The inheritance of chemical phenotype in Cannabis sativa L. (II):: Cannabigerol predominant plants

This paper aims to clarify the genetic mechanism that is responsible for the accumulation of cannabigerol (CBG) in certain phenotypes of Cannabis sativa L. CBG is the direct precursor of the cannabinoids CBD, THC and CBC. Plants strongly predominant in CBG have been found in different fibre hemp accessions. Inbred offspring derived from one such individual were crossed with true breeding THC predominant- and CBD predominant plants, respectively. The segregations in the cross progenies indicate that CBG accumulation is due to the homozygous presence of a minimally functional allele, tentatively called B-0, at the single locus B that normally controls the conversion of CBG into THC (allele B-T) and/or CBD (allele B-D). The fact that CBG accumulating plants have so far been found in European fibre hemp populations that are generally composed of B-D/B-D plants, and the observation that the here investigated B-0 allele possesses a residual ability to convert small amounts of CBG into CBD, make it plausible that this B-0 is a mutation of normally functional B-D. Therefore, B-0 is considered as a member of the B-D allelic series encoding a CBD synthase isoform with greatly weakened substrate affinity and/or catalytic capacity.