The mother plant looks healthy. The cuttings root. The seed germinates normally. So everything is fine? Not necessarily. New research on Hop Latent Viroid shows how inconspicuously HLVd can move through cannabis crops and why plant health begins with the origin of the genetics.
The mother plant looks good.
No conspicuous leaves. No stunted growth. No obvious problems.
The cuttings root as well.
And if you are starting from scratch and germinating a seed, the problem should be resolved anyway.
Right?
This is exactly where Hop Latent Viroid becomes interesting.
Researchers have now detected HLVd in asymptomatic mother plants, rooted cuttings, roots, nutrient solution, flowers, trichomes, pollen and seeds.
And contaminated seed can in turn produce HLVd-positive plants.
This means:
A plant can look completely inconspicuous and still be part of an infection chain.
And that is exactly why we should talk about HLVd much more seriously.
HLVd is not a virus
Although it is often referred to colloquially as “hop latent virus,” this designation is scientifically incorrect.
HLVd stands for Hop Latent Viroid.
A viroid is even more simply structured than a virus. HLVd consists of a small, circular RNA molecule with just 256 nucleotides.
No viral envelope.
No proteins of its own.
And yet this tiny RNA molecule can have a massive impact on plant metabolism.
In cannabis, an HLVd infection is associated with what is known as dudding.
Affected plants may remain smaller, develop weaker roots and produce less well-formed flowers, among other effects.
Trichome development may also be impaired.
In a recent study, the trichomes of infected plants were visibly smaller and less developed than those of healthy comparison plants. HLVd was even detected directly within the trichome fractions examined.
This is particularly relevant for growers.
Because this is precisely where many of the compounds for which we grow cannabis are produced and stored.
The actual problem begins earlier
Recognizing a severely affected plant at some point is one thing.
Recognizing an infected plant before it shows symptoms is something entirely different.
And this is one of the greatest difficulties with HLVd.
Studies have found the viroid in mother plants that showed no clear external disease symptoms.
Rooted cuttings from such crops could also test positive.
This leads to an important statement:
Looking healthy does not mean being HLVd-free.
A visual inspection alone is therefore not sufficient.
This is especially important with mother plants.
A regular grow plant remains in the crop for a few months.
A mother plant, on the other hand, can supply new plant material repeatedly over a long period.
An infected mother can therefore produce not just one or two problematic plants.
It can produce many.
A cutting copies more than just the genetics
Vegetative propagation has an enormous advantage.
A cutting carries practically the same genetic foundation as its mother plant.
This is precisely why exceptional phenotypes can be preserved for years.
Unfortunately, this advantage does not apply exclusively to desirable traits.
Systemic plant pathogens can also be passed on with the plant material.
Current research shows high transmission rates from infected mother plants to their cuttings in the case of HLVd. The extent can depend on genotype and infection status.
Therefore, the statement
“But the cutting looks healthy”
is not sufficient evidence of clean starting material.
And this brings us to the next problem.
HLVd does not necessarily remain in a single plant
Cannabis plants are often irrigated together in professional cultivation.
In hydroponic systems in particular, they may share the same nutrient solution.
This is exactly where researchers also found HLVd.
The viroid was detected in recirculating nutrient solution and on irrigation components.
Controlled trials also showed that HLVd can be transmitted from infected roots to previously healthy plants.
However, the authors point out that this transmission route is particularly relevant to hydroponic systems.
How significant the risk is in biologically active soil or Living Soil is much less clear. The conditions in a root zone containing substrate and microbiology differ considerably from those in a shared hydroponic nutrient solution.
Nevertheless, the experiment demonstrates something fundamental:
Plants can appear separate and still be part of the same biological system.
And then there are the seeds
Up to this point, one might still say:
Okay.
Mother plants and cuttings are vegetative plant material.
Then I will simply start over with seeds.
This is exactly where the more recent HLVd research becomes particularly interesting.
Because seed is not automatically a pathogen-free fresh start either.
One study involving industrial hemp already showed high transmission rates through seed.
In this study, HLVd-positive female plants were crossed with negatively tested pollen. In another group, negatively tested female plants were pollinated with HLVd-positive pollen.
Depending on the experiment, 58 to 80 percent of the resulting hemp plants tested positive for HLVd.
That is remarkable.
Because it shows not only possible transmission through the female plant.
Infected pollen can also be relevant.
Cannabis seeds also tested positive
A study published in 2025 went one step further.
Researchers created a cannabis cross from the M1 and G11 genotypes.
A random sample of 16 seeds produced from this cross was then tested, and all 16 tested positive for HLVd.
