What is tissue culture cloning?

Whether you're a Master Grower or a home gardener, when it comes to growing cannabis genetics will play an important role in the quantity and quality of bud you get to finally harvest.

Over decades of dedicated work on pheno hunting, breeding and cloning, breeders and cultivators have worked hard to develop reliable methods for capturing and replicating desirable genetics. Until recently perhaps the most widely used method has been through traditional cloning techniques, but as the science and technology of cannabis forges ahead a new option is emerging that could revolutionize cloning and the industry as a whole.

Tissue culture cloning is a technique that has been used for decades in commercial agriculture, and is now gaining traction in cannabis. What is tissue culture? How does tissue culture cloning work for cannabis? And what are its major advantages and disadvantages? Read on to understand this emerging propagation technique.

What is tissue culture cloning?

No matter the plant—vegetables, trees, flowers, herbs or medicinal plants—all cultivators share the desire for healthy and vigorous plants of known genetics that are pest and disease-free.

Plant tissue culture (TC) is a collection of techniques to harvest, clean and replicate plant cells, tissues or organs in sterile conditions. Within tissue culture is a method known as micropropagation, a process that is used to produce plant clones.

“Micropropagation is a trusted method of propagating plants that has been used for decades in the agricultural and horticultural industries to propagate a wide variety of plants such as bananas, berries, fruit and nut trees, hops, orchids, ornamental plants, and sugar cane," explained Nikolaus Matheis, Senior Director of Quality Assurance at Conception Nurseries, a company that specializes in cannabis tissue culture.

Austrian botanist Gottlieb Haberlandt began working out the rudimentary techniques of plant tissue culture at the beginning of the 20th century. By mid century, more research refined these techniques, but it wouldn't be until the 1990s that plant tissue culture became widely used in commercial horticulture and agriculture.

By taking just a few cells from a desirable plant and initiating them into tissue culture, countless identical copies can be produced. How does the process work? After harvesting a section of healthy plant tissue it is cleaned and sterilized before being lodged in a test tube or dish with a gel-like growth medium that contains nutrients and growth hormones. “The most common media used is agar gel, which has a consistency of Jell-O," explained Lauren Avenius, CEO at Node Labs, a California based company that specializes in tissue culture for the cannabis industry. “Since the media has all the necessary components needed to provide sustenance to the plant, it is possible to propagate plants or grow plants from parts that would otherwise be impossible such as leaves, stems, flowers or even pollen or anthers."

The plant tissue is kept in a completely sterile environment, where it progresses through different stages of growth until the sample is mature enough to be cloned. Then, cuttings are taken and these go through a similar sterilization and growth process until they are ready for root growth and eventual transplantation into a growing or production environment.

These new plants have identical genetics to their “mother" and are completely free of pests and diseases. Tissue culture cloning, or micropropagation, can reliably produce scores of plants with impressive accuracy.

What is cannabis tissue culture cloning?

Photo by: Gina Coleman/Weedmaps

Traditional cannabis cloning involves keeping fully grown plants, called “mother plants" or “moms," of various cultivars (strains) in a continuous vegetative state so that cuttings can be taken from the plants for propagation.

“This is not a natural state for the plant, and it is not well-evolved to be maintained in the vegetative growth phase without flowering for months, years or decades," explained Avenius. Over time, the quality of the mother plants and their genetics declines in a process called bioaccumulation. “Exposure to disease, insects, and stress send it on a steady decline until eventually, the plant succumbs to the pressure and can no longer be efficiently propagated, or the flowers decline in quality."

With tissue culture, once plant tissue is harvested from a desirable mother plant, these cells can be replicated almost endlessly without having to maintain the original donor plant in an endless vegetative state. Prized genetics can be preserved, and clones can be produced when needed.

“Plant tissue culture can successfully interrupt the cycle of bioaccumulation by maintaining the plants in a low-stress environment without exposure to insects or disease," said Avenius. “Additionally, populations that have already been exposed to disease can be effectively screened and quarantined to ensure their cleanliness, which is extremely difficult to do in the [production] environment."

This might be the most valuable application of tissue culture for the industry. “The primary use of plant tissue culture overall is to maintain cultures that are free of disease and to stop the spread of disease," explained Avenius. The spread of diseases like powdery mildew, botrytis, and hops latent viroid amongst crops can be truly devastating to cannabis cultivators, and in some cases, can wipe out entire harvests.

