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RESEARCH ARTICLE
Diversity, distribution and management of yam landraces(Dioscorea spp.) in Southern Ethiopia
Muluneh Tamiru Æ Heiko C. Becker ÆBrigitte L. Maass
Received: 26 September 2006 / Accepted: 24 January 2007 / Published online: 11 April 2007� Springer Science+Business Media B.V. 2007
Abstract Yam (Dioscorea spp.) is widely grown
in many parts of Ethiopia and plays a vital role in
local subsistence. Nevertheless, its diversity has
not been studied in detail. A survey covering 339
farm households and eight districts was conducted
in the major yam growing regions of Southern
Ethiopia to investigate the diversity and distribu-
tion of yam landraces using structured and semi-
structured questionnaires. A total of 37 named
landraces were recorded, with a range from one
to six (mean 2.9) on individual farms. Farmers’
decisions regarding the number and type of
landraces maintained was influenced by tolerance
of the landraces to drought, their maturity time
and market demand. Most landraces had limited
abundance and distribution, and only a few
dominant landraces were widely grown. There
was also variation amongst districts with respect
to diversity, distribution and abundance of the
landraces found. In the majority of the localities
surveyed, farmers reported a decreasing trend in
the number of landraces maintained on individual
farms and in the overall yam production. Besides,
in those limited areas where yam production is
expanding, farmers are increasingly relying on a
few selected landraces that mature early. Findings
of this study suggest that local farmers in Wolayita
and Gamo-Gofa zones maintain considerable
yam diversity that remains to be further explored
for sustainable utilization and conservation of the
available genetic resources.
Keywords Dioscorea � Ethiopia � Genetic
resource � Landrace diversity � Yam
Introduction
Yam (Dioscorea spp.) belongs to the genus
Dioscorea, representing more than 600 species
worldwide (Coursey 1967). The Dioscoreales are
believed to be amongst the earliest angiosperms
that originated in Southeast Asia, but followed a
divergent evolution in three continents separated
by the formation of the Atlantic Ocean and
desiccation of the Middle East (Hahn 1995). As a
result, the major food species occur in three
isolated centers: West Africa, Southeast Asia and
tropical America (Alexander and Coursey 1969).
These centers are also considered areas for
M. Tamiru � B. L. Maass (&)Department of Crop Sciences: Agronomy in theTropics, Georg-August-University Goettingen,Grisebachstr. 6, Goettingen 37077, Germanye-mail: [email protected]
H. C. BeckerDepartment of Crop Sciences: Plant Breeding, Georg-August-University Goettingen, Von-Siebold-Str. 8,37075 Goettingen, Germany
M. TamiruHawassa University, P.O. Box 05, Awassa, Ethiopia
123
Genet Resour Crop Evol (2008) 55:115–131
DOI 10.1007/s10722-007-9219-4
independent yam domestication, and represent
considerable diversity (Asiedu et al. 1997).
Yam is a crop of major economic and cultural
importance in sub-Saharan Africa that accounts for
about 95% of the world production (FAO 2004),
the so called ‘yam belt’ of West and Central Africa
being the principal area of production (Coursey
1967; Hahn et al. 1987). Following the establish-
ment of research institutions such as the Interna-
tional Institute of Tropical Agriculture (IITA),
yam has attracted considerable research attention
in recent decades. Consequently, substantial pro-
gress was made in understanding the origin,
domestication, phylogeny, diversity and produc-
tion of the major food species. Orkwor et al. (1998)
give a review of the recent advances in yam
research. However, much of the studies so far
concentrated in the ‘yam belt’, whereas little is
known about the status of yams in the other parts of
Africa. This has led to the perception that yam is an
important food crop only in parts of West Africa, a
view that triggered concerns decades ago but still is
largely valid (Ayensu and Coursey 1972; Quin
1998).
In Ethiopia, which is the center of origin and
diversity of a large number of crop species
(Engels et al. 1991; Harlan 1969; Vavilov and
Chester 1951), studies into genetic diversity have
mainly focused on cereals. Other crops, includ-
ing the widely consumed root and tubers, have
been relatively neglected by research and
conservation efforts. Yams in Ethiopia are
hardly known to the scientific community. The
country is only referred to as an isolated center
of yam cultivation (Norman et al. 1995), where a
number of Dioscorea species are grown in
complex cropping systems together with cereals,
and other root and tuber crops (Westphal 1975).
There has been no systematic study on diversity,
production and use of the crop. Although brief
and passing remarks are available in the more
general references (Engels et al. 1991; Westphal
1975), most of these materials contain only lists
of one or a few of the yam species found in the
country.
About 23 indigenous yam types belonging to at
least four Dioscorea species were reported in
Sheko, Southeast Ethiopia (Hildebrand et al.
2002). The importance of yam for local subsis-
tence and its indigenous knowledge, as well as
priorities for conservation and improvement of
the crop were highlighted. Miege and Demissew
(1997) described eleven Dioscorea species, both
wild and cultivated, found in the country. These
reports indicate that yam is widely distributed in
Ethiopia, and is amongst the main root and tuber
crops grown by subsistence farmers in the South-
ern, Southwestern and Western parts of the
country. Nevertheless, the extent and distribution
of the available inter and intraspecific diversity is
poorly investigated.
In situations where documented data are
hardly available, the local farmer is the first
source of information to initiate diversity studies.
Farmers’ perception of local varieties is of
utmost importance because it is not only the
unit of diversity they recognize but also the unit
they actually manage and conserve (Hoogendijk
and Williams 2002). Yam is a traditional crop
that has long been cultivated in Wolayita and
Gamo-Gofa zones as co-staple with enset (Ensete
ventricosum (Welw.) Cheesman), cereals, and
other root and tuber crops (Westphal 1975). As
the crop is adapted to dry season planting
(mainly at the onset of the dry season in
October) early harvests in May fill a seasonal
gap in food supply. The fact that it is preferred to
the other root and tuber crops means yam is also
an important cash crop, generating additional
income for farm households (personal observa-
tion). This study forms part of a project initiated
with the main objective of characterizing the yam
diversity in Ethiopia (Tamiru 2006), and aims to
investigate farm-level diversity and distribution
of yam landraces in Wolayita and Gamo-Gofa
zones, the major yam production areas in South-
ern Ethiopia, and to describe how the landraces
are selected, managed and utilized by local
farmers.
