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DOMESTICATION OF D. EDULIS; STATE-OF-THE-ART 3
Forests, Trees and Livelihoods, 2002, Vol. 12, pp. 3–13
1472-8028 $10
© 2002 A B Academic Publishers—Printed in Great Britain
DOMESTICATION OF DACRYODES EDULIS:
STATE-OF-THE-ART
Z. TCHOUNDJEU1, J. KENGUE2 AND R.R.B. LEAKEY3,4
1IRAD/ICRAF, P.O. Box 2067, Yaoundé, Cameroon. Email: z.tchoundjeu@cgiar.org
2IRAD/CIRAD, Nkolbisson, P.O. Box 2067, Yaoundé, Cameroon.Email: irad-fruits@camnet.cm
3Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian, EH26 0QB, Scotland,
UK.
4Current address: Agroforestry and Novel Crops Unit, School of Tropical Biology, James
Cook University, PO Box 6811, Cairns, Queensland 4870, Australia. Email:
roger.leakey@jcu.edu.au
ABSTRACT
Dacryodes edulis is one of the important local fruit tree species of West and Central Africa. This
paper reviews the activities of a regional programme to domesticate high-value indigenous fruit
trees in the region. This programme is coordinated by the International Centre for Research in
Agroforestry (ICRAF) and implemented in Cameroon in collaboration with the Institute of
Agricultural Research for Development (IRAD), National Agricultural Extension and Research
Programme (PNVRA) agents and NGOs and universities of the region. It is based on a
participatory approach to domestication that is in marked contrast to that of food crop
domestication under the Green Revolution. The participatory process with farmers started with
priority setting between species, progressed to germplasm collection and the establishment of
village nurseries for clonal propagation of superior trees, and is currently involved in the selection
of superior trees for cultivar development. Work is also in progress on post-harvest processing,
market development and the integration of cultivars into agroforestry systems.
Key words: Safou, Dacryodes edulis, domestication, vegetative propagation, marcot, germplasm
collection, cultivar development, phenotypic selection, community nurseries.
RESUME
Dacryodes edulis est l’une des plus importantes espèces fruitières arboricoles de l’Afrique de
l’Ouest et du Centre. Le présent article passe en revue les activités du programme de
domestication des arbres fruitiers locaux à grand potentiel dans la région. Sous la coordination du
Centre International de Recherche en Agroforesterie (ICRAF), ce programme est réalisé avec la
collaboration de l’Institut de Recherche Agricole pour le Développement (IRAD), du Programme
National de Vulgarisation et de Recherche Agricoles (PNVRA), des ONGs et des Universités de
la région. Il est basé sur une approche participative à la domestication, ce qui contraste
grandement avec la domestication des plantes vivrières de la Révolution Verte. Le processus
participatif avec les paysans a débuté par la prioritisation des espèces, suivie par la collecte de
germoplasme et l’établissement des pépinières paysannes en vue d’une propagation clonale des
“arbres supérieurs”. Actuellement, ce processus est orienté vers la sélection des “arbres
supérieurs” pour le développement des cultivars. Des travaux sont aussi en cours sur la
technologie post-récolte, la commercialisation et l’intégration des cultivars dans les systèmes
agroforestiers.
Mots clés: Safou, Dacryodes edulis, domestication, propagation vegetative, marcotte, collecte de
germoplasme, développement de cultivars, sélection phénotypique, pépinières communautaires.
4 TCHOUNDJEU, KENGUE AND LEAKEY
INTRODUCTION
The West and Central African region is characterised by a growing season of
271–365 days, with annual rainfall ranging from 1400 to more than 4000 mm.