When it comes to getting started with tissue culture cloning for cannabis, home gardeners and small cultivators may opt to start out with tissue culture kits available at specialty gardening stores and online. Cultivators can also set up their own tissue culture labs or seek out the services of tissue culture specialists. As this technology gains traction in cannabis, a variety of tissue culture companies like Conception, Node Labs, and others, are emerging to provide services such as consulting on lab construction, restoration, and preservation of genetics and tissue culture clone production.

Some cultivators have married the use of tissue culture with traditional cloning through cleaning and restoring mother plant genetics to then propagate using traditional techniques, for example. Still others use tissue culture techniques as a way of preserving and banking genetics in a process called germplasm storage.

What is germplasm storage?

“Plant tissue culture has so many more functions for cannabis than just multiplication and cloning," said Avenius. For tissue culture specialists like Node Labs and Conception, banking genetics may be one of the most attractive features of tissue culture technology since it offers a way for cultivators and breeders to indefinitely preserve any highly valuable genetics they have developed or acquired.

“Germplasm storage is a fancy term for a genetic bank—where we keep many accessions of clones and withdraw them for special projects, genetic licensing, and for nurseries to build clone mothers from for large-scale propagation," explained Avenius. “This allows us to hold 250+ cultivars in our library and to work with many different clients on a range of projects."

The pros of tissue culture for cannabis

There are some impressive benefits when using tissue culture technology in cannabis. Among some of the biggest advantages:

• Preserved genetics. As compared with maintaining a mother room, stored plant tissue culture takes little space and can preserve genetics indefinitely. This allows growers to store genetics they may wish to breed or simply reintroduce into production later on.
• Increased productivity in a smaller footprint. “Traditional cloning methods require setting aside a substantial amount of space for cloning," explained Matheis. Tissue culture needs less starting material, and a lab takes a fraction of the space as compared to mother rooms. Plus, TC can produce more plants in that space.

• Consistency. Cannabis growers want consistent appearance, size, cannabinoid, and terpene profiles over time, and micropropagation produces genetically identical copies of plants. “Clones produced using micropropagation provide a high level of consistency across plants and over time by keeping the plants free of pests and pathogens and by maintaining juvenility during the micropropagation process," said Matheis.
• Pest- and disease-free plants. Like any plant, tissue culture clones are still susceptible to pests and contaminants that may be present in a growing environment. However, at least initially, clones produced using TC are pest and disease free. “Using clones produced via micropropagation helps to protect against infections and infestations and provides more consistent plant growth during vegetative and flowering cycles," said Matheis. “These advantages provide cultivators with more consistent production cycle after cycle."

The cons of tissue culture for cannabis

Clean, consistent, and replicable genetics that can be used and banked indefinitely may sound like a cultivator's dream, but tissue culture is not without its downsides.

• It is expensive. While a starter kit is reasonably inexpensive and can get you up and running, to do tissue culture well and at large scales requires a significant investment in a high-tech and completely sterile lab. Even at small scales, it can be relatively expensive, resource-intensive, and time-consuming.
• It's a slower process than traditional cloning. To get traditional clones up and running using clippings, it can take about two weeks, whereas the initial tissue culture process can take much longer. “The tissue culture process is exhaustive and time-consuming if done correctly, requiring multiple rounds of screening for pathogens, genetic fingerprinting, and identification and optimization of the plant growth medium," said Matheis. “This process can take up to 12 months for some of the more challenging cultivars." Once complete, tissue culture cloning can produce orders of magnitude more plants.
• TC clones need an acclimatization period. When tissue culture clones are ready to be introduced to their growing environment, they tend to have different needs than traditional clones. “Clones produced via micropropagation respond best to a modified acclimation process that requires increased relative humidity during the first couple of days of acclimation, so some slight adjustments in the growth environment might be necessary," said Matheis.

The bottom line

Tissue culture technology has been used to propagate a wide variety of plants, including orchids, bananas, and hops, for example. Today, it is being used in the cannabis industry with increasing interest and frequency.

Tissue culture techniques, including cannabis tissue culture cloning, offer several strong advantages over traditional cloning and propagation techniques. Tissue culture cloning provides consistent, healthy, pest- and disease-free plants. Tissue culture can also allow breeders and cultivators to bank desirable genetics indefinitely. With that said, it is still a relatively new technology in the space, and it can be quite expensive to do at scale.

There are a growing number of cannabis tissue culture specialists emerging to support the industry in building in-house labs, cleaning and restoring genetics, and providing flowering stock for production. “Plant tissue culture is a really fascinating set of tools with a broad range of applications, many of which we have yet to understand," said Avenius. As the adoption of these new tools continues, costs to the industry should continue to decrease while benefits for both cultivators and end consumers will grow.