Material and methods
The study area
The study area is located approximately between
latitudes 6�46¢ and 7�26¢ N, and longitudes
37�01¢ and 38�08¢ E in the Southern Nations,
116 Genet Resour Crop Evol (2008) 55:115–131
123
Nationalities, and Peoples Regional State
(SNNPRS) of Ethiopia (Fig. 1), including Wolay-
ita zone and Kucha district from the neighboring
Gamo-Gofa zone (Table 1). Wolayita zone is
composed of seven districts and 273 peasant
associations (PAs), the lowest administrative unit
in Ethiopia. The zone is one of the most densely
populated areas in the country, with an estimated
size of about 4,500 km2 inhabited by around 1.5
million people. This corresponds to an average
density of 355 people per km2, which ranges from
141 to 629 people per km2 in Humbo and Damot-
Gale districts, respectively (CSA 2000). The
district of Kucha, with an estimated area of
1,384 km2, was considered in the study to inves-
tigate the distribution of yam landraces beyond
Wolayita. The Wolayita language belongs to the
Omotic family, and is closely related to Gamo, a
language of the same family spoken by neighbor-
ing farmers in Kucha district. The two languages
have lexical similarity of 79–93% (Girard 2002).
This provides a good setting for studying crop
diversity in traditional agriculture based on
named landraces with a minimum influence of
language polymorphism.
Sampling and data collection
A household-level survey covering eight districts
was conducted from October 2003 to September
2004. A stratified sampling procedure was
followed to define the sampling unit. The area
was first stratified in terms of geographic distance
and elevation to cover the approximate ecological
range of yam so that valid generalizations can be
drawn from the results. Four to six peasant
associations (PAs) were selected from each
SRPNNS
sretemoliK00210080040004
N
enoZatiyaloW
eroS-ossoloB
odniKahsiyoK
ahcuK)enoZafoG-omaG(
affO
oddoSairuZ-oddoS
obmuH
-tomaDedyoW
tomaDelaG
enoZafoG-omaG
Fig. 1 Location of the study area in Southern Ethiopia, indicating administrative districts and the administrative capital ofthe Wolayita zone, Soddo (SNNPRS = Southern Nations, Nationalities and Peoples Regional State)
Genet Resour Crop Evol (2008) 55:115–131 117
123
district in consultation with district agricultural
officers and key informants knowledgeable in the
area. Then, 10 households were randomly se-
lected from each PA, bringing the total number of
PAs and households covered by the study to 34
and 339, respectively (Table 1). The elevation
ranges where yam farmers were interviewed
varied among districts (Table 2). Lower eleva-
tions fall within the warm semiarid climatic zone
of Ethiopia, traditionally known as Kola, that is
characterized by longer dry seasons and a mean
annual rainfall of 200–800 mm (MoA 2000). The
intermediate and higher elevations correspond to
the cool sub-humid (Woinadega) climatic zone
with the mean annual rainfall varying from 800 to
1,200 mm (MoA 2000).
Data were collected through individual inter-
views with the member(s) in each household
responsible for the management of yam fields,
using structured and semi-structured question-
naires. The semi-structured questionnaire was
included to enable full consideration of open-
ended questions such as how farmers evaluate and
identify the different landraces. Most of the
Table 2 Number of yam landrace growing farms surveyedat three different altitude ranges, mean farm size perindividual farmer, and ratio of land allocated to yam
cultivation in Wolayita and Gamo-Gofa zones, SouthernEthiopia (figures in parenthesis refer to minimum andmaximum values)
District Number of farms according to elevation Mean farm size (ha) Ratio of land allocated to yam
Lowa Intermediate High
WolayitaBolosso-Sore 0 40 0 0.70 (0.38–2.00) 0.16 (0.01–0.50)Damot-Gale 0 18 24 0.54 (0.25–1.00) 0.12 (0.03–0.33)Damot-Woyde 0 40 16 0.68 (0.13–2.00) 0.15 (0.03–0.50)Humbo 10 32 0 0.69 (0.38–1.25) 0.08 (0.02–0.25)Kindo-Koyisha 39 0 0 0.54 (0.13–1.00) 0.18 (0.04–0.50)Offa 31 9 0 0.66 (0.13–0.55) 0.11 (0.04–0.50)Soddo-Zuria 0 40 0 0.68 (0.10–2.00) 0.15 (0.05–0.50)
Gamo-GofaKucha 7 23 10 0.99 (0.25–2.00) 0.30 (0.06–0.50)
Total 87 202 50
a Low (1,550–1,750 m asl), intermediate (1,750–2,000 m asl) and high (2,000–2,225 m asl)
Table 1 Description of the districts included in the study of Wolayita and Gamo-Gofa zones, Southern Ethiopia
District Areaa
(km2)Elevation range(m asl)
Meana
populationdensity per km2
No. of PAsb
surveyedNo. of householdsinterviewed
WolayitaBolosso-Sore 633 1,830–1,980 491 4 40Damot-Gale 429 1,765–2,200 629 4 42Damot-Woyde 783 1,777–2,220 236 6 56Humbo 846 1,600–1,832 141 4 42Kindo-Koyisha 776 1,660–1,730 224 4 39Offa 588 1,600–1,950 234 4 40Soddo-Zuria 481 1,850–1,950 528 4 40
Gamo-GofaKucha 1,384 1,690–2,100 91 4 40
Total 34 339
a Data source CSA (2000)b Peasant Associations
118 Genet Resour Crop Evol (2008) 55:115–131
123
respondents were men even though women
farmers were also interviewed in places where they
were head of the family or responsible for yam
production. Since yam is a crop of much economic
and social significance and involves a laborious
production system, it is generally considered a
man’s crop.