Over 80% of food crops (cassava, maize, yam, plantain and cocoyam) produced
in the region are grown by small-scale subsistence farmers, who typically use
traditional shifting cultivation systems. Long fallow periods are required to
restore soil fertility, suppress weeds and reduce pest and diseases. However,
increasing population pressure and rural to urban migration of the work force
have reduced the fallow period to less than five years in most areas, with
consequences of soil degradation, reduced nutrient cycling in soils, etc. These
subsistence farmers often grow small areas of cocoa and coffee under the shade
of larger trees. Since the late 1980s, the world market price for the region’s
major cash crops has dropped significantly. This, coupled with the devaluation
of the local currency in French speaking countries, has resulted in accelerated
forest clearing, loss of biodiversity, increased poverty and lower quality of life
both for rural populations and the urban majority. Nevertheless, the degraded
forest has tremendous potential. It is endowed with high-value fruits and
medicinal plants, which are currently traded locally as well as in regional and
international markets. Unfortunately, they are mostly exploited from the wild
and, until recently, there has been little or no focused research effort to
domesticate and cultivate them, or to improve their genetic base.
The domestication of traditionally important indigenous trees has recently
become a major programme in international agroforestry research (Sanchez and
Leakey 1997). Their commercial importance has led farmers to identify these
local species as candidates for domestication through agroforestry (Franzel et al.
1996), and to the initiation of a domestication programme for indigenous fruit
and medicinal trees (Simons 1996, Leakey and Simons 1998, Tchoundjeu et al.
1998). Dacryodes edulis (G. Don) H.J. Lam, also known as safou or African
plum, in the Burseraceae, is one of these candidate species. The present paper
reviews the current state of this domestication programme, with particular
emphasis on safou. Non-timber forest products from safou and a few other
species constitute an important source of revenue for the region. In 1997, the
trade of safou in Cameroon alone was worth about US$7.5 million (Awono et
al. 2002). In the international market, Tabuna (1999) has reported that 105
tonnes of safou fruit are exported every year from Central Africa to Europe. Of
this, Cameroon produces 100 tonnes and the Republic of Congo and the
Democratic Republic of Congo produce 2 and 3 tonnes respectively.
There is some confusion with regard to the natural range of safou, which
Vivien and Faure (1985) and Keay (1989) have indicated to be limited to SE
Nigeria, while others have reported it to range from Uganda to Sierra Leone
(Troupin 1950), or Cameroon, Gabon, Congo and Equatorial Guinea (Aubreville
1962). The species is, however, now distributed widely in Central Africa in
farmers’ fields, but nothing is known about the history of this distribution, if
indeed it is not indigenous to the region. A molecular ecology study could
determine the genetic structure of the population and resolve this uncertainty.
DOMESTICATION OF D. EDULIS; STATE-OF-THE-ART 5
Safou is mainly cultivated for its nutritional and market values. Locally prices
are about US$1per kg of flesh, but on the international market whole fruits fetch
from 350BF (US$7)/kg in Brussels to FF40 (US$5)/kg and FF50 (US$6)/kg in
Paris and Lyons. The mesocarp, which is eaten raw, boiled in water or roasted,
is an important source of lipids and proteins. The oil content of the fresh pulp
varies between 33 and 65% depending on the variety and the state of maturity
(Omoti and Okiy 1987). Kiamouama and Silou (1987) have characterised the
lipid fraction as consisting of mainly palmito-oleic acids with 47.33% of palmitic
acid (C16:0), 27.35% of oleic acid (C18:2) and 20.46% of linoleic acid. The high
content of fatty acids combined with its amino-acid content makes safou an
alternative source of vegetable oils for the food, pharmaceutical and cosmetic
industries.
Despite some existing studies on safou (Okafor 1983, Nya Ngatchou and
Kengue 1986, Kengue and Schwendiman 1990, Kengue 1996, Leakey and
Ladipo 1996, Ayuk et al. 1999) more research is needed to provide the data on
which to base the domestication, large-scale cultivation and genetic improvement
of this important species. The provenance collections made by Cameroon’s
Institute of Agricultural Research for Development (IRAD) 12 years ago have,
however, provided knowledge about phenology, growth and yield (Kengue and
Singa 1998). They have also served as a stock of material for propagation. This
has led to the establishment of the first series of clonal variety trials on station
and on farms (Kengue et al. 1998). The present paper reviews current activities
towards the domestication of safou with active participation of farmers of
Southern Cameroon and Nigeria.
