Journal:Broad-scale genetic diversity of Cannabis for forensic applications

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Full article title Broad-scale genetic diversity of Cannabis for forensic applications
Journal PLOS ONE
Author(s) Dufresnes, Christophe; Jan, Catherine; Bienert, Friederike; Goudet, Jérôme; Fumagalli, Luca
Author affiliation(s) University of Lausanne, Centre Universitaire Romand de Médecine Légale,
Primary contact Email: Luca dot Fumagalli at unil dot ch
Editors Scali, Monica
Year published 2017
Volume and issue 121
Page(s) e0170522
DOI 10.1371/journal.pone.0170522
ISSN 1932-6203
Distribution license Creative Commons Attribution 4.0 International
Website http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0170522
Download http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0170522&type=printable (PDF)
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Abstract

Cannabis (hemp and marijuana) is an iconic yet controversial crop. On the one hand, it represents a growing market for pharmaceutical and agricultural sectors. On the other hand, plants synthesizing the psychoactive THC produce the most widespread illicit drug in the world. Yet, the difficulty to reliably distinguish between Cannabis varieties based on morphological or biochemical criteria impedes the development of promising industrial programs and hinders the fight against narcotrafficking. Genetics offers an appropriate alternative to characterize drug vs. non-drug Cannabis. However, forensic applications require rapid and affordable genotyping of informative and reliable molecular markers for which a broad-scale reference database, representing both intra- and inter-variety variation, is available. Here we provide such a resource for Cannabis, by genotyping 13 microsatellite loci (STRs) in 1,324 samples selected specifically for fiber (24 hemp varieties) and drug (15 marijuana varieties) production. We showed that these loci are sufficient to capture most of the genome-wide diversity patterns recently revealed by next-generation sequencing (NGS) data. We recovered strong genetic structure between marijuana and hemp and demonstrated that anonymous samples can be confidently assigned to either plant types. Fibers appear genetically homogeneous whereas drugs show low (often clonal) diversity within varieties, but very high genetic differentiation between them, likely resulting from breeding practices. Based on an additional test dataset that includes samples from 41 local police seizures, we showed that the genetic signature of marijuana cultivars could be used to trace crime scene evidence. To date, our study provides the most comprehensive genetic resource for Cannabis forensics worldwide.

Introduction

Cannabis is one of humanity’s oldest cultivated plant. It is thought to have originated in central Asia and was domesticated as early as 8,000 BP for food, fiber, oil, medicines and as an inebriant. This crop was since distributed across the world during the last two millennia and, due to its recent legalization in several countries, is increasingly exploited by several industrial sectors (hemp) and as a recreational drug (marijuana). The taxonomic status of Cannabis has always been disputed, as it encompasses multiple cultural, geographic, historical, and functional aspects.[1][2][3][4] Whereas most authors now consider it a monotypic panmictic taxon, Cannabis sativa, three species or subspecies (sativa, indica and ruderalis) are often mentioned but without a comprehensive taxonomic grouping so far. The nomenclature may thus differ depending on whether it refers to morphological or chemical variation, geographic distribution, ecotype, as well as crop-use characteristics and intoxicant properties resulting from human selection.[4][5][6][7] Cannabis presumably diversified following selection for traits enhancing fiber and seed production (”hemp”) or psychoactive properties ("drug"). Importantly, Cannabis types differ in their absolute and relative amounts of terpenophenolic cannabinoids, notably Δ1-tetrahydrocannabinol (THC), the well-known psychoactive compound of marijuana, and the non-psychoactive cannabidiol (CBD). In this context, drug-type Cannabis (marijuana) is broadly characterized by a higher overall cannabinoid content than fiber-types. However, the most widely recognized criteria to assign a Cannabis plant to either “drug” or “hemp” type is the THC:CBD ratio, according to which three main chemical phenotype (chemotype) classes are recognized: hemp-type plants with a low ratio (THC:CBD < 1), drug-type plants with a high ratio (THC:CBD > 1), and intermediate-type plants with a ratio close to one.[6][8] The informal designation sativa and indica may have various, controversial meanings. Morphologically, the name sativa designates tall plants with narrow leaves, while indica refers to short plants with wide leaves. Among the marijuana community however, sativa rather refers to equatorial varieties producing stimulating psychoactive effects (THC:CBD ≈ 1), whereas indica-type plants from Central Asia are used for relaxing and sedative drugs (THC:CBD > 1).[8]


References

  1. ↑ Small, E.; Crongquist, A. (1976). "A practical and natural taxonomy for cannabis". Taxon 25 (4): 405–435. doi:10.2307/1220524. 
  2. ↑ Clarke, R.C.; Merlin, M.D. (2013). Cannabis: Evolution and Ethnobotany. University of California Press. pp. 434. ISBN 9780520270480. 
  3. ↑ Small, E. (2015). "Evolution and Classification of Cannabis sativa (Marijuana, Hemp) in Relation to Human Utilization". The Botanical Review 81 (3): 189–294. doi:10.1007/s12229-015-9157-3. 
  4. ↑ 4.0 4.1 Welling, M.T.; Shapter, T.; Rose, T.J. et al. (2016). "A Belated Green Revolution for Cannabis: Virtual Genetic Resources to Fast-Track Cultivar Development". Frontiers in Plant Science 7: 1113. doi:10.3389/fpls.2016.01113. PMC PMC4965456. PMID 27524992. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4965456. 
  5. ↑ de Meijer, E.P.M.; van Soest, L.J.M. (1992). "The CPRO Cannabis germplasm collection". Euphytica 62 (3): 201–11. doi:10.1007/BF00041754. 
  6. ↑ 6.0 6.1 de Meijer, E.P.M. (2014). "The Chemical Phenotypes (Chemotypes) of Cannabis". In Pertwee, R.. Handbook of Cannabis. Oxford University Press. pp. 89–110. ISBN 9780199662685. 
  7. ↑ Hillig, K.W. (2005). "Genetic evidence for speciation in Cannabis (Cannabaceae)". Genetic Resources and Crop Evolution 52 (2): 161–80. doi:10.1007/s10722-003-4452-y. 
  8. ↑ 8.0 8.1 Hillig, K.W.; Mahlberg, P.G. (2004). "A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae)". American Journal of Botany 91 (6): 966–75. doi:10.3732/ajb.91.6.966. PMID 21653452. 

Notes

This presentation is faithful to the original, with only a few minor changes to presentation. In some cases important information was missing from the references, and that information was added.

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