Hop latent viroid (HLVd), a major threat to cannabis growers in the United States and Europe, is now under increased scrutiny as researchers seek ways to control its spread and develop resistant cannabis cultivars.

Natural Resistance in Some Cultivars

Some cannabis cultivars, such as Gelato 33, exhibit a natural resistance to HLVd, though the factors contributing to this resistance remain unclear. Viroids are ancient RNA remnants, but HLVd, first identified in 1987, causes significant problems for cannabis growers by mutating plants, stunting growth, and reducing THC levels. According to a study in the journal Viruses, HLVd results in $4 billion in losses annually for cannabis growers.

How HLVd Spreads

HLVd is highly contagious and can be spread through tools used for harvesting, shared water, or insects. It can also exist on or within seeds for extended periods, with HLVd detected on cannabis seeds stored for over two years.

Studying Pest Resistance

Researchers are still working to understand how to stop HLVd and potentially make cannabis plants resistant. Zamir Punja, a professor of biological sciences at Simon Fraser University, notes the lack of data on what makes certain cannabis strains more resistant to HLVd. Concerns also exist about viruses from other crops potentially infecting cannabis.

Prevention in Practice

Rob Baldwin, VP of cultivation and greenhouse operations for Pure Sunfarms in Vancouver, highlights the importance of testing and sanitation to prevent HLVd spread. Pure Sunfarms tests all mother plants to avoid transmission.

Identifying HLVd Susceptibility

Cannabis cultivars vary in their susceptibility to HLVd. Some strains show no symptoms initially but may present them later in their life cycle. Research has revealed that testing plants post-propagation is most predictive of whether they will exhibit severe symptoms. For instance, the Illemonati cannabis strain had high levels of HLVd but showed no symptoms.

Resistant Cultivars

Cultivars like Gelato 33, Motorhead, and Oreoz demonstrated low levels of HLVd after three weeks, while others like Chilled Cherries, Purple Milk, and Wedding Pie showed high levels of infection. Researchers aim to identify genes responsible for HLVd resistance, potentially using Crispr-Cas9 gene-editing technology to develop resistant strains.

Cannabis Gene Editing

Gene editing could involve removing or altering specific DNA sequences to enhance resistance. Previous studies have shown success in using Crispr for virus resistance in plants by targeting viral genomes or enhancing plant immunity.

Stopping HLVd Spread

For now, intensive testing, facility sanitation, and eradication of infected plants are essential. Pure Sunfarms reduced HLVd incidence from 25% to 1% in eight months using these methods. Baldwin emphasizes the need for further breeding to incorporate disease resistance into cannabis strains.

Collaboration for Future Resistance

Saldi suggests that collaboration among researchers could achieve viroid resistance in approximately five years. The unpredictable nature of science means that some progress may come down to luck in finding and altering the relevant genes.

Efforts to understand and combat HLVd are ongoing, with promising developments in identifying resistant cultivars and potential gene-editing solutions. Continued research and collaboration are crucial to protecting cannabis crops from this pervasive threat.