It later became clear that both parent plants carried HLVd. The authors therefore expressly point out that the transmission rate is likely to be lower if only one parent is infected.
This is an important limitation.
This experiment must not be interpreted as:
“HLVd is transmitted through cannabis seeds 100 percent of the time.”
That would be incorrect.
The correct statement is:
In this cannabis cross, all 16 randomly tested seeds were HLVd-positive.
And the story does not end there.
The seed can germinate normally
HLVd was initially detected on the seed coat of the infected cannabis seeds.
It could not initially be detected in the freshly emerging radicle.
Later, however, HLVd appeared in the opened cotyledons and subsequently in the true leaves. Still later, it was also found in the roots of the young plants.
This is precisely what makes the matter so relevant to growers.
A seed can germinate.
The seedling may initially look normal.
And yet HLVd may later be detectable systemically throughout the plant.
A seed is therefore not automatically a clean fresh start.
This is likely to be one of the most surprising findings of current research for many growers.
Pollen is also part of the equation
In cannabis breeding, a great deal is said about the female parent.
Flower structure.
Aroma.
Potency.
Resin production.
Growth.
But HLVd makes clear why the health status of the pollen donor is also important.
In the 2025 study, the viroid was detected in both anthers and pollen from infected plants.
Together with the findings from industrial hemp, this presents a fairly clear picture:
It is not only the mother plant that deserves phytosanitary attention. Both sides of a cross are relevant.
This is a decisive point, especially for professional breeders.
Breeding means more responsibility than good genetics
If a home grower has an infected plant, this initially affects their own crop.
With a breeder, the scale changes.
A single parent combination can produce hundreds or thousands of seeds.
These seeds can then be distributed among completely independent grows and across large geographical distances.
This potentially turns an individual phytosanitary problem into a multiplier.
That is why, for us, professional breeding involves more than:
Selecting genetics.
Selecting phenotypes.
Assessing stability.
Evaluating aroma.
Observing cannabinoid profiles.
It also involves:
Knowing whether the starting material is healthy.
Anyone who propagates genetics is responsible for more than their genetic traits.
A beautiful phenotype is not yet clean genetics
HLVd makes conventional selection particularly difficult.
A plant may appear vigorous.
It may have an interesting structure.
It may smell exceptional.
It may still be infected.
Visual inspection therefore cannot replace laboratory analysis.
In our view, phytosanitary management should therefore be part of professional work when dealing with mother crops maintained over the long term, breeding parents and newly introduced plant material.
This includes, in particular, testing, quarantining new material and maintaining clean workflows.
A scientific review of HLVd likewise recommends testing newly received plant material before integrating it into a crop and initially keeping it separate. The frequent absence of symptoms makes this precaution necessary.
Seed banks are also part of this chain
Not every seed bank necessarily produces all the genetics it offers itself.
Depending on the business model, seeds may come from different breeders, production partners or external sources.
That is fundamentally nothing unusual.
But it increases the importance of a controlled supply chain.
A brand name alone does not make plant material pathogen-free.
The processes behind it are what matter.
Where did a batch come from?
Who produced it?
How were the parent plants controlled?
How is new starting material brought in?
What happens in the event of a positive result?
These questions will presumably become more important in the future.
As the cannabis industry becomes increasingly professionalized, plant health can no longer be treated solely as the grower’s problem.
HLVd can cause damage precisely where quality is created
Why is all of this relevant at all?
Because HLVd does more than simply produce a positive PCR test.
An infection can have real effects on plant development.
Reported effects include:
- reduced growth
- shorter internodes
- weaker root development
- smaller or less well-developed flowers
- chlorosis
- reduced trichome development
- changes in secondary plant compounds
In the 2025 study, infected flowers produced visibly fewer and less well-developed trichomes than healthy comparison plants. HLVd was detected directly in flower tissue and trichome fractions.
This is particularly problematic for cannabis.
Because glandular trichomes are key sites of cannabinoid and terpene production.
A pathogen that impairs precisely this area does not merely affect plant mass.
It affects the actual quality of the harvest.
And the viroid can remain unnoticed for a long time
HLVd does not carry the word “latent” without reason.
Being infected does not automatically mean looking sick immediately.
A plant can carry the viroid without showing typical symptoms.
This makes HLVd particularly troublesome.
No one would willingly take a plant with severe powdery mildew as a new mother into their crop.
They might well take a mother plant that looks perfect.
This is precisely why an invisible crop may be more problematic than an obviously diseased plant.
Testing is not entirely straightforward
Even with laboratory analysis, sampling plays a role.
