Variability of cannabinoid contents depending on breeding methods

Abstract

Purpose and objectives. To reveal new possibilities for the expression of cannabis genotypes to obtain starting material with increased contents of non-psychotropic cannabinoids, without tetrahydrocannabinol and stabilized biological traits.

Material and methods. In our study, we took Ukrainian hemp cultivars, the populations of which were distinguished by high stability of cannabinoid contents in comparison with foreign cultivars, as a basis. The study was carried out using breeding, biochemical and statistical methods: physical mutagenesis, inbreeding, individual selection, thin-layer and gas-liquid chromatography to evaluate plants for cannabinoids (HP 6890 Series Hewlett Packard chromatograph using an internal standard).

Results and discussion. It was found that gamma rays at a dose of 200 Gy disrupted the genotypic relationships between cannabinoids, with accumulation of their minimum or maximum amounts. Lowering the irradiation dose to 150 Gy does not destabilize the population in terms of the cannabinoid contents.

Inbreeding can be also used in breeding for both to create inbred lines that are homozygous for the ‘no cannabinoids’ trait and to identify lines with increased contents of cannabidiol, cannabigerol or cannabichromen.

A lot of early-bred and modern cultivars (French, Polish, Hungarian, German) show a high population variability of the cannabinoid contents, proving that no systemic breeding was conducted to stabilize these traits in the populations of these cultivars. High homogeneity of populations in terms of the formation and accumulation of cannabinoids is only intrinsic to monoecious hemp cultivars bred by the Institute of Bast Crops of NAAS.

The homozygosity of a population primarily depends on the control of targeted cross-pollination between cannabinoid-free plants using an express testing plants for these compounds prior to anthesis onset and subsequent analysis of the selected elite plants by thin-layer chromatography.

Given the relevance of creating hemp varieties with therapeutic properties, breeding methods have been developed to shift the balance of ‘no cannabinoid at all’ towards a genetically determined increase in one of the cannabinoids (cannabidiol, cannabigerol, cannabichromene) combined with eliminated psychotropic activity (the THC content does not exceed 0.08%).

Studies of cannabinoid accumulation revealed differences in their formation during the growing period. Based on the fact that the maximum accumulation of cannabinoids occurs during the seed ripening onset, and, in particular, their synthesis is the most intensive in perianths and small leaves, it is possible to evaluate the prospects for creating hemp cultivars with a branched diamond-shaped inflorescence, which will provide, in addition to a high content of one or another cannabinoid, an increased yield of plant biomass.

Conclusions. Physical mutagenesis, inbreeding and selection are promising breeding methods for reducing psychotropic tetrahydrocannabinol, stabilizing cannabis cultivars in terms of the absence of cannabinoids, increasing the contents of cannabidiol, cannabigerol and cannabichromene gaining advantage from valuable collection accessions