Note: This is the third post of a three part series. The first is an introduction to the pathogen and its biology, the second covers management practices and identifying it in the garden, and the third covers research Dark Heart Nursery that is doing and some commonly asked questions about HpLVd.
Part III: Research
There is not a lot of published research about HpLVd in cannabis. One of Dark Heart’s goals is to do some research to answer some fundamental questions about the disease. Some of these questions are: is HpLVd present in pollen? If it is present in pollen, can that cause seed infections? What is the seed transmission rate, and does it differ between the female or male being the infection source? How many plants can be infected from contaminated shears? How large of an impact can HpLVd have on yield and quality? How long is HpLVd infectious outside the plant? Are there other pathways of infection that are important?
DHN now has dedicated research space at its Half Moon Bay facility. We are currently working on a contaminated pruning shear experiment in the greenhouse, with three replicates of ten plants that were sequentially pruned after pruning a HpLVd infected plant. We are screening the plants weekly for viroid infection, and so far, it looks like shears can transmit HpLVd out to the eighth plant. More importantly, infected plants may not have detectable levels of the viroid until week seven. We will take the experiment through harvest and compare yield and quality metrics with infection dates. We will post an update when those results are finalized.
We also have a dedicated plant breeder, Dr. Kay Watt. Our lab is working with her on the breeding aspects of HpLVd, including pollen infection and transmission, and seedling infection rates by parentage. She will be guiding us through pollen collection and seed production in a parallel but separate space. We must be extremely careful both with pollen production in general and particularly with HpLVd infected plants.
One interesting anecdote we have heard several times is the following scenario: a facility that has cleaned up their garden and has no positive tests for months finds one or two positive plants. No new plants have been introduced, and greenhouse sanitation practices are followed. Where is the viroid infection coming from? Our theory is infected bud. We have tested dried bud samples from dispensaries, and some have tested positive for the viroid. We then used positive dried bud to mechanically inoculate cannabis plants and was able to cause infection. Then we handled positive dried bud and touched healthy cannabis plants, and this also caused infection in the plants. These results suggest that a person can handle infected bud then infect plants in the garden. This is another reason to require hand washing before entering grow spaces, and not allow smoke breaks during work hours.
Taken together, we hope to publish results from all the experiments in a peer-reviewed journal later this year. None of this research is very enthralling but is important for better understanding the epidemiology and impacts of HpLVd in cannabis cultivation. Have ideas for other HpLVd experiments? Send us an email!
Is HpLVd seed transmitted?
Yes. It is not always present in each seed from an infected mom but seems to be transmitted to about 5% of the seedlings. More research is needed for seed transmission rates.
Is HpLVd transmitted through irrigation water?
In general, no. HpLVd is a naked RNA molecule and doesn’t last long outside a living host. There are lots of RNA degrading enzymes in the environment, and UV light quickly degrades it.
Is HpLVd in the air?
Again, no. It doesn’t aerosolize and infect new plants through air flow, again because it is so easily broken down.
How long is HpLVd infectious on surfaces?
Since HpLVd is a naked RNA molecule outside of plant hosts it is degraded quickly, and HpLVd on surfaces, such as benches and pots, is likely noninfectious within two hours.
Can plants rubbing together spread it?
Yes, this can happen, especially when there is vigorous movement that causes bruising or if plants rub across the same surface. It won’t be the cause of a big outbreak in the facility but will cause a cluster of infected plants.
How often should I test plants?
For mother plants of strains that you have had for a while, test all moms before starting to propagate. Cull all positive plants, and repeat testing every two weeks until no additional positive plants are found. When purchasing new plants, test when they arrive, again at two weeks, and once more at four weeks. For large production facilities that buy clones, test approximately 5% of shipments upon arrival and expand testing if HpLVd is detected.
If I find it in my garden, what should I do?
This is situation dependent. If it is in production plants, take extra care to not transmit it further. Terminating the plants will decrease yield more effectively than HpLVd infection, so your goal is to mitigate the impact. Increase sanitation practices and minimize plant handling. Work with infected plants after the rest of the garden. If it is found in mother plants, destroy those immediately and test all other mothers of the infected strain. There is not way to cure greenhouse plants of infection, so cull all infected plants to save the healthy plants.
How do I get my plants tested for HpLVd?
DHN diagnostic services offer HpLVd testing as a stand-alone test or as part of a panel with LCV and BCTV. We have a submission form and instructions to help you through the sampling and shipping process. Please email firstname.lastname@example.org to get those documents. Pricing available upon request.
How do I clean up my favorite strain?
DHN offers tissue culture services. To remove HpLVd infection, we offer meristem tissue culture. If you want a healthy strain revitalized, we also offer nodal tissue culture. Please email email@example.com to discuss starting a TC project. We can offer TC services to licensed California growers.