How Does Hop Latent Viroid (HLVd) Spread?
Professor DeBacco

CannaMed23 Presentation
Medicinal Genomics. (2023a, June 8). Understanding and Managing HOP latent viroid in cannabis - Zamir Punja, PhD [Video]. YouTube.    • Understanding and Managing Hop Latent...  

How Does HLVd Spread?
Mechanical damage (ex. Trimming)
Sap contact
Grower is the most common vector
Insect vectors still not well understood
If you are trimming one and move to the next you have just inoculated (infected) the next plant.
Root contact
Viral load is high here
Seeds

Potential Routes of Transmission…
Through the water
Roots
Growing substrate
Irrigation tube
Warning for DWC, Clone trays, Flood and Drian… really any operation that recirculates water.
HLVd is very stable in water as it can survive for 7 days

Phloem Transmitted
Entry into the phloem is what allows it to move up and down the plant
Xylem is mainly a roots to shoot movement
It follows the sugars, and does translocate throughout the entire plant in about 6-weeks.

Experiment by Zamir Punja, PhD
Stem cut made
Viroid inoculated at wound site
2-weeks post inoculation it can be detected in the roots
Upper stem to roots
4 and 6 weeks post infection the entire plant becomes infected

Experiment by Zamir Punja, PhD
What is interesting is the path of infection which is based on a stem top inoculation
Roots are the first point it is observed
Then the other top growing tips
Lastly the lower leaves/branch area show positive of HLVd

Experiment by Zamir Punja, PhD
Viroid travels down first to the roots (indicating the phloem transmission) and then spreads to the apical meristem followed by full plant infection.
Flowering Can Increase Viroid Load
The stress of flowering can increase the amount of viroid that is present in the plant.
This only shows the importance of testing a plant multiple times as early in veg it could be below detectable levels.
However, testing in veg is still important as if a positive is found that plant should be removed, but just because it tested negative early on following up with another test during flower would be advised.

Water Transmitted
This is in part how it can travel so fast through a growing operation.
Plants that do not even come in contact with one another can spread the infection via water transfer contact.
Any recycling of water is at risk but two common ways this can occur…
Cloner transfer based only on water
Flood and drain growing


Infected Mothers
Since the viroid is systemic to the plant cloning a plant will produce many (infected) offspring.
This is why testing and retesting of mother plants is so important.
All cuttings pictured tested positive for HLVd infection

Seed Transmitted
When the female plants are infected this can increase the odds (percentages) of the seeds infected.
Most of the HLVd found on the outside of the seed coat.
10-15% infection can still be found on the inside of the seeds.
If the seedling (typically cotolyedon) has any physical damage the HLVd can easily enter into the plant from the seed coat.

Present in Dry Flower
40% sampled from dispensaries
Also, found in male flowers
Glove Transmission
Survives as sap on gloves up to 5 days at room temperature

Leaf Transfer
Can survive up to 4-weeks so be sure to clean and remove leaves that are being trimmed.

Root Tissues
Very stable viroid
Heating to 70C (158F) for 30min did not destroy the RNA
Male Flowers?
At this time there is no evidence that HLVd can be present in pollen.

Link to Lecture Slides: https://drive.google.com/file/d/1SHU0...

*Due to the description character limit the full work cited for "How Does Hop Latent Viroid (HLVd) Spread" can be viewed at... https://docs.google.com/document/d/1R...