HLVd is not completely evenly distributed throughout a plant at all times.
Studies of different plant tissues showed, for example, that root samples from young mother plants could be particularly reliable in producing positive results. Some plants were positive in their roots even though simultaneously tested leaf or petiole samples were negative.
This does not mean that growers should now generally submit only roots.
Testing providers use different validated methods and sampling protocols.
But it does mean:
A test is only as good as the method and sampling behind it.
Especially with valuable mother plants and breeding material, it is therefore worthwhile to work with a specialized laboratory using a suitable testing protocol.
Scissors, hands and workflows remain relevant
HLVd can also be spread mechanically.
Sap from an infected plant can enter healthy tissue through wounds.
Pruning, taking cuttings and other tasks can therefore create routes of transmission when tools are used between plants. Current research also found HLVd RNA after extended periods in dried plant material and on various work objects.
An important distinction is necessary here:
Detectable RNA does not automatically mean that the material remained infectious under all conditions tested.
Nevertheless, its high stability shows why hygiene should not be optional with HLVd.
Clean tools.
Clean hands or gloves.
Controlled work between plants.
Do not place new genetics directly into existing mother crops.
And do not simply continue propagating suspicious plants.
These are not excessive laboratory rules.
It is simply sensible crop management.
Valuable genetics do not necessarily have to be lost after a positive test
There is also a positive aspect.
For particularly important genetics, remediation through tissue culture may be possible.
The recent study tested meristem culture in eight cannabis genotypes for this purpose.
On average, around 41 percent of the regenerated plants were HLVd-negative after six months. However, the results differed extremely between genotypes, ranging from no successful clean-up to 100 percent HLVd-free plants.
This means:
A positive result does not automatically have to mean the end for irreplaceable genetics.
But simply continuing to take cuttings from an infected mother is not a strategy either.
What does this mean for the regular grower?
HLVd should not be a reason to panic.
But it is a reason to improve processes.
We would be particularly cautious about three things:
Cuttings from an unknown source
A clone is not a sterile fresh start. It brings the biological system of its mother plant with it.
New mother plants
Valuable mother crops are multipliers. The longer a plant is used for propagation, the more important a clean starting status becomes.
Seed
Seeds reduce many risks associated with vegetatively transmitted diseases. But they are not a guaranteed HLVd-free fresh start.
This does not mean that every grower now has to test every individual seed.
It means:
Origin takes on new significance.
What the research has not yet answered
Despite all the attention, we must also clearly state what we do not know.
There are currently no reliable data showing how widespread HLVd actually is in German home grows or in European seed batches.
We also do not know which seed transmission rates apply to all modern cannabis genetics.
Transmission apparently depends, among other things, on the infection status of the parents and possibly on the genotype. The authors of the recent study explicitly call for further research on this topic.
Therefore, the statement
“HLVd is everywhere in cannabis seeds”
would be just as irresponsible as
“Seeds cannot transmit HLVd.”
Science now clearly lies somewhere in between.
Seed can be part of the transmission route.
And that alone significantly changes the discussion.
For CannaSelection, a good grow does not begin with fertilizer
At CannaSelection, we focus intensively on soil, roots, microbiology and plant nutrition.
But a functioning system can only work with the plant material we put into it.
Living Soil cannot correct poor genetics.
MicroBio+ cannot turn infected starting material into an HLVd-free plant.
And perfect climate, light or nutrient values cannot replace clean genetics.
That is why, for us, the quality of a grow also includes the question:
Where does the plant actually come from?
Not only:
What genetics is it?
But also:
How was it propagated?
How was the mother crop managed?
How was the breeding material controlled?
And what standards does the provider follow?
This is just as much part of assessing the system as soil, light and water.
Conclusion: The greatest HLVd risk does not have to look diseased
HLVd is problematic precisely because it contradicts our conventional understanding of a diseased plant.
An infected plant does not have to look sick immediately.
A mother plant can carry HLVd.
A cutting can carry it along.
A shared root environment can become a transmission route.
Pollen can contain HLVd.
Seeds can carry HLVd.
And these can in turn produce infected plants.
The consequence is not panic.
It is care.
Looking healthy does not automatically mean being healthy.
A cutting copies more than just the genetics.
And a seed is not automatically a clean fresh start.
Perhaps we therefore also need to redefine what we mean by truly good cannabis genetics.
Stability must not mean exclusively that a cultivar displays reproducible traits.
Professional genetics also includes plant health.
And this means that part of the responsibility lies long before a grower plants their first seed in the soil.
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