This part covers the main reason cannabis growers use tissue culture: producing plants free of Hop Latent Viroid (HLVd). It also covers setting up a small lab, cannabis-specific problems, storing a cultivar without a mother plant, certified production, and running a culture room in Thai heat. Tissue culture here means growing tiny plant pieces on a nutrient gel in sterile containers to produce many identical plants.
The article draws on eight published studies, listed under References; numbers in square brackets point to them. Sections start at 5 because Part 1 holds sections 1–4: what tissue culture is, how it compares with cuttings, the hormones that control it, and the four working stages with recipes.
This is Part 2. Part 1: Tissue Culture & Micropropagation for Cannabis: Laboratory-Scale Cloning for the Modern Grower
5. Clearing Hop Latent Viroid: the main reason to use tissue culture
What the viroid is
HLVd is a small, ring-shaped strand of disease-causing RNA, with no protein coat and no genes of its own. It infects the whole plant. It was first found in hops, the plant used to flavour beer, and first reported in cannabis in California (USA) in 2019, in the journal Plant Disease [3].
A 2023 review in the journal Viruses reports that about 90% of California cannabis facilities tested positive, and estimates industry losses of up to USD 4 billion a year [1].
Symptoms, when they appear
“Latent” means hidden: many infected plants look normal until flowering, when the damage shows:
- Stunting, poorer flower-cluster development and smaller plants [2]
- Fewer stalked glandular trichomes (the large resin heads), and more small, poorly formed ones [2]
- Reported losses of 50–70% in THC content, and up to 50% less cannabinoid and terpene production [1]
- Brittle stems, and sometimes deformed leaves
Symptoms appear late, so a mother can look healthy for years while every cutting from her carries the viroid.
What to do: If a cultivar you have kept for years now grows shorter or makes less resin, have it tested before you change feed or lights.
How it spreads: more routes than most growers assume
In a 2025 study of HLVd in North American cannabis, Punja and colleagues identified four routes of spread [2]:
- Cuttings. Every cutting from an infected mother carries it.
- Root-to-root contact in hydroponic systems that recirculate the nutrient solution.
- Wounds on stems, from contaminated blades, trellis netting and leaf stripping.
- Seed and pollen, producing up to 100% infected seedlings.
The same study found the viroid stayed detectable for 7 days in crushed leaf sap, and for 4 weeks in dried leaves or roots at room temperature [2]. So starting from seed does not automatically protect you, and plant debris left in a room keeps the viroid around.
Translator’s note: Many Thai farms share cuttings and run recirculating systems, combining routes 1 and 2. The study’s room temperature is not a 30–35 °C Thai grow room; do not assume heat clears debris faster, remove it. Treat every bought cutting as untested until a lab result says otherwise.
What to do: Sterilize cutting tools between plants, not between rooms. Clear leaves, roots and stems out of the room after every harvest. For disinfectants that work on tools, see the HLVd topic linked above.
Why cuttings cannot fix it
HLVd lives in the vascular tissue, the channels that carry water and sap through the plant, so every cutting from an infected mother carries it. No chemical treatment cures an infected plant. The reliable routes are:
- Meristem tip culture. The meristem is the growing point at a shoot tip. You cut an explant so small (0.4 mm, with two or fewer leaf primordia, the tiny bumps that become leaves) that vascular tissue has not reached it. Punja and colleagues report that about 41% of resulting plants tested HLVd-negative on average, ranging from 0% to 100% across eight genotypes (a genotype is a cultivar’s genetic makeup) [2].
- Meristem culture combined with heat or cold. Holding plants at 36 °C for 14 days quickly lowered the viroid titre (the amount of viroid in the tissue). Cold treatment (2–4 °C in darkness for 8–21 months) combined with small-meristem culture worked better than either alone [1].
Results depend on genotype, so no single success rate applies to all cultivars. That is why every plantlet from meristem culture must be tested by RT-qPCR (a lab test that detects the viroid’s genetic material) before you call it clean. Only negatives go into multiplication. The test, not the technique, proves a plant is clean.
Cleaning a line step by step: meristem culture with heat or cold treatment
Combining the published results, a clean-up run looks like this:
- Confirm the problem. Test the mother by RT-qPCR to confirm she is infected.