The number of landraces grown by individual
farmers was recorded on farm where farmers
were asked to distinguish and name the differ-
ent landraces. This was conducted during the
time of the year when the plants were still
growing in the field to assist identification of the
different morphotypes. Data were also recorded
on elevation, total farm size, size of land
occupied by yams, cultivation practices and uses
of the landraces. Besides, farmers were asked to
verbally report names of landraces they knew
and/or heard about other than the ones they
were currently growing on their farms.
Data analysis
For the purpose of this research, a landrace
refers to a morphologically distinct population
of yam that farmers recognize, name and
manage. Accordingly, a list of all the landraces
recorded throughout the study area was sum-
marized after grouping known synonyms with
the help of elderly farmers. All data were
calculated on a district basis assuming that they
could reflect a certain geographic pattern. As
richness of the district, the overall number of
distinct landraces recorded, without accounting
for the number of farms where they were
found, was considered.
As measures of diversity that take into account
the proportional abundance of landraces (rich-
ness and evenness), Simpson and Shannon diver-
sity indices were calculated for all the districts.
Simpson’s diversity index (D) basically measures
the probability that two individuals randomly
selected from a sample belong to the same
category (Simpson 1949) and, hence, as D
increases, diversity decreases. The index was,
therefore, transformed as 1 – D so that greater
diversity corresponds to higher values:
Simpson’s diversity index ð1�DÞ ¼ 1�Xðni=NÞ2
where ni represents number of farms where
landrace i was found, and N sum of the number
of farms where individual landraces were found.
Shannon diversity index (H¢) combines both
number and evenness of categories considered,
and can be increased either by greater evenness
or more unique species (landraces in our case).
The index is defined as
Shannon diversity index ðH0Þ ¼ �XS
i¼1
pi ln pi
where s is number of landraces, and pi frequency
of landrace i (ni/N).
Evenness (E) was also calculated separately
as a measure of the ratio of the observed
diversity to the maximum diversity. It is defined
by the function E = H¢/ln s, where H¢ is Shan-
non index and s refers to the number of
landraces recorded in each district. High even-
ness resulting from all landraces having equal
abundance is normally equated with high diver-
sity (Magurran 1988).
To assess differentiation or beta (b) diversity
(Magurran 1988), Sørenson’s similarity index was
employed. This index estimates how different or
similar habitats are regarding diversity of the
categories under consideration, using similarity
measures of pairs of sites. The index was com-
puted based on the presence or absence of
landraces (qualitative data) to estimate landrace
similarity between all possible pairs of districts as
follows:
S�renson’s similarity index ¼ 2c
ðaþ bÞ
where a represents number of landraces in district
A, b number of landraces in district B , and c
number of landraces common to both districts.
Frequency distributions, descriptive statistics,
correlations and other relevant data analyses
were carried out applying SPSS statistical soft-
ware (SPSS 12.0.1, SPSS Inc. 2003).
Genet Resour Crop Evol (2008) 55:115–131 119
123
Results
Landrace diversity
Overall, local farmers described a total of 37
recognized yam landraces (Table 3). Of these,
two landraces (bola-boye and bunde-buchi) be-
long to a species of aerial yam (D. bulbifera L.),
and are apparently identified based on variations
in shape and size of the bulbils (aerial tubers).
However, the same characters vary within a
landrace or even among bulbils of the same plant.
The remaining landraces belong to a yet uniden-
tified species or group of species (Tamiru 2006)
that are distinct from the Dioscorea species
widely cultivated in West Africa (Tamiru et al.
2007). Most of these landraces (70%) are early-
maturing types, and are harvested twice
Table 3 Yam landraces described in Wolayita and Gamo-Gofa zones of Southern Ethiopia and respective number of farmsin the various districts where they were encountered
Landrace Number of farms per district
Bolosso-Sore
Damot-Gale
Damot-Woyde
Humbo Kindo-Koyisha
Offa Soddo-Zuria
Kucha
Afrad – – – – – 2 1 –Arkiyad – 7 – – – – – –Ayino or Ayinas 9 8 – 4 1 – 1 6Banchuwad – – – 2 – – – –Barcha or Barchyad – – – – 1 5 – –Barchahuwad – – – – – 1 – –Bola–boyea – – – – – – – 1Bota–boyed 1 – – – – – 3 –Buha, Buhed – – – – – 1 – 1Buluwad – – – – – – 1 –Buna, Bune, or Buniyad – – – 1 – 8 – 23Bunde–buchia – – – – – – 1 2Chamias – 1 – – – – – –Chawulas – 1 – – – – – –Chichiyad – 1 – – – – – –Fara, Furad – – – – 14 1 4 –Gajelas 2 20 – – – – – –Gasad 3 1 4 – 2 – – –Genad 28 – 1 2 35 12 1 3Hatiye or Hatiyad 25 22 53 40 38 40 35 40Lohuwad – – – – – – 1 –Machad – – – 1 – – – –Maleho or Malehuwad – – – – – 4 – 3Martabod – 1 – – – – – –Molchad – 1 – – – – – –Mortawa or Mortabuwas 3 – – – – – – –Natrad – – 3 1 – – 1 –Olama or Alamad – – – – – – 2 –Ochied – – – – – – – 1Ohad 11 23 56 23 7 – 26 15Sasas,w – – – – 2 – – –Suyitiyad – 10 – – – – 1 –Wadalas 12 7 31 33 38 37 29 40Welluwad – – – – – 1 – –Wolabua, Walabo, or
Walabuwos11 5 2 – – – – –
Woyichas 13 – – – – – – –Zorewuwad – – 1 – 8 – – –
d double-harvested; s single-harvested; a aerial yam; s,w single-harvested and wild
120 Genet Resour Crop Evol (2008) 55:115–131
123
(double-harvested). The remaining 30% mature
late and are harvested only once. Wild yam,
referred to by the name sasa, was encountered
only in some localities especially of Kindo-
Koyisha where forest patches still exist.
The number of landraces recorded on individ-
ual farms ranged from one to six with a mean and
standard deviation of 2.9 and 1.1, respectively.
