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Date and time: Thu, 24 Jun 2021 18:05:10 GMT

Over the last decade, the legal status of Cannabis has shifted and is now legal for medical and some recreational adult use, in the majority of the United States as well as several other countries that have legalized or decriminalized Cannabis. The recent legal changes have led to an unprecedented increase in the number of strains available to consumers. There are currently no baseline genotypes for any strains, but steps should be taken to ensure products marketed as a particular strain are genetically congruent. Although the sampling in this study was not exhaustive, the results are clear: strain inconsistency is evident and is not limited to a single source, but rather exists among dispensaries across cities in multiple states. Various suggestions for naming the genetic variants do not seem to align with the current widespread definitions of Sativa, Indica, Hybrid, and Hemp (Hillig 2005; Clarke and Merlin 2013). As our Cannabis knowledge base grows, so does the communication gap between scientific researchers and the public. Currently, there is no way for Cannabis suppliers, growers or consumers to definitively verify strains. Exclusion from USDA protections due to the Federal status of Cannabis as a Schedule I drug has created avenues for error and inconsistencies. Presumably, the genetic inconsistencies will often manifest as differences in overall effects (Minkin 2014). Differences in characteristics within a named strain may be surprising for a recreational user, but differences may be more serious for a medical patient who relies on a particular strain for alleviation of specific symptoms.

To accurately address reported variation within strains, samples were purchased from various locations, as a customer, with no information of strains other than publicly available online information. Evidence for genetic inconsistencies is apparent within many strains and supported by multiple genetic analyses. Soler et al. (2017) found genetic variability among seeds from the same strain supplied from a single source, indicating genotypes within strains are variable. When examining the STRUCTURE genotype assignments, it is clear that many strains contained one or more divergent samples with a difference of > 0.10 genotype assignment (e.g. “Durban Poison” – Denver 1; Figs. 1, 3a). Of the 30 strains examined, only four strains had consistent STRUCTURE genotype assignment and admixture among all samples. The number of strains with consistent STRUCTURE assignments increased to 11 and 15 when one or two samples were ignored, respectively. These results indicate that half of the included strains showed relatively stable genetic identity among most samples. Six strains had only two samples, both of which were different (e.g., “Trainwreck” and “Headband”). The remaining nine strains in the analysis had more than one divergent sample (e.g., “Sour Diesel”) or had no consistent genetic pattern among the samples within the strain (e.g., “Girl Scout Cookies”; Table 3, Figs. 1, 2, Additional file 3: Figure S2). It is noteworthy that many of the strains used here fell into a range of genetic relatedness indicative of first order siblings (see Lynch & Ritland analysis below) when samples with high genetic divergence were removed from the data set (Table 3; Figs. 3, 4). Eight of the 30 strains examined are identified as clone only (Table 2). All eight of the strains described as clone only show differentiation of at least one sample within the strain (Fig. 1). For example, one sample of “Blue Dream” is clearly differentiated from the remaining eight, and “Girl Scout Cookies” has little genetic cohesiveness among the eight samples (Figs. 1, 2). Other genetic studies have similarly found genetic inconsistencies across samples within the same strain (Lynch et al. 2016; Soler et al. 2017; Sawler et al. 2015). These results lend support to the idea that unstable genetic lines are being used to produce seed.

Cannabis is becoming an ever-increasing topic of discussion, so it is important that scientists and the public can discuss Cannabis in a similar manner. Currently, not only are Sativa and Indica types disputed (Emboden 1974; Hillig 2005; Russo 2007; Clarke and Merlin 2013; Clarke et al. 2015; Clarke and Merlin 2016; McPartland 2017; Piomelli and Russo 2016; Small 2015b; De Meijer and Keizer 1996), but experts also are at odds about nomenclature for Cannabis (Emboden 1974; Hillig 2005; Russo 2007; Clarke and Merlin 2013; Clarke et al. 2015; Clarke and Merlin 2016; McPartland 2017; Piomelli and Russo 2016; Small 2015b; De Meijer and Keizer 1996). We postulated that genetic profiles from samples with the same strain identifying name should have identical, or at least, highly similar genotypes no matter the source of origin. The multiple genetic analyses used here address paramount questions for the medical Cannabis community and bring empirical evidence to support claims that inconsistent products are being distributed. An important element for this study is that samples were acquired from multiple locations to maximize the potential for variation among samples. Maintenance of the genetic integrity through genotyping is possible only following evaluation of genetic consistency and continuing to overlook this aspect will promote genetic variability and phenotypic variation within Cannabis. Addressing strain variability at the molecular level is of the utmost importance while the industry is still relatively new.

