Areas of Growth: A Closer Look at Research on Cannabis Propagation

Published on: 
Cannabis Science and Technology, April 2023, Volume 6, Issue 3
Pages: 28-29

Columns | <b>Cannabis Voices</b>

The field of cannabis horticulture is ever-evolving and offers many opportunities for innovation and experimentation. In this interview, Jessica Lubell-Brand, PhD, professor of horticulture at the University of Connecticut with the Department of Plant Science and Landscape Architecture provides insights into the findings of her laboratory’s recent studies of the “retipping” method of propagating cannabis. She also shares details on her current research with cannabis breeding techniques and how studies like these can benefit the future of cannabis growing.

Can you tell our readers about your background and how you first became involved in cannabis horticulture?

Dr. Jessica Lubell-Brand: I received my PhD in horticulture from the University of Connecticut in 2008 and began as an assistant professor there the same year. My early work focused on invasive plants and native plant alternatives. My laboratory conducted research to identify new native shrubs for landscaping and how to propagate and produce them in containers. I began working with cannabis in 2017 conducting work on feminized seed production and tissue culture micropropagation.

Can you tell us more about the current research subjects in your laboratory, such as ploidy breeding and micropropagation? What have been some of your major findings?

Dr. Lubell-Brand: My recent research with cannabis has been to develop tetraploid plants and breed triploids, which produce significantly less seed than normal diploids and could be an alternative for flower production in situations where pollen drift is an issue. My laboratory has also demonstrated that triploids bred using a tetraploid autoflowering seed parent, flower much earlier (with harvest in early August in northern locations), which could benefit growers. We have also done work to optimize micropropagation of cannabis by controlling hyperhydricity and extending the life of healthy shoots in vitro.

Can you tell us more about your recent study involving the “retipping” method of propagating cannabis plants?

Dr. Lubell-Brand: Retipping is the process of taking stem cuttings from micropropagated plants that were recently acclimated to greenhouse conditions, but are still quite small. So, the cuttings are shorter than traditional stem cuttings. For this process, the micropropagated plant is used as a “mini-mother” plant instead of going straight to the production flower room. Shoots emerge from low on the plant (from the portion of stem that was in vitro) and these become the retip cuttings. As retip cuttings are taken, the pruning effect encourages proliferation of more shoots, which may be taken as retip cuttings over and over again. So, retipping is a process that occurs at frequency (that is, every week for 10+ weeks). Our recent publication in HortScience (1), showed that retip cuttings root very effectively, even without application of root enhancing products, and that plants from retipping produce similar biomass and cannabinoids to micropropagated plants and plants from traditional stem cuttings.


How does propagating cannabis plants in general compare with plants propagated in typical nurseries (such as commercial plants)?

Dr. Lubell-Brand: Retipping is actually a method borrowed from the nursery industry. Nursery growers conduct retipping with micropropagated plants like rhododendron, mountain laurel, and lilac. Prior to cannabis, most of my propagation work was with woody plants. Compared to woodies, propagation of cannabis is more sensitive and requires closer management of the cutting microenvironment. For example, intermittent mist, which is frequently used for woody cuttings, does not work well with cannabis. However, cannabis roots much faster than woody shrubs do.

The University of Connecticut (UConn) started the first US cannabis horticulture course. What are some of the major challenges and achievements students have encountered in this field?

Dr. Lubell-Brand: I think many students are attracted by the opportunity to study a dynamic plant like cannabis. It’s a plant that everybody knows and is therefore exciting. A challenge is that there is a lot of uncertainty and turnover in the industry.

Your Instagram recently featured photos of sectorial chimera in hemp. Can you tell us more about them (2)?

Dr. Lubell-Brand: A sectorial chimera begins with a mutation in an actively dividing cell. In the picture that I shared to social media, the mutation was loss of chlorophyll, so the cells appear white instead of green. The mutated cells divide and grow to occupy a sector of plant tissue, like part of the leaf lamina or stem. Sectorial chimera is usually unstable.

What are you most excited to learn and share at the UConn cannabis symposium this March?

Dr. Lubell-Brand: I am looking forward to presenting my hybrid micropropagation/retipping production protocol for cannabis. And my graduate student, Lauren Kurtz, will share findings from our work to evaluate triploid cannabis. I am also looking forward to hearing from scientists in both academia and industry about their research.

Where should focus be in the future for improving cannabis cultivation?

Dr. Lubell-Brand: Future research for my laboratory will include evaluating the benefits of hybrid vigor for seed production. Better seed is needed for all sectors of cannabis production. While there is always going to be a superior clone that is hard to stabilize with F1 hybrid seed, in those situations, micropropagation will likely be necessary. I also plan to continue studying polyploidy for cannabis crop improvement.