- Optional heat or cold step. Hold plants at 36 °C for 14 days to lower the titre, or use the cold treatment above [1].
- Cut the smallest tips you can. Under magnification, take meristem tips under 0.5 mm, with two or fewer leaf primordia [1][2].
- Start many tips. Start 10–20 tips per clean line you hope to keep (Stage 1, Part 1).
- Test every plantlet once it has enough tissue to sample. Keep negatives, discard positives.
- Multiply only the negatives. Give each clean line its own ID in your records. Retest clean mother lines periodically, because tools, roots or pollen can bring the viroid back.
Translator’s note: 36 °C is close to Thai hot-season air, but a hot room is not a heat treatment. The review reports a 14-day hold at 36 °C without describing light or humidity, and notes the titre came back after six months in the field [1]. A greenhouse swings up and down daily, so it does not repeat a controlled hold. The review’s cold treatment lasted 8–21 months at 2–4 °C in darkness [1]; no study cited here tested a household fridge for this. Without a confirmed HLVd test, label meristem-culture lines “untested”, not “clean”.
What to do: Choose one high-value cultivar for your first clean-up run. Find a testing lab before you cut the first tip.
6. Setting up a small tissue-culture lab at home
You do not need a university laboratory. The equipment list is short:
| Item | What it is for |
|---|---|
| Laminar flow hood or still air box | A clean space to open containers without contamination |
| Pressure cooker rated to 15 PSI | Sterilizing medium with pressurized steam |
| Glass or polycarbonate containers | Holding the cultures |
| Scale accurate to 0.01 g | Weighing salts, sugar and agar |
| pH meter | Setting the medium to pH 5.7–5.8 |
| Scalpels and forceps | Cutting and moving tissue |
| MS premix, agar and sucrose | The medium itself |
| Hormones: TDZ or BAP, and IBA (plus NAA for the BAP recipes) | Pushing tissue toward shoots or roots |
| 70% ethanol and bleach | Cleaning surfaces and explants |
| Low-intensity LED light | Lighting the culture shelf |
PSI means pounds per square inch; 15 PSI is about 1 bar above normal air pressure. Prices vary too much by country and import duty to quote, so price the list locally before budgeting.
Translator’s note: In Thailand, MS premix, agar and plant hormones are sold as laboratory chemicals. Ask an official distributor of laboratory or plant tissue-culture supplies in Thailand, or ask members in the forum’s Tissue Culture section where they buy. Ask the seller for each product’s data sheet, which explains how to dissolve and store it.
Working clean: still air box or laminar flow hood
Each time you open a container, airborne spores and bacteria can land on the medium. Its sugar feeds them, and they outgrow the plant tissue. Sterile technique keeps them out.
A laminar flow hood is a cabinet that blows a steady stream of filtered air across the work surface, pushing spores away from open containers.
A still air box is the budget option: a large clear plastic storage bin turned on its side, with two arm holes. Spray the inside with 70% ethanol before each use. It gives more contamination than a hood, so start more explants for each culture you want to keep.
Translator’s note: These general habits reduce contamination in either setup:
- Wipe the box, tools and the outside of every container with 70% ethanol before they go in.
- Wash your hands and forearms, wear gloves, and spray them with ethanol.
- Move slowly in a still air box; fast movements stir up air.
- Open containers only inside the box or hood, and never pass your hands over an open one.
- Sterilize the scalpel between explants.
- Keep ethanol away from flames and hot plates; it catches fire easily.
What to do: Before cutting any cannabis, make 10 containers of plain medium and open and close them in your box as in real work. After a week, count how many have turned cloudy: that is your starting contamination rate.
Making the medium
- Weigh MS premix as the maker instructs: typically 4.4 g/L at full strength, or 2.2 g/L at half strength. Add 30 g/L sucrose and dissolve in distilled water.
- Add hormones from stock solutions (1 mg/mL, stored frozen).
- Adjust the pH to 5.7–5.8 with 1 M sodium hydroxide (NaOH) to raise it, or 1 M hydrochloric acid (HCl) to lower it. “1 M” is the standard strength these are sold at.
