Legal cannabis (Cannabis sativa L.) production in Canada, and in many U.S. states where cultivation is legal, for plants with high tetrahydrocannabinol (THC) levels has rapidly expanded. With the rise of cannabis producation as an industry, growers are now looking for solutions to the problem of destructive plant pathogens.

One such example is Hop latent viroid (HLVd). HLVd is a viroid – an infectious pathogen even smaller than a virus – that replicates inside the plant using the plant's machinery. HLVd severely affects the cannabis plant and leads to  stunted growth, reduced root development, smaller flowers and an overall reduction in THC, CBD and other cannabinoids and terpenes. These impacts result in significant yield and economic losses for commercial cannabis producers.

Additionally, HLVd affects the quality of cannabis products for medical and recreational users. Since its first detection in 2019, HLVd is estimated to have caused more than $4 billion in economic losses to the cannabis industry in North America.

Simon Fraser University researcher, Dr. Zamir Punja, has shown that HLVd moves readily between cannabis plants. It passes from parent plants to cuttings during propagation and can spread from the roots of one infected plant to another through root contact, via shared, contaminated nutrient solutions and through routine handling of plants and seeds. Consequently, this pathogen is difficult to manage.

A long-term solution to HLVd is to find cannabis genotypes that naturally resist infection and disease. Previous studies have shown that some varieties can limit the replication and spread of the viroid within infected plants. Under this project, Dr. Punja and sector partner PureSun Farms will examine the basis for the tolerance of these varieties to infection and identify the genes that provide this resistance. They will do this using genomic and transcriptomic analysis.

This research aims to reveal how certain cannabis varieties resist HLVd and to find genetic markers that can be used to screen breeding populations of cannabis plants for this trait. This approach will provide a long-term solution for PureSun Farms to reduce the spread of this destructive pathogen in commercially produced cannabis and minimize financial losses.