The variation among districts with respect to
number of landraces per farm across all farms
visited is summarized in Table 4. A relatively
high number of farms with four or more landraces
were encountered in Kindo-Koyisha, Offa and
Kucha districts. All the farms surveyed in Kindo-
Koyisha and about 78% of those surveyed in Offa
districts were located at elevations below 1,750 m
asl., whereas Kucha farms were mostly located at
intermediate elevations (Table 2).
The total number of landraces recorded in each
district (richness) varied from eight at Damot-
Woyde to 14 at Soddo-Zuria and Damot-Gale
districts with a mean and standard deviation of
11.0 and 2.1, respectively (Table 5). Both Simp-
son and Shannon diversity indices revealed that
the neighboring districts of Bolosso-Sore and
Damot-Gale were the most diverse, while
Damot-Woyde was the least diverse, despite its
adjacency to Damot-Gale. As expected, Shannon
diversity index was significantly correlated with
number of total (r = 0.69) and unique (r = 0.70)
landraces. A similar relationship was observed
between Simpson index of diversity and number
of total (r = 0.60) and unique (r = 0.62) landraces.
Although Damot-Gale and Soddo-Zuria were
similar in terms of richness, the latter was found
less diverse partly due to the relatively lower
number of unique landraces. The difference
between the two districts could also be due to
the variation in the abundance of landraces,
which was evident from their respective evenness
values. The lowest number of landraces, none of
which was unique, represented the least diverse
district of Damot-Woyde.
The similarity between all possible pairs of
districts with respect to named landraces was
assessed using Sørenson’s similarity index
(Table 6). Overall, the similarity between two
districts varied from 0.16 to 0.67. Damot-Woyde
and Kindo-Koyisha were the most similar dis-
tricts, followed by Damot-Woyde and Bolosso-
Sore, and Humbo and Kucha. On the other hand,
the most dissimilar district pairs were Damot-Gale
and Offa, Bolosso-Sore and Offa, Damot-Gale
and Kucha, and Damot-Woyde and Offa in
ascending order of similarity. Both the most
similar and dissimilar pairs of districts were among
those located relatively farther apart, and this
suggested that similarity of districts did not
entirely correspond to their geographic distance.
Distribution and abundance of landraces
There was a considerable difference among the
landraces with respect to their distribution across
the districts covered (Fig. 2). Eighteen (49%) of
the landraces had a narrow distribution and were
specific to single districts. The remaining 21 (51%)
were recorded in more than one district. But, only
two (5%) were ubiquitous, being found in all the
districts surveyed. These were the early-maturing
Table 4 Variation in the number of landraces planted per farm across the districts of Wolayita and Gamo-Gofa zones inSouthern Ethiopia
No. of landraces perfarm
Number of farms per district
Bolosso-Sore
Damot-Gale
Damot-Woyde
Humbo Kindo-Koyisha
Offa Soddo-Zuria
Kucha Total
1 2 13 0 4 0 3 7 0 292 11 8 11 15 2 22 11 10 1003 14 10 32 19 20 3 14 14 1264 13 7 2 4 4 4 4 9 475 0 3 1 0 12 5 4 5 336 0 1 0 0 1 6 0 2 4
Total 40 42 56 42 39 40 40 40 339
Genet Resour Crop Evol (2008) 55:115–131 121
123
hatiye (hatiya) and the late-maturing wadala. The
other widespread landraces included oha, gena,
ayino (ayina), and gasa.
A similar trend was observed with regard to the
abundance (proportion of farms where the land-
races were found) of individual landraces. Hatiye
and wadala were the most abundant landraces as
they were recorded on 86% and 67% of the farms
surveyed, respectively (Fig. 3). Most of the land-
races (70%) were encountered on less than 3% of
the farms surveyed. Furthermore, 12 (32%) land-
races were recorded on single farms. Landrace
abundance also varied across the districts
(Table 3). Few landraces were well represented
in some districts, but virtually missing from the
others. For example, gajela was encountered on
more than 45% of the farms visited in Damot-
Gale. But outside this district, it was only found in
the adjacent Bolosso-Sore with a very low
abundance. Landraces walabua (walabo) and
woyicha, buna (bune), and fara (fura) and zor-
euwa showed similar patterns in Bolosso-Sore,
Kucha and Offa, and Kindo-Koyisha districts,
respectively. In general, there was a significant
correlation between the distribution and abun-
dance of the landraces (r = 0.85, P < 0.01).
Distribution of the landraces throughout the
study area and in two selected districts was
summarized by the abundance and frequency
matrix given in Fig. 4. Most landraces described in
this study were local (found in limited districts) and
rare (encountered on a limited number of farms in
each district) (Fig. 4a). The trend in the least
diverse district of Damot-Woyde was similar to
the overall study area (Fig. 4b). The landraces
described in this district were either local and rare
(63%) or widespread and common (37%). In the
most diverse district of Damot-Gale, the majority of
the landraces was fairly distributed with a relatively
lower but comparable abundance (Fig. 4c). This
was also reflected in the relatively higher evenness
of landrace abundance in Damot-Gale (Table 5).