PROGRESS ON DIFFERENT ASPECTS OF PARTICIPATORY DOMESTICATION
The domestication of safou is constrained by a limited knowledge base, since the
existing literature has focussed on reproductive biology (Kengue 1990), chemical
analysis (Silou 1991) and management and economic potential (Ayuk et al.
1999). Furthermore, there is a need for a novel strategy as the domestication of
most plants is based on the needs of agricultural/horticultural crops, or industrial
forest species, grown in large-scale monocultures in northern-temperate
countries. These are not appropriate for agroforestry trees in the tropics. The
domestication of these species needs to take into consideration the requirements
of small-scale, resource-poor farmers and their subsistence farming systems.
Consequently, the International Centre for Research in Agroforestry (ICRAF)
and its partners in West and Central Africa are developing a new and more
participatory approach to the domestication of high-value agroforestry tree
species based on: priority setting by farmers, germplasm collection, low-
technology vegetative propagation in village nurseries, the genetic charac-
terisation of the marketable products for consumption and processing, the
integration of the species into agroforests managed by subsistence farmers and
the expansion of markets for the products. This participatory approach to
domestication is innovative and fundamentally important because it meets the
6 TCHOUNDJEU, KENGUE AND LEAKEY
needs of local farmers and conforms to the requirements of the Convention on
Biological Diversity (CBD), by allowing farmers to maintain the rights to their
indigenous knowledge and their genetic material. It also creates a model for
domestication, which is in marked contrast to the approach of the Green
Revolution, which was the prerogative of well-funded international research
centres. The Green Revolution model is also inappropriate for the large numbers
of agroforestry tree species, because it is very unlikely that international funds
will be made available on an adequate scale for species, which will not
individually become major cash crops. Consequently, a self-help approach for
farmers that will allow them to undertake their own domestication programme is
much more relevant. This more appropriate model could result in improvements
in a very wide array of species of local or regional importance to the livelihoods
of poor farmers practising subsistence agriculture.
Priority setting
The first step in participatory tree domestication is the determination at village
level of which species should receive priority for genetic improvement. This
important step of priority setting has already been widely reported (Jaenicke et
al. 1995, Franzel et al. 1996). It involves integration of researchers’ and farmers’
perspectives, taking into consideration market and genetic potential for choosing
the species that will give the greatest benefits and improve resource-poor
farmers’ conditions. The priority setting process was first conducted in four
countries (Cameroon, Gabon, Ghana and Nigeria) of West and Central Africa,
and revealed the great interest of farmers of the region for their indigenous fruit
trees. Safou was ranked second on the priority list for the Humid Lowlands of
West Africa (Table 1).
Currently the focus of the ICRAF/IRAD tree domestication programme is on
the top five priority species, Irvingia gabonensis (Bush mango / Dika nut), D.
edulis (Safou / African Plum), Ricinodendron heudelotii (Njangsang), Garcinia
TABLE 1
Priority tree species selected for domestication by
implementation of farmer preference surveys and
priority setting guidelines (Franzel et al. 1996) by
ICRAF and partners
Humid lowlands of West
and Central Africa
Priority order
1Irvingia gabonenis/ I.wombolu
2Dacryodes edulis/D. klaineana
3Ricinodendron heudelottii
4Chrysophyllum albidum
5Garcinia kola/G. afzelii
DOMESTICATION OF D. EDULIS; STATE-OF-THE-ART 7
kola (Bitter kola), and Chrysophyllum albidum (Starapple). To this list have been
added some medicinal plants of commercial importance (Prunus africana and
Pausinystalia johimbe) because of opportunities to increase farmer income, fears
about the future of the resource for industry, and the perceived needs for
conservation of the species in their natural habitat.
