a= (European Investment Bank 2018)
In LC germination experiments, such as those using incubators, most
variables are kept constant (e.g. light intensity, sowing medium,
water-availability, timing of diurnal temperature cycle), and one or two
are manipulated with a few combinations (e.g. three or four temperatures
of diurnal cycles). Researchers select the conditions of variables based
on knowledge from NH microclimates, but in reality, these are
notoriously difficult to exactly define (e.g. Dinsdale, Dale & Kent
2000). Indeed, important variables may inadvertently be omitted from
experimental designs. Interpretation of LC experiments in an
ecologically meaningful way is difficult because it will be based on
many assumptions, both in selecting variables to test and extrapolating
interpretation to NHs - especially if NHs have not been adequately
studied.
By contrast, in NH experiments, many, often unknown, variables
interplay, one or two of which may be controlled. If researchers were to
control all combinations of NH variables in LCs they would soon run out
of seeds, time and space. Interpretation of NH experiments depends on
dynamically recorded variables that cannot be well controlled, some even
being irrelevant to germination ecology. It goes without saying that NH
experiments can only truly be performed in regions where the plant is
native, whereas LC experiments can be carried out anywhere with suitable
equipment.
Alternatives to NH and LC are semi-natural habitats (Semi-NHs) or
simulated natural environments (Simulated-NHs). Examples of Semi-NHs
include fields or farm edges, in or close to a species’ native region.
The term simulated-natural environment (or habitat as used here) was
used by Kaeberlein et al. (2002) to define an environment of
natural seawater and sediment the authors placed in aquariums to culture
previously ‘uncultivable’ marine microorganisms. Such Simulated-NHs are
less controlled than LCs, but allow better interpretation of findings
and may include important factors that are not well understood or known
and so may inadvertently be omitted from LCs. Glass houses, such as
those in botanic gardens, are examples of Simulated-NHs, as they mimic
NHs and variables are not well under control.
In botanic gardens, living collections are often arranged according to
geographic plant communities, each compartment or grouping representing
a pseudo or Simulated-NH. These living collections are a valuable
resource in studying plant ecology, particularly when NHs are
challenging to access (Perez et al. 2019). Many botanic gardens
also hold seed banks (469 gardens), and carry out seed or spore research
(155 gardens) (BGCI 2021). As botanic gardens are biased towards
temperate regions in the Northern hemisphere (Mounce, Smith &
Brockington 2017), there is opportunity to enhance interpretation of
seed germination studies using botanic gardens as Simulated-NHs when it
is not possible to do so in native regions (Faraji & Karimi 2020).
Wild banana species (Musa L.) are native to tropical and
subtropical Asia to the western Pacific (Govaerts & Häkkinen 2006).
Their fruit contains many hard darks seeds, 3-7 mm in diameter (Chin
1996). The conditions for germination are not well understood and
germination is notoriously inconsistent and often very low (Kallowet al. 2020; Panis, Kallow & Janssens 2020; Singh et al.2021). LC experiments show a requirement for alternating temperatures
(Stotzky & Cox 1962; Kallow et al. 2021), but no NH experiments
have been executed to interpret this. For instance, is this requirement
a gap or depth detection mechanism affected by microclimates? And do
species respond differently?
Understanding seed germination ecology of wild bananas is not only of
ecological interest, it is also important for global food security. Seed
banking crop wild relatives efficiently protects genetic material and
makes it available for phenotyping and breeding (Dempewolf et al.2017), it is included in UN Sustainable Development Target 2.5 (UN
General Assembly 2015). Optimized germination is a vital component of
seed bank management and breeding - without it, viability is difficult
to monitor and access to plants for research and breeding is constrained
(FAO 2014; Batte et al. 2019; Amah et al. 2020).
In the present study we examined germination responses in a Semi-NH and
Simulated-NHs of the two primary crop wild relatives of banana:Musa acuminata (subsp. siamea N.W. Simmonds, and subsp.burmanicca N.W. Simmonds), and M. balbisiana Colla (De
Langhe et al. 2009). Specifically, we aim to answer the following
questions that cannot be answered in LCs: (1) What environments
stimulate or inhibit Musa germination? (2) Are Musa seeds
dormant, and if so how is this broken in the environment? (3) CanMusa seeds remain viable in the soil?
Materials and methods
- Semi-natural habitat (nursery, Philippines)
- Plant material
We collected a bunch (an infructescence) of Musa balbisiana(accession GB61996) containing seeds from the field genebank at the
National Plant Genetic Resources Laboratory (NPGRL), Institute of Plant
Breeding, University of the Philippines, Los Baños. Seeds were extracted
by opening fruit and washing seeds in flowing water to remove all pulp.
Seeds were then left on a tray in the laboratory to surface dry for
seven days prior to sowing.
Table 2. Accessions used for germination experiments in
simulated natural environments, V= viability percentage from embryo
rescue tests in 2019 and 2020.