Cannabis growers need to know the nuances of tissue culture

Bum seeds. Females that turn into males. Hemp plants that go into THC overdrive and must be destroyed.

Cannabis producers have seen firsthand the devastation that inconsistent genetics and pests can have on a crop.

The good news is that as the cannabis industry begins to mature, horticultural companies are pouring research and money into cannabis to advance the science of breeding new varieties and establish clean stock standards to ensure supply-chain integrity.

Tissue culture is a key area where advances are being made. The biotechnology could lead to consistent, successful cannabis crops.

But cannabis producers must understand the different types of tissue culture – and the risks and opportunities that come along with them.

Tissue-culture background

Plant-tissue culture, or micropropagation, has been widely used for specialty crops such as citrus, strawberries and ornamentals. The technique is used to:

  • Keep plants safe from infections that can’t be removed or treated.
  • Avoid infection that can damage plants and prevent commercial distribution.
  • Provide a way of storing plants and plant germplasm in a simpler way that takes up less space.
  • Produce clean stock clones that can be used to establish clean stock mother plants.

Tissue-culture storage helps protect plants that are healthy and disease-free by archiving them in tissue-culture labs under sterile conditions.

“In order for cannabis to be welcomed as a mainstream agricultural crop, cultivation must be responsible and not put other valuable crops at risk by serving as a disease reservoir,” said Josh Schneider, CEO of Cultivaris Hemp in San Diego.

Pathogens such as viroids, phytoplasma, fungus and bacteria can severely diminish plants’ vigor or kill them outright.

Schneider points out that two common pathogens – hop latent viroid and hop stunt viroid – are attracting attention right now because they both diminish plant vigor and yield and can spread to other crops.

Recently, it has come into vogue among some producers to market direct-from-tissue culture cannabis plantlets as clones to go straight into flower production.

This comes with substantial risk for a plant as vigorous as cannabis because the hormones used in tissue-culture production can linger in the plant and cause unusual growth or flowering delay.

Though micropropagation is often more expensive than seed or vegetative (clonal) propagation, tissue culture has advantages.

In addition to space savings, genetic preservation and pathogen protection, the tissue-culture process helps increase yield by returning some vigor of the juvenile state of plant growth.

Two ways to go

Two types of tissue culture are most relevant to cannabis producers.

Nodal culture involves establishing a plant cutting on a growing media such as agar with plant-growth hormones.

As the plant grows and fills out the vessel, it can be propagated by taking cuttings or segmenting the plant and resetting the cuttings into new vessels, allowing for multiplication of the plant exponentially under sterile conditions so many plants can be grown in a small space.

“This is the part of tissue culture that is most often used to justify the process because it can be shown on paper as a way to get a lot of plants from limited space, but this process only sounds easy,” Schneider said.

Nodal culture:

  • Stores plants safely.
  • Can eliminate surface pathogens such as powdery mildew.
  • Protects plants from infection from a range of pathogens.
  • Multiplies plants on a large scale.

However, nodal culture won’t eliminate systemic pathogens such as virus, viroid, fungus or bacteria, nor will it change the genetic composition of the plant.

And nodal culture can leave trace pathogens that tests won’t detect.

Meristem culture, conversely, is a process that helps further refine plants initiated into tissue culture.

Meristem initiation can either be from plant cuttings taken directly from the plant or cut from plants growing in nodal culture.

“The meristem is a group of undifferentiated cells at one of the top growing points of the plant that have not yet developed a vascular connection to the rest of the plant,” Schneider said.

Meristem culture:

  • Can be used repeatedly to eliminate viral and other infections.
  • Does not guarantee the removal of pathogens, as some pathogens can penetrate nonvascular tissue.
  • Can be extremely difficult and technical, requiring tissue-culture and plant-physiology experience and education.
  • Often takes one to two years to complete.

“Not all tissue culture labs can successfully harvest meristem tissue and get it to regenerate new shoots,” Schneider said.

A complex process

In both nodal and meristem culture, the process of identifying ideal plant candidates can take time.

That’s because some plants will die in the early stages.

Once a plant started from tissue culture has successfully transitioned from the lab, it can be potted up for its life as a mother plant.

After the plant has established itself and is growing actively, cuttings can be harvested regularly and rooted for clone production.

More to come

Tissue culture is only one opportunity for cannabis advancement through the application of agricultural and horticultural practices, according to Aaron Van Wingerden, CEO of Dutch Heritage Gardens in Denver.

“In the last two to three years, there’s been so many debunked myths that have dominated cannabis for the last 50 years, because of the science and the data-driven companies and professionals that are just pouring research and money into what really goes into a cannabis plant, what comes out of it and how to grow and harvest it,” said Van Wingerden, who is part of the Green Horizon Alliance, a six-company venture formed this fall that’s aiming to invest in cannabis breeding, trialing and propagation technology starting with the hemp space.

“I think we’re just scratching the surface.”

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