By Dr. Cindy Orser | Chief Science Officer of Digipath Labs
The in vitro sterile micropropagation of plants in tissue culture provides an option for preserving plant germplasm for the future; however, the likelihood of somaclonal variation, where the desired genotype is not strictly maintained, has been a drawback for the past decades. Somaclonal variation is commonly observed in plant tissue culture where plants are often regenerated from callus tissue. This non-fidelity in DNA is often the result of chromosomal rearrangement in the form of changes in chromosome numbers, both ploidy and aneuploidy, chromosome structure and actual DNA sequence as well as epigenetic events, that can affect both qualitative phenotypes as well as genetic quantitative traits.
Nonetheless, tissue culture is the future of the commercial cannabis industry because it duplicates the mother plant’s tissue and DNA as performed in a sterile laboratory environment. While somaclonal variation remains a real concern, tissue culturing does eliminate genetic drift that has been observed for many famous cannabis strains, such as OG Kush, over decades of cloning.
Aseptic propagation and regeneration of Cannabis has been reported by a few research groups for a limited number of marijuana and industrial hemp cultivars with the goal of minimizing genetic change. Clearly one additional advantage of tissue culture is the elimination of any carryover of pests or pathogens and guarantees that each grow cycle starts with sterile plantlets. The following images document the tissue culture growth stages.[1]
The scientists at the University of Mississippi’s School for Natural Products Research has had the most extensive experience with establishing conditions for regeneration of Cannabis sativa L through shoot organogenesis with claimed subsequent rooting as high as a 95% frequency.[2] Recently the same University of Mississippi academic group has taken the next step to look at the genetic stability of micropropagated plantlets through the sequencing of inter-simple sequence repeat (ISSR) markers to determine the impact of micropropagation on the genetic fidelity of C. sativa variety MX-1.[3] The group looked at a total of 15 DNA amplicons ranging in size between 177 bp to almost 3,000 bp for consistent DNA banding patterns across the micropropagated plants as compared to the mother plant and the banding did not vary. In addition the group compared the cannabinoid profile between the microplants and mother plant and found strong agreement, leading them to report that clonal stability was attained.IBID
The maintenance of clonal fidelity is an important issue in developing a secure and stable in vitro clonal repository of elite C. sativa germplasm. Assurance of genome stability should go hand in hand with the establishment of any in vitro cannabis propagation effort.
[1] GrowBlox.com
[2] Lata H, Chandra S, Khan I, ElSohly M A. (2009) Thidiazuron induced high frequency direct shoot organogenesis of Cannabis sativa L. In Vitro Cell Dev Biol Plant 45:12-19
[3] Lata H, et al. (2010) Assessment of the Genetic Stability of Micropropagated Plants of Cannabis sativa by ISSR Markers. Planta Med 76:97-100.