Cannabis growers entered the field in relatively new territory as they navigate through legal, medical, and breeding terrains that have never been explored before.
Although it is one of the first plants domesticated by humans, what makes growing cannabis difficult is the persecution and destruction that wiped out many medicinally and industrially viable cultivars. The biggest obstacles to researching cannabis on an academic level are still the legal hoops one must jump through to be able to work with the plant. Growing hemp is still regulated, but it’s considerably easier to obtain permits.
Breeding research has been further complicated by farmers selectively cultivating plants to produce more delta-9-tetrahydrocannabinol (THC). The body of scientific literature available to breeders is currently lacking for the study of cannabis as a holistic plant. Instead, the bulk of current research tends to focus on individual cannabinoids for specific therapeutic uses.
Traditional industrial uses of cannabis have typically focused on biofuels or hemp fiber production for textiles like clothing and rope. Medicinal use has often focused on cannabidiol (CBD) and THC, although this is certainly changing as more research is published on cannabidiolic acid [1], cannabigerolic acid [1], cannabichromene [2], and cannabinol [3], in addition to flavonoids and compounds in cannabis stalks and roots. Much more research exists regarding terpenes, since they are ubiquitous in nature, i.e., in many other legal plants, however, research on cannabis-derived terpenes is fairly scant, as well as tetrahydrocannabinolic acid, or the nutritional benefits of raw cannabis.
Breeding for Specific Physiological Traits
Some of the emerging literature shows specific cannabis cultivars can replicate different physiological traits, including stem size, leaf pattern, flower yield, and distribution of cannabinoids within the plant. [4] For example, flower weight correlated with plant height and stem width, but not with the time it took until the plant was considered mature. Plant height and stem width demonstrated correlation with growth rate during reproductive and vegetative stages; the size of the plant when planted; the amount of elapsed time before the effects of daylight change was observed; growth deceleration; and the amount of time between short daylight growing conditions and growth termination.
This research group also devised an equation to use for predicting flower weight based on inputs from the vegetative stage. Ultimately, the team reported that selecting for taller and faster growing plants would lead to increases in flower yields.
As more countries and research opportunities emerge, we expect more research and development will become available for breeders and researchers alike. In addition, many hope expanding the range of cannabis cultivars will allow more production into older types of industrial output. For example, applications for breeding low cannabinoid (CBD and THC) cultivars have been submitted for use in biofuels, fibers, and livestock feed. Time will tell if these applications will be profitable, but there’s hope for this because cannabis is more environmentally sustainable than many other crops.
References
[1] van Breemen RB, Muchiri RN, Bates TA, et al. Cannabinoids block cellular entry of SARS-CoV-2 and the emerging variants. J Nat Prod. 2022;85(1):176-184. [journal impact factor = 4.05; times cited = 8][2] Udoh M, Santiago M, Devenish S, McGregor IS, Connor M. Cannabichromene is a cannabinoid CB2 receptor agonist. Br J Pharmacol. 2019;176(23):4537-4547. [journal impact factor = 8.739; times cited = 35]
[3] Russo EB, Marcu J. Cannabis pharmacology: The usual suspects and a few promising leads. Adv Pharmacol. 2017;80:67-134. [journal impact factor = 4.81; times cited = 160]
[4] Naim-Feil E, Pembleton LW, Spooner LE, et al. The characterization of key physiological traits of medicinal cannabis (Cannabis sativa L.) as a tool for precision breeding. BMC Plant Biol. 2021;21:294. [journal impact factor = 4.14; times cited = 6]
Image Credit: Tim Fisher, Unsplash
