In recent years there has been a huge boom in the number of documented cannabis strains and types. At present, the genetic information required to underpin claims that these strains are truly unique is simply not available. With that in mind, a team of researchers from the University of Northern Colorado recently conducted a study on the reliability of strains. The research is currently available on the pre-print server, BioRxiv.





The facts behind existing cannabis strain nomenclature



The traditional nomenclature system divides cannabis into well-known categories based on the percentage of Δ9-tetrahydrocannabinol (THC) present in the product. Those with very low THC content are classed as hemp-type and those with moderate to high THC are considered drug-type. The drug-type strains are usually divided further into Sativa, Indica, and Hybrid type strains. Further, drug-type strains with relatively low THC and high cannabidiol (CBD) levels are currently generating a lot of interest for their proven and potential medical properties.



Conventional nomenclature centers mostly on the physical properties of plants. Tall plants with narrow leaflets are associated with the Sativa type strain, and, shorter plants with broader leaflets are indicative of an Indica type strain. Hybrid strains display a mixture of these characteristics. It is also reported that the different strain types have different effects of the human body, with Sativa type strains resulting in invigorating and stimulating effects, while Indica strain types have been shown to be effective at pain management and are believed to provide a more relaxing “high”.



Each of these strain types encompasses hundreds, if not thousands, of different strains, all with reportedly different effects and different popularities.





Assessing the reliability of existing cannabis strain types



The pre-publication article from researchers Anna Schwabe and Mitchell McGlaughlin at the University of Northern Colorado describe their study of samples purchased from multiple points of sale. The researchers set out to examine if there is any genetic variability within a labeled strain purchased from different locations, as well as looking for any possible genetic support for the conventional nomenclature.



The study comprised 122 samples from 30 strains purchased at different dispensaries across three states: Colorado, California, and Washington. Microsatellite genetic analysis was used to check for any shared genetic features that could indicate strain type. Microsatellite analysis is an established technique and is already commonly used in the classification of other plant species. Statistical analysis was also carried out on the microsatellite data in order to quantify the genetic relatedness of the samples.



Two distinct genotypes were found during the study, but they did not appear to have a strong correlation to the reported proportions of Sativa and Indica phenotypes expected from many strains. If the Sativa and the Indica phenotypes were genetically distinct, then a genetic examination should categorize strains that are 100% Sativa as belonging to one genotype, and strains that are 100% Indica as belonging to a second distinct genotype, with Hybrid strains showing a mixture of the two genotypes.



The strain “Durban Poison” is listed as a 100% Sativa strain, but on average only has an 86% assignment to genotype 1. Perhaps a starker illustration is the 90% Sativa “Sour Diesel” strain, which only has an average assignment of 14% to genotype 1. This is also the case for the labeled Indica strains. Three of the four samples of the 100% Indica type “Purple Kush” showed a genotype 2 assignment of greater than 89%. But a second 100% Indica strain, “Grape Ape”, shares no predominant assignment to genotype 1 or 2.



It is clear that the observed genotypes do not correlate consistently with the conventional strain types. This will probably not come as a surprise to many in the scientific community. The lack of genetic evidence to support the existing strain distinctions means that many consumers may be unwittingly, or otherwise, misled about the cannabis product they are using. Potentially disappointing or unsettling for a recreational user but, more importantly, possibly dangerous for a medical patient who relies on a specific strain to relieve specific symptoms.



It is clear that while historically there once may have been a clear genetic link between the strain types and the genotypes, years of selective hybridization and breeding has muddied that link.

A lack of consistency in cannabis strain names is clear

In an ideal scenario, all samples being sold under a single strain name should either be clones or very close relatives of each other. A good example of this is the Blue Dream strain. The Blue Dream labeled samples in this study contained a high proportion of clones or first-generation relatives, with no unrelated samples being found. This indicates reliability, especially considering the large geographical separation between the dispensaries the Blue Dream samples were purchased from.



After the removal of the most extreme outlier data, it was found that only 15 of the 30 strains tested were first order or higher relatives (i.e. clones or share a parent plant) among the samples within a strain. Six of the remaining fifteen strains that showed low orders of relativity had a very small sample size of only two samples, and without increasing this it is very hard to comment on how reliably related the strain can be. The final nine strains were made up of a mixture of strains that had near-completely unrelated genetics but also contained a number of strains that had multiple obvious outliers.



Many strains have similar names and may even be variations of the same plant. The strains Golden Goat and Sweet Island Skunk were found to be more related than some pairs of samples that were both being sold under the Sour Diesel strain name. In addition, Larry OG and Tahoe OG were found to be genetically identical, despite being sold under different strain names. Furthermore, the researchers originally assumed the multiple common Chemdawg strains (e.g. Chemdawg 91, Chemdawg D, Chemdog 1) were just local spelling and numbering variants of a single strain. However, genetic analysis now lends some weight to the legend that they are distinct strains originating from a singular source: a plant that a person named Chemdog grew from seeds he found in cannabis he bought at a Grateful Dead concert.



The unusual way in which strains like the Chemdawg variants have come to the market highlights the need for genetic testing of strains. The current system has led to overlap between seemingly unrelated strains, and the lack of any genetics-based regulation has allowed the spread of inconsistent, mislabeled and, misidentified strains.



It is clear that there needs to be change in terms of nomenclature and regulation to enable clearer, more useful naming of cannabis strains. While at one time the Sativa, Indica, Hybrid and Hemp descriptors may have been easily distinguishable, it appears that they no longer correlate with observed genotypes. In addition to this, the legal inability to introduce a system for the verification of cannabis strains has created the potential for inconsistency. A study with a wider sample database may help pin down the exact causes of these inconsistencies and help to identify a more effective naming system.