Flower power: floral reversion as a viable alternative to nodal micropropagation in "Cannabis sativa"

The legalization of recreational and medicinal Cannabis sativa L. has been gaining global momentum, therefore increasing interest in Cannabis micropropagation as growers look for large-scale solutions to germplasm storage and clean plant propagation. Mother plants used in commercial propagation are susceptible to pests and disease and require considerable space. While micropropagation can produce disease-free starting material in less space, current published in vitro methods are not robust and few report high multiplication rates. Furthermore, these micropropagation methods rely on photoperiod-sensitive plants maintained in a perpetual vegetative state. Current methods are not adaptable to long-term tissue culture of day-neutral cultivars, which cannot be maintained in perpetual vegetative growth. In this study, we developed a micropropagation system which uses Cannabis inflorescences as starting materials. This study used two Cannabis cultivars, two plant growth regulators (PGR; 6-benzylaminopurine and meta-topolin) at different concentrations, and two different numbers of florets. Here, we show that floral reversion occurs from meristematic tissue in sativa florets and that it can be used to enhance multiplication rates compared to existing in vitro methods. Floret number was shown to have a significant impact on percent reversion, with pairs of florets reverting more frequently and producing healthier expiants than single florets, while cultivar and PGR had no significant effect on percent reversion. Compared with our previously published nodal methods, the current floral reversion method produced up to eight times more expiants per subculture. Floral reversion provides a foundation for effective inflorescence-based micropropagation systems in Cannabis.