In March 2025, Zamir Punja's lab at Simon Fraser University published the most detailed study yet of how hop latent viroid moves through a commercial cannabis operation. The paper, co-authored with a researcher from Pure Sunfarms in Delta, B.C., appeared in the journal Plants. Read it as a buyer and it doubles as a supplier audit checklist.
Hop latent viroid in cannabis is a 256-nucleotide RNA pathogen that stunts plants, shrinks flower and trichome development and lowers cannabinoid output, often while the mother plants look perfectly healthy. For B2B buyers, the risk is commercial. It shows up as missed volumes and potency drift between batches of the same cultivar, and the standard COA you receive won't flag it.
How hop latent viroid affects cannabis flower quality
Viroids are the smallest known plant pathogens. HLVd carries no protein-coding genes at all, so it replicates entirely on the host plant's machinery. It was first recorded in cannabis in 2019 and 2020 in the United States and Canada, and growers now call the symptom pattern "dudding": shorter plants, smaller leaves, tighter node spacing and small, loose buds with few trichomes.
Yield and cannabinoid losses vary by cultivar
Punja has estimated the hit to fresh flower weight at 20 to 25%, with cannabinoid reductions of 30 to 50% in heavily affected plants. Controlled studies show smaller but still meaningful losses. A University of Colorado inoculation study measured an 8.5% drop in total cannabinoids and an 8% drop in THCA in one cultivar. Genetics decide most of the spread between those numbers.
The SFU team also sieved trichomes from healthy and infected flower of the same genotype. Infected plants produced fewer large trichomes, more small underdeveloped ones, and a lighter colour overall. Since trichomes hold the cannabinoids and terpenes, that's the mechanism behind the potency loss.
Why your COA won't show it
The viroid survives into the finished product. SFU detected it in 5 of 8 dried flower samples, in trichome preparations and in crude CO2 oil. Yet the testing required under the Cannabis Regulations, administered by Health Canada, covers cannabinoid content, microbial and chemical contaminants and pesticides. Plant pathogens like HLVd aren't on the panel, so a clean certificate of analysis says nothing about viroid status.
That's the real exposure for an importer. HLVd won't fail a release test, but it makes a cultivar's specification sheet unreliable, and your supply contract is written against that sheet.
How HLVd spreads through an indoor cannabis facility
Most commercial cannabis is still propagated from cuttings. That single practice explains most of the spread. The SFU study traced four routes inside indoor and greenhouse facilities:
- Cuttings from infected mother plants. Rooted cuttings tested positive at rates of up to 100% within four weeks, and infected cuttings rooted more slowly than healthy ones.
- Roots and recirculated nutrient solution. The viroid turned up on propagation tables, in pooled water, in drainage and in irrigation nozzles. Healthy plants sharing a flood tray with an infected plant became positive within two weeks.
- Tools and surfaces. Infected sap stayed detectable for 7 days and dried leaves and roots for 4 weeks at room temperature. Researchers found it on watering cans and even on autoclaved, reused lab pestles.
- Seeds and pollen. Pollen from infected males and seed from infected females carried HLVd, producing up to 100% infected seedlings.
Infection happens weeks before symptoms
Timing is where facilities lose control. After stem inoculation, SFU detected the viroid in roots within two to three weeks and in foliage within four to six. Plants moved to a 12:12 flowering photoperiod spread it faster than plants kept under 24-hour light. A cutting infected in propagation can look normal through veg and only stunt once it reaches the flower room, long after it has shared water and tools with the rest of the batch.
Common sanitation doesn't work
Seventy percent ethanol, the default wipe in many grow rooms, left HLVd RNA intact after 10 minutes. UV-C exposure for 3 to 5 minutes and heat of 70 to 90 °C for 30 minutes also left amplifiable RNA. In sap tests, a 10% bleach dilution for two minutes and 1,000 ppm hypochlorous acid did degrade it. On intact infected roots, though, none of the treatments worked. Infected plant material has to be destroyed, not cleaned.
So ask what your supplier uses on cutting tools between plants. If the answer is alcohol alone, write it down as a finding.
HLVd testing, tissue culture and clean stock
RT-PCR and RT-qPCR are the standard assays, and the SFU lab put its detection limit at roughly 10 viroid copies. Sampling is the weak point. HLVd spreads unevenly through the foliage of stock plants, so a single leaf sample can come back negative from an infected mother. Roots gave the most consistent results in every genotype tested.
