Hop stunt viroid (HSVd) is a small RNA plant pathogen that affects a variety of economically important crops, including cannabis. HSVd is a member of the family Pospiviroidae, which contains some of the smallest known plant pathogens. Although HSVd and Hop Latent Viroid (HLVd) are both viroids that were first identified in hop, they are more like distant cousins than close relatives, with HLVd being classified in the Cocadviroidae family. Currently, HSVd infection of cannabis does not appear to be as severe or as widespread as HLVd, but in the case of a high value crop such as cannabis, even small decreases in yield can lead to large revenue losses, making it crucial for cultivators to ensure their crops are free of such diseases and pests.
Much of what is known about HSVd infection comes from hop, as (to our knowledge) no studies on HSVd infection in cannabis have been released. Symptoms of HSVd infection in hop plants include stunted growth, reduced yield and a decrease in α- and β-acids. A recent study by Kappagantu et al (2017) found that while certain hop cultivars showed >50% reductions in yield due to HSVd infection, other cultivars were completely unaffected. It is unclear, however, how this information translates to cannabis, as a close relative of hop.
We know is that HSVd can infect cannabis, but we do not have data on the symptoms it causes, or if there is cultivar-specific resistance. We also know that HSVd is not as widespread as it’s cousin, HLVd. Until more is known about this viroid, it is best to proceed cautiously. If your plants appear stunted in growth or if flowers are undersized, it is a good idea to send a sample to a lab that tests for HSVd. Regular testing for HSVd is also an option, but one must keep in mind that (as for hop) some plants could be unaffected by HSVd, despite presence of the viroid.
To prevent the spread of HSVd, it is important for cannabis cultivators to follow strict sanitation protocols and implement quarantine procedures for new plant material. This can include sterilizing equipment, washing hands and utilizing appropriate personal protective equipment. Additionally, the use of healthy, disease-free seed or clones is critical in reducing the risk of HSVd infection. Unlike in hop, there are currently no known cultivars with natural resistance to HSVd, so the best way to source healthy material is to start with plants derived from meristematic tissue culture.
In summary, Hop Stunt Viroid is a small but potentially damaging plant pathogen that may impact the cultivation of cannabis. Strict sanitation protocols and healthy starting material can help to prevent its spread, but once infected, the only was to remediate plants with HSVd infection is through meristematic tissue culture. As more is learned about the impact of this viroid on cannabis, it is important for cultivators to be vigilant and take steps to prevent the introduction of HSVd into their growing operations. These measures will help prevent the spread not only of HSVd, but also other viroids, viruses, fungal and bacterial pathogens, and is critical to growing the healthiest, highest yielding crop possible.
Kappagantu M, Nelson ME, Bullock JM, Kenny ST, and Eastwell KC (2017) Hop Stunt Viroid: Effects on Vegetative Growth and Yield of Hop Cultivars, and Its Distribution in Central Washington State. Plant Dis., 101:607-612.