Balthazar, C., Novinscak, A., Cantin, C., Joly, D. L., Filion, M. (2022). Biocontrol activity of Bacillus spp. and Pseudomonas spp. against Botrytis cinerea and other Cannabis fungal pathogens. Phytopathology. DOI: https://doi.org/10.1094/PHYTO-03-21-0128-R
Pathogens kind of suck
Bud rot. Wilt. Grey mold. These words strike fear into the hearts of Cannabis growers everywhere. Very few commercial sprays are labeled for use in Cannabis, especially for organic growers. Contact fungicides can leave residue on leaf and bud material, rendering it potentially dangerous.
For persons who consume Cannabis for medical needs, the contamination of material with potentially unsafe chemicals can be life threatening. This means the best option for growers lies in either plant extracts or biocontrol methods.
For proper control of fungal pathogens, one most begin with correctly identifying the pathogen.
One problem with using biocontrols or plant extracts is that their activity can be limited to certain fungal species only. Fungal identification often needs to be confirmed using microscopic imaging and is difficult to do with the naked eye.
In addition, different fungal pathogens can produce very similar symptoms, further complicating identification. Because of these issues, broad spectrum fungicides are preferred by growers.
So what’s up with biocontrol?
In this paper, the authors screened several Bacillus and Pseudomonas species for biocontrol potential against a panel of 10 pathogens.
The pathogens selected represent some of the major fungal pathogens for both indoor and outdoor growers, including the genera Botrytis, Fusarium, Nigrospora, and Alternaria.
To test the effectiveness of the bacterial biocontrol agent, the authors performed petri dish trials to test inhibition. The authors inoculated plants with pathogens and assayed the effectiveness of the bacteria in planta as well.
Of the bacteria tested, six strains showed inhibition for most or all the pathogens assayed in petri dishes. Of the six strains, four were Bacillus species and two were Pseudomonas species. For the in planta trials, the authors report decreased disease severity when plants were treated with B. velazensis, B. subtilis, or P. protegens.
To ensure the safety of the biocontrol agents when used on consumable material, the authors did a genome dive to search for pathogenic genes. None of the bacteria used in the study had genes related to toxicity in humans when compared to known pathogenic strains of the bacteria.
That’s cool man, why should I care about this paper?
This study is the first to show the effective biocontrol of grey mold in Cannabis. The results agree with trials on different crops using different Bacillus or Pseudomonas strains.
Importantly, the authors applied the biocontrol agent as a preventative before infection. This means if you already see the pathogen, you may be too late to treat and must switch to salvage mode.
Biocontrol should be a part of a disease suppression program and not the only answer.
Ensuring proper ventilation, humidity, air flow, and plant nutritional status will also help with curbing infections.
A regular scouting program should be used to check plants for signs of disease and quarantining new or infected plants is the best way to help stop the spread.