Germplasm collection
Rangewide germplasm collection is the second step in tree domestication, and is
both expensive and time consuming. Maintaining the genetic diversity of a
species is essential to its domestication and the maximum amount of diversity
should be present in the collected germplasm. The collected material can be
distributed to users (farmers, horticulturists) for widescale planting. For safou the
germplasm collection strategy has primarily targeted the identification of
superior trees of immediate benefit to farmers, as existing provenance collections
by IRAD (Kengue 1990) provide some conservation of genetic diversity.
Consequently, the main activity has been to work together with farmers to
identify, select and collect germplasm (seeds and marcots) from superior trees.
This activity has been centred on four sub-regions in Cameroon (Mbouda and
Kekem in West Province, and Boumnyebel and Makénéné in Centre Province.
These sub-regions were chosen as they are likely to cover the geographical range
and the different uses of safou. The collections focus on both mature fruits and
rooted marcots (air layering) set at the beginning of the rainy season.
Seed collections
Seed collection involved detailed planning and extensive training of field teams
in Cameroon, Equatorial Guinea, Gabon and Nigeria, and then, through Material
Transfer Agreements, the exchange of the germplasm between these countries
for the establishment of live regional genebanks. In each selected village, farmers
identified 20-30 trees with desirable fruits and kernel traits, with the restriction
that not more than 10 trees should be chosen from any one farm. Participating
villages were separated by at least 25 km. Further selection by the collection
team (ICRAF scientists, NARS, NGOs and farmers) narrowed the number down
to two trees per village. During the collection, a GPS (Geographical Positioning
System) was used to record the position of the tree for future reference. In
addition, information on the age of the tree, the frequency and the duration of
fruiting were requested from the owner of the tree. All seed collections are
identified, through the identity number given to each tree, with the farmer
owning the tree, to ensure that his or her rights are secure under the CBD. More
than 3000 seedlings are currently being raised in nurseries for the establishment
of regional genebanks and for subsequent vegetative propagation.
8 TCHOUNDJEU, KENGUE AND LEAKEY
Collection of marcots for cultivar development
Marcots were collected from the Cameroon sites mentioned above. In 1998, at
the beginning of the rainy season (May-June), a maximum of 10 marcots on each
selected tree was jointly set by a team consisting of ICRAF and NGO staff and
farmers. During the marcot setting, farmer selection criteria, identity of farmers
and other normal germplasm passport data (exact location of the tree using GPS,
soil and tree characteristics) were recorded. Marcots were mainly set on younger,
more accessible, trees with a history of several years of productive fruiting, to
enable meaningful selection. Marcots were set on the same branch class (3–5 cm
diameter) and approximately at the same position in the middle of the canopy,
with a similar light environment. Three or four months later, the rooted marcots
were harvested and labelled to record the farmer’s identity. Sixty percent of the
rooted marcots were taken back for weaning in the on-station nursery, while 40%
were left with the farmers for weaning in a village nursery. This division of the
rooted marcots between the stations and the farmers is to maximise the chances
that each genotype is successfully propagated, without jeopardising farmers’
property rights. It also ensures that the genetic diversity of the selected on-station
germplasm collection, and any germplasm exchange between villages, is
maximised. Moreover, the on-station material can be used to replenish the village
stock in case of any losses.
Currently, safou marcots have been planted in demonstration plots in eight
pilot villages in Southern Cameroon and two pilot villages in South East Nigeria,
while marcots taken to the station have been planted in 3 ha of experimental
plots at Minkoameyos near Yaoundé to assess their performance in different
cropping systems. In the villages, these plantings also serve as demonstration
plots to show that they fruit earlier than plants established from seeds or juvenile
cuttings, and that they are genetic ‘copies’ of their mother plant. Some marcots
have also been established as stockplants for subsequent mass production using
stem cuttings.
