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Testing Cannabis for Hop Latent Viroid: In Conversation with SC Labs

By Alexander Beadle

Published: Jun 06, 2023   
Two gloves handle cannabis buds with tweezers & the SC Labs logo.

Image credit: iStock and SC Labs

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Hop latent viroid (HLVd) is increasingly being recognized as a major concern for cannabis cultivators worldwide. Infections can be extremely hard to detect, and once a plant is infected its yield can suffer dramatically. Moreover, the viroid is spread easily through contact with contaminated tools or propagative materials, meaning that a single case of HLVd infection can rapidly affect the yield of an entire farm.

Thankfully for cultivators, help is on the way. Using quantitative polymerase chain reaction (qPCR) techniques, laboratory analysts are able to detect the presence of the viroid’s RNA, making diagnosis much easier.

Now, the cannabis and hemp testing laboratory SC Labs has announced the launch of its new, more affordable, nationwide HLVd testing service.

To learn more about HLVd and to hear some top tips for how to test crops, Analytical Cannabis caught up with Josh Wurzer, SC Labs’ president and co-founder, to discuss how HLVd testing works.

What is hop latent viroid?

Viroids are a type of specialist plant-infecting pathogens consisting of only a single-strand circle of RNA, making them around 50 times smaller than the smallest viral genomes. First discovered in hops in the 1980s, HLVd is notable for causing seemingly no outward symptoms that can be used to quickly diagnose an infection. However, once the infected plant hits maturity, cultivators will notice a seemingly unexplainable reduction in the plant’s yield.

“Mites are really hard to identify, but their effect on the plant is dramatic; whereas, with HLVd, the effect on the plant is so minimal that it can be mistaken for other things or disregarded as lethargic or non-prolific plants,” Wurzer explained.

“But then you get to flowering, and you notice long internodes, you’re noticing the buds aren’t fully developing, your trichomes aren’t fully developing,” he continued. “And it’s sort of too late at that point.”

Cultivators may be relieved to know that current scientific research has found very little evidence to suggest that HLVd can spread through pollen or seed. Instead, it appears that the main ways in which infections are spread are through the use of infected propagative materials, grafting with infected plants, or the use of contaminated tools or machinery.

SC Labs announces new affordable HLVd testing service

SC Labs announced that its labs had added the capability to offer testing for HLVd back in May. Using reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR), the SC Labs method has been designed to be as sensitive and as affordable as possible, and therefore more accessible to cultivators who wish to carry out frequent testing.

“This is one of those tests where you have to be able to do 20,000 of them and not make a mistake, because you get that one infected plant and you’re not sensitive enough for whatever reason, now you’ve just allowed that contamination to enter your customer’s facility, and they’re going to have problems down the road,” Wurzer said. “We took an off-the-shelf kit and sort of modified some of the procedure to allow for that, so we were able to improve the sensitivity as well as improve the cost.”

Making a cost-effective HLVd testing service is essential, as cultivators will often want to test plants multiple times or in multiple locations to ensure that there is no trace of the viroid that could later spread within a facility. Frequent testing early on in the plant’s lifecycle, even before flowering, can help to catch an infection early.

“If anything pops up, the crop can be destroyed and replanted, and you haven’t invested too much time and energy into integrating that crop,” Wurzer added.

Testing tips for HLVd

SC Labs recommends that samples sent for testing be taken from multiple parts of the young hemp or cannabis plant, in order to maximize the chance of finding any infection that might be present.

“HLVd can reside in a particular part of the plant until it moves throughout the entire plant. And so we want to make sure that we’re getting a few different types of tissue for the plants, so we recommend both leaf and stem [samples],” Wurzer said.

But perhaps an even more important tip, Wurzer suggests, is to ensure that there is no opportunity for cross-contamination when these samples are being collected. Clean tools, the proper labeling of samples, and the proper sterilization of any surfaces that might come into contact with the equipment being used is key to producing a proper sample cutting.

“You are going to get a lot of false positives because you’re going to be transferring the HLVd into the next sample and subsequent samples if you’re not properly cleaning your utensils,” he said. “But beyond that, you are also transferring the viroid around your room as you are collecting the samples if you’re not using good hygiene.”

HLVd testing can be used forensically once an outbreak is suspected in a crop. But Wurzer also recommends cultivators be proactive with their testing regimens. Continuously checking mother plants, as well as quarantining and testing any new plants or materials being brought into the facility, can help to spot and eliminate HLVd infections as early as possible.

“The place to be doing [testing] is continuously monitoring your mother plants. Obviously, your mother plants are propagating all of the stuff that’s going to come after, so you want to ensure that you are not spreading the disease around,” Wurzer said. “And then when you are bringing new clones into your facility, any new plants, a lot of people want to screen those plants before they come into the facility.”

“The goal is to make sure that you never allow the HLVd to enter your grow in the first place.”

Alexander Beadle

Science Writer

Alexander Beadle has been working as a freelance science writer since 2017 and has covered the cannabis industry for Analytical Cannabis since 2018. He has also written for our sister publication, Technology Networks, and the cannabis industry consultant firm Prohibition Partners, among others. Alexander holds a Master's in Materials Chemistry from the University of St. Andrews, where he won a Chemistry Purdie scholarship, and conducted research into zeolite crystal growth mechanisms and the action of single-molecule transistors.


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