1.2 Problem statement
Decades back, Ethiopia was covered with dense natural forests. Unfortunately this became a
history for the present generation. A long history of land clearing and sedentary agriculture has
changed the vegetation cover of Ethiopia. The natural vegetation types have disappeared from
most parts of the country except in few patches in holy places and inaccessible areas (Feoli et
., 2002). Deforestation is followed by soil erosion and loss of soil fertility which affects the
land productivity of the country.
Studies have shown that some species of plants in the country are threatened with different
factors which need different approaches of conservation actions. Indigenous tree/ shrub species
are at high risk of genetic erosion due to the rapid decline of the natural forests. Reforestation
of degraded lands through plantation of native species depends up on the possibility of raising
seedlings either from seeds or vegetative propagules (Demel Teketay, 1993). Access to seeds
and seedling and storage problems limit the use of many potentially high value indigenous
species in tree planting and conservation programs (Leggesse Negash, 1995).
Loss of traditional value of a given species in an area is also one of the plant conservation
challenges. Local peoples are aware of many uses of the trees. They know how to harvest it
and which part can be used. This invaluable knowledge is being lost by the destruction of the
Indigenous knowledge of people about individual species should be part of conservation
researches. The knowledge gathered through scientific methodology has to be associated with
indigenous knowledge practices to make sure that the plant resources are conserved and used
in sustainable manner (Zemede Asfaw, 2006). Therefore, studies about seed storage
physiology of the indigenous trees of the country and documentation of traditional knowledge
must be part of different conservation actions.
This work therefore is an attempt to build up scientific knowledge about seed storage behavior
of S. guineense which includes tree seed collection, drying and viability test. The other aim of
this study was to assess and document the local people’s knowledge on the uses, threats and
conservation status of the species in Bombaso Regi peasant association of Arsi Negle Woreda,
West Arsi zone of of Oromia Region.
Two main factors were mainly considered for selection of the species. It is one of the species in
the priority list of the IBC (Taye Bekele et al., 2004) and the availability seeds during the time
of the study. The results of this research can reinforce the experimental investigation, it helps
to kindle the interests of local people and raise awareness on the seed storage behavior of the
1.3 Objectives of the study
The main objective of this study was to investigate the desiccation-sensitivity of seeds and
ethnobotany of S. guineense
To record and analyze the indigenous knowledge of the local people in the study area
on the use, propagation and conservation status of S. guineense
To investigate the impact of moisture content on the viability of seeds of S. guineense.
To study and describe the desiccation sensitivity of seeds of S. guineense both from
the experimental results and the ethnobotanical investigations.
2 Literature review
2.1 Conservation measures of biodiversity
The two basic approaches to conservation are in-situ and ex-situ methods. In-situ refers to
maintaining plants and animals in their original habitat while ex-situ
conservation is the
conservation of components of biological diversity outside their natural habitats in a controlled
condition. The in-situ approach of conservation is at an ecosystem level and natural habitats,
and it includes the maintenance and recovery of viable populations of species in their natural
surrounding. The preservation of species in-situ offers all the advantages of allowing natural
selection to act which cannot be recreated in ex-situ conservation (Taye Bekele, 2004).
In ex-situ conservation the genetic resources are conserved in identified genebanks. These
genebanks can be storage of seed (≈5 to -20ºC), in vitro storage of plantlets (≈ 4 to 25 ºC),
Cryostorage of propagules using liquid nitrogen (≈-150 to -196 ºC) or in the form of field
genebank (Dhillon et al., 2004).
Since in-situ conservation is the conservation of ecosystems and natural habitats, priority
should be given to this conservation measure whenever feasible for maintenance and recovery
of viable populations of species in their natural surroundings. However, there are conditions
where in-situ conservation is not feasible. Habitat destruction of endangered and rare species
requires ex-situ conservation efforts to prevent extinction. Ex-situ conservation is means of
conservation of plant genetic resources when there is a shortcoming to conserve natural
habitats which is really the fate of our earth.
