What is plant tissue culture?

Plant tissue culture is the practice of growing whole plants or plant parts in an entirely sterile setting. This is usually accomplished using plastic or glass containers that contain sugars, nutrients and sometimes hormones suspended in a liquid or solid media. The most common media used is agar gel, which has a consistency of Jell-O. It has the distinct advantage of being transparent, so that it is easy to see all the plant parts and diagnose if they are unhealthy or contaminated.

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. These special abilities provide a host of interesting advantages in commercial propagation, biotechnology, breeding and germplasm storage. It is used ubiquitously in many agricultural production processes for crops such as banana, orchids, sugar cane, potatoes, berries, forestry, and other ornamental plants.

The primary use of plant tissue culture overall is to maintain cultures that are free of disease and to stop the spread of disease- many of which can be devastating without the use of this essential tool.

Why it is used for Cannabis?

Cloning is an essential and well-known process for cannabis cultivation since it creates such a uniform product. The problem is that mother plants can accumulate disease and insect pressure over time and steadily decline in health. Tissue Culture helps prevent that by maintaining the clones much in the same way as clone mothers, but in a completely sterile environment. This is a sustainable way to protect the world’s best cannabis clone library.

Standard clonal propagation involves cutting a section off a plant that has stem, leaves and nodes and placing it in a substrate that causes it to root- thus generating a brand new plant. For tissue-culture cloning, plants undergo a more slightly more involved process. 

The first stage is called Initiation- this is where small dissections of plant tissue are washed in bleach and soap (many other disinfecting agents can also be used) and then placed onto the agar gel medium. This phase is mostly about trying to establish sterile cultures and has the highest rate of contamination. Any amount of fungal or bacterial contamination will cause the entire container to be destroyed. Many laboratories use fungicides/bactericides at this stage, but it is generally frowned upon by tissue culturists who value true sterility since these agents often mask the pathogens instead of eradicating them.  

The second stage is called Elongation and Multiplication. This stage consists of growing the plant from a small dissection into a more functional plant that can then be clonally propagated into even more plants. Many laboratories add phytochemicals at this phase to induce more rapid growth, which also alters the morphology of the plant to allow for a more efficient propagation. Unfortunately, these chemicals can have a negative impact on the plants long-term growth and should be avoided as much as possible. Laboratories with deficient protocols during this phase may find themselves reliant on phytochemicals or Plant-Growth Regulators (PGRs). 

The third stage is Rooting. The plant is then placed onto media that contains nutrients and/or hormones which is specially formulated to induce the plant to root. Sometimes, the rooting and multiplication stages can be combined into one. 

Lastly, the final stage is called Acclimatization. This is the process of transitioning the plant from the sterile (in-vitro) environment to non-sterile (ex-vitro) environment. Sometimes, this stage is done at the same time as the rooting stage. 

There are a lot of different ways to accomplish the same goals and different laboratories may have devised radically different protocols to meet nearly the same end. Using these four stages, the plants are multiplied like this until they reach the desired number, and are then acclimatized and transitioned ex-vitro (the state of being in a non-sterile environment). However, this process is slow and more expensive than standard clonal propagation. For large scale propagation, it is often preferred to hybridize tissue culture cloning and standard cloning by multiplying a small number of plants in-vitro, acclimatizing them, and then using these plants for standard propagation. This is the model that Node Labs uses. 

Why is plant tissue culture used for cannabis if standard propagation is more efficient?

Cannabis is an annual plant, which means that it grows from seed, grows large stems and leaves (vegetative growth), flowers, spreads seeds, and dies- all in one year. Most cannabis plant’s flowering cycles are governed by photoperiod, which refers to how many hours of light/darkness there are in a 24 hour day. If the photoperiod is kept above 16-18 hours of day or more of light, the plants will remain in a perpetual state of vegetative growth. This is how clone mothers are made, which then are used to make large numbers of clones. 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. During this time, the plant experiences a process called Bioaccumulation, where 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. 

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. 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 ex-vitro environment. This is the primary function of plant tissue culture for Node Labs and for the industry at large. 

What are the pros and cons in using tissue culture cloning for cannabis propagation?

Pros:

Verifiably clean and stable

Repeatable and scalable

Less space and resources to keep many different cultivars

Cons:

Expensive

Specialized labor, equipment and processes

Slow compared to standard propagation

What more can I learn about tissue culture cloning?

Plant tissue culture has so many more functions for cannabis than just multiplication and cloning. Node Labs primarily uses it as a germplasm storage. 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. This allows us to hold 250+ cultivars in our library and to work with many different clients on a range of projects. Plant tissue culture is a really fascinating set of tools with a broad range of applications- many of which we have yet to understand yet!

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