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What are the effects of growth-promoting rhizobacteria on cannabis cultivation?

The beneficial phytomicrobiome is a sustainable approach with the potential to enhance plant growth. While it has been evaluated for a number of crop species, it has not for Cannabis sativa. An important challenge in the cannabis industry is achieving a high yield with minimum input for indoor production. Therefore, a recent study, conducted by McGill University’s Department of Plant Science, evaluated three individual plant growth-promoting rhizobacteria (Bacillus sp., Mucilaginibacter sp. and Pseudomonas sp.) on the root development and subsequent plant growth of cannabis cuttings. The hypothesis tested was that the application of plant growth-promoting rhizobacteria would improve the rooting speed of cuttings, yield attributes, and physiological variables.

What are rhizobacteria?
Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria, usually isolated from soil associated with host plants or their roots. The PGPR can improve nutrient availability and trigger hormone production (Lyu et al., 2020, Shah et al., 2021), improving root development and increasing plant enzymatic activity (Fan et al., 2020, Lyu et al., 2020); these effects have been verified across various crops. However, there have been only a few research reports regarding the application of PGPR resulting in effects on final cannabis yield and chemical profile. In the context of cannabis production, PGPR inoculation can be a sustainable and inexpensive (economic) practice to enhance plant growth.

Improving early root development.
This new study found that in the vegetative stage, cuttings treated with bacteria showed different levels of root morphological responses. Treatment with each of the three bacteria enhanced root length per initial cutting weight. The highest value of root length/initial cutting was for cuttings treated with Pseudomonas sp. (240.06 cm g-1), which was 1.32 times longer than the control. Root length per initial cutting weight was increased by 12.96% and 17.48% compared with the control, in response to Bacillus sp. or Mucilaginibacter sp. inoculation, respectively.

Increased flower number
At harvest, flower weight was increased by 5.13%, 6.94% and 11.45%, compared to the control, for plants inoculated with Bacillus sp., Mucilaginibacter sp. and Pseudomonas sp. respectively. However, the plant height, node number, branch number and leaf area of plants treated with plant growth-promoting rhizobacteria were rarely different from the control group. Inoculation with Pseudomonas sp. resulted in the greatest increase in photosynthetic rate during the vegetative and reproductive growth stages, and harvest index, while Bacillus sp., and Mucilaginibacter sp. increased flower number and axillary bud outgrowth rate.

Lyu, Dongmei & Backer, Rachel & Smith, Donald. (2022). Three plant growth-promoting rhizobacteria alter morphological development, physiology, and flower yield of Cannabis sativa L.. Industrial Crops and Products. 178. 114583. 10.1016/j.indcrop.2022.114583. 

To read the complete study, go to


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