Cannabis sativa: From Therapeutic Uses to Micropropagation and Beyond

Abstract

The development of a protocol for the large-scale production of Cannabis and its variants with little to no somaclonal variation or disease for pharmaceutical and for other industrial use has been an emerging area of research. A limited number of protocols have been developed around the world, obtained through a detailed literature search using web-based database searches, e.g., Scopus, Web of Science (WoS) and Google Scholar. This article reviews the advances made in relation to Cannabis tissue culture and micropropagation, such as explant choice and decontamination of explants, direct and indirect organogenesis, rooting, acclimatisation and a few aspects of genetic engineering. Since Cannabis micropropagation systems are fairly new fields, combinations of plant growth regulator experiments are needed to gain insight into the development of direct and indirect organogenesis protocols that are able to undergo the acclimation stage and maintain healthy plants desirable to the Cannabis industry. A post-culture analysis of Cannabis phytochemistry after the acclimatisation stage is lacking in a majority of the reviewed studies, and for in vitro propagation protocols to be accepted by the pharmaceutical industries, phytochemical and possibly pharmacological research need to be undertaken in order to ascertain the integrity of the generated plant material. It is rather difficult to obtain industrially acceptable micropropagation regimes as recalcitrance to the regeneration of in vitro cultured plants remains a major concern and this impedes progress in the application of genetic modification technologies and gene editing tools to be used routinely for the improvement of Cannabis genotypes that are used in various industries globally. In the future, with more reliable plant tissue culture-based propagation that generates true-to-type plants that have known genetic and metabolomic integrity, the use of genetic engineering systems including "omics" technologies such as next-generation sequencing and fast-evolving gene editing tools could be implemented to speed up the identification of novel genes and mechanisms involved in the biosynthesis of Cannabis phytochemicals for large-scale production.

Keywords: cannabinoids; in vitro organogenesis; medical marijuana; plant growth regulators; plant tissue culture; tetrahydrocannabinol.

Figure 1

(A–C) Large-scale conventional cultivation of Cannabis leading to tissue culture. (A) Large greenhouse for the growth of Cannabis at the Cannsun Medhel™ facility in Atlantis. (B) Various different growth stages of the Indica variety. (C) A 2-month-old mature Lesotho Swazi ready for the flowering stage. (D) Cannabis seed explants grown on an agar-based medium for tissue culture. Cannabis leaf morphology (E,F): (E) Cannabis var sativa; (F) Cannabis var indica.

Figure 2

Analysis of Cannabis literature (Web of Science). (A,B) Analysis of Cannabis literature in terms of years and number of publications published. (C) Pie chart showing an analysis of Cannabis micropropagation literature in terms of publication type and percentage of publications published. (D) Analysis of Cannabis micropropagation literature in terms of country and percentage of overall of publications published.