Micropropagation Technique Shows Promise For Cannabis, Study Finds
In commercial cannabis and hemp production, there is an onus on producing large numbers of plants with very predictable genetics, and therefore very predictable properties. To do this, commercial growers will collect seeds or cuttings from a large “mother” plant and then propagate new plants from these materials. This propagation method produces very predictable plant crops, but these mother plants require large amounts of space and resources to maintain. They also must be replaced every six months or so as they lose their vigor or fall victim to disease, making the process heavily labor-intensive and inefficient.
Other areas of horticulture avoid these problems by using a different propagation technique, micropropagation. But this practice has never been adopted widely by the cannabis industry, as the cannabis and hemp plants are seen as particularly difficult to micro-propagate.
Now, a new paper published in the American Society for Horticultural Science journal HortTechnology reports a new method for the micropropagation of hemp which overcomes some of the largest challenges with previous micropropagation methods – potentially opening the door to a new, more efficient cannabis production sector.
Bringing cannabis up to speed
In micropropagation, extremely small cuttings from a mother plant are taken and then grown in laboratory conditions to produce clones of the mother plant. The technique requires far fewer mother plants than traditional cannabis cultivation, and the plant tissue cultures produced in the laboratory can be stored for longer and in less space than additional mother plants.
“Micropropagation produces many more clones than other methods. Since it is not relying on seed, the clones are uniform, and they will perform similarly to the parent plant. Plants that come out of tissue culture also have the benefit of being disease-free, they frequently show enhanced vigor, and you can grow a lot more in less space,” explained study author and University of Connecticut Associate Professor Jessica Lubell-Brand, in a statement.
The difficulty comes with how these plants in tissue culture are managed, as the cultivator assumes the responsibility of administering nutrients and growth hormones in the growth media, and in controlling exposure to other variables, such as light and heat. While there have been previously published micropropagation methods for cannabis and hemp plants, no method has translated well to large-scale production. Oftentimes, the plants would display inconsistencies in shoot elongation, an inability to maintain good quality growth, and problems with hyperhydricity – a malformation in the plant roots due to oversaturation with water.
“Cannabis does not really want to be in tissue culture. This research is a lot of trying to figure out, What more does the plant need?” added Lubell-Brand.
Cracking the cultivation code
In their new cultivation study, the University of Connecticut trialed a range of different growth media and nutrient treatments to optimize healthy shoot and leaf growth in hemp plants. They also experimented with the use of vented-lid vessels with 0.2 millimeter-wide pores to see if it were possible to prevent shoot hyperhydricity.
“We start the culture using shoot tips from greenhouse-grown plants,” Lubell-Brand recalled. “Then we subculture those and if we suspect something is lacking, for instance, that the plant isn’t getting what it needs in the media, we experiment with nutrients like calcium, magnesium, phosphorus, and nitrogen to try to increase the length of time that they grow in culture.”
The University of Connecticut researchers discovered that significant improvements could be made to previously published methods by altering the composition of the culture medium at different stages of the hemp plants’ life.
The original methodology used a common Murashige and Skoog (MS) plant growth medium containing small amounts of sucrose, metatopolin, agar, and activated charcoal, contained in non-vented glass culture vessels. In the improved method, the culture vessels were replaced for vented-lid vessels and no activated charcoal was used. During the shoot initiation step, the researchers found best results when the amount of agar in the culture medium was increased. With respect to shoot multiplication, the plants responded best when the amounts of mesos components and ammonium nitrate in the MS medium were adjusted, and when the plant growth regulator gibberellic acid was added.
“Tissue culture is not that well worked-out for cannabis in the literature. People are aware of the complications, problems, and downfalls, so people have been pretty receptive to the paper,” Lubbel-Brand said.
“Despite all our efforts, it’s still not easy to grow cannabis in tissue culture. However, now we can multiply shoots, root shoots, and transition them from the lab to the greenhouse, which is a step forward.”