8.3. Cannabis breeding for medicine
Cannabis sativa is a versatile multi-purpose crop which requires
a simple, low-input cultivation technique, adapts to various ecological
conditions, produces sustainable products, and provides raw material for
a wide range of applications, including medicine
(Amaducci et al.,
2015). Research into the synergistic pharmacological effects ofCannabis metabolites suggests that ratios of phytocannabinoids,
terpenoids and other Cannabis metabolites influence a plant’s
therapeutic potential.
More research is needed to determine the influence of environmental and
genetic factors on the phytochemical profile of the Cannabisplant. Existing studies show that total phytocannabinoid yields are
related to environmental conditions. Phytocannabinoid and terpene levels
are affected by factors such as the humidity, rainfall and temperature
of the growth environment
(Meier and Mediavilla,
1998; Murari et al., 1983; Pavlovic et al., 2019). However, the
relative ratios of the different Cannabis metabolites are
dependent on the genotype (see Chapter 3)
(Janatová et al.,
2018; de Meijer et al., 2003; Toonen et al., 2006; Vanhove et al.,
2011). Identifying the environmental and genetic factors that influence
phytochemical production by Cannabis could aid in the development
of new Cannabis cultivars with tailored ratios of various
metabolites.
The therapeutic effects of a given plant reflects the proportions of the
various pharmacologically active components. The development of Cannabis chemotypes containing high levels of specific
phytocannabinoids can be achieved through breeding. De Meijer et
al . produced Cannabis chemotypes high in specific single
phytocannabinoids, including THC, CBD, CBG and CBC
(de Meijer et al.,
2009a, 2003; de Meijer and Hammond, 2005). Cannabinoid-free chemotypes
were also developed, which could aid investigation into the
contributions of non-cannabinoid bio-actives, such as terpenoids, to the
pharmacological effects of Cannabis (de Meijer et al.,
2009b; Russo, 2011). The development of these chemotypes through
conventional breeding demonstrates the high diversity of the Cannabis genome, which may obviate the need for genetic
engineering of Cannabis(Russo, 2019).
Understanding the interactions between different Cannabisbio-actives remains one of the key challenges to harnessing the full
medicinal potential of the Cannabis plant. Research into Cannabis-based medicines highlights the importance of various Cannabis metabolites in producing therapeutic effects. Further
research is needed to elucidate the mechanisms underlying the entourage
effect observed with whole Cannabis extracts, and to assess the
contributions of various Cannabis metabolites to determine the
most effective combinations for various pharmaceutical applications.
Applying our knowledge of the entourage effect in Cannabis to the
development of tailored chemotypes has the potential to provide improved Cannabis-based therapies for various medical conditions, which
could benefit many patients.
9. Hemp for houses: Cannabis as building material
Many hemp varieties of Cannabis are fibre crops with multiple
inherent qualities as building material. The high tensile strength of
hemp fibres, traditionally exploited in rope and fabric applications,
also enables mechanical advantages for building construction
applications. Additionally, shiv particles of the woody-core are a
biobased alternative to mineral aggregates for low-impact concrete.
Therefore both the plant fibres and the shiv particles are suitable for
developing biobased, environmentally friendly building materials that
have been shown to have inherent thermal, hygrothermal and acoustic
characteristics
(Kinnane et al., 2016;
Reilly et al., 2019; Shea et al., 2012).
Building products that integrate hemp are many, but reductively may be
grouped into two general categories, hemp concrete and hemp insulation
blankets: Hemp concrete are those mixed with a binder to form a porous
concrete composite with thermal insulation qualities. Hemp insulation
blankets are thermo-formed without an added binder to create a low
density, blanket type product. These respectively encompass shiv and
fibres, and are distinguished by their dry densities; typically in the
range 390-670 kg/m3 in the case of the hemp-concrete
(Collet-Foucault et
al., 2004), and about 38 kg/m3 for the
hemp-insulation
(‘Technichanvre’,
2017). The concretes have a wide density range as they are typically
bespoke and include varying levels of binders, often lime, but also
cement. As noted, both products are recognised for their good thermal
properties. The hempcretes have a low thermal conductivity (λ = 0.12
W/(m*K)) (Walker and
Pavía, 2014) relative to other standard concretes (λ = 1-2 W/(m*K)).
