The inheritance of chemical phenotype in Cannabis sativa L. (V): regulation of the propyl-/pentyl cannabinoid ratio, completion of a genetic model

Abstract

In order to complete a genetic model for the inheritance of chemotype in Cannabis, this paper explores the regulation of the propyl-/pentyl cannabinoid ratio. Plants almost pure in compounds with a C5 side chain are by far the most common, and such a chemotype can be considered a wild-type condition. Mutant progenitors with higher levels of the rarer cannabinoid THC-C3 (tetrahydrocannabivarin) were identified. Their propyl cannabinoid proportion in the total cannabinoid fraction (PC3) ranged from 14 to 69 %, which, through selective inbreeding, could be increased to highly specific lineage maxima. Inbred plants with maximised PC3 derived from the different progenitors, were then crossed with a pure C5 wild type and the PC3 distribution patterns of the F2s examined. Distinct patterns, compatible with oligogenic and polygenic segregation appeared. It was hypothesised that the PC3 regulating loci of the six source progenitors would be at least partially different, complementary, and additive in their phenotypical effect. So, high PC3 offspring from the different lineages were mutually crossed. Inbred lines derived from multi-cross hybrid combinations reached unprecedented PC3 levels of up to 96 % which supports the hypothesis. For the regulation of C3/C5 ratios, a model of a multiple locus A 1–A 2–…A n is proposed, with the pentyl- and propyl cannabinoid pathway being enhanced by alleles A pe 1−n and A pr 1−n , respectively.