected with HLVd, or to submit a sample to your partner lab to ensure plant health prior to introducing them to the facility. Due to the often-latent existence of HLVd, the signs are not always obvious, and infection can often be overlooked.

Are cases of Hop Latent Viroid infections on the rise? What are we seeing in Oklahoma?

As awareness of HLVd increases among cannabis growers and quality assurance professionals, and testing protocols are implemented at more testing labs across North America, it provides the ability to start reliably detecting the pathogen and track its spread into geographies that may have never tested for it previously. Since its initial confirmed detection in cannabis plant samples in California in 2017 (published 2019)(Warren et al., 2019 & Bektas et al., 2019), we have seen testing capacities expand into several new geographies, which has led to HLVd detection in cannabis samples from the west coast (California) to the east coast (Maine), Oklahoma, and now being detected in samples from cannabis plants being grown across Canada (Brown, 2022). HLVd may be present in other states/geographies as well, but data collection and publication are still in the early stages.

Steep Hill Oklahoma is one of the few labs currently offering testing for HLVd in Oklahoma. They make it easy for anyone looking to confirm the presence or absence of the viroid in their cannabis plant sample(s). The test only requires a small amount of plant material to be performed, and results can be delivered in as little as 2 to 3 days. Approximately 35-40% of the samples being tested for HLVd at Steep Hill Oklahoma indicate positive results. With so much value being tied to the optimal growth performance of cannabis plants in commercial facilities, HLVd testing has become an obvious step for growers to take when looking to mitigate risks associated with plant pathogens in their grow facilities.

Resources:

Bektaş, A., Hardwick, K. M., Waterman, K., & Kristof, J. (2019). Occurrence of hop latent viroid in cannabis sativa with symptoms of cannabis stunting disease in California. Plant Disease, 103(10), 2699. https://doi.org/10.1094/pdis-03-19-0459-pdn

Brown, D. (2022, January 30). Hop latent viroid continues to infect cannabis across Canada. StratCann. Retrieved May 4, 2022, from https://stratcann.com/2022/01/24/hop-latent-viroid-continues-to-spread-across-canada/

Warren, J. G., Mercado, J., & Grace, D. (2019). Occurrence of hop latent viroid causing disease in cannabis sativa in California. Plant Disease, 103(10), 2699–2699. https://doi.org/10.1094/pdis-03-19-0530-pdn

Wilson, T. (2021, July 4). The hop latent viroid's warning shot to the Canadian Cannabis Industry. StratCann. Retrieved May 4, 2022, from https://stratcann.com/2021/04/01/the-hop-latent-viroids-warning-shot-to-the-canadian-cannabis-industry/