The uniqueness of biological characteristics of technical hemp and prospects for its practical use

Abstract

Purpose and objectives. The study purpose was development of new hemp varieties of for different uses, identification of biological characteristics of the monoeciousness traits and diversity of cannabinoid compounds, and evaluation of prospects of developing varieties for seeds, fiber, oil, and medicinal drugs.

Material and methods. Hemp varieties grown in breeding variety trials and breeding nurseries were taken as the test material. The oil content was determined by C.V. Rushkovsky’s method; the fatty acid composition of oil - by gas chromatography on a chromatograph Selmichrom-1; the contents of cannabinoids and terpenes – by an internal standard method on a gas-liquid chromatograph HP 6890 Series Hewlett Packard. Relationships between the traits were assessed with correlation coefficients.

Results and discussion. The breeding was hampered because of a number of biological features of hemp: specific odor, cross-pollinating, heterozygosity, sex polymorphism, dominance of the cannabinoid presence, a direct correlation between the contents of cannabidiol and tetrahydrocannabinol, formation of glandular hairs (trichomes) and essential oils on leaves and perianths.

It was demonstrated that in varieties with an increased THC content there was a direct correlation between the number of glandular hairs and the contents of cannabinoids, and if THC is absent, or if its content is very low, this relationship is broken. Almost all industrial hemp varieties with a minimum THC content or without THC at all were revealed to contain essential oils (0.06–0.24%).

Hemp breeding is also complicated by sex polymorphism, the ontogenetic and phylogenic characteristics of which are determined by the habit factors and the male/female flowers ratio. Universal check variety Hliana is the best variety in terms of sex composition and monoeciousness stability with minimal segregation of male plants in reproductions.

There are universal varieties (check variety Hliana) with a certain yield (fiber and oil contents – 30%, stem yield – 7.5–8.0 t/ha, and seed yield – 1.0–1.2 t/ha) and specialized varieties – for fiber (variety Hlukhivskyi 51, the fiber content is 38–40%), seeds (variety Hlesiia, the seed yield is 1.5–1.8 t/ha) and oil (variety Mykolaichyk, the oil content is 38–40%).

The prospects of breeding to create medicinal varieties have been proven. The direct dependence of synthesis of one cannabinoid on another (r = 0.7–0.9) restricts breeding for an increased cannabinoid content in the range of 1.5–3.0%. In this case, the content of tetrahydrocannabinol does not exceed 0.08%.

The breeding methods developed to increase the cannabidiol content made it possible to create new starting material stabilized in terms of the cannabidiol and tetrahydrocannabinol contents at the level of 1.5–3.0 and 0.04–0.07%, respectively.

For the first time, we established that there was no relationship between CBG and THC. Targeted selection for increase in the CBG content led to the creation of hemp variety Vik 2020 with a cannabigerol content of up to 1.0% and without THC.

Conclusions. The results obtained prove the uniqueness of technical hemp as a biological object of research, possibilities of developing new scientific theories, breeding methods, genetic mechanisms of cannabinoid synthesis and practical use of such hemp products as oil, hulled seeds, fiber and medicinal agents in different production areas, where, as more advanced processing techniques are developed, the effectiveness of hemp rises.

The technical hemp varieties, universal, seed and fiber ones, are noticeable for the absence of THC and CBD and can be used for fiber (the fiber content is 30, 28 and 38% in universal, seed and fiber varieties, respectively), seeds (the seed yield is 1.0–1.2, 1.5–1.8 and 0.8–0.9 t/ha in universal, seed and fiber varieties, respectively) and oil (the oil content in seeds is 30, 34–38 and 28% in universal, seed and fiber varieties, respectively).

For the first time in the history of hemp breeding, studies have has been conducted to develop medicinal hemp varieties.

A medicinal hemp variety has been created (variety Mriia). It, in addition to leaf biomass with an increased CBD content, gives a seed yield of 0.8–1.0 t/ha with oil content of up to 28% and a stem yield of 7.0 t/ha with a fiber content of 28-30%. Variety Vik 2020 with an increased content of KBG (1.0%) and without THC has been created.