Diversity in Cannabis

The PhD thesis, "Diversity in Cannabis" (available through the IHA), which Etienne de Meijer defended on 22 December 1994, reports on the evaluation of a collection of Cannabis germplasm at the Centre for Plant Breeding and Reproduction Research, at Wageningen, in the Netherlands. About 160 accessions were evaluated for traits related to stem production, stem quality, psychoactive potency and resistance to soil pathogens. Prospects for the breeding of improved cultivars for paper pulp production were based on the diversity for these traits, their stability, and mutual relations.

Variation in stem production could be attributed largely to differences in phenological development, which again was related to the latitude of origin of the accessions. Large variation was found for the fraction of bark tissue, woody core and primary and secondary bark fibre in the stem. Since woody core fibres of Cannabis are on average too short to produce high quality paper, the evaluation was directed at variation for core fibre dimensions as well. This variation proved to be very limited and breeding for improved core quality was not considered promising. Accessions were classified into the phenotypes 'drug', 'intermediate' and 'non-drug' on the basis of their contents of the cannabinoids delta-9-tetra-hydrocannabinol and cannabidiol. There were no strict relationships between the cannabinoid profiles and other traits. Significant variation was further revealed in host reactions to the root-knot nematode Meloidogyne hapla.

The study indicated that many combinations of character states can be established through breeding. An a priori grouping of accessions based on the purpose and status of domestication (fibre cultivars, fibre landraces, drug strains, and wild or naturalized populations) was validated by the experimental observations. Contents of bark fibre and cannabinoids discriminated most between groups. A genetic characterization on the basis of electrophoretic patterns of seed proteins was unsatisfactory as it neither reflected common ancestry, nor showed a relation with groupings based on origin or agronomic and morphological traits.