Phenotypic manifestation of the traits of presence and content of cannabinoids in the process of self-pollination in monoecious hemp and selection

Abstract

Purpose and objectives. To reveal peculiarities of the inheritance of the traits of cannabinoid compound presence and content upon self-pollination in monoecious hemp, to compare the pair correlation coefficients between the contents of major cannabinoid compounds in initial genotypes and self-pollinated lines, and to evaluate the effectiveness of self-pollination in hemp breeding.

Material and methods. The study was carried out at the Institute of Bast Crops of the National Academy of Agricultural Sciences (Hlukhiv, Sumy Oblast, Ukraine) in 2009–2019. Inbred lines of industrial hemp varieties Hlukhivski 58, Hlesiia, Mykolaichyk, and Hlukhivski 46 belonging to the Central European eco-geographical type and variety Zolotoniski 15 belonging to the Southern eco-geographical type were taken as test objects. Self-pollination of plants (with and without cannabinoids) was carried out under individual agrotextile bags in a greenhouse. The offspring were grown in a nursery. Evaluation and analysis of cannabinoid compounds were conducted by thin-layer chromatography. In all the genotypes under study, the tetrahydrocannabinol (THC) content did not exceed 0.08% that is standard allowed by the current legislation of Ukraine. Data were statistically processed with calculating arithmetic mean, sampling mean error, pairwise correlation coefficients, and curvilinear regression.

Results and discussion. Provided directional selection of initial plants that do not contain cannabidiol (CBD), THC or cannabinol (CBN), self-pollination reduced their contents to complete absence. Stabilization (homozygation) of the lines occurred in I₂–I₆ and was specific to a particular variety. Inbred lines of these generations are recommended to involve as parents in crossing. The ability to segregate CBD-, THC-, and CBN-free families as early as in I₁. is a characteristic feature of the hemp varieties under investigation. There were strong positive correlations between the cannabinoid contents, in particular there was a strong positive correlation was found between the CBD and THC contents (r = 0.72–0.79 and 0.71–0.90, respectively), a strong or medium positive correlation between the CBD and CBN contents (0.68–0.80 and 0.67–0.82, respectively), a strong positive correlation between the THC and CBN contents (0.71–0.83 and 0.80–0.85, respectively) in I₁–I₃ Hlukhivski 58 and I₁–I₃ Zolotoniski 15. This makes selection for reduced contents of all cannabinoid compounds and easier, but at the same time significantly complicates breeding for increased CBD content with concurrent reduced THC content or increased contents of non-psychotropic cannabinoids. The correlations between the contents of cannabinoid compounds in inbred genotypes are weaker than those in the original breeding genotypes, with the coefficients ranging significantly, which allows using closely related reproduction in breeding aimed at reducing THC content or increasing non-psychotropic cannabinoid contents.

Conclusions. Self-pollination is an effective method of determination of the hemp population stability in terms of the cannabinoid compound presence and contents and at the same time is a method of creating breeding genotypes with stable traits of cannabinoid absence or presence