- Add 7 g/L agar, then heat and stir until it dissolves. Pour 25–30 mL into each container.
- Sterilize at 121 °C / 15 PSI for 15–20 minutes, in an autoclave or a 15 PSI pressure cooker.
- Let it cool and set inside the hood or still air box.
Hormone stock solutions. A 1 mg/mL stock holds 1 mg of hormone per mL, for example 100 mg dissolved and made up to 100 mL. Dissolve each hormone as its data sheet says. Each 1 mL of this stock per litre of medium gives 1 mg/L.
| Medium | Hormones | Stock per litre (1 mg/mL stock) |
|---|---|---|
| Initiation | 0.5 mg/L BAP + 0.1 mg/L NAA | 0.5 mL BAP + 0.1 mL NAA |
| Multiplication, BAP | 1.0–2.0 mg/L BAP + 0.1 mg/L NAA | 1–2 mL BAP + 0.1 mL NAA |
| Multiplication, TDZ | 0.5 µM TDZ (about 0.11 mg/L) | 0.11 mL, or 1.1 mL of a 0.1 mg/mL stock |
| Rooting (half-strength MS, 500 mg/L activated charcoal, no cytokinin) | 2.5 µM IBA (about 0.5 mg/L) | 0.5 mL IBA |
Shelf life. Poured medium keeps a few weeks at room temperature, longer if sealed and refrigerated. Throw out any container that turns cloudy before use.
Translator’s note: Many kitchen pressure cookers do not reach 15 PSI, so check the maker’s rating. Below 15 PSI the steam does not reach 121 °C, and the medium may not be sterile. Thai rooms are warmer than temperate labs, so check stored medium more often.
What to do: Write the date, recipe and batch number on every container of medium, so that when a culture fails you can trace it back to the batch.
7. Problems specific to cannabis
Browning
Cut cannabis tissue releases phenolic compounds, natural plant chemicals that react with air and turn brown. This slows growth and can kill the explant. Four ways to reduce it:
- Add activated charcoal (1–2 g/L) to the initiation medium. It also absorbs some hormones, so you may need to adjust hormone doses.
- Move explants to fresh medium within the first 24–48 hours.
- Use an antioxidant such as ascorbic acid (vitamin C) or citric acid. The studies behind this article give no dose, so start from a published tissue-culture recipe and test it on a few explants.
- Cut fast, so wounds are exposed as briefly as possible.
What to do: If many explants brown, change your next batch in two ways: add charcoal and transfer within 24–48 hours. Compare results with the earlier batch.
Glassy shoots (hyperhydricity)
Shoot tips become see-through, swollen and glassy, also called vitrification. It is a documented form of culture decline in cannabis. The 2021 review by Monthony and colleagues notes it was seen specifically on MS medium with 0.5 µM TDZ [4], the same dose that gives good multiplication. So watch closely whenever you use TDZ.
Causes: too much cytokinin (the shoot-promoting hormone), humidity trapped in sealed containers, and high salt concentration.
Fixes:
- Lower the cytokinin dose.
- Switch to containers with breathable lids or small vents.
- Raise agar to 8–9 g/L for a drier medium surface.
- Switch from TDZ to BAP for one cycle.
Translator’s note: In a humid tropical room, choose vents covered with a filter membrane rather than open gaps, so spores cannot get in.
What to do: Change one factor at a time, so you know which change fixed the problem.
Genetic stability: why to avoid callus
New shoots can grow directly from existing buds (“shoot from shoot”, or direct organogenesis). This usually gives few mutations and plants true to the mother [4]. Going through callus, a lump of unorganized cells, is different, and in cannabis also unreliable. In the reviewed studies, regeneration from callus was as low as 1.35%, and 14% in the best treatments [4].
So callus is both a genetic risk and very unlikely to succeed. Both reasons lead to the same rules:
- Use direct organogenesis, not regeneration through callus.
- Keep cytokinin at the lowest dose that still works.
- Check identity periodically, by comparing visible traits (phenotype) or with DNA markers.
Lata and colleagues confirmed this kind of check by DNA analysis, showing that plants regrown from stored encapsulated material matched the original [8]. So the check is documented practice, not excessive caution.
