A PCR marker linked to a THCA synthase polymorphism is a reliable tool to discriminate potentially THC-rich plants of Cannabis sativa L.
Neither absolute THC content nor morphology allows the unequivocal discrimination of fiber cultivars and drug strains of Cannabis sativa L. unequivocally. However, the CBDTHC ratio remains constant throughout the plants life cycle, is independent of environmental factors, and considered to be controlled by a single locus (B) with two codominant alleles (B(T) and B(D)). The homozygous B(T)B(T) genotype underlies the THC-predominant phenotype, B(D)B(D) is CBD predominant, and an intermediate phenotype is induced by the heterozygous state (B(T)B(D)). Using PCR-based markers in two segregating populations, we proved that the THCA synthase gene represents the postulated B locus and that specific sequence polymorphisms are absolutely linked either to the THC-predominant or the THC-intermediate chemotype. The absolute linkage provides an excellent reliability of the marker signal in forensic casework. For validation, the species-specific marker system was applied to a large number of casework samples and fiber hemp cultivars.