In addition to the landraces grown on their
farms, farmers verbally reported 46 landrace
Table 5 Yam landrace diversity in the various districts of Woalyita and Gamo-Gofa zones in Southern Ethiopia expressedas richness, Simpson (1 – D) and Shannon (H¢) diversity indices, and evenness
District Richness %a ofthe total
Numberof uniquelandraces
1 – D H¢ Evenness
Bolosso-Sore 11 29.7 2 0.85 2.08 0.87Damot-Gale 14 37.8 6 0.85 2.14 0.81Damot-Woyde 8 21.6 0 0.70 1.36 0.65Humbo 9 24.3 2 0.72 1.46 0.67Kindo-Koyisha 10 27.0 1 0.79 1.76 0.76Offa 11 29.7 2 0.74 1.66 0.69Soddo-Zuria 14 37.8 3 0.76 1.71 0.65Kucha 11 29.7 2 0.78 1.75 0.73
a Calculated on the basis of the 37 landraces described throughout the study area
Table 6 Sørenson similarity estimates of yam landrace diversity between the different districts in Wolayita and Gamo-Gofazones of Southern Ethiopia on the basis of presence and absence of landraces
Bolosso-Sore
Damot-Gale
Damot-Woyde
Humbo Kindo-Koyisha
Offa Soddo-Zuria
Kucha
Bolosso-Sore 1.00Damot-Gale 0.56 1.00Damot-Woyde 0.63 0.45 1.00Humbo 0.50 0.35 0.59 1.00Kindo-Koyisha 0.57 0.42 0.67 0.53 1.00Offa 0.27 0.16 0.32 0.40 0.48 1.00Soddo-Zuria 0.48 0.36 0.45 0.52 0.50 0.48 1.00Kucha 0.45 0.32 0.42 0.60 0.48 0.55 0.48 1.00
122 Genet Resour Crop Evol (2008) 55:115–131
123
names that were no longer found in their
community and thought to be lost. Twenty-five
(59%) of these names corresponded to those
landraces encountered on farms of other house-
holds visited. The widely distributed landraces,
such as hatiye, wadala, oha, gena and gassa were
also among those verbally reported as missing.
The remaining 19 vernacular names (41%) were
new in the sense that they were never encoun-
tered on farmers’ fields during the survey. These
additional landraces were mostly reported by a
single or two and, at most, by six (about 2%) of
the households interviewed.
Management of yam diversity
and its determinants
In Wolayita and Gamo-Gofa zones, yam is
cultivated on an annual cycle of planting that
commences at the onset of the dry season. The
majority of the farmers interviewed (90%) car-
ried out planting in October; whereas very few
48.6%
24.3%
18.8%
2.7% 2.7%5.4% 5.4%
0
4
8
12
16
20
1 2 3 4 5 6 7 8
Number of districts where the landraces were found
secrdnalfo
rebmu
N
Fig. 2 Distribution range of yam landraces across thedistricts surveyed in Wolayita and Gamo-Gofa zones ofSouthern Ethiopia
86.467.0
47.524.2
9.48.6
6.55.65.3
3.83.22.92.72.12.11.81.51.20.90.90.90.60.60.60.60.30.30.30.30.30.30.30.30.30.30.30.3
0 20 40 60 80 100
Hatiye, Hatiya Wadala
OhaGena
Buna, Bune, BuniyaAyino, Ayina
GajelaFara, Fura
Wolabua, Walabo, WalabuwoWoyichaSuyitiya
GasaZorewuwa
ArkiyaMaleho, Malehuwa
Barcha, BarchyaNatra
Bota-boyeAfra
BundebuchiMortawa, Mortabuwa
BanchuwaBuha, Buhe
Olama, AlamaSasa
BarcheuwaBola-boye
BuluwaChamia
ChawulaChichiyaLohuwa
MachaMartaboMolcha
OchieWelluwa
dedrocersecardna
L
% of farms visited
Fig. 3 Relative abundance of yam landraces recorded throughout Wolayita and Gamo-Gofa zones of Southern Ethiopia
Genet Resour Crop Evol (2008) 55:115–131 123
123
farmers delayed planting till December (4%) or
January (1%). Factors such as soil moisture
content, anticipated severity of the dry season,
and tuber sprouting were considered in timing
field planting. Land is prepared while the soil is
still moist enough from the preceding rainy
season to meet the requirements of yam for loose
and deep soils, as well as permitting planting
before the onset of the dry season so that early
growth can make use of the residual soil moisture.
There is no formal seed supply system for yam
in the study area nor do farmers specialize in the
production of yam planting-materials. Farmers
mostly rely on their own planting-materials saved
from the previous cropping season. Some farmers
partly meet their demand for seed tubers through
purchases from local markets or exchanges with
neighbors (Fig. 5). About 60% of the farmers
interviewed used pieces of tubers, while others
depended on whole tubers (3%) or both types of
tubers (37%) for planting. The type of tubers
used corresponded to type of landrace grown. For
single-harvested landraces that normally produce
a single tuber per plant, the head region (prox-
imal end) is retained for propagation (while the
remaining part is consumed), and is planted either
as a single piece or further divided into smaller
pieces. With double-harvested landraces, a single
plant produces multiple tubers following the first
harvest, and these small whole tubers serve as
ideal planting materials.
Yam is mainly established as a sole crop in the
field (Table 7). The late and early-maturing
landraces occupy separate rows on the same plot,
and those with similar maturity time are planted
in mixtures with no regular patterns. It is widely
0.18.06.04.02.00.0
0.0
2.0
4.0
6.0
8.0
0.1
0.18.06.04.02.00.0
0.0
2.0
4.0
6.0
8.0
0.1
a
b
lacoL
0.18.06.04.02.00.0
0.0
2.0
4.0
6.0
8.0
0.1
AB
UN
DA
NC
E
nommoC
eraR
c
YCNEUQERFdaerpsediW
Fig. 4 Frequency and abundance matrix of yam landraces found throughout the study area in Southern Ethiopia (a), in theleast diverse district of Damot-Woyde (b), and most diverse district of Damot-Gale (c)
124 Genet Resour Crop Evol (2008) 55:115–131
123
perceived that intercropping reduces yield and
complicates cultural practices (Table 7). There is
also a common belief in the area that yam does
not appreciate frequent ‘visits’, which apparently
reduce yield. Accordingly, frequency of entrance
to yam fields is kept to a minimum, and mono-
cropping is one way to achieve this. Even those
farmers who practiced intercropping shared these
opinions but adopted the system due to shortage
of land. In intercropping, the crops planted with
yams included maize (Zea mays L.), sweet potato
(Ipomoea batatas (L.) Lam.), cabbage (Brassica
spp.), beans (Phaseolus spp.) and, to a lesser
extent, coffee (Coffea arabica L.). Yam is usually
planted on relatively fertile plots, or gets the most
attention during applications of manure that is
incorporated into the soil during land prepara-
tion. There is no use of commercial fertilizers in
yam production. Rotation of yam plots on inter-
vals of 1–4 years, depending on land availability,
is practiced to achieve sustainable yields.
