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Annals of Botany XX: 1–20, 2019
doi: 10.1093/aob/mcy214, available online at www.academic.oup.com/aob
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REVIEW
Enset in Ethiopia: a poorly characterized but resilient starchstaple
JamesS. Borrell1,*, ManoshK. Biswas2, Mark Goodwin2,†, Guy Blomme3, Trude Schwarzacher2,
J.S.(Pat) Heslop-Harrison2, AbebeM. Wendawek4, Admas Berhanu5, Simon Kallow6,7, Steven Janssens8,
ErmiasL. Molla9, AaronP. Davis1, Feleke Woldeyes10, Kathy Willis1,11, Sebsebe Demissew1,9,12 and
Paul Wilkin1
1Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, UK, 2Department of Genetics and Genome Biology, University of
Leicester, LE1 7RH, UK, 3Bioversity International, c/o ILRI, PO Box 5689, Addis Ababa, Ethiopia, 4Department of Biology,
Hawassa University, Hawassa, Ethiopia, 5Department of Biology and Biotechnology, Wolkite University, Hawassa, Ethiopia,
6Conservation Science Department, Royal Botanic Gardens, Kew, Wakehurst Place, Ardingly, West Sussex, RH17 6TN, UK,
7Division of Crop Biotechnics, Katholieke Universiteit Leuven, Willem de Croylaan 42, 3001 Leuven, Belgium, 8Laboratory
of Plant Systematics, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, Kasteelpark, Arenberg 31, PO
Box 2437, 3001 Leuven, Belgium, 9Department of Biology, Addis Ababa University, PO Box 3293, Addis Ababa, 5 Ethiopia,
10Ethiopian Biodiversity Institute, PO Box 30726, Addis Ababa, Ethiopia, 11Department of Zoology, University of Oxford,
Oxford, UK, and 12Gullele Botanic Garden, PO Box 153/1029, Addis Ababa, Ethiopia
*For correspondence. E-mail: j.borrell@kew.org
†Deceased 25 August 2018; see tribute at the end of the article.
Received: 24 August 2018 Returned for revision: 24 September 2018 Editorial decision: 31 October 2018 Accepted: 16 December 2018
• Background Enset (Ensete ventricosum, Musaceae) is an African crop that currently provides the staple food
for approx. 20 million Ethiopians. Whilst wild enset grows over much of East and Southern Africa and the genus
extends across Asia to China, it has only ever been domesticated in the Ethiopian Highlands. Here, smallholder
farmers cultivate hundreds of landraces across diverse climatic and agroecological systems.
• Scope Enset has several important food security traits. It grows over a relatively wide range of conditions, is some-
what drought-tolerant, and can be harvested at any time of the year, over several years. It provides an important dietary
starch source, as well as bres, medicines, animal fodder, roong and packaging. It stabilizes soils and microclimates
and has signicant cultural importance. In contrast to the other cultivated species in the family Musaceae (banana),
enset has received relatively little research attention. Here, we review and critically evaluate existing research, outline
available genomic and germplasm resources, aspects of pathology, and explore avenues for crop development.
• Conclusion Enset is an underexploited starch crop with signicant potential in Ethiopia and beyond. Research
is lacking in several key areas: empirical studies on the efcacy of current agronomic practices, the genetic diver-
sity of landraces, approaches to systematic breeding, characterization of existing and emerging diseases, adapt-
ability to new ranges and land-use change, the projected impact of climate change, conservation of crop wild
relatives, by-products or co-products or non-starch uses, and the enset microbiome. We also highlight the limited
availability of enset germplasm in living collections and seedbanks, and the lack of knowledge of reproductive and
germination biology needed to underpin future breeding. By reviewing the current state of the art in enset research
and identifying gaps and opportunities, we hope to catalyse the development and sustainable exploitation of this
neglected starch crop.