Discussion

Matching genotypes within the same strains were expected, but highly similar genotypes between samples of different strains could be the result of mislabeling or misidentification, especially when acquired from the same source. The pairwise genetic relatedness r-values were examined for incidence of possible mislabeling or re-labeling. There were instances in which different strains had r-values = 1.0 (Additional file 4: Figure S3), indicating clonal genetic relationships. Two samples with matching genotypes were obtained from the same location (“Larry OG” and “Tahoe OG” from San Luis Obispo 3). This could be evidence for mislabeling or misidentification because these two samples have similar names. It is unlikely that these samples from reportedly different strains have identical genotypes, and more likely that these samples were mislabeled at some point. Misspelling may also be a source of error, especially when facilities are handwriting labels. An example of possible misspelling may have occurred in the sample labeled “Chemdog 1” from Garden City 1. “Chemdawg 1”, a described strain, could have easily been misspelled, but it is unclear whether this instance is evidence for mislabeling or renaming a local variant. Inadvertent mistakes may carry through to scientific investigation where strains are spelled or labeled incorrectly. For example, Vergara et al. (2016) reports genome assemblies for “Chemdog” and “Chemdog 91” as they are reported in GenBank (GCA_001509995.1), but neither of these labels are recognized strain names. “Chemdawg” and “Chemdawg 91” are recognized strains (Leafly 2018a; Wikileaf 2018; cannabis.info 2018; NCSM 2018; PotGuide.com 2018; Seedfinder 2018), but according to the original source, the strain name “Chemdawg” is incorrect, and it should be “Chem Dog” (Danko 2016), but the name has clearly evolved among growers since it emerged in 1991 (Danko 2016). Another example that may lead to confusion is how information is reported in public databases. For example, data is available for the reported monoisolate of “Pineapple Banana Bubba Kush” in GenBank (SAMN06546749), and while “Pineapple Kush”, “Banana Kush” and “Bubba Kush” are known strains (Leafly 2018a; Wikileaf 2018; cannabis.info 2018; NCSM 2018; PotGuide.com 2018; Seedfinder 2018), the only record we found of “Pineapple Banana Bubba Kush” is in GenBank. This study has highlighted several possible sources of error and how genotyping can serve to uncover sources of variation. Although this study was unable to confirm sources of error, it is important that producers, growers and consumers are aware that there are errors and they should be documented and corrected whenever possible.

This study shows that in neutral genetic markers, there is no consistent genetic differentiation between the widely held perceptions of Sativa and Indica Cannabis types. Moreover, the genetic analyses do not support the reported proportions of Sativa and Indica within each strain, which is expected given the lack of genetic distinction between Sativa and Indica. There may be land race strains that phenotypically and genetically separate as Sativa and Indica types, however our sampling does not include an adequate number of these strains to define these as two potentially distinct genotypes. The recent and intense breeding efforts to create novel strains has likely merged the two types and blurred previous separation between the two types. However, categorizing strains this way helps consumers communicate their preference for a spectrum of effects (e.g.: Sativa-dominant Hybrid), and the vernacular usage will likely continue to be used, despite a lack of evidence of genetic differentiation.

Unlike other plants, Cannabis sativa is excluded from regulation by the United States Department of Agriculture (USDA). Distinctive Cannabis varieties are ostracized from registration and therefore nearly impossible to verify. As Cannabis has become legal for medical and recreational consumption in many states, consumers have been exposed to a wave of novel Cannabis products with many distinctive names. Despite more than 2000 named strains being available to consumers, questions about the consistency of commercially available strains have not been investigated through scientific methodologies. As Cannabis legalization and consumption increases, the need to provide consumers with consistent products becomes more pressing. In this research, we examined commercially available, drug-type Cannabis strains using genetic methods to determine if the commonly referenced distinctions are supported and if samples with the same strain name are consistent when obtained from different facilities.

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