Nonetheless, it can be speculated that infertility might improve cannabinoid yield by the following two different mechanisms: by avoiding the termination of inflorescence development and/or by avoiding reductions in cannabinoid accumulation. Similarly to Arabidopsis, C. sativa has an indeterminate inflorescence architecture, which means the inflorescences keep growing and developing additional flowers until a specific event sends a signal to halt the flowering process . In the Arabidopsis model, successful pollination can induce AGAMOUS expression , which will trigger downstream signals to end flowering and begin flower senescence . The triploid plants in our research showed no response to pollination, which could be a sign that the terminal flowering signals might not initiate in the triploid plants following a pollen challenge. On the other hand, seed development after pollination may alter carbon resource allocation, which might reduce the development of inflorescences and secondary metabolism synthesis.
Our research showed that triploid plants rarely produced seeds following pollination, and could therefore suggest that plants will not allocate carbon resources from flower development or cannabinoid synthesis to seed development. It is also possible that neither of these physiological processes are impacted, but rather the reduction in cannabinoid content in pollinated flowers is merely due to a dilution effect of the presence of seeds, which do not contain the cannabinoid-producing trichomes. More research on the effect of infertility on cannabinoid development is warranted to further confifirm the value of commercial triploid cultivars. Although plants containing even numbers of chromosomes are generally considered fertile, reduced fertility or even infertility have been reported in other species containing even ploidies. For example, the allotetraploid, or natural tetraploid, Hibiscus acetosella ‘Panama Red’ has been reported as producing no viable seeds.Reporting the reduced fertility of tetraploid C. sativa has important implications for the hemp breeding and hemp seed industries. Our results indicate that the investment of producing triploid seeds may be higher than producing diploid seeds, due to the lower seed numbers produced in the tetraploid × diploid crosses studiedin this research.
To compensate for the reduced seed number, more intense pollination or extending the pollination period may be recommended. Furthermore, the asymmetric nature of the crosses involving the tetraploid, at least as observed in the genotypes tested in the current study, indicate that the selection and breeding of the pollen recipient as the tetraploid parent has important ramifications for the success in breeding triploid C. sativa. The unidirectional compatibility or asymmetric interploidy crossing compatibility of hemp might be caused by an asymmetric triploid block. A triploid block is a phenomenon in which seed development fails due to an imbalance in genome size and gene expression between the parents of different ploidies; in many cases, triploid block leads to abnormal development or underdevelopment of the endosperm and embryo . Studies in Brassica oleracea showed the same asymmetrical interploidy compatibility pattern as we observed in C. sativa; that is, when the paternal parent had the higher chromosome number, there was a lethal disruption in embryo development, whereas when the maternal parent contained a chromosome excess, viable seeds were formed . Imbalances in the expression levels of the AGAMOUS-like gene families appeared to play important roles in the endosperm and embryo development failure in B. oleracea .
Research on potato showed that the strength of triploid block can vary among genotypes . Therefore, research into multiple genotypes and gene expression variations may be useful in obtaining a full understanding of asymmetrical compatibility and asymmetric triploid blocking in C. sativa as a species. Plant growth, development, metabolism, and morphology can be greatly manipulated by the quality and duration of light . Light quality denotes the color or wavelength adjacent to the surface of the plant, which affects plant growth, foliar and floral morphology, biochemical changes, and photosynthesis process.Plants use light sources both as energy sources and to adjust to environmental conditions.It was demonstrated that wavelengths ranging from 430 to 500 nm is effective for pigmentation, secondary metabolites production, chloroplast development, and functioning in photosynthesis . The wavelength range 500–600 nm also influences chlorophyll production and photosynthetic activity . On the other hand, the wavelength range 640–670 nm was found effective in leaf area, photosynthetic activity, and plant biomass accumulation.