Keywords: Biodiversity, biotic and abiotic resistance, climate adaptation, crop wild relatives (CWRs), domesti-
cation, Ensete ventricosum, false banana, food security, germplasm collections, pests and pathogens, sustainable
agriculture, tropical crop ecology.
INTRODUCTION
Enset [Ensete ventricosum (Welw.) Cheesman] is a large peren-
nial monocarpic herbaceous plant, similar in form to the related
bananas of the genus Musa (Fig.1). The two genera, together
with the monotypic Musella (Franch.) C.Y. Wu ex H.W. Li, form
the family Musaceae within the Monocot order Zingiberales
(Fig.2A). Like banana, enset has a pseudostem of overlapping
leaf sheaths, large paddle-shaped (oblong-lanceolate) leaves and
produces a massive pendulous inorescence with banana-like
fruits. However, unlike sweet and starchy banana (with the latter
called plantain in some contexts, although there is no botani-
cal distinction between banana and plantain), which are widely
farmed for their fruits, it is instead the swollen pseudostem base,
leaf sheaths and underground corm that provide a year-round
dietary starch source, typically harvested 4–7years after plant-
ing. Despite a widespread distribution in eastern, central and
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Borrell etal. — Enset in Ethiopia
2
southern tropical Africa (Baker and Simmonds, 1953; Lock,
1993), enset has only been domesticated in Ethiopia (Brandt
etal., 1997). Here, hundreds of landraces are found in diverse
climatic and agroecological systems (Birmeta et al., 2002;
Tesfaye and Lüdders, 2003; Yemataw etal., 2014a) where they
provide the staple food source for approx. 20 million rural peo-
ple (Supplementary Data, Fig. S1 – see Supplementary data
Information for population estimation methods).
Enset has historically been ascribed as a ‘tree against hun-
ger’ (Brandt et al., 1997), due to the domesticated plant having
AB
CD
E
F.1. Domesticated Enset ventricosum in Ethiopia. (A, B) Original plates of ‘Ensete’ from Bruce (1790). (C) Large enset plants (landrace ‘Medasho’) grown
by small scale farmers in Teticha (Sidama Zone, SNNPR region). (D) Atypical enset home garden near Butajira (Gurage Zone, SNNPR region). (E) An enset
germplasm collection at Yerefezy research station, University of Wolkite (Gurage Zone, SNNPR region). Clear differences in morphology can be observed, with
substantial differences in growth rate under local environmental conditions.
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Borrell etal. — Enset in Ethiopia 3
important attributes that support the food security of communities
that cultivate it. These attributes were evident during the devas-
tating famines of the 1980s, where enset-growing communities
reported little-to-no food insecurity (Dessalegn, 1995). Most sig-
nicant is the apparent ability of enset to withstand environmental
stress, including periods of drought (Quinlan et al., 2015). Enset
can also be harvested at any time of the year and at any stage
over several years (including when it is immature), and enset-
derived starch can also be stored for long periods (Birmeta, 2004).
Ensetalso provides bres, medicines, animal fodder and packag-
ing material (Brandt etal., 1997). It stabilizes soils and microcli-
mates (Abate et al., 1996) and is culturally signicant (Kanshie,
2002; Negash and Niehof, 2004; Tewodros and Tesfaye, 2014).
Enset has a complex management system supported by exten-
sive ethnobotanical knowledge (Borrell etal., unpubl. res.). In a
comparison of starch crops, enset has been reported to produce
the highest yield per hectare in Ethiopia (Tsegaye and Struik,
2001; Kanshie, 2002) with relatively low inputs and management
requirements. Enset therefore has the ability to support a larger
population per unit area than regions relying on growing cereals
(Yirgu, 2016). As a result of these qualities, enset farming provides
a long-term, sustainable food supply capable of buffering not only
seasonal and periodic food decits, with minimum off-farm input,
but also demonstrates potential that exceeds its current utilization
in South-West Ethiopia.
