Hop latent viroid, aka Hplvd. Have you ever heard about it? If not, you’re in the right place to learn about what could be called a silent killer of Cannabis plants.
In case you have already heard about it, stay with us as we will try to debunk and clarify a few things about Hplvd and, in the final bit of the post we will also cover possible ways to treat contaminated plants and avoid the spreading of the viroid.
First of all: it’s a viroid, not a virus. What does that even mean?
A viroid is a small infectious pathogen that only affects angiosperms. Compared to a virus it has just one strand and a circular RNA.
Now, let’s focus on the name, as it suggests the origin of this very pathogen. As we know now, Hplvd was first discovered in hops and then in Cannabis around 2019, though it was probably roaming around before that year.
A silent killer
The main issue hemp growers face with Hplvd is that it’s somewhat hard to tell its symptoms apart from other common issues one has to face when growing Cannabis.
Hplvd is detected when the following symptoms, which in growers’ lingo are jointly called “dudding syndrome”, show up:
- Decreased production of metabolites, and cannabinoids.
- More fragile stems, less elasticity, you can see this when you bend one and it does not spring back up.
- Under-developed roots
- Smaller flowers
- The whole plant growth is hindered
As you may have guessed by now, these symptoms are not exclusive to Hplvd. And this, so far, has been the major issue with the viroid.
Many growers did not realize that their plants’ poor performance was not due to genetic issues, lack of fertilization, or other more mundane issues.
This has allowed the virus to circulate and spread from the US to the EU in an almost undisputed fashion.
How does Hplvd spread?
We are still somewhat in the dark when it comes to understanding how plants can transmit the viroid to each other.
What we do know is that most transmission happens by using tools such as pruning shears and gloves. If you use these on a contaminated plant and then work with the same tools on a clean one, you can spread Hplvd by coming in contact with the latter if it has any open wounds.
However, it is important to understand that some contaminated plants lay dormant, showing no symptoms and thus facilitating the spread of the viroid.
Where is Hplvd spreading?
It all started in the US, namely in California during the legalization boom.
Now it has become a startling phenomenon here in Europe as well. From Spain, where many growers got their Cannabis strains from the US, to the Netherlands, Italy, and other countries.
One additional issue is that the viroid can also contaminate seeds, at an 8% rate.
The fact is, it is difficult to point the finger against anyone considering how hard it is to tell Hplvd’s symptoms apart, not to mention when it is dormant.
Thus, you could buy some Cannabis cuts and later discover that they are contaminated.
How can we stop Hplvd? Is there a cure?
Not exactly. At the moment, we can count on a technique that helps detect the viroid and there are some provisional solutions. On top of that, prevention and compliance with GACP help a lot.
Testing can be done through a qPCR screening method, which can be performed by a lab, or even by buying a kit. Of course, having it performed by a lab warrants more accurate results. There are other methods, but qPCR is currently the most accurate one, allowing you to quickly isolate the contaminated crops.
Currently, there is no definitive solution to Hplvd, i.e. we (as an industry) cannot eradicate the viroid.
If only a small portion of the plants are contaminated, then one could still isolate these and enforce better preventive measures.
But, when your whole cultivation is contaminated, and especially if you need to save your cultivar, then the solution is tissue culture.
As incongruous as it may seem with an industry that has always promoted natural cultivation methods, tissue culture is the best shot the industry has to save precious strains that are under threat of disappearing because of Hplvd.
And, truth be said, it just seems unnatural but in fact it is not. The medium of an in vitro culture is made up of water, macro and micro nutrients in mineral forms, vitamins, and other organic compounds such as phytohormones and growth regulators which are biosynthesised (meaning produced/extracted) from plants and bacteria.
Due to the sterile environment wherein they are grown, tissue culture plants are freed from pests, viroids, and similia. Also, cold and heat treatment cycles help eradicate the viral load.
However, these are time-consuming processes, a cleaning cycle through tissue culture may take from 6-8 months up to 24 in case of high viral load.
In recent years, growers are becoming much more aware of the risks posed by the viroid.
The very first thing one can do if he reckons that a clone or even seeds may be contaminated is a qPCR screening test.
The other thing to do is to fully embrace GACP. Tools should always be cleaned and sterilized.
Usually, ethanol is enough, but in the case of Hplvd, we now know that bleach is even better.
Does Hplvd only infect indoor cultivations?
There is not enough data to determine whether outdoor cultivation preserves Cannabis strains from being infected by Hplvd.
What we do know is that the whole thing started in California from indoor-cultivated mothers.
Another interesting fact is that if you take an infected mother and let it go through a full vegetative cycle in open ground, the viral load will lower significantly.
All in all, we are still far from finding a clear-cut solution to Hplvd. But, if it turned out that outdoor cultivation is somewhat safer, that would come as no surprise to us at Enecta.
We always preferred outdoor growing to indoor. In a sense, Cannabis and CBD are a bit like grapes and wine, you should always think about the terroir, i.e. the ensemble of qualities that a given territory bestows on the plants it feeds.
This article would not have been possible without the help of Alessio Fabbro and his thorough knowledge of the matter.
Many thanks to the Catalan Institute of Agrifood Research and Technology