Cannabis is probably best known for one secondary compound, the
psychotropic substance tetrahydrocannabinol (THC). Depending on the THC
content of the plant or more specifically the dried inflorescence, Cannabis is either classified as marijuana (or drug-type, plants
above 0.3% THC) or hemp (fibre-type, below 0.3% THC), which is mainly
a legal and not a strict taxonomic classification. A more refined
classification of Cannabis according to the phytocannabinoid
profile into distinct ’chemotypes’ can also be useful, with chemotype I
and II being marijuana while chemotypes III, IV and V can be seen as
hemp (see chapter 3).
Many countries have been easing the ban on medical and even recreational
use of THC during the past decade. However, because of the prohibition
of Cannabis in many countries throughout the last century, it was
not bred to the same extent as other high-value crops. Hence, hemp and
marijuana lines retain a high level of genetic variability and
heterozygosity, that is not found in other crops
(Sawler et al.,
2015).
Here, we review the biology as well as the applications and future
perspectives of Cannabis research and breeding. We discuss Cannabis taxonomy and cannabinoid synthesis as well as flower
development and flowering time control with an emphasis on sex
determination in this predominantly dioecious species. We also summarize
the currently available genomics resources. Since Cannabis is so
versatile, we discuss its applications in medicine as well as in the
building industry. Cannabis ’ future role in a sustainable society
is summarized as well as the future of cannabinoid production via cell
suspension cultures.
2. Cannabis systematics
Cannabis is the botanical name of a genus that historically
includes three species, C. sativa, C. ruderalis andC. indica. However, since the three species can intercross, they
are also often considered one single species, C. sativa (Small, 2015). Recent genetic data support the single-species concept and recommend
that three subspecies should be recognized: Cannabis sativa
subsp. sativa, subsp. indica and subsp. ruderalis (Q. Zhang et al.,
2018).
Cannabis is a dioecious species, meaning there are male and
female individuals (Figure 2a-c). However, through breeding, monoecious
lines with male and female flowers on the same plant have also been
generated (Figure 2d)
(Moliterni et al.,
2004).