Despite the current and potential importance of enset, rela-
tively little is known about its biology and ecology. In this review
we aim to (1) summarize the existing knowledge and current
research effort both nationally in Ethiopia and internationally;
(2) identify critical knowledge gaps in the ecology, diversity
and distribution of enset to direct future research effort; and
(3) catalyse the development of resources needed to enable the
sustainable exploitation of enset diversity as a resilient climate-
smart crop of the future. Concurrently, we also acknowledge the
importance of local ethnobotanic knowledge, management and
plant processing; these topics will be reviewed in due course
(Borrell et al., unpubl. res.). Finally, we introduce the online
resource www.enset-project.org to make various tools and data
available to researchers both in Ethiopia and internationally.
THE GENUS ENSETE: EVOLUTION AND SYSTEMATICS
Ensete Bruce ex Horan. is a monophyletic genus (Li et al.,
2010) with seven described species in Africa and Asia (Table1).
Although rst reported by Bruce (1790) during travels in Ethiopia
(Fig. 1A, B), and formally described by Horaninow (1862) it
was not until almost a century and a half later that Cheesman
(1947) elevated the informal ‘giant bananas’ group within Musa
to re-establish the genus Ensete. Of the 20 reported synonyms,
65 % relate to Ensete ventricosum (Welw.) Cheesman. The sister
genus Musella (Li, 1978) was originally placed under Musa and
Ensete (Cheesman, 1947; Simmonds, 1960). Whilst the sole
species of this genus, M.laisocarpa (the golden lotus banana),
occupies a unique geographical distribution, drier and cooler
than any other member of the family, there is continuing debate
as to whether it should be treated as a member of Ensete or as its
sister (Liu etal., 2003; Li etal., 2010).
Currently, Ensete (seven species) and the sister genera Musa
(approx. 70 species) and Musella (one species) belong to the
Musaceae within the order Zingiberales, together with eight
tropical plant families (Fig.2B, Supplementary Data TableS1),
some including genera known for their medicinal properties
and ornamental use. APG IV (Chase etal., 2016) has conrmed
the position of Zingiberales as a monophyletic order within the
monocots, placing it in the commelinoid clade, as the sister
group to Commelinales, but has not addressed the interfamilial
relationships of the other families belonging within the order
(Fig.2B). Understanding the relationship and genomic organ-
ization of Ensete as sister to Musa may provide novel insights
into the evolution of the globally important Musaceae family.
BA
Commelinids
Poales
Arecales Musa
Musella
Ensete ventricosum (HBG)*
Ensete homblei
Ensete ventricosum (CR)*
Ensete livingstonianum
Ensete glaucum
Ensete superbum isolate Thailand Enset
e
Ensete superbum isolate India
Ensete glaucum isolate Myanmar
Ensete superbum
Ensete glaucum isolate Yunnan
Orchidantha
Ravenala
Heliconia
Canna
Maranta
Zingiber
Costus
Boesenbergia
78
100
100
100
100
100
100
100
100
100
100
100
100
100
76
60
98
92
92
43
57
72
97
99
94
98
52
Zingiberales
Commelinales
A
F.2. Evolutionary relationships of genus Ensete. (A) The genus Ensete is included in the Musaceae, one of eight families of the monocot order Zingiberales
which together with the Commelinales is sister to the Poales that contain the cereal crops including wheat, maize and rice. (B) Evolutionary relationships of the
genus Ensete within the Zingiberales based on ITS sequences, including collapsed sister genera within Musaceae and outgroups representing the eight families
(see Supplementary Data Fig.S2 for an expanded tree and Supplementary Data Information for method details). Provenance of the two E.ventricosum accessions
are Hamburg Botanic Garden (HBG) and Costa Rica (CR; Introduced).
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Borrell etal. — Enset in Ethiopia
4
Like the other Musaceae genera, Ensete originated in north-
ern Indo-Burma during the early Eocene, probably followed
by a single African colonization via gradual overland disper-
sal during a more mesic climate period (Janssens etal., 2016).
