Hemp Tissue Culture: The Power of Predictability

hemp tissue culture

The need for predictability and quality among cultivators has led to renewed interest in the unique benefits of tissue culture propagated plant stock.
Photo by Hope Jones

Plant tissue culture (a.k.a, micropropagation) is widely used in the commercial horticulture industry for the mass production of clonal plants. Though more costly than traditional seed or vegetative propagation, micropropagation has several potential advantages over these methods, including:

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  • Rapid (exponential) and continuous multiplication of true-to-type clones
  • Increased plant yields, plant vigor, and pest resistance
  • Virus elimination
  • Space and labor savings
  • Genetic preservation and recovery

Despite the many benefits, the cannabis and hemp industries have been slow to adopt this proven propagation methodology, due in part to the long history of prohibition of these crops. But rapid market growth, shrinking margins, and recent high-profile crop failures are driving producers to reevaluate their current vegetative or seed propagation practices.

Hemp, the Second Green Rush: Boom and Bust

When the 2018 Farm Bill legalized hemp flower extract, it heralded the second “Green Rush” of the new legal cannabis era. Hemp flower provides a rich source of CBD, a valuable cannabinoid used to enhance wellness and treat a wide range of ailments. Because of high consumer demand for CBD and related cannabinoids, the most profitable hemp varieties invest most of their energy into production of CBD-rich flowers. This is best illustrated by the current hemp biomass pricing standard: $/CBD%/pound (dollars, per % of CBD potency, per pound). To maximize profit and avoid crop failure, producers must pay careful attention to the genetic potential, gender, and virus and disease. While there are numerous talented and trustworthy hemp breeders, the market is in its infancy. Most farmers are growing hemp for the first time, and there are many opportunists who have rushed in to take advantage, offering seed and stock fraught with quality variations in terms of seed gender, potency, and seed-coat diseases.

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Genetic Potential: As with any crop, genes are the primary determinant of the plants’ potential to produce commercially desirable products. In the case of hemp, it is the profile and quantity of particular phytocannabinoids produced primarily in the flowering structures of the plant. Flower cannabinoid ratios (e.g. CBD to THC – the psychoactive cannabinoid), must be carefully monitored and managed. CBD flower crops that fail to achieve the anticipated CBD percentage profile could result in thousands of dollars lost per acre. Even worse, if the percentage of psychoactive cannabinoid THC becomes “hot” (rises above the 0.3% federal limit), many states require that the entire crop be destroyed.

Not surprisingly, the 2018 and 2019 seasons were plagued by crop failures associated with unpredictable seed and stock. For example, many growers in the Northeast who purchased stock advertised as producing 10% to 14% CBD by weight realized only a fraction of that, racking up thousands in losses. In Hawaii, more than half of CBD hemp crops cultivated in 2018 had to be destroyed due to THC levels above federal limits.

Gender: Industrial hemp is generally dioecious, relying on the wind to carry out pollination. Because unpollinated hemp flowers produce the majority of cannabinoids, producers must pay careful attention to plant gender and the presence of male plants within the crop. Partial or complete loss of CBD production can result from flower fertilization.

Virus and Disease: Seed-coat diseases such as the tobacco mosaic virus (TMV) and hop latent viroid (HpLV), often introduced by inexperienced growers using poor cultivation practices, have resulted in crop losses and significantly reduced crop yields. Because few testing standards are in place in the cannabis and hemp industries, viruses and pathogens tend to persist in crops for years through vegetative propagation and lack of prevention and intervention strategies.

Hemp cultivators face a far greater number of variables than ever before, and these added challenges have them questioning whether seed planting remains their best option. Unpredictable and unreliable starting materials have resulted in the loss of millions of dollars of anticipated yield in industrial hemp. Cultivators have an immediate need for a large supply of stable, reliable, virus-indexed (clean) all-female CBD hemp plants with consistent growth habits and cannabinoid yields. This need for predictability and quality has led to renewed interest in the unique benefits of tissue culture propagated plant stock.

Hemp genetics research in lab

To maximize profit and avoid hemp crop failure, producers must pay careful attention to the genetic potential, gender, and virus and disease.
Photo by Hope Jones

Barriers to Tissue Culture Adoption

With the numerous risks introduced by seeds, why wouldn’t cultivators move to micropropagated planting stock? One of the main obstacles to the adoption of transplants is the higher upfront costs of plants. Hemp seeds are roughly $1 each, while young plants can start at $3 to $4. With germination rates and seedling costs added in for seeds, planting stock can still require as much as a 65% higher upfront investment. But these upfront costs can reward the cultivator with returns on investment significantly higher than seeds when demonstrated hemp seed risks are factored into the business case (e.g., the risks of catastrophic crop failure associated with THC levels beyond federal standards, seed coat diseases, mixed gender crops, and excessively low CBD profiles, for example).

An additional challenge to adoption is the difference in root architecture of seed versus tissue culture plants. Seed propagated plants have tap roots, while clones and micropropagated plants do not. There is a legitimate argument to be made around tap roots and overall plant vigor. However, crop profitability and return on investment are based on CBD% profile and THC compliance, not on vigor alone. Hemp crops raised for cannabinoids tend to be highly managed and provided with optimum growing environments and not left to fend for themselves under suboptimal conditions when a tap root would be most critical. There are numerous examples of successful, large-scale, clonally propagated crops and programs, including reforestation programs, strawberries, and nut trees, for example.

The risks and benefits concerning the presence of a tap root must be weighed in light of the horticultural, market, and legal challenges that must be met to optimize crop profitability.

Success is a Numbers Game

Hemp provides a lucrative crop opportunity if there is a robust and healthy harvest. Profitable crop yield is a game of numbers, and every single percentage point counts. Seeds that miss on the anticipated plant characteristic can drop crop value precipitously. And with prices being driven down and margins getting tighter, cultivators must secure a reliable supply chain of healthy robust planting materials. The need for stock reliability is moving hemp in the direction of many modern commercial crops, toward micropropagated plants. Although micropropagation is not new, it does deliver a new path to profitability for hemp cultivators and one well worth their time and attention.

Author Note: Special thanks to Kerry Starr and Chris Pagliarulo from Adivina for also contributing to this article.

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