Pharmaceutical cannabis requires uniformity of product on a mass scale. Because there is so much variation between cultivars, this means producers must grow large amounts of genetically consistent plants. The best way to ensure this is through the process of “cloning”: cutting branches from a “Mother” plant, and inducing them to root and become independent plants with the same genetic make-up as their parent. Many other horticultural sectors employ cloning for the same reasons as the medical cannabis industry. Under the right conditions, one cannabis mother can yield several hundreds of clones and be kept vital and productive from 6 months up to a year!
Selecting a Mother from Seed
When seeds of a specific cultivar have been purchased, it must be noted that although similar, each seed has a different combination of DNA, or “genotype”, much like human siblings or cousins. Sisters and brothers can share outwardly visible features, or “phenotypes”, such as hair or eye color, face and nose shape, etc., and similarly cannabis plants grown from seed of the same cultivar may share a similar phenotype, but they do not have identical genetics. Breeders work hard to stabilise phenotypes among seeds, however, the more seeds one starts with, the more genetic variation there is guaranteed to be in one’s crop. Clones provide a way to virtually eliminate this variation (spontaneous mutation on a cellular level, as well as epigenetic changes inducing phenotypic differences can still occur).
After starting a group of seeds of one cultivar, and identifying and separating the males from the females, what is best way to ensure that you select the right mother for your production goals? The method which provides the grower with the most certainty is as follows. First, begin by keeping careful records of each plant’s characteristics; useful metrics to compare are plant growth rate, root development, proliferation of branches, stem thickness, leaf color, susceptibility to pathogens, and overall plant health. Another interesting trait to note is the number of points of the leaves; plants with 7, 9 or more points per leaf generally exhibit more genetic stability and better quality flowers than plants that only generate 3 to 5 pointed leaves. When the female plants have four or more side branches, take a minimum of two clones from each plant. The process of cloning is described in detail in the “Cloning” article in this month’s issue; briefly, it involves making clean cuts to the branch and exposing its stem cells, which are then soaked in natural rooting hormones. The clones are kept in a humid environment because, until they form roots, they can only imbibe water through their leaves. Usually, a clone roots within 7-10 days. If one clone from a plant experiences stress or dies, the other clone(s) with the same genetics will still be viable, and if both clones are healthy it improves your sample size. Once the clones are rooted, they are planted into substrate, and immediately induced into flowering.
During the flowering cycle, the cultivator monitors the same plant characteristics as described above, as well as closely examining the structure of the developing flowers: their density, shape, aroma, and appearance. When the flowers have been harvested and cured, the grower should send adequate samples to a professionally certified laboratory to receive an accurate and complete analysis of the cannabinoids and terpenes present in each different plant. Using this information along with the data collected on plant growth and flower characteristics, the cultivator can then determine which original seed plant should be chosen as the mother to best suit their production needs.
While the clones are flowering, the original seed plants should be kept in the vegetative phase, and maintained in the best possible conditions to ensure they remain vigorous and free of pests and diseases. Data on their development should continue to be collected, and certainly should factor into the mother selection decision. Typically, the healthiest plants, excelling in more than one area of the plant growth criteria, will correspond to the flowers that tested with the highest cannabinoid or terpene contents. However, this is not always the case.
Another method of selecting mothers without waiting for clones taken from the seed plants to complete a flowering cycle, is to use data from a cannabinoid/terpene analysis of the plant’s vegetative leaf. Scientific studies as well as many cannabis testing labs in the US have collected enough data with a large enough sample size to observe a direct positive correlation between levels of cannabinoids and terpenes in the leaf during the vegetative phase and levels of these compounds in the harvested flower . This method is gaining popularity among US growers, as it can be used to save time waiting to analyse the flower produced from the clones; however, important characteristics of the flower development remain unknown; the grower must simply wait to see the type of buds produced.
One can also choose a mother solely based upon their own analysis of the plant growth characteristics, usually selecting the one or two plants which show the best performance in the most areas, I.e. the most vigorous plant, with the best root development, vibrant green color, most leaf points, showing the greatest resistance to moulds or insects and healthiest proliferation of branches. Usually the clones share these characteristics with their mother, so when laboratory testing of the leaf or flower material is not possible, this method is a viable way to ensure that one is propagating robust genetics.
Selecting Cannabis Mothers from Clone
When the seed mother has neared the end of her productivity, a new mother plant must be selected from one of her clones. In the US, where clones of specific cultivars are widely propagated and sold, many growers choose to skip the germination of seeds entirely, and trust the determination of desired phenotype done by the clone proliferators. Whether choosing a new mother to replace your original seed mother, or simply selecting one from a batch of clones, usually the quality and average cannabinoid/terpene content of the flowers is known. Therefore, it is important to use the plant health criteria we have described to determine 3-5 of the healthiest plants as candidates. Further testing of the vegetative leaves of these clones can help determine which one or two plants to select. In this instance, differences observed in the cannabinoid or terpene levels of the clones’ vegetative leaves will be based upon epigenetic factors; plants undergoing the least environmental stresses will usually show higher levels of these medicinal compounds, expressing the true potential of the cultivar’s genetics. The most stable and vigorous plants normally correlate to the ones which test highest.
Finding the right mother plant and her successive replacements is vital to the success of any large scale pharmaceutical operation. With the combination of these techniques to determine desired genetics, and propagation of these genetics in ideal environmental conditions, the cultivator can eliminate guess-work, and rely upon scientific analysis to achieve the the full medicinal potential of a specific variety, and provide a consistent, high-quality product on the scale required, to patients throughout Europe.
By Angela Swift
Forensic Sci Int. 1984 Jan;24(1):37-42.
Cannabinoid level in the leaves as a tool for the early discrimination of Cannabis chemiovariants.