According to Phartyl et al. (2002), in-situ conservation in tropical ecosystem is difficult not
only due to environmental disasters, landslides, unpredictable rainfalls, and flood but also due
to human made disasters and pressures like forest fire and over exploitation of wild resources
for commercial purposes. Thus in tropics ex-situ conservation of forest genetic resources have
become a common practice due to the alarming rate of deforestation and the loss of species and
genetic diversity. In situations where in-situ conservation programs do not prove to be
adequate, appropriately maintained samples of living collections reduce the risk of extinction
(Gurrent and Raven, 2003). Engels (2001) also suggested that ex-situ
should be applied as a back up system to avoid possible loss of genetic diversity.
conservation can serve a variety of different roles depending on the sort of the plant
and the purpose for which they are being stored. The roles can be extended from collections of
agriculturally important crop plants and their relatives to collections of threatened native
species (Guerrant and Raven, 2003). Ex-situ conservation can provide the opportunity to study
the biology of, and understand the threats to, endangered species in order to eventually
consider successful species recovery programs which would include restoration and
reintroduction. Ex-situ facilities can be used for germplasm evaluation, as centers of
documentation and information systems and for providing information on genetic resources on
a commercial basis (NBSAP, 2005).
According to Frensco (1998) there are three major forms of ex-situ conservation
provide a controlled environment where seeds can be dried to low
moisture content and stored at low temperature without losing their viability.
Approximately 90% of all "ex-situ" accessions are stored as seeds.
such as arboreta, plantations and botanical gardens are useful for
species that are difficult or impossible to store as seed, including vegetatively
propagated crops and tree species. Field genebanks account for approximately 8% of all
accessions in "ex-situ" storage.
In vitro methods
are techniques for conserving plant parts, tissue or cells in a nutrient
medium. This method is used to conserve species that do not readily produce seeds, or
where the seeds cannot be dried without damaging them. Only 1% of all accessions are
held "in vitro".
The other measure to conserve biodiversity is to study indigenous knowledge of local
community. Ethnobotanists explore how plants are used by the people for such things as food,
shelter medicine clothing, hunting and religious ceremonies. This information is critical to
study the interaction between people and plant in an area and to plan the conservation actions
for specific species.
Ethnobotanical Studies are significant in revealing locally important plants species and
documentation of traditional knowledge. According to Tigist Wondimu et al. (2006), there is a
wide gap between the perception of elder people and their descendents, older people remain
with more knowledge about the environmental components and their uses than younger ones.
Therefore, indigenous knowledge should be protected as an important natural heritage.
2.2 Roles of seed banking for biodiversity conservation
Among the various ex-situ conservation methods, seed storage is the most convenient for long-
term conservation of plant genetic resources. Seed banking is one form of garden-based
conservation. Because such efforts occur away from the plants' natural habitats, they are called
off-site or ex-situ conservation (Dhillon et al., 2004; Rao, 2004). When a species or an
ecologically significant or taxonomically distinct section of a species is either needed for
research or endangered in its natural habitat, conservation of seeds, live plants, or both can be
The preservation of plant germplasm in seedbanks (or genebanks) is one of the more useful
techniques of ex-situ
conservation of wild plant species. Through seedbanks researchers can
obtain access to rare and endangered species without disturbing or damaging natural
populations (Phartyal et al., 2002). Unlike most agricultural species that can generate crop
varieties with multiple breeding cycles over a few years, forest tree breeders can not rapidly
produce new varieties, nor can they quickly breed for new variations among populations
(Girma Balcha, 2004). Conserving the existing genetic diversity among population is very
critical and this can be archived by long–term storage of seeds in gene banks.
As plant genetic resources programs have increased in number and expanded in scope so, the
range of species requiring ex-situ
conservation has broadened from major crops to include
forestry species, and wild and underutilized species. Assembling ex-situ collections from wild
populations is an important component of wider conservation goals (Schoen and Brown, 2001).
Seed banking is relatively new and under-exploited tool in combating the loss of global plant
diversity and has the unique feature as conservation techniques of making rapidly and easily
available. Conventional seed storage is believed to be safe, effective and inexpensive method
of ex-situ conservation of plant genetic resources (Phartyl et al., 2002).
collections for conservation purposes is not a new concept and is extremely useful
if based with a sense of purpose. Many people store native plant seeds quite effectively without
a lot of money. Storing germplasm in seed banks is both inexpensive and space efficient as an
conservation method. It successfully allows for the preservation of large populations
with minimal genetic erosion (Dhillon, et al., 2004).
