UBC researcher identifies new kind of root rot affecting cannabis plants

| David Brown

Researchers at UBC Okanagan (UBCO) recently identified a new type of disease affecting the roots of cannabis plants.

The paper, published in early 2023, is the first to report on the fungal plant-pathogen Berkeleyomyces rouxiae, commonly known as black root rot, infecting non-hemp cannabis plants. 

The plants, which had been displaying root discoloration and rot symptoms, did not test positive for any of the usually associated pathogens. This led Delaney Bray-Stone, an employee at the production facility, to reach out to a former grad school classmate, Chris Dumigan, now a Plant Microbiologist and PhD Candidate at UBCO, for help.

Dumgian says the problem, resembling a “black sludge,” had spread through much of the facility and, had caused crop loss and even equipment loss. While it resembled other forms of “root rot” like Fusarium that is often associated with indoor cannabis crops, he says this was obviously not the case.

When conventional methods of reproducing and proving the origins of the pathogen didn’t work, Dumigan ended up making a medium out of blended carrots from his kitchen, successfully reproducing the same fungal rot overnight.

He then sequenced the genome of the pathogen and re-inoculated several cannabis plants to again confirm he had the right suspect. Interestingly, through this inoculation process, he says he and Bray-Stone noticed some cultivars were more or less resistant to the pathogen, something he would like to see a further investigation of.

Once identified, he was then enabled to begin looking at how to treat the issue. Commercial cannabis growers in Canada are limited to a list of approved pest and disease control methods, and the usual treatments for similar diseases weren’t working. Instead, Dumigan began investigating new, novel ways to treat it with biological controls. 

He found several species of bacteria that live within the roots and secrete compounds that can kill certain fungi. As part of Dumigan’s thesis, he has a library of hundreds of bacterial and fungal endophytes that have been isolated from different hemp and other cannabis cultivars that aid in plant health—something he hopes to develop further and publish in the future. 

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He and Mike Deyholos, head of Biology at UBCO, also released the genome sequences of the black sludge to help other growers and researchers better identify it, ideally much earlier. 

“The idea behind making a sequence-based diagnostic is to be able to detect it based on wastewater from a hydroponic facility or an aeroponic facility and then you test it and monitor pathogen levels. You could be able to detect it before it becomes a real problem.

“The issue is that this is a pathogen many in the industry haven’t yet been looking for, causing people to use inaccurate treatments because they are assuming it’s something they’re familiar with, like Fusarium. 

“They couldn’t detect what this was because they didn’t know this was a cannabis pathogen so they didn’t have any tests for it, and they didn’t have any genomic information to make a specific primer test for it. I bet others in Canada have seen this.  

“It’s likely a lot more widespread than people know, but it’s just not been classified as a cannabis pathogen so it’s flown under the radar.”