Horticulture Techniques

Cultivating Medical-Grade Cannabis

Lance Griffin
Written by Lance Griffin

Nature blends order with chaos in magnificent ways. Medicinal cannabis cultivators thus wrestle with a sobering truth: plants resist rote standardization. And yet, stable chemovars are necessary for medical patients and research efforts because they provide consistent therapeutic outcomes. The standardized chemovar is a step beyond the wild west of plant names and into the predictable contemporary pharmacy. With almost 600 distinct chemicals [1], ­is it actually possible to mass-produce standardized medicinal cannabis?

In 2017, Chandra et al [2] explored this issue. They published a study in Epilepsy & Behavior describing the solutions implemented by GW Pharmaceuticals and the University of Mississippi. Both organizations have “extensive experience in producing large-scale cannabidiol chemotype Cannabis.” [2]

GW Pharmaceuticals

The producer of Sativex® and Epidiolex® has developed methods for intensive “indoor” greenhouse cultivation, less intensive greenhouse cultivation, and outdoor cultivation. [2] Cloned females come from a small genotype pool and single accession. GW is a fairly conventional cultivator.

The most intensive grow condition maintains an average daily temperature of 25° C. A supplementary lighting system is used around the clock to ensure plants always receive at least 70 W m−2 photo active radiation (PAR). To induce flowering, cultivators move the plants to an area with roof blinds and lights for 12 hours of light and 12 hours of darkness. The water used for irrigation must achieve a certificate of conformity for pH, nutrients, pesticides, and heavy metals. Beneficial insects are used as integrated pest management. Fans ensure continuous air flow and proper water vapor exchange. Growth variables are monitored closely and recorded throughout the process.

GW’s less intensive greenhouse operation removes the supplemental lighting during the flowering period. This limits flowering to the period between the vernal and autumnal equinoxes, and reduces total yield (but not quality) by one-third.

The company’s outdoor cultivation paradigm produces plants with lower amounts of cannabidiol (CBD)—around 10% instead of 20%. They treat the female parent plant with silver thiosulfate; it then secretes pollen with a female-only chromosome. This ensures all-female seed production when plants are crossed. The objective is massive, low-cost harvests that must be processed with machinery. [2]

University of Mississippi

Ole Miss screens for “elite mother clones” among seed-grown cannabis and cuttings. [2] Plants with the highest cannabinoid yields are identified using gas chromatography with flame ionization detection (GC-FID). Cuttings are then either grown intensively indoors or outdoors.

Interestingly, UM has developed in vitro propagation with “no detectable variations in morphologic, physiologic, biochemical, and genetic profiles as compared to the mother plants.” Most in vitro propagation occurs through callus cells (forming indirectly in response to a wound), which can lead to genetic variation. This is indirect organogenesis. Researchers at Ole Miss employ a “one-step regeneration protocol” using meta-Topolin (a cytokinin, or plant growth hormone) for adventitious shoot induction. Instead of regeneration from callus cells, plants regenerate directly from young leaf explants. This is direct organogenesis. These in vitro duplicates have a 95% survival rate in soil.

The university uses synthetic seed technology for its germoplasm database of superior cannabis genetics.

“The protocols developed would be helpful for large-scale mass propagation of elite Cannabis varieties for further use in phytopharmaceuticals,” Chandra et al report. [2]

As the quest for truly medical-grade cannabis continues, these strategies are sure to evolve. What’s certain is that medical cannabis has entered the upper echelons of scientific endeavor.

References

  1. ElSohly MA, et al. “Phytochemistry of Cannabis sativaProg Chem Org Nat Prod, Springer, vol.103, 2017, pp.1-36, doi: 10.1007/978-3-319-45541-9_1. Times Cited: 67
  2. Chandra S, et al. “Cannabis Cultivation: Methodological Issues for Obtaining Medical-Grade Product.” Epilepsy & Behaviour, vol.70, 2017, pp.302-312. Journal Impact Factor: 2.378, Times Cited: 23

Photo by Aphiwat chuangchoem from Pexels

About the author

Lance Griffin

Lance Griffin

Lance

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