The banks provide a controlled source of material of high quality and genetic diversity for
research and for the rehabilitation and restoration of degraded ecosystems and the recovery of
threatened species. Genebank collections are very important for post–war rehabilitation of
Richards and Ruivenkamp, 1997;
Guerrant and Raven, 2003
2.3 Establishing priorities for plant conservation program
Conservationists need to assess the conservation needs of all plant species and establish
detailed and appropriate management plans. But there is very little information about the plant
species. What is known in reality is many plant species are threatened (Tenner, 2003). The
number of woody species that require attention for conservation could be very large; therefore,
setting priority is very essential for efficient allocation of scares resources and time (Girma
Balcha, 2004). When choosing species for ex-situ conservation priority should be given to
endangered species. A list of priority species and/ or habitats for conservation is developed
based on the institutional remit and expertise, political priorities and botanical information such
as Red Data Lists (Tenner, 2003; Miranto, 2005).
The basic criteria for determining the necessity of gene conservation are the degree of threat
and socioeconomic importance of the woody species. Ethnobotanical studies can also help to
identify conservation issues such as cases where rates of harvest of plants exceed rates of re-
growth (Aumeeruddy-Thomas and Shengji, 2003).
The Forest Genetic Resources Conservation Project which was organized and implemented by
forest and aquatic plants resources conservation department of IBC has carried out woody plant
diversity and structural studies including socioeconomic survey in several forest areas of
Ethiopia and prioritized 154 woody species of the country from nine moist montane forests of
Ethiopia (Taye Bekele et al., 2004). The selection of species for the present study was based on
the priority lists of IBC and the availability of seeds by the time of the study.
2.4 Seed storage behavior and general storage principles
Roberts (1973) classified plant seeds as orthodox (desiccation-tolerant) and recalcitrant
(desiccation-intolerant) according to their storage properties. A large proportion of plant
species produce seeds that can be dried to a sufficiently low moisture content that permits them
to be stored at low temperatures. These seeds are termed orthodox seeds (Roberts 1973).
Orthodox seeds can survive complete water removal and can be stored for many years by
drying and cooling.
Orthodox seeds can be dried without loosing viability to low levels of moisture content. Mature
seeds survive desiccation to low moisture content at least 2-6% depending on the species
usually much lower than those they would normally achieve in nature. These seeds are
generally easy to store if basic processing and storage facilities are available. (Hong and Ellis,
1996). Drying seed and placing in cold storage is relatively simple way of conserving large
amounts of germplasm in a small space. This method of conserving a germplasm is achieved
only for orthodox seeds. Orthodox seeds undergo a period of desiccation before being shed
from the tree (Corner and Sowa, 2002).
On the other hand, many species of tropical or subtropical origin have recalcitrant seeds which
are sensitive to drying and chilling and cannot be stored in conventional genebanks (Bonner,
1996). A number of tropical fruit and timber species fall into this category including coconut,
avocado, mango and cacao (Krishanapillay and Engelmann, 1996). Recalcitrant seeds do not
survive drying to any large degree and are thus not amenable to long term storage. Although
the critical moisture level for survival varies among species, there is a threshold of minimal
value of water content below which there is damage to germination of recalcitrant seeds. Thus
the water content of recalcitrant seeds and storage temperature must be reduced until near the
minimum critical water content (Hong and Ellis, 1996; Barbedo and Bilia, 1998; Pritchard,
A further characteristic of recalcitrant is that the seeds are actively
metabolic when they are
shed, in contrast to orthodox types
which are quiescent. This affects all aspects of the handling
and storage of recalcitrant seeds (Schmidt, 2000). However; the
type and intensity of
metabolism differ among recalcitrant seeds
of different species, depending on the
and water concentration at shedding.
Recalcitrance is not an absolute phenomenon and that there is a continuum of seed behavior
graduating from that characterized by desiccation tolerance, through a decreasing ability to
withstand dehydration stress, to that of extreme sensitivity to even the slightest water loss
(Berjak and Pammenter, 1994). According to Tompsett and Pritchard (1998), tropical
recalcitrant seeds which must, in most cases be held at non-chilling temperatures are limited to
storage for a year. But desiccation- intolerant seeds can survive well for three years.
Improved methods for short-or medium-term storage and for handling are required to enable
the uses of recalcitrant species in reforestation programs. Optimum seed moisture contents,
temperatures and atmospheric conditions should be determined for important species.
