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Forensic plant science deals with the use of plants as evidence in court. Plant genetic techniques, such as DNA barcoding or DNA fingerprinting, can be used to combat trafficking of illicit drugs by providing leads for law enforcement concerning entry points into the country and linking cases. Additionally, they can be used in court as evidence of environmental crimes, including illegal logging, which often go unpunished due to lack of forensic evidence. DNA barcoding is a technique that involves sequencing regions of the genome to identify a species or population of origin (biogeographical origin), and DNA fingerprinting involves individualizing samples based on their unique genetic profile, usually by using short tandem repeat markers (STRs).

Cannabis sativa L. is the source of both an illegal drug, marijuana, and a legal crop, hemp. Marijuana is the most commonly used illicit drug in the United States, and due to state-specific legalization of the drug, law enforcement must prevent and investigate trafficking of marijuana between states, as well as from international sources (e.g., at the border with Mexico). Current methods of identifying C. sativa use microscopic features of the plant or quantify delta-9-tetrahydrocannabinol (THC), the psychoactive component of marijuana. A DNA barcoding method could assist investigations by indicating the biogeographical origin and crop type of a sample and providing a means for linking cases from common growers and distributors. In the first phase of this study, seven polymorphic regions in the chloroplast genome of C. sativa were reported and explored as DNA barcodes for determining biogeographical origin and crop type. An MPS assay was then developed to genotype these hotspots in a high throughput manner, which will facilitate the creation of a worldwide haplotype database, similar to the model of human mitochondrial haplotypes.

Additionally, single nucleotide polymorphisms (SNPs) in the tetrahydrocannabinolic acid (THCA) synthase gene were evaluated for their ability to distinguish between marijuana and hemp. The majority of marijuana samples and hemp flowers were classified correctly; however, other variables influence cannabinoid content in C. sativa, resulting in incorrect classifications for some sample types (i.e., hemp seeds and cannabigerol strains). Quantification of THC and THCA is the gold standard for distinguishing between marijuana and hemp, but several sample types (including juvenile plants, seeds, roots, and trace residues) may yield inconclusive chemical results. An alternate DNA approach should be taken with these samples, and the chloroplast DNA barcoding regions proposed in this dissertation may offer a viable future approach.

Papaver somniferum (opium poppy) is the source of opiates and opioids, a class of narcotic drugs with high abuse potential. Users who become addicted after being prescribed opiates may turn to alternatives, such as heroin or poppy seed tea, once their prescriptions end. There is currently no forensic method for genetically individualizing samples in cases of poppy seed tea overdoses. The Drug Enforcement Agency’s Heroin Signature Program uses chemical analyses to determine the origin of heroin samples; however, addition of a genetic method would supplement the program and be capable of analyzing difficult sample types (such as trace residues found on drug paraphernalia). Three DNA extraction methods were evaluated for poppy seeds, and a novel quantitative real-time PCR assay was developed and validated for future genetic studies involving P. somniferum. STR markers from the literature were evaluated, and a preliminary STR multiplex was used in a proof-of-concept study to show the potential of future STR panels for individualizing or determining biogeographical origin of heroin or poppy seed tea samples.

Eucalyptus is a genus of gum trees (eucalypts) planted around the world for use in the production of paper pulp, hardwood, essential oils, and other industrial products. Illegal logging of eucalypts and other trees costs the world economy billions of dollars annually, and cases of wood theft are often dismissed due to a lack of forensic evidence. Over 1,200 STRs have been discovered in eucalypts, but there has been a lack of forensic research testing these markers for evidence of illegal logging. This project evaluated nine STR markers for Eucalyptus and applied them to a case of illegal logging to demonstrate the utility of STR analysis for providing evidence in court.



Biology, Botany