Scientists probe DNA to create game-changing strain of mildew resistant cannabis

University of B.C. researchers are on the hunt for genes that protect cannabis from the destructive ravages of powdery mildew, which will be a game-changer for commercial growers.

Loren Rieseberg and Marco Todesco are comparing the natural resistance with four mildew strains in about 500 different cannabis cultivars maintained by Aurora Cannabis.

“These are the strains of mildew that are commonly found in Canadian greenhouses,” said Rieseberg.

Grey mould — known in the industry as bud rot — can quickly devastate a cannabis crop. Only a tiny fraction of infected plants will recover from an infection.

Although the project will require massive computing power to sort through genetic information, finding candidate cultivars is relatively simple.

“You just infect the plants by sprinkling them with mildew spores and see if they become diseased,” he said.

Once the researchers identify the most resistant cannabis varieties, they will sequence the genomes of the best candidates and compare them with identified genes and genetic variants associated with resistance. The genetic variants that are strongly associated with broad resistance to mildew and specific resistance to the most damaging mildew strains can quickly be incorporated into Aurora’s breeding program.

“Cannabis is a terrible crop in the sense that it’s not particularly resistant to disease and insects,” said Rieseberg.

The focus of breeders has always been to make cannabis a more potent intoxicant rather than making a resilient plant. As a result, the most highly prized strains of cannabis are relatively feeble plants, requiring strict control of light and humidity usually in a greenhouse-like environment.

Better cannabis strains would greatly reduce losses due to disease, according to a statement from Genome B.C.

The $4.2-million project — Fast-Track Breeding of Powdery Mildew-Resistant Cannabis — is jointly funded by Aurora, Genome B.C. and Genome Canada.

Because cannabis is ingested or inhaled, commercial growers are forbidden from using most chemical pesticides, and testing for residues of those products is strict.

“For something like powdery mildew, there is a strong incentive to develop really strong genetic resistance,” he said.

Studies of illicit cannabis have found pesticide residues, heavy metals and microbes in products intended to be smoked or eaten.

Commercial growers are reluctant to use genetic engineering to introduce desired traits into their crops, anticipating resistance to genetically modified organisms in their target markets, Rieseberg said.

The genomic data from the project will be made public for other researchers to use. The same sequences used to find genes associated with mildew resistance could also be used to identify and enhance other traits.

“I’ve been told by cultivators that different strains require different growing conditions, but obviously it would be more efficient if they could all be grown the same way,” he said. “The idea would be to make it into a crop more like tomatoes.

“Right now we are focused on mildew, because that is the industry’s biggest problem, but once the genomic data is developed, you could apply it to any sort of trait you want to target,” he said.

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