Minimum storage temperatures that avoid chilling damage are the most important, since lower
temperature should in general decrease seed metabolism and pathogen activity and extend the
storage life of seeds (Bonner, 1996). According to Engels (1996), ex-situ conservation of
recalcitrant seeds is very problematic and much more research is required to allow medium or
long-term storage of such materials.
There is also an intermediate category between the orthodox and recalcitrant seed groups
Intermediate storage behavior implies that the seeds are shed
at relatively high water
concentrations, but will withstand
considerable dehydration, although not to the extent
by orthodox seeds (Ellis et al., 1990; Girma Balcha et al., 2000). Intermediate seeds
withstand partial dehydration, but they cannot be stored under
conditions because they are cold-sensitive
and desiccation does not increase their longevity.
The intermediate category contains numerous important
tropical cash crops, such as oil palm
coffee (Coffea arabica) and neem tree (Azadirachta indica) (Hor et al.,
2.5 Approaches to predict storage behavior of seed
The first step in developing an ex-situ
conservation strategy for a particular species is to
determine seed storage behavior. In order to obtain the preliminary information for their
storage it is important to examine the desiccation responses of seeds of unknown storage
behavior. Engels (1996) suggested that a simple protocol is needed to allow easy determination
of unknown seed storage behavior (orthodox-recalcitrant-intermediate).
According to Hong and Ellis (1996), the first step of the protocol to determine seed storage
behavior considers desiccation tolerance to low moisture content and the second step of the
protocol requires investigation of the survival of seeds following storage in different
environments as shown in flow chart (Appendix, 1).
In principle investigation of desiccation tolerances and temperature requires quite a lot seeds.
In cases where there is a short supply of seeds it is difficult to apply such investigation. There
are certain approaches to predict seed storage behavior in species for which experimental
results are not currently available. There have been a number of attempts to correlate seed
storage behavior with seed characteristics such as shape, size, mass, seed coat ratio and
moisture content at shedding. Desiccation sensitive seeds have been reported to be, on average,
larger than desiccation tolerant seeds which will reduce the rate of seed drying and are more
frequent in wet habitats (Tropical rainforests) or shed in wetter periods of drier habitats.
Pritchard et al. (2004) presented data for 10 African dry land species and examined the
relationships between desiccation sensitivity and seed size, rainfall at the time of seed shed and
germination behaviors. The authors found that desiccation species producing desiccation-
sensitive seeds had larger (> 0.5 g) seeds, shed in months of comparatively high rainfall,
germinated rapidly and had comparatively small investments in seed physical defenses.
There is also association between level of desiccation tolerance and SCR (i.e. ratio
coverings: mass). Desiccation sensitivity was found to
be significantly related to relatively low
SCRs, typified by
large seed size coupled with thin covering (Daws et al., 2006). Hong and
Ellis (1998) also investigated patterns of response to seed desiccation in 40 species of
Meliaceae. According to their report, species with desiccation–sensitive seeds typically occur
in moist areas, particularly rainforests, and produce large (>1g), round seeds which are shed at
high moisture content.
Desiccation-sensitivity of seeds can also correlate with plant ecology. According to Pritchard
. (2004), desiccation- sensitive seeds are largely restricted to regions with comparatively
high rainfall. Species producing recalcitrant seeds are common in humid tropical forests, where
the seeds of climax species germinate immediately after shed rather than contributing to the
soil seed bank (Pammenter and Berjak, 2000).
In a study of 886 tree and shrub species, Tweddle et al. (2003) reported that desiccation -
sensitive seeds are most common in tropical rainforests, where they contribute about 47% of
species and are infrequent in drier environments such as savanna where about 12% species are
found. Species which show orthodox seed storage behavior occur in arid habitats, desert and
savanna. And few species may show intermediate storage behaviors in theses habitats.
Recalcitrant seeds which are shed in a highly hydrated state and endure a chilling spell during
their maturation are adapted to low temperatures in storage in comparison to those which have
no such opportunity as in warm tropical environments. These responses served as the basis for
the identification of recalcitrant types as temperate recalcitrant and tropical recalcitrant seeds
(Phartyal et al., 2002).
One potential advantage of seed desiccation sensitivity may be rapid germination. Rapid
germination may reduce the period during which seed desiccation can occur and also have the
advantage of reducing seed predation levels. In contrast seed desiccation tolerance may form a
soil seed bank and have been potentially exposed to seed predators for extended periods of
time (Pritchard et al., 2004).