Translator’s note: We found no Thai lab that publicly offers DNA marker testing of cannabis cultivar identity. Until you find one, compare traits: grow one plant from the culture line beside one from the original mother under the same conditions. Record height, flowering time, smell and photos. A certificate of analysis for both plants adds a chemical comparison.
What to do: Every few cycles, pick one plant from each culture line and grow it out next to a reference plant.
8. Encapsulated seeds and slow-growth storage
One of the most useful jobs for tissue culture is keeping a cultivar without a living mother plant.
Encapsulated (“synthetic”) seeds
A stem segment or shoot tip is sealed in a bead of sodium alginate, a nutrient-containing seaweed gel. Lata and colleagues, a team at the University of Mississippi (USA), tested this in 2012 [7]. They stored encapsulated cannabis stem segments at 15 °C for up to 24 weeks, with maximum regrowth and survival of 60%.
Regrown plants showed 90% survival during acclimatization, with cannabinoid profiles matching the donor plants [7]. A separate 2011 study used DNA analysis to confirm that plants from stored encapsulated seeds were genetically true [8].
Read these numbers as they are: 24 weeks, not years, and 60% survival. Encapsulation is a practical way to hold a cultivar for a season without a mother room. It does not replace a genebank, a facility for long-term storage of plant genetics.
Slow-growth storage
Cultures can also be stored without beads, kept cooler so they grow slowly and need subculturing less often. In the same study, some unencapsulated cultures got osmotic agents (mannitol or sorbitol), substances added to the medium to restrict water uptake and slow growth [7]. Among these, regrowth and survival were best at the lowest dose tested, 2% [7].
What to do: Even in the lab, about 40% of stored beads died. So store several times as many beads or containers per cultivar as you need, and keep a living backup of any irreplaceable cultivar. Section 10 covers the equipment to hold 15 °C.
9. Tissue culture in certified, medical-grade production
Some farms target pharmaceutical markets, such as EU-GMP buyers or export through the Thai FDA (Food and Drug Administration of Thailand). For them, tissue culture provides records, hard to get from cuttings, that support GACP and GMP audits:
- Defined starting material: every batch traces to a known, pathogen-tested mother culture.
- Uniform batches, which simplify quality control.
- Documented pathogen removal: meristem culture followed by a confirming RT-qPCR test.
- An audit trail: every subculture is logged with date, medium composition and operator.
Translator’s note: In Thailand, cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568, in force since 26 June 2025. Since 30 April 2026, the Ministerial Regulation on Controlled Herbs (No. 2) B.E. 2569 has tightened licence criteria for flower. The draft Cannabis Control Act is not law yet: Cabinet approved it on 22 September 2026 and sent it to the House. This article does not cover whether producing or transferring cannabis plantlets needs its own licence. Before selling or giving plantlets to another farm, ask the authority that issued your licence, in writing.
What to do: Set up your log now, even for a small lab, with these columns: date, cultivar, mother ID, medium batch, hormone doses, operator, shoots in and out, contamination, and test result.
10. Running a culture room in a tropical climate
Most published methods come from labs in cooler climates. Three adjustments matter in Thailand and across Southeast Asia.
- Control room temperature first. Cultures are kept at 24–26 °C, and outdoor air is routinely hotter, so the room needs its own air conditioner running constantly, plus a plan for power cuts. A culture that would survive 24 hours at 25 °C may not survive 24 hours at 34 °C. When power fails, the air conditioner stops, the room warms toward outdoor temperature, and cultures overheat.
- Expect more mould spores in the air. A still air box that works acceptably in a dry, cool room gives more contamination in a humid one. Work in your cleanest, least-used room, keep the box closed between sessions, and start more explants than a foreign recipe suggests.
- Storage at 15 °C needs its own equipment. A household fridge runs near 4 °C; holding 15 °C reliably needs a wine cooler or temperature-controlled cabinet. Budget for it before planning around 24-week storage.
Translator’s note: If power cuts are common where you work, consider a generator or battery backup that can run the air conditioner. A thermometer that records the highest temperature shows how hot the room got during a cut. Humidity peaks in the rainy season, so start extra explants in those months.
