Through the detailed cannabis genetic research of academicians, we are learning that the genetic identity of a marijuana strain cannot be reliably inferred by its strain name or by its reported ancestry; ie. indica versus sativa. In a recent article by Sawler et al. (2015), cannabis samples were found to be more genetically similar to samples with different names than to samples with the same name. This unaccountability in cannabis ancestry is the result of the covert status of amateur plant breeders for at least the past century. Compounding this confusion has been the long-standing goal of selecting for higher THC content, the consequence being that resultant “hybrid” strains have predominantly migrated toward indica at the loss of sativa genetics.
There is no other agronomic plant of such high economic value and yet so poorly understood as cannabis. Even though the first draft genome of C. sativa L. was published in 2011 (van Bakel et al.), it is only quite recently that hi-throughput genotyping of cannabis populations has been done. One of the notable high-level findings has been that hemp is more genetically similar to indica strains than to sativa strains (Sawler et al. 2015); whereas previously, hemp had consistently been classified as a sativa strain. And additional genetic loci have been identified to further distinguish cannabis strains than just THCA synthase and CBDA synthase genes.
Thanks to the burgeoning recognition of cannabis around the world as both a worthy medicinal as well as agricultural species, it is imperative that an organized horticultural system of varietal names be adopted based on cannabis population genetics and not colloquial strain names. The cultivated varieties of hemp and strains of marijuana are all members of the same Cannabis sativa species that are phenotypically distinguishable but also chemically distinguishable by their resulting content of tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA) through the action of two different synthase enzymes. Simplistically, it had been assumed that either a cannabis plant expressed THCA synthase or CBDA synthase since the resultant enzymes compete for the same substrate, cannabigerolic acid (CBG); but in detailed experiments carried out by Weiblen et al. (2015), we see that a genetically stable hybrid with a functional copy of both genes, produces more CBDA, suggesting that the CBDA synthase is a more competitive enzyme for CBG. Furthermore, it appears that high-THC content marijuana strains maintain both genes but that the CBDA synthase is non-functional.
From a regulatory standpoint, Weiblen and his colleagues at the University of Minnesota have now demonstrated that a single gene can be used to discriminate hemp from marijuana. Plants that have two copies of a functional CBDA synthase gene are incapable of making >0.3% THC and qualify as hemp extracts; however, if one copy is nonfunctional then the plant can make >0.5% THC and are not qualified as hemp extracts.
The medicinal value of the cannabis plant is abundantly clear as is its gigantic economic potential. As a requisite step toward the development of cannabis plant material into sanctioned medicinal products, the quality control and taxonomic discrimination of the starting material is a necessity.
However, accomplishing an appropriate and applicable classification system with registered varieties of cannabis will require a well-funded unified scientific effort. For success, the classification effort will also require buy in by the Cannabis Industry as well as an accepted legal framework to work within. Until cannabis genetics comes up to speed, a preferable guideline to ‘strain’ naming would be the resultant drug content which is variously referred to as the potency profile, metabolic profile or “chemo” profile of a particular cannabis crop.
Sawler J. et al. (Aug 26, 2015) The Genetic Structure of Marijuana and Hemp. PLOS ONE
van Bakel et al (2011) The draft genome and transcriptome of Cannabis sativa. Genome Biol 12:R102 doi:10, 1186/gb-2011-12-10-r102 PMID: 22014239
Weiblen et al. (2015) Gene duplication and divergence affecting drug content in Cannabis sativa. New Phytologist doi: 10.1111/nph.13562