Evaluation of factors having an effect on cannabidiol amount in cannabis sativa L.

Abstract

Industrial hemp is a multipurpose crop, supplying fibers, seeds, and pharmaceuticals. The non-psychotropic cannabidiol (CBD) derived from hemp is a promising pharmaceutical raw material. It shows no psychotropic effects, is not listed in UN Single Convention on Narcotic Drugs, but demanded for the production of medicine products. Regretfully, there are no domestic cultivars of hemp in Russia specialized in phytocannabidiol. Currently, there is a big need in industrial varieties of pharmaceutical specialization (CBD-cultivars). This paper is the first to report on selection of the accessions with high CBD content (above 9%) and trace amounts of Δ9-tetrahydrocannabinol (THC), the main psychotropic cannabinoid, among the studied genotypic diversity of hemp plants. The objective of the study was the assessment of the effects of field watering, lighting conditions, sexual type of plants and stage of ontogenesis on CBD and THC accumulation on a broad in situ genotypic diversity of Cannabis L. germplasm accessions in order to form the optimal morphophysiological and agronomical model of CBD-producing cultivar (ideotype) well adapted to field growing. Cannabis populations in situ, genotypically original, spatially separated (and, thus, not undergone to random cross pollination), were surveyed in 2008-2011 in four Russian regions. A total of 128 populations were selected for the research; among them, 52 populations were studied for the effect of shading, and 58 for the moisture excess/deficit. For each population, plants (not less than n = 10 per each variant, i.e. shading vs. lighting, and moisture excess vs. deficit) were collected randomly and representatively to form summarized sample, and then analyzed to reveal the effect of the said factors. The plants were collected from initial budding and flowering of male plants, up to the moment when fimbles have just begun to dry out and the first seeds at the basal parts of female inflorescences have started to ripen. Air-dry samples (with and without inflorescences, female plants, male plants) were crushed and biochemically analyzed. Inflorescences (generative parts) and only leaves (vegetative parts) of the two conventional sexual types were analyzed separately. The analysis of the CBD and THC contents in the studied accessions revealed a statistically significant (p = 0.05) genotypic variability for CBD between the samples. Natural sexual polymorphism in the content of CBD and THC is statistically unreliable. Both male and female plants contain approximately equal CBD concentrations from the budding time until the seed ripening. THC amount was insignificantly increased in female plants. From the budding phase until the start of seed ripening, plants increase their CBD content more than twice. From the budding phase until the seed ripening, CBD amount in inflorescences is significantly thrice more than in vegetative parts. The difference in THC content is significant as well, but not so noteworthy. By the start of budding of different sexual types CBD content in generative parts is twice as high as that of THC. CBD accumulation reaches its maximum in generative plant parts by the time when seed ripening starts initially. The effect of shading on plants of any sexual type has shown that CBD content significantly responds to the exposure and intensity of natural lighting. Any breach in daylight illumination will reduce the CBD content. The factor of excessive/deficient natural moistening has no significant effect on CBD and THC accumulation in plants, regardless of the development phase of an adult plant of any sexual type. Unlike to dioecious cultivars specialized for seed/oil production, both female and male plants may be used for CBD production. Female plants must have extended time of budding-full flowering in conditions of reduced amounts of pollen in air and deferred seed ripening. Flowering and maximum pollen production from male plants must be deferred, because the lack of pollen in field promotes CBD formation in female inflorescences. CBD cultivar plants should have a maximum inflorescence size, a maximum budding and flowering period, and a minimum foliage.