Yam is chiefly cultivated along rows of stakes,
except for wild yams that are planted near trees for
support. Young Eucalyptus, and maize and sor-
ghum (Sorghum bicolor (L.) Moench) stalks are
among the materials widely used for supporting
yam plants. Staking commences after the tubers
have sprouted and produced vines of considerable
size. Every plant is supplied with a vertical stake
and trained along it. Individual staking is the only
method of staking encountered in the survey area.
The majority of the farmers interviewed (74%)
obtained staking materials from surrounding
forests and trees planted on their farms, while
about 11% bought the materials on local markets.
The others depended on both sources to secure the
materials required for staking.
Two practices exist with respect to yam har-
vesting. The late-maturing landraces are har-
vested only once at full senescence, whereas the
early-maturing types are harvested twice (double-
harvested). For yam planted in October, double
harvesting involves a first harvest in May or June,
when the tubers are severed at their point of
attachment to the corm with maximum care to
avoid damage to the root system. Visible onset of
senescence is used as a guide for timing harvesting
of the late-maturing landraces and the second
harvest of double-harvested landraces. However,
there is no easy way of determining the optimum
time for the first harvesting of double-harvested
landraces. Farmers in the study area are guided by
different, largely phenological signals to subjec-
tively judge the first harvesting (Table 8). The aim
here is to avoid harvesting too early (lower yield)
or too late that can compromise the second
harvest due to insufficient time for re-tuberization.
According to farmers’ account of trends over
the last 20–30 years, yam production and the
number of landraces maintained on individual
farms are on the decrease in most localities
(Table 9). Even those areas where yam produc-
tion has been an increasing business (for example,
the case in Damot-Woyde) are characterized
Table 7 Methods of yam establishment in the field andreasons for their preference given by farmers in the majoryam growing areas of Wolayita and Gamo-Gofa zones,Southern Ethiopia
Method of field establishmentand reasons for preference
Responses byfarmers
No. %a
Monocropping 326 96Lowers competition 223 95Convenient for cultural practice 76 22
Intercropping 7 2Shortage of land 7 100
Both 6 2
Total 329 100
a Sums over 100% are due to multiple responses
+tsevraHnwOtekraM)%23(
tsevraHnwO)%74(
tekraM)%7.2(
egnahcxE+tekraM)%3.0(
egnahcxE)%3.0(
egnahcxE+tekraM+tsevraHnwO)%61(
egnahcxE+tsevraHnwO)%5.1(
Fig. 5 Major sources of planting-materials (seed tubers)for field planting of yams as reported by farmers inWolayita and Gamo-Gofa zones of Southern Ethiopia(figures in parenthesis are percentage values based on thetotal 339 farmers interviewed)
Genet Resour Crop Evol (2008) 55:115–131 125
123
either by a low level of landrace diversity
(Table 5) or a decreasing trend in the number
of landraces maintained on individual farms
(Table 9).
The distribution pattern of yam landraces
revealed that the type and number of landraces
grown by individual farmers were influenced by
factors such as elevation. Overall, the number of
landraces grown per farm was negatively corre-
lated (r = –0.40; P < 0.05%) with elevation
(Fig. 6). However, elevation might be con-
founded with drought tolerance. At relatively
lower elevations with extended dry season, land-
races that are perceived to be drought-tolerant
(for example, wadala) are widely cultivated.
Besides, farmers plant double harvested landraces
to ensure early harvests although some of these
landraces are less adapted to drier conditions.
There was no significant correlation between farm
size and number of landraces per farm. On the
other hand, the proportion of land allocated for
yam production was negatively correlated with
total farm size (r = –0.13, P < 0.05), indicating
that even those farmers with smaller landholdings
Table 8 Criteria employed by farmers in Wolayita andGamo-Gofa zones of Southern Ethiopia for timing the firstharvesting of double-harvested yam landraces
Criteria Proportion offarmers (%)
Senescence of inflorescence 19.8Senescence of inflorescence + flower
scent13.0
Senescence of inflorescence + wiltingof vine tips
9.7
Wilting of vine tips 5.9Senescence of inflorescence + digging
and checking of tubers5.0
Senescence of inflorescence + flowerscent + wilting of vine tips
4.7
Time from planting + wilting of vinetips
3.8
Senescence of inflorescence + flowerscent + soil cracking
3.5
Senescence of inflorescence + soilcracking + wilting of vine tips
3.2
Senescence of inflorescence + timefrom planting
3.2
Time from planting 2.7Othersa 25.5
Total 100.0
a Include the use of the above criteria in various forms ofcombinations
Table 9 Trends in the number of landraces maintained onindividual farms and in the overall yam production inSidama and Gamo-Gofa zones of Southern Ethiopia as
perceived by farmers (number in parenthesis refer topercentage values based on total number of farmersinterviewed in each district)
District Number of landraces Total production
Increasing Decreasing No change Increasing Decreasing No change
Bolosso-Sore 27 (68) 4 (10) 9 (23) 13 (33) 27 (67) 0 (0)Damot-Gale 10 (24) 21 (50) 11 (26) 10 (24) 32 (76) 0 (0)Damot-Woyde 2 (4) 17 (30) 37 (66) 34 (61) 22 (39) 0 (0)Humbo 5 (12) 28 (67) 9 (21) 2 (5) 40 (95) 0 (0)Kindo-Koyisha 8 (21) 31 (79) 0 (0) 2 (5) 37 (95) 0 (0)Offa 2 (5) 34 (85) 4 (10) 4 (10) 36 (90) 0 (0)Soddo-Zuria 7 (18) 13 (33) 20 (50) 3 (8) 37 (92) 0 (0)Kucha 26 (65) 14 (35) 0 (0) 14 (35) 26 (65) 0 (0)Total 87 (26) 162 (48) 90 (26) 82 (24) 257 (76) 0 (0)
r = - 0.40
0
1
2
3
4
5
6
1500 1600 1700 1800 1900 2000 2100 2200 2300
Elevation (m asl.)
mrafrep
secardnalfo
rebmun
naeM
Fig. 6 Mean number of yam landraces per farm related toelevation in Wolayita and Gamo-Gofa zones of SouthernEthiopia
126 Genet Resour Crop Evol (2008) 55:115–131
123
allocate a significant share of their land for yam
cultivation in order to get a reasonable produc-
tion and meet family needs.
