August 21, 2026
A cannabis crop infected by powdery mildew is a very costly problem for a producer. Even a light infection can cut yields by 20%. And because there are strict rules on the use of chemical pesticides in Canada, growers have had few good options for fighting back.
A four-year Genome BC and Genome Canada-funded research project between the University of British Columbia (UBC) and Aurora Cannabis has changed that. The team has identified a new source of genetic resistance to powdery mildew, a discovery that is already being bred into Aurora’s commercial cultivars.
Applying new tools to an old problem
Cannabis has been cultivated for millennia, but decades of prohibition meant it missed out on the breeding tools and genetic research that shaped crops like wheat or strawberries. When legalization arrived in Canada in 2018, growers were left to fight plant disease with limited genetic knowledge and few approved tools.
Powdery mildew, recognizable by the white, dusty patches it leaves on leaves and flowers, is one of the most damaging cannabis diseases that producers face. It spreads easily in the dense, large-scale indoor operations where most commercial Canadian cannabis is grown, and once established, it is difficult to eliminate.
“The main challenge was to actually find resistance, and that sounds simple, but it’s not,” said Dr. Jose Celedon, Principal Scientist at Aurora and co-principal investigator on the project. “You have to first develop a tool to infect the plants and find those that are resistant. It needs to be controlled. It needs to be reproducible. And after that, you need to sift through lots of different plants and germplasm.”
Building a genomic foundation for cannabis
The research team, led by Dr. Celedon from Aurora and Drs. Loren Rieseberg and Marco Todesco from UBC, set out to build the genetic infrastructure needed to tackle the problem.
The team sequenced and reconstructed the complete genome of 12 different cannabis plants, some of the most detailed genetic profiles ever created for the species. They then used that foundation to study a much larger and more diverse group: 537 cannabis lines, spanning commercial production strains, older legacy varieties and rare exotic strains. By comparing nearly seven million points of genetic variation across all of them, the team built the largest genetic resource of its kind ever created for cannabis.
“We grew more than 500 cannabis lines, representing most of the diversity in cultivated drug-type cannabis,” said Dr. Todesco, of UBC’s Department of Botany. “At Aurora’s R&D facility, we infected them all with powdery mildew and looked at which lines were susceptible and which were resistant.”
“Then we sequenced the genome of all these plants, so we had both pieces of information: which plants resisted the disease, and what their genomes looked like. Genome-wide association studies eventually led us to identify regions most likely responsible for that resistance.”
Follow up studies pointed to a single, previously unknown gene within the cannabis genome strongly associated with powdery mildew resistance. That gene has now been named PM2 and is strongly associated with powdery mildew resistance. The finding has been published in the peer-reviewed journal Frontiers in Plant Science.
From a discovery in the lab to plants in production
Finding a resistance gene was only half the job.
“The next question (was): is it heritable? Can we pass it from one generation to the next after a cross?” said Dr. Celedon. “That’s another big hurdle you have to get through. After that, you need to develop a genetic marker, and that’s what we did.”
Aurora is introducing PM2 resistance into its breeding lines. Lines carrying the resistance are now being trialed at production sites, with commercial cultivars expected to follow.
“For industry, the advantage of adding genetic resistance to powdery mildew is that you don’t need pesticides to control it,” said Dr. Todesco. “And I think, more importantly, it’s great for consumers and for the environment.”
Dr. Celedon believes this discovery will improve the consumer experience of their cannabis products. “It’s going to be a really transforming technology, once deployed at the commercial production level,” he said. “It’s going to mean healthier plants that are fully utilizing the nutrients and the lights we provide them to grow. It’s going to mean better product quality for consumers, once these plants are free of the risk of powdery mildew.”
Lana Culley, Vice President of Innovation and International Operations at Aurora, connects the discovery to the company’s broader research investment. “At Aurora, our team is advancing some of the most sophisticated cannabis genetics research in the industry,” she said. “The discovery of powdery mildew resistance, with support from Genome BC and UBC, will improve plant health, increase yields and reduce crop loss. It’s a meaningful step toward more resilient, efficient cultivation and a more consistent, high-quality supply of medical cannabis for patients globally.”
A resource to solve future problems
The genomic tools built for this project, the genome assemblies and the 537-line mapping population, will continue to provide benefits even after PM2 is bred into commercial lines. They remain available to search for resistance to other pathogens, or traits like aroma, and they are already seeding new UBC-Aurora collaborations in those areas.
“These genomic resources give BC’s cannabis sector a real advantage. This is what foundational investments in genomics can do: solve costly, hard-to-manage problems and equip a growing sector with the tools to keep building,” said Dr. Tony Brooks, Genome BC’s Interim President and CEO.
The work has also trained 19 students and researchers across UBC and Aurora and contributed genome assembly expertise to other projects, from Douglas fir to sunflower genomics. For a plant that has been grown by humans for thousands of years but studied by scientists for only a few, the PM2 discovery is a reminder of how much is still left to learn, and how much genomics can accelerate that process once the right tools are in place.
