“Everywhere I go, I’m constantly meeting cannabis growers who are not yet aware of a widespread disease that has been appearing more and more across the United States – hop latent viroid (HpLVd),” Joseph Ramahi, Ph.D., chief science officer for Cultivaris Hemp, shared with me at an MJBizCon-related networking event. Naturally, I was curious to learn more about this potentially devastating plant pathogen that was wiping out crops in some of the nation’s largest markets… and Ramahi had much to say on the subject.
Hop Latent Viroid (HpLVd) is not very well known, but if left untreated, it can greatly reduce a crop’s yield, potency, and overall quality, resulting in roughly $44 million dollars in annual losses. During a largescale study of marijuana and hemp farms in the United States (mostly along the west coast and Canada), nearly every garden tested positive for this viroid in some capacity. Most gardens had a 25-50% infection rate, meaning that’s how many of their plants had been exposed. There are a couple different modes of introduction and transmission, but once HpLVd infiltrates a garden, it can spread at an alarming rate and can be extremely difficult to eliminate. In this scenario, education and prevention is key, rather than taking a wait-and-see approach and risk losing up to half of your plants.
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What is a Viroid?
Viroids are infectious, pathogenic, single-stranded circular ribonucleic acids (RNAs). Although commonly confused, viroids are NOT viruses. The main difference is that a virus is a small infectious agent with a protein outer coating that can only replicate inside most living cells, while a viroid does not have the protein coating and can only infect plants. All known viroids so far inhabit angiosperms (flowering plants) and most cause diseases. While these diseases doesn’t affect humans by way of causing illness, the economic impact can be substantial.
The first known viroids presented in potatoes back in the 1920s, although it wasn’t immediately known what was causing the symptoms. Initially, the tubers on affected potatoes became misshapen and elongated, and the illness was dubbed “potato spindle tuber disease.” Over the years, symptoms appeared on budded, flowering sections of various different plants. Fungus and bacteria was ruled out, but what was causing this plant disease remained a mystery.
It wasn’t until 1971 when Theodor O. Diener, Swiss-American plant pathologist from the U.S. Department of Agriculture’s Research Center in Beltsville, Maryland, realized that this was not your run-of-the-mill novel pathogen. It was only 1/80th the size of a typical virus. This is when he proposed the term “viroid” to describe these extra small infectious cells.
According to Diener’s research, “Viroids are shown to consist of short stretches (a few hundred nucleobases) of single-stranded RNA and, unlike viruses, did not have a protein coat. Compared with other infectious plant pathogens, viroids are extremely small in size, ranging from 246 to 467 nucleobases; they thus consist of fewer than 10,000 atoms. In comparison, the genomes of the smallest known viruses capable of causing an infection by themselves are around 2,000 nucleobases long.”
Viroids can be transmitted in a few different ways: aphids, cross-contamination from poorly sanitized equipment, or plant to plant when the leaves of infected plants touch other plants. They replicate in the nucleus or chloroplasts of plant cells in through an RNA-based system.
Hop Latent Viroid
Hop Latent Viroid is the infectious pathogen known for causing “dudding” or “dudding disease” in cannabis plants. A dud crop can be characterized by abnormal branching, poor trichome/resin production, lower potency and overall quality, and reduced yield. However, HpLVd can remain asymptomatic, or dormant, in some plants for many years.
“It is possible for the pathogen to enter a production system and spread quietly while never showing any symptoms,” says Joseph Ramahi. “I have seen many plants test positive but show no symptoms, even over time. What appears to happen is a secondary stress occurs (heat/nutritional/pest) during vegetative growth and flowering, at which point 10%-30% of a crop can be lost to dudding.”
“It is also possible that no secondary stress is necessary,” Ramahi added. “It’s possible that with time, even over years, a tipping point is reached and asymptomatic infections become symptomatic as viroid levels in the plants grow.”
Like other viroids, HpLVd is transmitted through the above listed common ways – mechanical spread from contaminated tools and equipment, insects like aphids or thrips, and plant to plant transmission – although the extent of which the latter two methods cause disease remains a topic of debate that warrants further research.
Testing and Prevention
When it comes to HpLVd, prevention, or early detection at the very least, will be your best bet. Yes, your plants can be treated for the disease via plant tissue culture, but it’s a very time consuming and labor-intensive process. Most growers prefer not to waste their time battling an established case of HpLVd unless they’re trying to preserve a very important cultivar.
That said, the easiest and most effective way to prevent the onset and spread of HpLVd is by practicing good sanitation… it’s really as simple as that. Use freshly cleaned tools and new gloves whenever handling a plant in any way. Minimize foot traffic and visitors around your grow area, and make sure anyone who comes in contact with your plants takes proper precautions.
A 10 percent bleach solution, the same as in healthcare settings, is the best way to prevent the spread of viroids, as well as pretty much all other pathogens. It’s common industry practice to sanitize tools with a mix of 70% isopropanol/ethanol, but according to newly established standards from the horticulture and agriculture industries, bleach is much more efficient.
Growers should also make sure to screen mother plants and incoming clones with qPCR (polymerase chain reaction) assays – a technique used to detect specific DNA and RNA sequences – to make sure they are not infected. Keeping mother plants for longer periods and constantly clipping clones off them could also be an issue. If the mother plant has say a dormant HpLVd infection, it could be spread through her clones and infiltrate the entire growing area.
This is not just a passing pathogen that will quickly run its course and disappear. We expect to hear about HpLVd for a long time as the industry continues to grow. According to Ramahi, “With the asymptomatic nature of hop latent viroid, this disease will impact both the marijuana and hemp industries for many years.” Make sure to protect your harvest by keeping your tools clean and immediately removing any infected plants from your garden to prevent spread.
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Disclaimer: Hi, I’m a researcher and writer. All information in my articles is sourced and referenced, and all opinions stated are mine. I am not giving anyone advise, and though I am more than happy to discuss topics, should someone have a further question or concern, they should seek guidance from a relevant professional.
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