Significant proportions of farmers interviewed
in Kindo-Koyisha (87%), Kucha (70%), Offa
(63%) and Humbo (33%) districts stated the
presence and use of wild yam in their area. The
figure was relatively lower in Soddo-Zuria (8%)
and Bolosso-Sore (3%), while there was no such
report in Damot-Woyde. Wild yam was found
predominantly in localities situated at lower
elevations (mainly below 1,700 m asl.) that are
sparsely populated, and where patches of forest
could still be found. Wild yam tubers collected
from surrounding forests are either consumed
directly or planted on farms under big trees,
where they are left to grow for up to 3 years.
These tubers are normally consumed during
periods of relative food shortage.
Discussion
Status of yam diversity
Farmers in the study area maintain diverse yam
landraces with respect to attributes such as envi-
ronmental adaptation and length of growing
period. This finding confirms the salient feature
of traditional farming systems in the tropics,
where diverse crop species or varieties of the same
species are maintained on a single farm (Boster
1983; Brush 1995; Clawson 1985) in response to
economic, social, cultural and natural factors (Cox
and Wood 1999). Similar observations were made
in various traditional farming systems for clonally
propagated crops such as enset (Tesfaye and
Ludders 2003; Tsegaye and Struik 2002), cassava
(Manihot esculenta Crantz) (Boster 1985; Salick
et al. 1997), and potato (Solanum tuberosum L.)
(Brush et al. 1981). Tsegaye and Struik (2002)
recorded a total of 55 named enset landraces in
Wolayita, where individual farmers on average
maintained eight landraces. They also reported
that landrace diversity was affected by factors such
as household resources, cultural background, pop-
ulation pressure and agro-ecology.
Two of the landraces described, bola-boye and
bunde-buchi, belong to the species D. bulbifera.
However, the species identity of the remaining
landraces is yet to be established (S. Demissew,
personal communication). Preliminary observa-
tions based on morphological features seem to
indicate that some of the landraces belong to the
D. cayenensis/D. rotundata species complex
(Tamiru 2006) as presently understood by most
researchers working on yams (e.g. Dansi et al.
1999). However, this was not supported by
molecular data (Tamiru et al. 2007).
Most named yam landraces are morphologi-
cally distinct. Farmers consider a combination of
characters viz. morphological, growth and orga-
noleptic, as well as ecological adaptation to
classify yam landraces (M. Tamiru et al. submit-
ted to Genetic Resources: Characterization and
Utilization). Tuber flesh color is the most impor-
tant selection criterion to distinguish the so-called
‘female’ (macha) landraces. Nevertheless, macha
does not seem to be a distinct landrace. The same
name is used as a reference to a group of the so-
called ‘female yams’ (macha boye) that include
the early-maturing landraces such as hatiye and
oha (M. Tamiru et al. submitted to Genetic
Resources: Characterization and Utilization).
But, there are no peculiar characteristics that
distinguish the landrace macha from members of
the group macha.
The extent of landrace diversity detected in
this study is comparable to an earlier report from
Sheko, Southwest Ethiopia, where 23 separate
indigenous yam types belonging to at least four
species of Dioscorea were described (Hildebrand
et al. 2002). But, it is considerably lower than the
level of diversity reported from some West
African countries. For Example, about 300 dif-
ferent named yam landraces were described
across 10 different ethnic groups throughout
Benin (Dansi et al. 1997, quoted by Dansi et al.
1999), while Baco et al. (2004) recorded 88
varieties in the Sienende district of Benin. How-
ever, such records are not entirely comparable.
First, some reports cover an entire region or
country, whereas others, including our study, deal
with relatively smaller areas. Furthermore, when
conducting such studies across ethnically diverse
regions, like in the above reports, linguistic
polymorphism may lead to an overestimation of
diversity based on named landraces.
Genet Resour Crop Evol (2008) 55:115–131 127
123
Yam production in Wolayita and Gamo-Gofa
is mainly based on a limited number of wide-
spread landraces such as hatiye, wadala and oha
(Table 3 and Fig. 3). The majority of landraces
recorded have a rather limited distribution and
abundance. This hierarchical nature of spatial
distribution, where a limited number of land-
races or cultivars are dominant, has been
documented for several crop species (Boster
1985; Louette et al. 1997; Tesfaye and Ludders
2003). The widespread distribution of some
landraces also challenges the view that tradi-
tional farming systems are isolated and closed,
with limited exchange of germplasm. Our
finding and those of others mentioned above
depict these systems rather as open and
dynamic, where local networks exist for moving
planting materials across wider areas and het-
erogeneous environments. Yam farmers in the
study area acquire part of their planting
materials either through purchases from local
markets or exchanges with neighbors (Fig. 5).
Such networks can cover relatively larger areas,
as getting to the next market often entails
long-distance travels.
One advantage of double-harvesting is that
the first harvesting induces the formation of
multiple tubers. Tubers from the second harvest
are mostly lignified and fibrous, and possess
several visible buds even at harvest (Onwueme
and Charles 1994), making them ideal planting
materials. Some farmers prefer to delay or forgo
first harvesting, opting for a single harvest of
apparently higher yields to maximize income.
These farmers purchase seed tubers from local
markets for the following production season
(Fig. 5). This has created a potential market
for seed tubers, where middlemen who are now
increasingly involved in the business move
planting materials even over longer distances.
This may offer some explanation as to why some
districts (for example, Damot-Woyde and Bo-
losso-Sore), although located further apart, are
relatively similar with regard to yam landrace
diversity. Nevertheless, addressing this issue
needs analysis of events in the past that might
have influenced movement of yam germplasm in
the study area, an important data that is missing
at the moment.
