American Journal of Botany 91(6): 966-975. 2004.
Karl W. Hillig & Paul G. Mahlberg
Department of Biology, Indiana University, Bloomington, Indiana 47405 USA
Keywords: cannabinoid, Cannabis, chemotaxonomy, evolution, genetics, taxonomy, tetrahydrocannabinol
Cannabinoids are important chemotaxonomic markers unique to Cannabis. Previous studies show that a plant’s dry-weight ratio of D9-tetrahydrocannabinol (THC) to cannabidiol (CBD) can be assigned to one of three chemotypes and that alleles Bd and Bt encode alloenzymes that catalyze the conversion of cannabigerol to CBD and THC, respectively. In the present study, the frequencies of Bv and Bt in sample populations of 157 Cannabis accessions were determined from CBD and THC banding patterns, visualized by starch gel electrophoresis. Gas chromatography was used to quantify cannabinoid levels in 96 of the same accessions. The data were interpreted with respect to previous analyses of genetic and morphological variation in the same germplasm collection. Two biotypes (infraspecific taxa of unassigned rank) of C. sativa and four biotypes of C. indica were recognized. Mean THC levels and the frequency of Bt were significantly higher in C. indica than C. sativa. The proportion of high THC/CBD chemotype plants in most accessions assigned to C. sativa was <25% and in most accessions assigned to C. indica was >25%. Plants with relatively high levels of tetrahydrocannabivarin (THCV) and/or cannabidivarin (CBDV) were common only in C. indica. This study supports a two-species concept of Cannabis.
concept of Cannabis.