What to do: Log the culture-room temperature twice a day for two weeks before starting cultures, to learn whether your cooling can hold 24–26 °C.
11. When tissue culture is not worth it
- Small home grows (1–10 plants per cycle): cuttings are faster, cheaper and need no equipment. Tissue culture’s benefits grow with volume.
- Autoflowers: they cannot be kept as mothers. Culturing them is possible but impractical for routine propagation.
- One-time grows from seed: if you are not keeping the genetics, tissue culture adds work for no benefit.
- Tight budgets: the equipment cost and learning time only pay off when you need many clones per cycle, or genuinely need pathogen-free material.
Translator’s note: For most home growers in Thailand, a cheaper plan covers most of the same risks. Buy seed from a vendor you have checked. Seed can carry HLVd, so test it if you can. Keep one tested mother, sterilize tools between plants, and quarantine bought cuttings.
What to do: Count the clones you take per cycle and the plants lost to suspected viroid or other disease. If both numbers are small, stay with cuttings.
12. Getting started: a practical plan
Months 1–2. Practise sterile technique on cheap, forgiving plants such as pothos or African violets. Build or buy a still air box. Make MS medium and practise sterilizing it. The point is to learn contamination control before you risk cannabis tissue.
Months 2–3. Start your first cannabis cultures from stem segments of a healthy, tested mother. Start far more than you need and expect heavy losses. Learn to tell clean growth from contamination.
Months 3–6. Subculture the survivors. Tune the cytokinin dose for your cultivar, a step no published recipe can do for you. Begin rooting and acclimatization trials.
Month 6 onward. Use meristem tip culture to remove viroids, and confirm each line by RT-qPCR. Record multiplication and decline rates per cultivar over several cycles. Then write standard operating procedures (step-by-step written methods) from your own numbers.
Translator’s note: Pothos is a common houseplant in Thailand and Southeast Asia, so practice material is easy to find.
Tissue culture takes longer to learn than cuttings. In return, a grower working at scale gets viroid-free lines, mass propagation and storage for months without a mother room.
What to do: Put the month 1–2 tasks in your calendar now, and buy only the equipment needed for that stage.
If you have tried tissue culture for cannabis, post below this topic: your biggest problem (contamination, acclimatization or something else), plus your cultivar, medium recipe and counts. Questions are welcome too.
References
- Adkar-Purushothama, C.R., Sano, T., & Perreault, J.-P. (2023). Hop latent viroid: A hidden threat to the cannabis industry. Viruses, 15(3), 681.
- Punja, Z.K., Scott, C., Tso, H.H., Munz, J., & Buirs, L. (2025). Transmission, spread, longevity and management of hop latent viroid, a widespread and destructive pathogen affecting cannabis (Cannabis sativa L.) plants in North America. Plants, 14(5), 830.
- 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.
- Monthony, A.S., Page, S.R., Hesami, M., & Jones, A.M.P. (2021). The past, present and future of Cannabis sativa tissue culture. Plants, 10(1), 185.
- Murashige, T., & Skoog, F. (1962). A revised medium for rapid growth and bio assays with tobacco tissue cultures. Physiologia Plantarum, 15(3), 473–497.
- Lata, H., Chandra, S., Khan, I.A., & ElSohly, M.A. (2009). Thidiazuron-induced high-frequency direct shoot organogenesis of Cannabis sativa L. In Vitro Cellular & Developmental Biology – Plant, 45(1), 12–19.
- Lata, H., Chandra, S., Mehmedic, Z., Khan, I.A., & ElSohly, M.A. (2012). In vitro germplasm conservation of high Δ9-tetrahydrocannabinol yielding elite clones of Cannabis sativa L. under slow growth conditions. Acta Physiologiae Plantarum, 34(2), 743–750. Client Challenge
- Lata, H., Chandra, S., Techen, N., Khan, I.A., & ElSohly, M.A. (2011). Molecular analysis of genetic fidelity in Cannabis sativa L. plants grown from synthetic (encapsulated) seeds following in vitro storage. Biotechnology Letters, 33(12), 2503–2508.
This article is part of the Asiannabis Community educational series. It is for legal, educational use only, in places where growing cannabis is permitted.