Yam production in the study area is con-
strained by several environmental and production
factors (Tamiru et al. 2005). This has led to a
decrease in production and yam diversity in the
majority of the localities surveyed, except in some
localities, mainly of Damot-Woyde, where pro-
duction is on the increase and yam is establishing
itself as an important cash crop. However,
Damot-Woyde is the least diverse district in
terms of total number of landraces found (Ta-
ble 5). It seems that the increase in production is
brought about at the expense of the overall
landrace diversity, as farmers are increasingly
growing a few selected landraces. Hatiye and oha
are among the widely cultivated landraces in this
district due to their early maturity and excellent
culinary properties and, thus, are replacing the
late-maturing landraces such as wadala. As noted
by Frankel and Bennett (1970), besides the
transition from landraces to advanced cultivars,
selection for closely defined objectives can lead to
a reduction in genetic variation.
Although detailed information is lacking as to
the extent of changes that might have occurred in
yam genetic diversity and the implications of such
changes, this study has provided a first perception
by farmers, and genetic vulnerability (Brown
1983) is a legitimate worry in Wolayita and
Gamo-Gofa (Table 9). Farmers are expressing
concerns that yam production is threatened by
changing environmental conditions (erratic rains,
increasing temperatures). This concern is partic-
ularly valid in view of the fact that most of the
early-maturing landraces that are being used for
expanding production are relatively more prone
to drought than the late-maturing ones.
Management and use of diversity
Wolayita and Gamo-Gofa farmers are familiar
with the diversity available in yams and attributes
of each landrace, which they utilize accordingly to
meet their needs. Unlike other crops, yam is
adapted to dry-season planting, an attribute
widely manipulated by local farmers to ensure
household food security. For yams planted in
October, the first harvest of early-maturing land-
races is expected around May or June. This is a
period of relative food shortage in the area, as
128 Genet Resour Crop Evol (2008) 55:115–131
123
most of the other crops are still in the field. Thus,
yam fills a seasonal gap in food supply. That is
why the early-maturing landraces such as hatiye
and oha are widely distributed throughout the
study area (Fig. 3).
Apart from early maturity, some landraces
such as hatiye are popular due to their sweet taste
and white tuber flesh color, and are preferred for
preparing fichata, a popular dish made of boiled
and mashed yam mixed with fermented milk and
butter. The white tuber flesh goes well with the
milk during mixing. Thus, such landraces are
widely distributed across different altitudinal
ranges although farmers are aware of the fact
that some perform poorly under drier and hotter
conditions. Wadala is more common at lower
elevations, and is highly valued for its sturdy
growth, drought tolerance and bigger tubers. Its
requirement for more stout staking materials,
regular training and, hence, intensive manage-
ment is usually tolerated because of its acceptable
performance under sub-optimal conditions. The
late-maturing nature of this landrace is exploited
to extend harvesting into late seasons.
There exists a striking similarity between the
management and use of yams in the study area
and other parts of Ethiopia such as Sheko
(Hildebrand et al. 2002), as well as different West
African countries (Asiedu et al. 1997; Hahn et al.
1987; Onwueme 1978). This provides an oppor-
tunity for sharing experiences mainly with West
African countries, where the yam-based agricul-
ture has been supported by research undertakings
that have achieved technology delivery and
adoption on farms (Quin 1998). On the other
hand, Wolayita and Gamo-Gofa farmers employ
unique practices with a certain degree of sophis-
tication in managing yam. For example, double
and single-harvestings are also common features
of yam production in other African countries
(Onwueme 1978). Among the main problems
often mentioned in connection with double-har-
vesting is the lack of a reliable index of maturity
to time the first harvesting (Onwueme 1978),
which farmers in the study area subjectively judge
by using a range of criteria based on experience
(Table 8). Such practices make the indigenous
knowledge of local farmers an important aspect
of the overall yam diversity.
Conclusions
The high value that local farmers place on yam is
expressed in its continued cultivation despite the
lack of any form of support from researchers and
policy makers. Due to its adaptability to dry
season planting, yam fits well into the traditional
cropping calendar, and this is widely utilized to
ensure food availability during critical periods of
the year. Given this practical importance of yam
in the local livelihood, there is an urgent need for
research programs to address the problems facing
yam production and its diversity taking into
consideration the multiple objectives of farmers
and the importance of diversity in the physical,
economical and cultural contexts of local agricul-
ture.
Findings of this study suggest that the
majority of the landraces recorded in Wolayita
and Gamo-Gofa face considerable risk of loss
mainly due to their rare occurrence and local
distribution. Besides, late-maturing landraces
are becoming increasingly vulnerable to replace-
ment by early-maturing ones. The diversity
available in these landraces needs to be studied
in detail in order to facilitate their conservation
as well as utilization in crop improvement
programs. Studies that address the problems
currently faced by yam production can enhance
the role that yam plays in household food
security. Considering the importance of yam in
local agriculture and tradition, such studies can
also ensure continuous maintenance of yam
diversity by farmers through increased utiliza-
tion of available landraces.
Describing the diversity in crop species based
on named landraces, such as in this report,
constitutes an essential step towards setting
research and development priorities aimed at
conservation and improvement of a traditional
crop. In view of the current taxonomical con-
fusion regarding the major African Dioscorea
species and the lack of information on the
status of yams outside the ‘yam belt’, broaden-
ing the knowledge base of yams in Ethiopia
contributes substantially to our understanding of
the diversity in African yams. To this end,
further research must include other regions in
Ethiopia that are not covered by the present
Genet Resour Crop Evol (2008) 55:115–131 129
123
study and give wider coverage to wild yams, as
well as consider elite genotypes from West
Africa to thoroughly investigate the available
diversity.
Acknowledgments We are grateful to all farmers whoparticipated in the study for their time, invaluableknowledge and hospitality. We also thank members ofthe regional, zonal and district agricultural offices and,particularly the development agents who gave us all thehelp we needed during site selection and throughout thestudy. The assistance provided by the DU-Norad(Norwegian Agency for Development Cooperation)project of Debub University (Ethiopia) during thefieldwork is highly acknowledged. The GermanAcademic Exchange Service (DAAD) sponsored thisstudy.
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