Tissue culture is slow and genotype-dependent
Meristem tip culture is the only proven way to clean an infected cultivar. SFU recovered 91 meristems from 8 infected genotypes and tested the shoots every six weeks for six months. On average, 40.66% came back HLVd-free, but individual genotypes ranged from zero to 100%. Rescuing a cultivar can take half a year and still fail.
The study's authors also noted that no disease certification program supplying viroid-free cannabis plants existed at the time. In practice, clean stock is whatever each LP can prove with its own records.
What a credible HLVd control program looks like
| Control | What the research found | What to ask for |
|---|---|---|
| Mother plant testing | Roots are the most reliable tissue | Dated test log per mother, tissue named |
| Cutting screening | Up to 100% transmission from infected mothers | Test results before cuttings enter flower |
| Tool sanitation | 70% ethanol failed, 10% bleach worked | Written SOP naming the disinfectant |
| Irrigation design | Viroid found in recirculated solution | Room isolation or treatment records |
| Clean stock source | Tissue culture success ranged 0 to 100% | Origin and test history of each mother |
This record sits naturally inside the propagation documentation that GACP principles already expect for starting material, as covered in our GACP certification checklist for B2B buyers. If a supplier's log shows leaf samples only, treat its negative results as unconfirmed.
The 5-question HLVd supplier check for importers
Qualifying a supplier on HLVd takes five answers, and the speed of the reply tells you as much as the content.
- When were your mother plants last tested for HLVd, and which tissue was sampled?
- Are cuttings tested before they move into flower, or only the mothers?
- Is nutrient solution recirculated between propagation, veg and flower rooms?
- Which disinfectant is used on cutting tools, and how often?
- What happened the last time a test came back positive?
Question five matters most. A supplier that has never had a positive result either tests rarely or tests the wrong tissue. A supplier that can walk you through a positive, the plants destroyed and the follow-up tests, is running a working program.
Pair these answers with the batch data covered in our guides to cannabis potency and batch consistency and cannabis cultivar consistency. Falling THC across consecutive batches of one cultivar, with no change in growing conditions, is the pattern HLVd leaves behind. The viroid also belongs in the same audit conversation as integrated pest management, and a testing commitment can be written straight into your quality agreement.
If a Licensed Producer can't show you a dated mother-plant test log, don't sign a multi-year supply agreement for that cultivar. The potency on this year's COA is no promise about next year's harvest.
AlphaLeaf is a Montreal-based Health Canada Licensed Producer of indoor-grown, hand-trimmed cannabis flower built on refined genetics. Our ISO/IEC 17025-tested batches, full batch traceability and export authorisation under the Cannabis Act give EU import partners a documented supply record to qualify against.
Planning a cultivar tender for 2027? Contact our team and ask us the hard questions. We expect them.
Frequently Asked Questions
What is hop latent viroid in cannabis?
Hop latent viroid (HLVd) is a small circular RNA pathogen, 256 nucleotides long, that infects cannabis and hops. It causes dudding disease: stunted growth, smaller and looser flowers and reduced trichome and cannabinoid production. Many infected mother plants show no visible symptoms.
Does hop latent viroid reduce THC potency?
Yes. A University of Colorado study measured an 8% drop in THCA in one inoculated cultivar, and Simon Fraser University's Zamir Punja has estimated cannabinoid losses of 30 to 50% in heavily affected plants. The size of the loss depends heavily on the cultivar.
Do cannabis certificates of analysis test for HLVd?
No. Testing required under Canada's Cannabis Regulations covers cannabinoid content, microbial and chemical contaminants and pesticides. HLVd status has to be confirmed separately through the supplier's mother-plant and cutting test records, ideally from RT-PCR or RT-qPCR on root tissue.
Can HLVd be removed from an infected cannabis cultivar?
Sometimes. Meristem tip culture can recover viroid-free plants, but a 2025 Simon Fraser University study found an average success rate of about 41% across eight genotypes, ranging from zero to 100%. The process takes several months of tissue culture and repeat testing.
Is hop latent viroid present in dried cannabis flower?
It can be. Researchers detected HLVd in 5 of 8 dried flower samples from infected plants, as well as in trichomes and crude CO2 oil. Its presence in finished flower indicates the source plants were infected, which is why buyers focus on upstream mother-plant testing.
