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Most Cannabis Plants Contain Mitoviruses, Study Finds

By Alexander Beadle

Published: Aug 23, 2022   
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Mitoviruses are an unusual group of viruses. While they were previously thought to only exist in fungi, over the past several years researchers have gone on to detect mitovirus genetic material in several plant crops, including beet and hemp.

Now, the agricultural technology company Segra International has developed a real-time polymerase chain reaction (PCR) test for detecting mitovirus in cannabis plants.

In a recently published white paper, Segra scientists report that 77% of the cannabis cultivars they have screened so far tested positive for the cannabis mitovirus, CaMV1. But far from being a point of concern, the scientists suggest that this mitovirus may even be somehow beneficial to the cannabis plant.

What is a mitovirus?

A traditional virus consists of a core of genetic material, either DNA or RNA, surrounded by a protective protein coat known as the capsid. This tough capsid shell protects the viral genome as it spreads to infect other cells.

Mitoviruses are unusual in that they do not have a capsid or other viral envelope to protect the viral DNA. This means that they have no real way to move from cell to cell or infect other organisms. As a result, mitoviruses are confined to the cell that they are in and spread only when that cell divides in two.

This isn’t the only oddity of mitoviruses. If they were simply contained to a host cell, then it might still be possible for them to spread by mechanical means, such as via insects or contaminated pruning tools. In fact, a mitovirus can actually only exist within the mitochondria, the powerhouse of a cell, as it uses mitochondrial genetic code. So even if a mitovirus was moved between cells, it could not survive within the nucleus or cytoplasm of another cell; the odds of it being injected directly into another mitochondria are astronomically low.

In real terms, this makes it incredibly difficult for a mitovirus to spread. But on the other hand, it also makes it incredibly difficult to “cure” a plant of mitovirus. Plant cells need their mitochondria in order to survive, so traditional methods of tackling viruses and bacterial infections will not work.

Mitovirus detected in majority of cultivars tested

Based on previously published genome sequencing data for CaMV1, scientists at Segra International developed a real-time PCR test that could be used to screen a library of common cannabis cultivars for this mitovirus.

Segra reports that 77% of its cultivars screened to date have tested positive for carrying CaMV1. These results were subsequently confirmed by fragment size analysis and sequencing a selection of the positive results.

The white paper does not list how many cultivars were tested in this trial. However, the authors suggest that a larger data set would be needed for more detailed analyses in the future.

“Sequence analysis of a sufficient population of CaMV1(+) cultivars could therefore potentially provide a means for tracking of maternal lineages of CaMV1(+) varieties, much as is done via mitochondrial SNP analysis in anthropoids,” the white paper reads.

“In theory, this could be used to do things such as identifying ‘most ancestral’ cannabis varieties likely to carry increased genetic diversity and novel breeding potential compared to highly inbred, more recently developed cultivars.”

Is CaMV1 a threat?

While the number of cultivars tested here is unknown, it is natural that the apparently high prevalence of CaMV1 would raise eyebrows. A difficult-to-cure virus that affects a plant’s mitochondria and is present in a majority of cultivars is, after all, maybe not the most comfortable discovery.

However, mitovirus presence in the Chenopodium quinoa species has been found to be beneficial to the plant. A study published in Biology (Basel) earlier this year found that Chenopodium quinoa varieties that tested positive for a mitovirus were significantly more resistant to drought, implying that the virus may help the plant deal with some external stressors.

This does not mean that the cannabis industry should immediately jump to thinking of CaMV1 as something that is beneficial, the Segra white paper authors caution, but it does mean that the presence of CaMV1 should not be assumed to be detrimental. Especially since CaMV1 is passed down through the mitochondria of mother plants, which likely would have been selected intentionally for breeding or cloning at one point, closer study into the differences between CaMV1 positive versus negative plants should be welcomed.

“With its identification, it’s likely that some commercial services will start to offer CaMV1 testing – and leave you to interpret what will almost certainly include some (+) results on your own,” the white paper reads.

“Hopefully the above material will help in that, as understanding that it is non-transmissible and to date only evidence is of beneficial impact, should help avoid knee jerk reactions to cull positive material. Doing so would be a real economic loss, and in light of all available present data, unwarranted.”


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