However, their conductivity is higher than the former insulation wool
blanket product (λ =0.04 W/ (m*K))
(Collet-Foucault et
al., 2004), which contains up to 90% hemp fibre, are formed in panels
or rolls and used for roof, attic and wall insulation.
Hempcrete, in contrast, is a composite material. It is commonly mixed in
a ratio by weight of 1:2:3 of hemp: binder: water. In contrast to
standard concrete, hempcrete has relatively low mechanical strength. It
is therefore typically cast around a load-bearing timber structure. The
wet mix is poured between temporary shuttering, and the hempcrete is
tamped down to compact it and form the wall. The thickness of these
walls typically ranges from 300-600 mm, to ensure structural stability
and to meet thermal requirements. These dimensions limit the widespread
applicability of hempcrete, particularly in urban infill sites. However,
new innovative products are enabling its wider applicability.
Increasingly, precast hempcrete blocks are appearing on the market.
Exhibiting higher densities, certain of these have load-bearing
capability and they generally enable time and labour efficiencies on
site. They are also popular for renovation and retrofit projects,
primarily because hempcrete is characterised by an open pore structure
which allows for the transmission of moisture. Moisture is often present
in the walls of old buildings, and breathable insulation allows this
water escape, instead of trapping it as do modern-day synthetic
insulations which can lead to mould growth, structural and air quality
issues.
These are just some example of advantages of biobased materials. However,
the construction industry and the agricultural industry diverged during
the modern post-war age of development. Synthetic products were
developed to meet high demand with a price point that enabled use, and
waste, of products during phased redevelopment
(Kinnane, 2020).
Today synthetic polymer and mineral wool products continue to command
almost full market share of the insulation industry, and that demand is
increasing as we aim to reduce the operational energy of buildings.
Hemp, and biobased materials more generally, remain niche products.
Today hemp insulation products are almost twice the price of the mass
produced alternatives
(Carus et al., 2013),
even though plant fibres have a lower cost of processing than synthetic
fibres.
However, the building sector, and its considerable environmental impact,
is increasingly in focus, and the environmental benefits of biobased
materials are giving them greater traction. Hemp, with its fast-growth
cycle and multi-purpose advantages is increasingly proposed as a
low-impact design solution. Although specific quantification of carbon
sequestration remains challenging
(Reilly and Kinnane,
2017), authors report levels of between 1.5-2.1 kgCO2per kg of plant grown and values of energy for production of 0.085-0.19
kgCO2 per kg of hemp shiv (see
Sáez-Pérez et al.,
2020 for review). It should be noted however that although hemp
exhibits carbon positive credentials, the embodied carbon of any
hempcrete is high due to the high quantity of binders often used, and
this is often underestimated by proponents of the material.
10. Also a medicine for the environment? Sustainability aspects of Cannabis farming
Considering global warming and consequential efforts to divest from
fossil fuels, bioenergy crops and biofuels are gaining increasing
interest (Rogelj et
al., 2018). Cannabis is a high-yielding, annual crop, and has
much-untapped potential for contributing to carbon sequestration efforts
(Finnan and Styles,
2013). Besides storing carbon in building materials, alternative uses
for this crop exist, and as such, there is a high potential for carbon to
be stored both short- and long-term in bioenergy, textiles, and paper
(Figure 1, Figure 9). Further contributing to the environmental
connotations of this species, hemp has been employed in phytoremediation
efforts to restore land implicated by heavy metal contaminants
(Citterio et al.,
2003). Hemp leaves and seeds also provide the basis for human
consumption (Figure 9).