Understanding Hop Latent Viroids and Their Impact on Cannabis Plants

The cultivation of cannabis plants has gained significant attention in recent years, primarily due to the increasing demand for their medicinal and recreational benefits. However, with this growing interest comes the need to understand and address the various threats that can potentially impact the health and viability of cannabis crops, which of course impacts your operation’s revenue.

One such threat is the presence of Hop Latent Viroid, which can have detrimental effects on cannabis plants if left unnoticed and unmanaged. We’re going to dive into this hot topic to discuss what viroids are, how to help prevent infection, and how to manage a viroid infection should your cannabis plants become sick.

Viroids: Definition

Most people haven’t heard the word “viroid” before, so let’s start with a basic definition. The term may sound like an Atari game or a bad science fiction movie. As it turns out, viroids are small, infectious particles that consist solely of short strands of RNA. Unlike viruses, they lack a protein coat and are therefore unable to sustain themselves without a host plant.

Viroids primarily infect and replicate in the nuclei of plant cells, causing diseases or abnormalities. They are highly stable and can withstand various environmental conditions, making them a persistent threat to a great many agricultural crops.

What are Hop Latent Viroids?

It’s difficult to say exactly who discovered this variation of viroid, as it’s been in our mists for quite some time, and is very elusive. It’s said to have been observed in Japan in the 1950’s, however, there have been numerous discoveries in countries like Spain, Europe, and here in the United States. Regardless of its original discovery, it’s clear that this circular RNA molecule has been plaguing horticulturists for decades. Most not even knowing it. Hop latent viroids are viroids that specifically infect hops (Humulus lupulus) plants.

Unfortunately, the Humulus lupulus terpene myrcene isn’t the only thing hops and cannabis plants share. They are in the same botanical family, Cannabaceae. As such, (you guessed it) it has since been recognized as a threat to cannabis cultivators due to its ability to infect cannabis plants as well.

Hop latent viroids encompass several different viroid species, including Hop Latent Viroid (HLVd), Hop Latent Viroid-Like (HLVd-L), and Hop Stunt Viroid (HSVd). These viroids are characterized by their small size, ranging from approximately 250 to 370 nucleotides, and their ability to induce latent infections, meaning they can remain hidden in a plant without exhibiting apparent symptoms for an extended period. Hence, why it’s been designated, “Hop Latent Viroid.” It is often found latent in hops plants showing no visual sign, all the while diminishing the hops plant’s essential oils.

Impact of Hop Latent Viroid (HLVd) on Cannabis Plants

As we’ve mentioned, Hop Latent Viroid – also known as “dudding” disease – can infect and have a range of adverse effects on cannabis plants. While some viroid infections may remain latent with no apparent symptoms, others can lead to stunted growth, reduced trichome yields, and overall plant decline.

HLVd can also disrupt a plant’s development by interfering with various physiological processes, including terpene synthesis. This means if you’re growing a crop of pungent Sour Diesel – then you may not be getting the terpene profile you signed up for, even if it started as a healthy clone.

Hop Latent Viroid Symptoms and Effects

The effects of Hop Latent Viroids on cannabis plants can vary depending on the strain of viroid and the stage of infection. Some common symptoms include:

  • Stunted growth
  • Leaf curling
  • Yellowing or chlorosis of leaves
  • Reduced cannabinoid and terpene yield (potency)
  • Poor resin production
  • In severe cases, necrotic lesions and death of the plant

In addition to the direct impact on the plant’s health, HLVd also compromises the quality of the harvested cannabis material. The presence of viroids can, in some cases, affect the chemical composition and potency of the final product, thereby diminishing its value. That is to say, viroids can cut into the revenue calculated for your harvest.

Tomato plant infected by a viroid
Much like viruses, there are a wide variety of viroids. They can negatively affect everything from avocado trees to tomato plants, hops, and cannabis crops. If you’re in agriculture, you’ll likely need to defend against viroid infections.

Last, (if all of that wasn’t bad enough) Hop Latent Viroid can also weaken the overall vigor of the plant, making them more susceptible to other diseases and pests. This is due in part to the detrimental effects on the cannabis plant’s trichomes and the composition of the resin inside. As we’ve discussed in past articles, trichomes are part of their biological self-defense against disease-carrying pests.

Transmission and Spread

HLVd can be transmitted through various means, including:

  • Vegetative propagation
  • Contaminated cutting tools
  • Insects such as aphids
  • Infected seedlings or clones

As viroids can become latent within the plants and go undetected, they can be difficult to spot at first. And once introduced into a crop, Hop Latent Viroid can spread rapidly through the plant’s vascular system. The viroids can also be spread through infected plant material, including leaves, stems, and roots. Growers should be cautious about using infected plant material for composting or any other purpose, as it can contribute to the spread of the viroid.

Detection and Diagnosis of Hop Latent Viroid

Early detection and accurate diagnosis of HLVd is crucial for effective management and control strategies. Several detection methods are available, including molecular techniques such as polymerase chain reaction (PCR) and reverse transcription PCR (RT-PCR). These methods can detect and identify specific viroid species based on their unique nucleotide sequences.