Provenance and reproductive biology
Provenance trials involving 20 accessions of safou from the western highlands
and humid forest lowlands of Cameroon were established in September 1995 by
IRAD. These accessions are being grown in the Barombi-Kang and Yaoundé
research stations. The study had three main objectives: safeguarding the genetic
diversity of safou, systematic characterisation, and the evaluation of production
by different accessions. Results obtained so far have shown important variation
between accessions and between individual trees within the same accession
(Kengue and Singa 1998).
Research has also been carried out into the reproductive biology of safou,
based on field and laboratory observations. The results indicate that safou is a
dioecious species with an allogamous reproduction system (Kengue et al. 2002).
The species is insect-pollinated with bees (Apis mellifera) being the main
pollinator. This type of reproduction results in great population heterogeneity.
DOMESTICATION OF D. EDULIS; STATE-OF-THE-ART 9
Vegetative propagation techniques
Vegetative propagation techniques are indispensable for the capture and
multiplication of the phenotypic variation expressed by superior individuals with
desirable characters. Leakey and Simons (2000) have listed eight situations when
the use of vegetative propagation is appropriate in tree domestication. Six of
these situations apply to the domestication of safou:
• the tree has extensive tree-to-tree variability and rare individuals have fruits
that combine several desirable traits;
• high uniformity is required in the fruit crop to meet the market
specifications;
• the high value of the crop warrants the extra expense to ensure a high-quality
product;
• there is an urgent need to shorten the timescale for the achievement of
domestication below that achievable through breeding;
• seed viability is limited to a short season; and
• knowledge of proven traits is available from farmers.
Vegetative propagation of trees can be done using a variety of techniques: -
rooting juvenile stem cuttings, grafting, budding, layering and in vitro tissue
culture. None of these techniques are well developed for the indigenous fruit
trees of West and Central Africa. As early as 1957, Philippe tried to propagate
safou vegetatively, but he reported that cuttings were difficult to root. Currently,
however, grafting, marcotting and the rooting of stem cuttings are being used
with some success. The use of single node cuttings (a portion of a stem with a
leaf and axillary bud) set in a high-humidity, non-mist, polyethylene propagator
has been found to be successful for many tropical trees (Leakey et al. 1990,
Tchoundjeu and Leakey 1996). In this volume, Mialoundama et al. report good
rooting (60-80% in 6–8 weeks) with juvenile cuttings, using non-mist
propagators. To implement these techniques of clonal propagation, farmers are
being helped to develop simple and inexpensive village nurseries and are being
trained in vegetative propagation. With this ‘self-help’ approach to domestication
and these nursery skills, farmers will be able to develop cultivars from the best
safou and other fruit trees in their village to meet their domestic needs and local
market demands.
Characterisation of safou
As part of a wider study to examine the constraints to tree domestication
(Schreckenberg et al. 2001), studies to characterise the tree-to-tree variation in
fruit characteristics have been conducted in 300 trees from five villages (four in
Cameroon and one in Nigeria) in West Africa (Waruhiu 1999). The aim of the
studies was to understand the variability of 13 characteristics of the fruits from
different trees so that the participatory domestication being implemented by
10 TCHOUNDJEU, KENGUE AND LEAKEY
ICRAF and its partners is firmly based (see Leakey et al. 2002). In all five sites,
very considerable and continuous tree-to-tree variation was found in each of the
13 measured traits, with the exception of kernel mass. The realisation that
variability is greatest at the level of the individual village underlines the
appropriateness of a village-based tree domestication programme for this species.
Importantly, the results of the characterisation will help to identify the best
individual trees for cultivar development using vegetative propagation, so taking
the domestication process forward more rapidly (Leakey et al. 2000).
