Hop Latent Viroid (HLVd) | 2025 Professional Guide for Cannabis Producers
Hop Latent Viroid (HLVd) is the most consequential pathogen in modern cannabis production. It can move silently through propagation and routine handling, eroding vigor, yield, and quality before anyone notices. This 2025 guide translates the science into concrete steps for licensed cultivators, nurseries, universities/R&D, and seed banks with extra notes for tropical/subtropical environments such as Thailand.
- What it is: a tiny, circular single‑stranded RNA viroid (no protein coat).
- How it spreads: primarily via sap on tools and hands; also through cuttings, shared water, and possibly seed.
- Why it’s hard: many infections are asymptomatic at first; there is no field “cure.”
- What works: exclusion + early detection + sanitation + clean workflow + culling.
1) What HLVd is it, and why it matters
Viroids are the smallest known infectious agents in plants: circular strands of RNA without a protective protein coat. They hijack the plant’s own polymerases to replicate and can persist at low, uneven levels inside tissues. In cannabis, HLVd is strongly associated with the “dudding” syndrome, reduced vigor, small or uneven flowers, muted aroma, and variable potency. Propagation amplifies problems: an infected mother can silently seed entire rooms with weak clones.
- Stunting, uneven canopies, brittle/narrow leaflets, leaf curl or odd morphology.
- Lower flower mass, poor trichome density, muted aroma; COA variability by lot.
- Clusters of underperformance that trace back to a specific mother lot.
2) How HLVd spreads (and why sampling is tricky)
The main driver is mechanical transmission: sap from an infected plant enters a wound or micro‑tear on a healthy plant. Trimming shears, topping tools, benches, gloves, and hands are the common vectors. HLVd titers can be higher in roots, and studies have detected viroid in runoff and shared water, so recirculating systems can move it across benches. Seed transmission in cannabis remains under investigation; it’s confirmed in hops and plausible in cannabis, so treat incoming seed lots as “unknown” until indexed. Insects are not a proven route for HLVd yet, but the precautionary stance is to maintain strong IPM because other viroids do use insect vectors.
- Sanitize or single‑use blades between plants/benches; place sanitation stations at every aisle.
- Quarantine new genetics (physically separate bench/room/airflow) for two test cycles before release.
- Label lots and keep chain‑of‑custody from intake → mother assignment → production benches.
3) Detection: testing that fits real operations
Treat testing as a routine program, not a one‑time event. RT‑qPCR or equivalent molecular assays are the practical standard. Because HLVd is not distributed evenly, where and when you sample matters: sample actively growing tissues, use pooled samples as triage, and re‑test individuals if a pool flags positive. Index mothers monthly; test quarantine on arrival and again after 10–14 days; spot‑check production at flip or when symptoms appear; and re‑test after stress events like heavy pruning.
- Prioritize mothers, stock plants, and incoming genetics; resample after stress events.
- Pool 5–10 leaves per lot for triage; re‑test individual plants from any positive pool.
- Log results by bench/room and link them to lot IDs and COAs for traceability.
4) Management: exclusion, sanitation, flow, and culling
There is no validated field “cure” for HLVd. Programs that succeed layer defenses and cut losses early. Accept only verified‑clean material; keep quarantine separate in space and airflow; and enforce clean‑to‑dirty workflow (start in mother/prop rooms and move toward production; change PPE if you backtrack). Use single‑use razors where possible or validated disinfectants with correct contact times. Clean benches, domes, trays, and irrigation fittings between runs. When positives persist in a mother line, culling is cheaper than months of patchy rooms. For elite genetics, consider professional meristem culture + therapy and re‑index the line before reintroduction.
- Monthly mother indexing (RT‑qPCR/LAMP), immediate hold/cull on positives.
- Dedicated, labeled tools per bench; disinfect between plants/benches or use single‑use blades.
- Foot baths/PPE at entries; daily sanitation logs; vendor/visitor controls.
5) Notes for Thailand/tropical facilities
High humidity elevates general disease pressure and increases the risk of wounding from leaf wetness and handling. Engineer airflow and dehumidification first; keep canopies open; and schedule night purge cycles to avoid condensation. Segregate import quarantine from domestic production and align with seed‑to‑sale records. Document disinfectant contact times and train on safe use. Validate that sanitation products are compatible with your materials and staff PPE.
6) FAQ (2025)
Is there a spray or dip that cures HLVd?
No validated field cure exists. Control depends on exclusion, sanitation, testing, and culling. Recovery of elite lines typically requires a clean‑stock program (e.g., meristem culture + therapy) and re‑indexing.
Can seeds carry HLVd?
Seed transmission is confirmed in hops and still being quantified in cannabis. Treat seed lots as “unknown,” and index seedlings before promoting to mother status.
How often should I test?
Index mothers monthly; test quarantine on arrival and after 10–14 days; spot‑check production at flip or when symptoms appear; and re‑test after stress events.
We found one positive, do we destroy the whole room?
Start with containment: isolate the bench/lot, increase testing intensity, and cull confirmed positives and directly connected lots. Escalate based on results and risk tolerance.
References & further reading:
• Adkar‑Purushothama, C.R. et al. “Hop Latent Viroid: A Hidden Threat to the Cannabis Industry.” Viruses (2023). PMCID: PMC10053334.
• TUMI Genomics. “Everything you need to know about Hop latent viroid.” (accessed 2025).
Educational content for professional audiences. Not legal advice or a substitute for lab diagnostics. Verify local regulations and safety guidance.