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Cannabis Breeding: Seed vs Clone vs Tissue

This is the second in a series of articles from Dr Gary Yates of Pharmaseeds.

Dr Gary has a BSc (Hons) in Molecular Genetics and wrote his PhD on post-translational modifications in plant stress and was published in several high-profile peer-reviewed journals. After working on photosynthesis in a Post-doctoral role, he joined PharmaSeeds’ senior team ready to apply his academic experience, knowledge and skills to the opportunities and challenges facing the medical cannabis industry.

Dr Gary is focused on how plant genetics relate to the unique biological and medicinal properties of this extraordinary plant.

In this article, Dr Gary explores the differences in growing cannabis via seed vs breeding using a clone

Much has been written about the advantages and disadvantages of using different genetic starting materials to start a grow. Whether it is the seed, cloned cut, tissue culture-derived or otherwise, it stands to reason there are pros and cons to all options in cannabis breeding.

Currently, there are four options for germplasm selection: Seed, Clone from seeded mother, Tissue culture plantlet, or clone from tissue culture-derived mother. See the table below for the differences.

Seed – Sexual Propagation

You have the highest possibility of genetic uniqueness with seed – even within a specified lot. This is since each seed produced is a result of individual pollen and ovule combing their DNA and creating a unique embryo, hence why it is called sexual propagation.

Cannabis is a highly adaptive species and, as such, is more likely to mutate and adapt; due to this, stable and uniform cannabis seed lots are not easy to achieve, but there are also ways to reduce the genetic variation further by inbreeding, selfing and backcrossing. Driving the genetics this way will often lessen the vigour over time, and a trade-off between uniformity and vigour will undoubtedly manifest at some point in cannabis breeding.

cannabis breeding

Seeds are great for phenohunting as this genetic variation can be used to find high-performing plants, and they are also suitable for certain outdoor cultivation sites, especially for extraction. Otherwise, seeds are easy to transport and store, and they provide an excellent stable source for your future stock replenishment.

Autoflowering seeds are a great way to produce crops in glasshouses and outdoors, where the day length is too long for photoperiod plants. The early versions of autoflowering genetics often came with flaws such as the loss of yield – however, modern-day autoflowering genetics are fast catching up with their photoperiod cousins, and some breeders claim their autoflowering lines are as good as their photoperiod lines.

Stable and uniform seed lots do exist, and they can be generated from nearly any generation, but they will nearly always have a proportion of variability.

Growing from seeds will require designated space; germination, plantlet establishment, vegetation and flowering all require variations on conditions. If a facility is staggering its growth cycles, it will need appropriate separation of growth spaces to operate optimally.

Rough Timeline Based on 7-week Flowering:

  • Week 1 germinate
  • Week 2 seedling establishment/hardening begins
  • Week 3 vegetative growth
  • Week 5-7 flowering growth begins
  • Week 12-14 harvest

Clone from Seeded Mother – Asexual Propagation

Cloning is a way to ensure there is no genotypic variation in the genetic starting material. Therefore unlike seeds, no combining of DNA from pollen and ovule takes place, hence asexual propagation. Taking a part of a maturing plant and turning it into an entirely new plant means no developmental opportunity to recombine the DNA, and the genotype should be fixed in place.

When highly consistent cannabinoid levels are to be produced in flowers, using a cloning system is usually best, whether in-house or externally provided. However, as this requires around 25-30% of a commercial facility’s floorspace, additional labour, and time requirements for selection and propagation, having an in-house cloning room/nursery is not always the most efficient way forward. Having clones delivered into the facility ensures maximum use of space for flowering.

cannabis breeding

Although clones can be more expensive than seeds, it does take the plants beyond the first two fragile parts of life and, if handled correctly, should not pose much of a challenge in terms of success rate, especially in well-seasoned hands.

Individual differences can still be observed from cut clones due to the plant’s ability to react to changes in its micro-environment. There is no doubt they are genetically identical. However, this does not necessarily mean they will express the same genes at the same point in time.

Without well-managed plant-touching techniques and consistency in the grow area, gene expression may vary from clone to clone, thus creating variability between individuals.

Read our full guide on cannabis cloning here.

Rough Timeline Based on 7-week Flowering:

  • Week 1 receive clone begin vegetative growth
  • Week 3-5 flowering growth begins
  • Week 10-12 harvest

Clone from Tissue Culture-Derived mother – Asexual Propagation

Tissue culture is best optimised for mother plant production. It is possible to create a clean, pathogen-free mother plant from which, still under sterile conditions, cuts can be taken and kept in a pathogen-free environment before reaching the grow space. This method will reduce the need for specialised handling and provide a very clean and healthy plantlet.

cannabis breeding

Whether a facility can create tissue culture mother plants in house, or the facility receives it as provided by an approved nursey, the same rules apply as above. Well-managed cultivation styles will have a more significant impact on uniformity than letting genetically identical plants grow as they are. Cloning from a tissue culture mother plant brings a lot of the advantages of the tissue culture method without the high cost of actual tissue culture plantlets.

Rough Timeline Based on 7-week Flowering:

  • Week 1 receive clone begin vegetative growth
  • Week 3-5 flowering growth begins
  • Week 10-12 harvest

The Best Way to Breed Cannabis?

As with most things, utilisation of all the above can be greater than the sum of the parts. It should be noted that this choice – seeds, over cut clones, over tissue culture – will be hugely influenced by the desired end product, the persons handling the plants, the budget, and of course, the growing environment – however, in the scenario of producing high-quality flower for the medical market for example, and not having a tissue culture lab on-site, here is how to progress:

Usually selected from good seed stock, a phenohunt is used to find individual plants with exceptional performance or output. Once this is identified, the plant is placed in a tissue culture lab for genetic cleanup, making it pest and pathogen-free.

Once this cultivar is ready, mother stock plants will be grown up from tissue culture, and from here, still in sterile conditions, cloned cuttings are nursed, hardened, and ready for vegetative growth. Most facilities offering this will provide a level of testing of the plantlet lots for pathogens before sending, and this is one way to ensure no diseases are sent with the plants.

Although it is very much a case of horses for courses in terms of germplasm choice, combining all three systems is a way of utilising the advantages of each and minimising the drawbacks of any one system when cannabis breeding. It is also true that there are many ways to cultivate cannabis and that this is just a part of the story. The best advice for those unsure of which options to pursue is to allow those dedicated to the genetic selection process to lead the way.

Commercial Grower?

One such company setting the benchmark in this field is PharmaSeeds, which is reimagining the genetic selection process for the industry on a global scale.

By combining horticultural and agricultural learnings with cutting edge data and scientific innovations, PharmaSeeds is able to offer the industry an entirely holistic approach to genetic selection, yield enhancement and cannabinoid optimisation. Through its proprietary database, PhytoLog, PharmaSeeds tracks and records multiple critical data points and performance indicators based on a diverse range of climatic and environmental parameters.

Having access to this level of tailored agronomic intelligence increases cultivators’ likelihood of a successful cannabis breeding crop – moreover, one that precisely matches the specific requirements of its off-takers and customers. This process includes the inclusion or elimination of certain germplasm types with specialist training provided on the topic by PharmaSeeds.

Click here to learn more about PharmaSeeds

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

Dr. Gary Yates