- Viruses are dominating the news more than ever, no doubt because the coronavirus has upended society and countless lives over the past two years.
- They are becoming increasingly prevalent in our environment and are having a lasting impact on more and more living organisms around the world. Plants in general, such as cannabis, are also affected by a wide variety of plant viruses.
- In this article, we explain the latest findings regarding these phytoviruses, even though many mysteries still surround these strange and devastating modern-day pests.
- Viruses and the cannabis plant
- Vectors that facilitate the spread of plant viruses
- The tobacco mosaic virus in cannabis cultivation
- The various viruses that harm the cannabis plant
- Prevention and Treatment of Cannabis Viruses
Viruses and the cannabis plant
Generally speaking, phytoviruses are, by definition, viruses that infect plant organisms. More specifically, they are intracellular parasites that require a host organism to reproduce. It is worth noting that, even today, our overall scientific understanding of phytoviruses is far less extensive than that of the animal kingdom.
This makes perfect sense, as it is certainly a better indicator of the symptoms that might occur in humans. However, various viruses are now clearly identified as harmful to cannabis plants with high THC or CBD content grown from seeds, as these viruses can cause serious problems, jeopardizing the harvest.
Although the origin of these viruses remains unexplained for the time being, the scientific community has put forward three theoretical hypotheses to explain their origins. The first is a regressive hypothesis, which clearly suggests that these viruses originated from microscopic cells that infected larger cells and lost part of their genetic makeup during their evolution.
The second hypothesis can be explained by a cellular origin theory, which suggests that viruses formed from different parts of the DNA and RNA of larger organisms. The third and final hypothesis is that of coevolution, which explains that they are composed of protein molecules and nucleic acids.
The tobacco mosaic virus (TMV) was the first of its kind to be discovered by Adolf Mayer in 1886. It was not until 1898 that Martinus Beijerinck was able to replicate the experiments previously conducted by Dimitri Ivanovsky in 1892.
It was at that time that he first used the term “virus” to describe the symptoms of tobacco mosaic virus. To him, it was therefore clear that the cause of this disease was neither a fungus nor a bacterium.
Most of the identified plant viruses specifically infect certain plant species, which clearly indicates that they require at least one specific type of host cell in order to reproduce, thereby limiting their potential infections to a limited number of species.
In any case, we are witnessing the emergence in the natural environment of a multitude of viruses capable of causing serious problems across a wide range of crop species, which is giving farmers around the world quite a scare.
Vectors that facilitate the spread of plant viruses
According to certain scientific observations, it appears that plant viruses are essentially protein capsules containing a portion of genetic material; the missing part prevents them from moving from one plant to another. This naturally raises the question: how, then, are they able to cause such widespread damage within a crop?
In fact, their spread is facilitated by the presence of various viral vectors; more specifically, these are living organisms that carry these viral particles from an infected plant to a healthy one, ultimately helping the virus to establish itself in new host cells.
Most of the time, it is cannabis pests and insects —such as aphids, scale insects, nematodes, spider mites, thrips, and whiteflies—that act as direct viral vectors. Without realizing it, growers themselves play this role in transmission by caring for and tending to cannabis plants grown from seeds with high THC or CBD content, working in close proximity to them.
The tobacco mosaic virus in cannabis cultivation
The tobacco mosaic virus, as its name suggests, is a viral pathogen that is particularly harmful to tobacco plants, although it can infect more than 125 species across nine different plant families. However, many growers remain uncertain and are seeking definitive answers regarding exactly how the tobacco mosaic virus affects cannabis.
It is worth keeping in mind, however, that a virus is sometimes identified by a specific acronym, even though it is actually a different strain associated with a different viral disease (such as the hemp mosaic virus (MHV), which is in fact the cowpeastrain of thetobacco mosaic virus).
The VMT capsid consists of at least 2,000 enveloping protein molecules and a single-stranded RNA molecule. Unlike many other viral infections, once it enters the host cell, its protein capsid detaches from the virus, releases the viral RNA, and begins to replicate its own genome.
The disease causes various symptoms in plants within the crop; we can observe significant discoloration between the veins of the youngest leaves, which must not be confused with symptoms of nutrient deficiency. These color changes are accompanied by the development of mosaic-like spots with varying light and dark patterns. It is also possible to see the leaves wilt, eventually becoming rough to the touch.
The lower parts of the marijuana plant are also affected, especially if the weather isn’t on our side—in other words, if we’re experiencing hot temperatures and dry conditions. You may also notice necrotic damage to the leaves, and you’ll see a general slowdown in growth or flowering in plants grown from seeds with high THC or CBD content.
The VMT, or TMV (Tobacco Mosaic Virus), is undoubtedly one of the most stable plant viruses in existence. As long as the ambient temperature does not drop below 4°C, it remains perfectly stable. A crop grown in greenhouses or located within a botanical garden provides ideal conditions for reproduction, thanks to their high and stable temperatures, as well as the very wide variety of different plants stored there.
