Plant tissue culture is a propagation technique used to develop and maintain sterile plant cells, allowing growers to reproduce genetically identical clones on a significant scale with less space required by mother and cloning rooms. As cannabis cultivators are just beginning to understand this decades-old agricultural practice, learning its logistics, drawbacks, and benefits remains an ongoing process for the industry.
Kevin Kuethe, chief cultivation officer for Michigan-based Lume Cannabis Co., says tissue culture’s versatility makes it a great tool for cannabis growers compared to more traditional propagation methods (seeds and cuttings). But the learning curve can be steep.
“You really have to dedicate your time and focus to tissue culture,” Kuethe says. “It’s a safeguard that protects you from so many different things.”
Generally, growing from tissue culture requires sterile conditions and specialized equipment, making it typically more suitable for bigger grows. However, the small size of tissue samples makes it possible for budding breeders to research and store cultivars in smaller spaces. Even larger growers won’t be overburdened, as experts says as little as 800 square feet is enough to contain a perfectly viable tissue lab area.
“You’re working with small parts of plants inside petri dishes or boxes; you can fit nine plants in a 3-square-inch box and stack those boxes on racks,” Kuethe says.
Tissue culture fosters genetic stability by propagating plants in closed vessels under germ-free conditions, virtually eliminating the spread of crop- destroying diseases and pests. Highly prized genetics contaminated with infectious pathogens also can be remediated using tissue culture.
“Tissue culture is an important tool to establish exciting, new disease-resistant cultivars,” says Hope Jones, co-founder and CEO of Emergent Cannabis Sciences, a cannabis consulting service specializing in tissue culture and controlled environment agriculture in Tempe, Ariz. “We can use it for disease indexing to get rid of pathogens at the bare minimum, then take it a step further to eradicate viruses plaguing the industry.”
A New, Old Option for Cannabis Growers
Tissue culture is a highly efficient growing technique, considering plant cells (including those collected from cannabis) have the ability to regenerate into an entirely new plant. Plant tissue cultures have a broad range of commercial applications—among them extensive propagation and preservation of endangered species.
Propagating plants via tissue culture dates back to the mid-20th century, when horticulturists were searching for a means of cultivating orchids and other plants difficult to produce from seeds. The technique, which became widespread during the 1990s, involves taking a small tissue sample from a mature plant (ideally a newer offshoot) and nurturing it under sterile conditions. Once taken from the mature plant, the sample is grown in a culture medium, typically an agar gel, along with a variety of nutrients, hormones, and other ingredients to stimulate cell replication.
Once the cell replication process begins, clones can be replicated infinitely as new samples can be taken from newly replicated cells and stored for future use.
“With tissue cultures, you can bank your genetics,” says Allister Malcolm, associate scientist at Harbor Farmz, a cannabis cultivation operation in Kalamazoo, Mich., highlighting one of the main benefits of micropropagation. “You can keep a large number of plants that take up a fraction of the space as full-sized plants.”
Kuethe adds that “synthetic seeds” are another beneficial offshoot of tissue culture. This alternative method for tissue culture propagation involves cryogenically storing genetic material. First, the genetic material gets collected through micropropagation in the form of a tissue culture plantlet. The material, which is genetically identical to the mother plant, is then encapsulated in gel and frozen, a process that preserves elite phenotypes without fear of genetic degradation. Once removed from its cryogenic state, the plantlet can be sown like a regular seed.
“In traditional tissue culture, we have a success rate in the upper 90 percentile, but the success rate in freezing, thawing, and repopulating [synthetic] seeds is closer to 50%,” Kuethe says. “Fifty percent is more than we need, since the purpose of cryo freezing is genetic preservation. Freezing the [synthetic] seeds protects them from anything that can live in a hot environment, like mold or pathogens. This kind of biosecurity is priceless to me, and the process is just really cool.”
For all its benefits, tissue culture involves an outlay of time, money, and skill—one likely more suitable for bigger cannabis grows that are well-capitalized.
“Smaller growers are typically trying to maximize everything they have at hand, including labor and space, so you don’t usually see this on a smaller scale,” Kuethe says. “There’s no question whether tissue culture is beneficial; it’s a matter of getting the lab set up and having the background and knowledge to operate it. At larger scale with tens of millions of dollars at risk, [tissue culture is] very applicable.”
Prospective micropropagators can start by indexing their most valuable cultivars, according to Jones. Indexing genetics is the first step in the tissue culture process, whether done in-house or by an entity like Jones’ that works directly with cannabis companies.
When it comes to building out the lab, “if you’ve got two sterile laminar flow hoods with two technicians, 2,000 square feet is a good example of the kind of footprint you’ll need,” Jones says. “You could even go for 800 square feet for a smaller, in-house space.”
Any lab space should be sealed against damaging spores or mites that can settle into crevices and cracks. Jones suggests building out vinyl floors with heat-welded seams for easy cleaning. As for a racking system to hold plants, powder-coated racks will hold up better against humid lab conditions and corrosive cleaning products than a typical steel set-up, she says.
Keeping a clean space also is critical. “Non-porous surfaces are good for counters and walls—countertops can be fiber-reinforced plastic,” Kuethe says. “Use hydrogen peroxide or bleach for surface cleaning. You’ve got to clean everything like you’re doing open-heart surgery.”
Regarding day-to-day equipment, most tissue culture labs will need an autoclave (a machine that uses steam and pressure for sterilization), alongside laminar hoods, a refrigerator and freezer, a stir plate, and a glass bead sterilizer or Bunsen burner. Kuethe says a dissecting microscope and high-definition screen are additional important add-ons for any well-run tissue culture lab, as the meristematic tissue involved cannot be seen with the naked eye.
An ideal ambient temperature for your lab area is about 70 to 75 degrees Fahrenheit, Jones says. She recommends paying special attention to HVAC systems, as an oversized unit will needlessly ramp up your power load. On the lighting side, Jones employs industrial-grade LEDs at a starting point of 50 PPFD (photosynthetic photon flux density, the amount of photosynthetically active radiation (PAR) light that reaches plants).
Growers first exploring building an in-house tissue culture lab may be intimidated by cost; even on the hobbyist level, building a 1,000-square-foot lab will require a $50,000 investment, Jones says. Through her business, she works with beginning budgets of $50,000 to $250,000, with high-end labs running between $1 million to $5 million. No matter the dollars spent, costs generally are split evenly between buildout and equipment.
Deb Sweeney, director of plant tissue culture at Harbor Farmz, puts pricing at a $100,000 minimum, even for modest arrangements.
“It depends on the scale of what you want to do,” Sweeney says. “We have 1,000 to 2,000 vessels [mother plants in different growth phases] in our grow area for tissue culture, which means lots of media being made and extra cost along with it. But for someone with a handful of genetics, you can have a tissue culture lab for less.”
Ultimately, the novelty of tissue culture within the cannabis industry is perhaps the highest current hurdle for widespread adoption, Jones says.
“We don’t have all of this figured out right now,” she says. “For other plants, there are decades of research and protocol around tissue culture. It will take a while for [the cannabis industry] to get healthy, stable, reliable genetics.”