Three plant growth-promoting rhizobacteria alter morphological development, physiology, and flower yield of Cannabis sativa L.

The beneficial phytomicrobiome is a sustainable approach with the potential to enhance plant growth; it has been evaluated for a number of crop species, but not for Cannabis sativa. The legalization of cannabis and awareness of its end-use applications has resulted in the renewed consumer demand. An important challenge is achievement of high yield with minimum input for indoor production. This study evaluated three individual plant growth-promoting rhizobacteria (Bacillus sp., Mucilaginibacter sp. and Pseudomonas sp.) on the root development and subsequent plant growth of cannabis (cv. CBD Kush) cuttings. The hypothesis tested was that the application of plant growth-promoting rhizobacteria would improve rooting speed of cuttings, yield attributes, and physiological variables. When compared with control plants (mock inoculation with MgSO4), plants inoculated with plant growth-promoting rhizobacteria increased root length at the vegetative stage. At harvest, flower fresh 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. Because cannabinoids composition is the one of most important attributes of cannabis flowers, future research should investigate the effects of plant growth-promoting rhizobacteria on flower secondary metabolite profile at harvest.