A sensory analysis was conducted to assess the effect of size on the relative
intensity of organoleptic characteristics of safou fruits. Three fruit sizes (small,
medium and large) were used to evaluate the level of acidity, aroma, bitterness
and oiliness. Moreover undesirable characteristics such as fibrosity, sourness,
saltiness, mustiness and wateriness were assessed. The results indicated that
acidity and oiliness varied significantly among fruit sizes. Medium sized fruits,
followed by large sized ones, had the lowest levels of undesirable characteristics
(Kengni et al. 2001). The results of this sensory evaluation illustrate the need to
add these techniques to the others being used to characterise tree-to-tree variation
within the tree domestication process.
Commercialisation and processing
There is growing international interest in the commercial use of genetic
resources, especially those from the tropics and consequently there are important
issues (reviewed by ten Kate and Laird 1999) regarding access to these resources
and the means of ensuring the sharing of benefits. Discussion of the role of tree
domestication cannot, however, be divorced from that of product com-
mercialisation, since without expanded or new markets, the incentives to
domesticate are insufficient. Conversely, if the market explodes, the incentive for
large-scale producers to establish monocultural plantations may sweep away the
benefits that agroforestry could deliver to small-scale, resource-poor farmers
around the tropics (Leakey and Izac 1996). As has been pointed out by Dewees
and Scherr (1996), policies that promote the linkages between the domestication
and commercialisation of non-timber forest products (NTFPs) are one of the
important areas for further work. In this regard, there is also a need for better
integration of the needs of the food and other industries using NTFPs with those
of the subsistence farmer (Leakey 1999, Leakey and Tchoundjeu 2001).
It has been recognised that expanded markets for these products would
increase the value of natural forests and benefit forest dwellers (Peters et al.
1989). Similarly, markets for NTFPs produced on areas already deforested could
improve the income of subsistence farmers, and provide an alternative to slash-
and-burn agriculture, one of the major causes of deforestation. For this to happen
there is an urgent need for the domestication of trees to run in parallel with the
development of post-harvest processing and the commercialisation of the
products (Leakey and Izac 1996, Leakey 1999). Studies are underway to promote
these activities in the rural communities, and on a small commercial scale (see
Kapseu et al. 2002).
DOMESTICATION OF D. EDULIS; STATE-OF-THE-ART 11
Integration into agroforestry
Agroforestry is increasingly providing on-farm sources of cultivated timber and
non-timber forest products for domestic use and for marketing, in ways that
potentially should reduce poverty and also provide some important
environmental services, such as biological diversity and carbon sequestration
(Leakey 2001). Consequently, filling some of the niches in farmland with
indigenous species that provide economically valuable products should result in
land use that is both sustainable and productive, such as the cocoa agroforests of
Cameroon (Leakey and Tchoundjeu 2001). The domestication of high value
agroforestry trees like safou, through genetic selection and cultivation, should
increase the quality, yield and marketability of their products, so enhancing the
incentive for more sustainable land-use practices.
CONCLUSION
The techniques of domesticating safou and other indigenous fruit trees and
medicinal plants of the humid zone of West and Central Africa are evolving
rapidly. Through the promotion of income generation they should help to reduce
rural poverty and enhance the livelihoods of subsistence farmers in the region.
The new emphasis placed on participatory domestication of the traditionally
important, and previously ignored, indigenous fruit trees, appears to be a good
strategy to help farmers to help themselves while, through the diversification of
cocoa agroforests, also having benefits for the sustainable management of
farmland in proximity to threatened tropical forests.
ACKNOWLEDGEMENTS
This publication is an output from a research project partly funded by the United
Kingdom Department for International Development (DFID) for the benefit of
developing countries. The views expressed here are not necessarily those of
DFID (R7190 Forestry Research Programme). The authors also wish to thank the
International Foundation for Agricultural Development (IFAD) for its funding of
this work at ICRAF. The views expressed are those of the authors alone. The
contributions of ICRAF staff in Nigeria and Cameroon are also gratefully
acknowledged.
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