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RESEARCH ARTICLE Diversity, distribution and management of yam landraces (Dioscorea spp.) in Southern Ethiopia Muluneh Tamiru Heiko C. Becker Brigitte L. Maass Received: 26 September 2006 / Accepted: 24 January 2007 / Published online: 11 April 2007 ȑ 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 the Tropics, Georg-August-University Goettingen, Grisebachstr. 6, Goettingen 37077, Germany e-mail: [email protected] H. C. Becker Department of Crop Sciences: Plant Breeding, Georg- August-University Goettingen, Von-Siebold-Str. 8, 37075 Goettingen, Germany M. Tamiru Hawassa University, P.O. Box 05, Awassa, Ethiopia 123 Genet Resour Crop Evol (2008) 55:115–131 DOI 10.1007/s10722-007-9219-4

Yam in Ethiopia

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Page 1: Yam in Ethiopia

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

Page 2: Yam in Ethiopia

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

Page 3: Yam in Ethiopia

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

Page 4: Yam in Ethiopia

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

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Page 5: Yam in Ethiopia

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

Page 6: Yam in Ethiopia

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

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Page 7: Yam in Ethiopia

(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

Page 8: Yam in Ethiopia

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

Page 9: Yam in Ethiopia

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

Page 10: Yam in Ethiopia

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

Page 11: Yam in Ethiopia

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

Page 12: Yam in Ethiopia

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

Page 13: Yam in Ethiopia

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

Page 14: Yam in Ethiopia

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

Page 15: Yam in Ethiopia

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

Page 16: Yam in Ethiopia

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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