The presence of Eocene Ensete fossils in North America
(Manchester and Kress, 1993) establishes that the genus also
reached the New World. Ensete differs from bananas in being
mainly African in distribution, monocarpic, having large seed
size (up to 18mm compared to 10mm) and an apparent adap-
tation to cooler and drier environments than most Musa spe-
cies (Cheesman, 1947; Baker and Simmonds, 1953). Musa
and Ensete can be further distinguished by the presence of
‘T’-shaped embryos and granulose papillose pollen grains in
Ensete, and their absence in Musa (Bekele and Shigeta, 2011).
Ensete does not normally produce suckers, whereas Musa does
– although a small number of suckering E.ventricosum land-
races are known to occur in Ethiopia (provenance unknown). In
the eld, Ensete are perhaps best distinguished from Musa by
their more rigid and upright leaves (J.S.B., pers. obs.).
A further distinction is that Ensete is currently only reported
to be diploid with 2n=2x=18 (Westphal, 1975; Diro etal.,
2003) and this is consistent with ow cytometry measurements
in ten individuals (J. S.Heslop-Harrison and P.Tomaszewska
pers. comm.) and chromosome counts (Fig. 3). By contrast,
Musa has species with x=7, 10 and 11 at various ploidy levels;
domesticated varieties are commonly sterile, parthenocarpic
triploids (2n=3x= 33) (Bartoš et al., 2005). Species in the
genus Ensete have a relative small DNA content, reported to
be about 620Mb per haploid genome for E.livingstonianum
(measured by ow cytometry, Bartoš etal., 2005) and 547Mb
T1. Accepted species of the genus Ensete, with details of conservation and domestication.
Accepted species* Common names and
synonyms
Conservation status† and
distribution
Domestication
status
Uses Notes
Africa
Ensete homblei None DD; possibly restricted
range
Crop wild relative Unknown The majority of locality information for
this species, is from historical herbarium
collections. Reported to die down to the
corm in the dry season (Timberlake and
Martins, 2010).
Ensete ventricosum Abyssinian banana,
False banana,
E.edule
LC; widely distributed Domesticated
& crop wild
relative
Human food;
animal
fodder; bre;
packaging;
medicine;
ornamental
Due to the practice of harvesting domestic
enset before the owers mature, there is
probably limited gene ow between wild
and cultivated populations (Birmeta etal.,
2004).
Ensete livingstonianum E.gilettii LC; widely distributed. Crop wild relative Unknown Reported to die down to the corm in the dry
season (J.S.B., pers. obs.).
Ensete perrieri Madagascar banana,
Musa perrieri
CR; endemic to
Madagascar; only
three known mature
individuals.
Crop wild relative Unknown Reported to die down to the corm in the dry
season (Schatz and Phillipson, 2011).
Possibly present in the ornamental trade,
but genetic conrmation of identity
required.
Asia
Ensete superbum Cliff banana EN; endemic to India Crop wild relative Human food;
packaging;
medicine;
ornamental
Overharvesting from the wild of leaves,
seeds and young plants has been reported
(Bhise etal., 2015).
Ensete glaucum Snow banana LC; widely distributed
(E.glaucum var.
wilsonii listed as DD)
Evidence of
utilization
Animal fodder;
cultural;
ornamental
Denham and Donohue (2009). There is
some doubt as to whether E.glaucum var.
wilsonii (Tucher) Häkkinen is distinct
from E.glaucum. The two species are
largely sympatric, with E.glaucum
var. wilsonii being a smaller, higher
elevation species endemic to Yunnan
(Wu and Kress, 2000). Possibly present
in the ornamental trade, but could be
E.glaucum.
Ensete lecongkietii Orphan banana NE (Not Evaluated);
endemic to Vietnam
Crop wild relative Unknown The most recently described Ensete species
(Luu etal., 2012).
Close relatives
Musella lasiocarpa Golden lotus banana
E.lasiocarpa,
Musella
lasiocarpum
DD; essentially
unknown in the
wild, but common in
agricultural areas.
