Characterization of new chloroplast markers to determine biogeographical origin and crop type of Cannabis sativa.

ABSTRACT

Marijuana (Cannabis sativa) is the most commonly used illicit drug in the USA. Despite its schedule I classification by the federal government, 33 states and the District of Columbia have legalized its use for medicinal or recreational purposes. This state-specific legalization has created a new problem for law enforcement preventing and tracking the diversion of legally obtained Cannabis to states where it remains illegal. In addition, trafficking of the drug at the border with Mexico remains an issue for law enforcement agencies. C. sativa crops can be classified as marijuana (a drug containing the psychoactive chemical delta-9-tetrahydrocannabinol) or hemp (the non-drug form of the plant). Differentiation between crop types is important for forensic purposes. In addition, investigation of trafficking routes into and within the USA requires genetic association of samples from different seizures, and determining where the crop originated could provide important leads. This project seeks to exploit sequence variations in C. sativa chloroplast DNA (cpDNA) to allow genetic determination of biogeographic origin, discrimination between marijuana and hemp, and association between cases for C. sativa samples. Due to the limited discriminatory ability of common barcoding markers, the authors sought to discover more informative polymorphic regions. By comparing published whole genome cpDNA sequences, 58 polymorphisms and seven hotspot regions were identified. Hemp samples from the USA and Canada, marijuana samples from Mexico and Chile, and medical marijuana samples from Chile were evaluated using two cpDNA hotspot regions, rpl32-trnL and trnS-trnG. Principal component analysis supported some differences between the groups based on their crop type and biogeographic origin.