The various viruses that harm the cannabis plant
Cannabis plants with high THC or CBD content are potentially susceptible to VMT, but also to many other phytoviruses, some of which have not yet been clearly identified. Fortunately, most of these phytoviruses do not affect only cannabis, as they also infect many other plant families and species.
We might add that plants can be infected by multiple viruses at the same time, making it very difficult for growers to distinguish between these different viral conditions. Growers must adapt to the specific characteristics of each viral condition—such as a disease—and apply the most appropriate treatment.
It appears that nearly 900 plant viruses have now been identified, but there is still a long way to go in terms of scientific research, as only a small number of them have been the subject of sufficiently in-depth and well-documented studies. Currently, only two viruses are clearly identified as particularly harmful to cannabis.
These are the Hemp Mosaic Virus (HMV) and the Hemp Streak Virus (HSV). These two viral diseases specifically affect cannabis plants through the transmission of viral vectors such as aphids, caterpillars, thrips, and spider mites.
Some studies by the scientific community have also shown that the Tobacco Ringspot Virus (TRSV) and the Tobacco Streak Virus (TSV) are also capable of causing such an infection, resulting in symptoms similar to those caused by the VMT.
The same is true for the alfalfa mosaic virus. Strangely enough, seeds and aphids are the primary vectors for these parasitic diseases. The Arabidopsis mosaic virus (ArMV) also appears to be capable of wreaking havoc on cannabis plants via nematodes and seeds, though it does so asymptomatically.
The cucumber mosaic virus (CMV) affects both cucumber and marijuana plants, once again due to the active involvement of aphids or seeds as viral vectors. To conclude this section, it appears that the tomato ring spot virus (TomRSV) also uses cannabis as a host plant.
There is also a viroid that originates in hops, which is quite virulent and has a profound effect on cannabis plants. The Hops Latent Viroid (HpLVd), which has been present in the United States for several years now, has become a serious problem for many professional growers in the U.S. in recent years.
A prestigious California nursery sold numerous infected clones to many companies in the industry there, and the vast majority of growers took a long time to realize what was happening in their crops. This viroid actually exhibits rather misleading symptoms, as the foliage shows signs resembling nutrient deficiencies, and plant growth or flowering slows down abruptly; growers are misled, yet the disease takes hold permanently.
This viral phenomenon may be asymptomatic for a certain period of time, after which symptoms can appear suddenly. This can lead to a significant loss of certain genetic traits, resulting in a marked decline in both flower and cannabinoid production.
Prevention and Treatment of Cannabis Viruses
Unfortunately, as with certain fungal diseases caused by parasitic fungi that affect plants, there is still no suitable treatment available to completely and quickly eliminate the infection or the adverse effects of phytoviruses affecting indoor and outdoor cannabis cultivation.
As with many diseases caused by parasitic fungi such as Botrytis, downy mildew, powdery mildew, Alternaria, Fusarium, or leaf septoria—whose symptoms are often characterized by the appearance of rot—it is necessary to implement a series of preventive measures.
It is essential for growers to thoroughly clean their indoor cannabis grow space, from floor to ceiling, removing all leaves and plant debris lying around. It is crucial to always strive to maintain a stable temperature when growing indoors. Also try to ensure good air circulation, such as even ventilation that will limit the formation of pockets of stale air, which are harmful. A key factor here is maintaining a stable humidity level, without excessive fluctuations.
Keep in mind that leaves provide an ideal environment for the development of the rot characteristic of these parasitic fungi. Unfavorable environmental conditions encourage these fungal issues. Be sure to water carefully, using an amount of water and nutrients appropriate for the stage of growth. Generally, cannabis plants require little water during the last two weeks of flowering. You need to be careful at this stage, as it is the ideal time for a fungus like Botrytis to appear.
You must be vigilant about poor climate control, as this can facilitate the onset of fungal diseases such as fusarium, which attacks the roots and is particularly difficult to eradicate. This may seem obvious, but we caution you that consuming cannabis flowers infected with fungi is dangerous to your health. It can cause serious respiratory problems in humans, so it’s best to refrain from doing so and avoid it altogether.
But that’s not all, because growing under such conditions could also easily attract pests, which could become a secondary problem and thus jeopardize the success of your harvest. A key factor lies, above all, in choosing the highest-quality cannabis seed varieties available.
It is very important to select varieties that are as resistant as possible to all of these pests and diseases, and whose characteristics are suited to the climatic conditions of your region. In indoor settings, climate control is of the utmost importance; proper air circulation and precise humidity management must be given the highest priority.
Apply a root stimulator once a week, as this will help produce strong, healthy roots with excellent absorption capacity. Root health is very important, as it directly contributes to strengthening the immune system of your marijuana plants.
We can conclude that these viral phenomena are a modern-day scourge of our time, shrouded in many mysteries, which we hope will be unraveled in the years to come. This shows us that chemicals do not seem to be as revolutionary as they appeared to be just two decades ago. Nature will continue to teach us many life lessons in the future.