Inspecting a cannabis plant
Knowing one of your plants has Hop Latent Viroid is the first step in preventing it from becoming a crop-wide infection. If the leaves of your plants look smaller, thinner, or deformed, consider immediate quarantine until you can assess why the plant is developing differently than its counterparts. This may include sending a leaf sample to a specialized lab for viroid testing.

Leaf tissue sampling, particularly from young leaves, is commonly used for this method of detection. The sampled leaves are subjected to laboratory analysis to confirm the presence of HLVd. It’s important to note that viroid detection requires specialized equipment and expertise, making it necessary to collaborate with qualified laboratories or diagnostic services.

Although lab tests are one of the surer ways to catch an HLVd infection early, it may not seem financially viable for many cultivators. It’s a risk assessment each grower must make. That said, companies like Purple City have innovated testing solutions to help make viroid detection easier, more convenient, and more affordable.

Purple City: Experience is the Best Teacher

HLVd testing can be expensive, time-consuming, and a pain in the bud. Due to the time spent and inconsistent results received by 3rd party lab tests, Purple City developed their own, in-house solution – OnSight. This method of accurately testing for Hop Latent Viroid is an in-house RT LAMP diagnostic (or Reverse-Transcription, Loop-Mediated Isothermal Amplification) diagnostic. Let’s break down the term:

  • Reverse Transcription – This is a process where an enzyme is used to transcribe or synthesize a strand of RNA (or DNA.) Reverse transcription used alongside LAMP or PCR testing, can identify or reveal the gene of interest. Vital in detecting a specific Viroid.
  • Loop-Mediated Isothermal Amplification – Whereas PCR testing requires a cycle of increasing and decreasing the temperature of a sample to amplify the genetic material being tested for, LAMP technology is isothermic, and can achieve nearly identical results without changing the temperature of the sample.

Wary of expensive, time-consuming results, Purple City’s OnSight diagnostic test allows one employee to test hundreds of plants with same-day results. It’s economical and was designed with convenience in mind. Not a bad bit of tech for cannabis cultivators concerned that their plants are being stunted by HLVd.

HLVd OnSight is the test Purple City Labs developed for our own nursery to eliminate HLVd. It was such a success for us that we decided to commercialize it and make it available to others.

Purple City Genetics. Retrieved August 7th, 2023, from https://labs.purplecitygenetics.eu/

Options are available for those that want to increase their chances of passing strict pathogen testing and want to provide the highest quality product to their customers. Purple City developed OnSight to solve a problem they were experiencing and has begun to offer that technology to others.

Prevention and Control Measures

The saying, “an ounce of prevention is worth a pound of cure” certainly applies to cannabis and HLVd. Preventing Hop Latent Viroid from infecting your cannabis plants is crucial for maintaining a healthy, profitable crop. As a bit of good news, many growers are already following best practices to prevent strain crossover and mold. Even so, here are some recommended HLVd prevention and control strategies:

Source healthy plant material

It is essential to start with healthy plant material from reputable sources. Double-check to ensure that the clippings, seedlings, or clones you’ve purchased are free from any signs of infection. You can also obtain plant materials from certified disease-free sources to minimize the introduction of viroids into your cultivation environment.

Quarantine and testing

Quarantine any new plants before introducing them into your main crop. Conduct regular testing for HLVd to identify any latent infections. If infection has already occurred, isolate the infected plants or areas to prevent viroid spread to healthy plants.

Sanitation practices

Maintain strict hygiene practices in the growing area to minimize the risk of contamination. Clean and disinfect all tools and equipment regularly, and avoid shared tools between infected and healthy plants. We’re sure this is already a standard process in most grow rooms, however, it’s worth mentioning.

Insect control

Implement effective insect control strategies to prevent the transmission of viroids by aphids and other insects. This is another tactic already implemented by most cultivators. If you’re already doing several of these techniques, you’re on the right track!

Crop rotation

Rotate crops regularly to reduce the buildup of viroids in the soil. This can help break the transmission cycle and reduce the risk of new infections.

Early detection and removal

Regularly monitor the health of cannabis plants for any signs or symptoms of viroid infections. Prompt identification and removal of infected plants can help prevent the spread of the viroids to healthy plants. Although you are likely monitoring the health of your plants to detect nutrient deficiencies, should your plant seem unhealthy “for no reason,” it’s worth considering having your plant tested for viroids.

Plant breeding

Explore the development of disease-resistant cannabis strains through selective breeding programs. This can help create varieties that are less susceptible to Hop Latent Viroids and other diseases. Not all strains are affected the same. Breeding our way out of HLVd is more of a long-term solution, but if you’re up for it, consider it along with the strategies above.

Viroids: Challenge Accepted

Hop latent viroids may pose a threat to cannabis plants, leading to reduced yields, poor plant health, and compromised product quality. But understanding their characteristics, modes of transmission, and control strategies can help lead to the successful cultivation of a healthy and disease-free cannabis crop.

Through proactive measures such as consistent sanitation practices, quarantine SOPs, and regular monitoring, growers can minimize the risk of hops latent viroid infections and safeguard the sustainability of their operations. And although not all of these preventative measures are feasible for all cultivators, by doing your due-diligence growers can effectively reduce the impact of viroids on their cannabis crop.

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