HLVd: The Culprit of Cannabis Crop Failure & Dudding
You’ve taken all the right steps, given the right fertilizers, had your plants on a perfect watering schedule, and yet, your plants are not showing the same results you’ve seen in the past. Don’t fret though, it’s not you, it’s your plants. Cannabis and hops are two commercially important crops that are susceptible to many of the same pathogens. This is because they are both in the same taxonomic family and could be thought of almost as cousins.1 Of particular interest in recent years is hop latent viroid disease, more commonly known as HLVd, which has only in the past two years been identified as the causative agent of a condition known as “dudding”.2 This is characterized by brittle stems, malformed leaves that are yellow or curled, horizontal plant growth, as well as reduced trichome and flower growth in cannabis plants.2
All of these symptoms can have severe negative impacts on the quality and volume of the final product. However, not all plants exhibit these symptoms and as the name implies, the disease can lay latent in plants over a long period of time, showing no signs of infection.3 HLVd is difficult to detect on a molecular level due to its nature as a viroid, and because viroids do not produce proteins, standard antibody tests are not effective for detection.4 Polymerase chain reaction (PCR) is the only reliable method of determining whether or not a plant is harbouring HLVd. Fortunately, natural transmission rates are low and there is no evidence of insect borne transmission. Although mother plant to seed transmission has been identified in hops, only around 8% of the seeds will be infected.5 The most common means of transmittance is improper sterilization of tools between individual plants.3
Economic Importance of HLVd Detection
Cannabis is a $2.6 billion dollar industry in Canada alone and the market continues to grow every year.6 In fact, just between 2019 and 2020, adult cannabis sales increased by over 100%.6 Although cannabis is quite a lucrative industry, a mere 1% loss due to damages equates to $26 million in lost revenue. Distressfully, a recent study showed HLVd infection rates between 25% and 50% in almost all nurseries sampled.3 Even though not all plants are symptomatic, loss rates are likely much higher than 1%. The potential economic impact of HLVd is tremendous. To put it in perspective, a 25% infection rate could result in $650,000,000 in lost revenue, which is equivalent to the cost of 1,400 brand new Lamborghini Aventadors or ten G650 private jets.
How to Test for HLVd
HLVd does not produce proteins and can lay dormant for long periods of time in infected plants without causing any symptoms.3,4 Being extremely small at only around 250 base pairs in length, this diminutive size is made even smaller due to the circular, internally paired form they take.2 These factors can make early detection extremely difficult. Fortunately, highly sensitive capture and detection methods exist. In general, extraction methods that rely on silica have a capture cut off point of around 200 base pairs.7 This can be an issue in terms of isolating HLVd particles as they are only slightly larger than this cut off, so any degradation of a piece could potentially mean that a segment of viroid genetic material may be lost as flowthrough. Silicon-carbide extraction methods, on the other hand, show no such bias and efficiently capture every piece of RNA present in the sample regardless of size or G/C content.8 This purified RNA can then be subjected to either qPCR or end-point PCR depending on the equipment available. TaqMan RT-qPCR is an efficient and effective method for high throughput sampling that also tells the degree of infection in the plant. It may also be helpful to know the sequence of the pathogen infecting your plants. This can be accomplished through Next Generation Sequencing (NGS) techniques, such as the Illumina system, which quickly provides the sequence of your amplified genetic material. In the case of an infected plant being identified, the unfortunate recommendation is to segregate and destroy the plant to prevent further infections to your crop, while testing the remaining plants that were grown nearby. If the infected plant is absolutely vital to your operation, there have been cases where the viroid has been eliminated from the plant through careful tissue culturing.
HLVd is a threat to the cannabis industry and could cause severe issues down the line if it is not dealt with properly. In order to detect HLVd, a PCR reaction must be performed on a plant tissue sample, preferably after an RNA isolation procedure. The isolation offers increased sensitivity which can be important, as the presence of the viroid may be minimal in the infected plant. If you require HLVd testing, check out Norgens HLVd Detection Kits. Weed love to help!View References
Pillay, M., & Kenny, S. T. (2006). Structural organization of the nuclear ribosomal RNA genes in cannabis and Humulus (Cannabaceae). Plant Systematics and Evolution, 258(1-2), 97–105. https://doi.org/10.1007/s00606-005-0396-3
Warren, J. G., Mercado, J., & Grace, D. (2019). Occurrence of Hop Latent Viroid Causing Disease in Cannabis sativa in California. Plant Disease, 103(10), 2699–2699. https://doi.org/10.1094/pdis-03-19-0530-pdn
Cabrales, J. (2021, March 5). Hop Latent Viroid, Part Two. Dark Heart Nursery. https://darkheartnursery.com/news/hop-latent-viroid-part-two/
Ryu, W.-S. (2017). Subviral Agents and Prions. Molecular Virology of Human Pathogenic Viruses, 277–288. https://doi.org/10.1016/b978-0-12-800838-6.00020-5
Matoušek, J., & Patzak, J. (2000). A Low Transmissibility of Hop Latent Viroid through a Generative Phase of Humulus lupulus L. Biologia Plantarum, 43(1), 145–148. https://doi.org/10.1023/a:1026531819806
Hasse, J. (2021, April 14). Canada cannabis sales doubled in 2020, HITTING $2.6 Billion: Here's what's next. Forbes. https://www.forbes.com/sites/javierhasse/2021/04/14/canada-cannabis-sales-doubled-in-2020-hitting-26b-heres-whats-next/
Schmitz, T. C., Dede Eren, A., Spierings, J., Boer, J., Ito, K., & Foolen, J. (2020). Solid‐phase silica‐based extraction leads to underestimation of residual dna in decellularized tissues. Xenotransplantation, 28(1). https://doi.org/10.1111/xen.12643
Diefenbach, R. J., Lee, J. H., Kefford, R. F., & Rizos, H. (2018). Evaluation of commercial kits for purification of circulating free dna. Cancer Genetics, 228-229, 21–27. https://doi.org/10.1016/j.cancergen.2018.08.005