Semi-cultivated Medicinal
use; human
food; animal
fodder; bre;
alleviation of
soil erosion;
ornamental.
There is some degree of conict in the
literature over whether the genus Musella
is truly distinct from the genus Ensete
(Liu etal., 2003; Li etal., 2010). We
follow recent evidence (Janssens etal.,
2016).
*Sources: All species reported here are considered accepted species by POWO (WCSP, 2018).
†IUCN Red List conservation status classications: NE, Not Evaluated; DD, Data Decient; LC, Least Concern; EN, Endangered; CR, Critically Endangered.
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Borrell etal. — Enset in Ethiopia 5
for E.ventricosum (estimated from whole genome sequencing,
Harrison et al., 2014). This is similar to the genome size of
haploid Musa species, ranging from 580 to 800 Mb measured
by ow cytometry (Bartoš etal., 2005), and the lower estimates
from whole genome sequencing of 523Mb for M. acuminata
(D’Hont etal., 2012). Ensete species have n=9 chromosomes
(Westphal, 1975) and the karyotype consists of mainly bi-armed
chromosomes of similar size, each slightly bigger than those in
banana (Fig.3). Musa species from the section Eumusa, which
includes the bananas M.acuminata and M.balbisiana, all have
n=11. Other Musa species outside the section Eumusa (in sec-
tions Australimusa and Rhodochlamys) have n=9 and n=10.
Molecular cytogenetics of E.ventricosum localized 5S rDNA
sequences at the short arm of a medium pair of chromosomes
(Fig.3) adjacent to the secondary constriction harbouring 45S
rDNA. In Musa species, 5S and 45S rDNA are usually adjacent
to each other and this has also been observed in E.livingsto-
nianum (Bartoš et al., 2005). The latter has been reported to
have additional minor 5S sites, which are either lost in E.ven-
tricosum, or more probably varietal differences exist. Whilst
phylogenetic relationships within the genus Ensete and to other
genera within the Zingiberales are poorly known (Fig.2), there
does appear to be support for a distinction between African and
Asian Ensete lineages (Li etal., 2010; Janssens etal., 2016).
In Musa there are over 1000 landraces with high genetic diver-
sity, indicating multiple origins from different wild M. acumi-
nata and its hybrids with M. balbisiana (Heslop-Harrison and
Schwarzacher, 2007). The movement and interactions of various
human groups have played an important role in generating this
diversity (Perrier et al., 2011). Most landraces arise via selec-
tion (by farmers) of spontaneously occurring mutants with par-
thenocarpic fruit production. These are brought under cultivation,
multiplied and distributed by vegetative propagation. Extensive
hybridization has occurred, including between diploid wild spe-
cies or genotypes, involving unreduced gametes, and perhaps
residual fertility of triploids (Heslop-Harrison and Schwarzacher,
2007). Due to the high levels of domestic diversity indicated in
genetic studies (Tobiaw and Bekele, 2011; Olango et al., 2015)
and the overlapping spatial distribution of wild and domesti-
cated enset, it seems likely that there were also multiple domes-
tication events in enset, and/or frequent local introgression from
wild populations. However, unlike Musa, we hypothesize that
all domesticated enset landraces arose from a single species,
E.ventricosum, as this is the only member of the genus present in
Ethiopia or the surrounding region. More detailed diversity stud-
ies of wild and domestic enset in Ethiopia are required to eluci-
date the number of domestication events and population structure.
Among communities in Ethiopia, E.ventricosum is unusual in
that human–enset interactions currently span the entire spectrum
of domestication intensity, from wild procurement to full domes-
tication (Hildebrand, 2001). As such, there is limited evidence
to elucidate the timeline of domestication, not least because the
crop has never moved outside its centre of origin and diversity.
Nevertheless, whilst wild enset is considered largely inedible,
except during periods of severe food insecurity, smallholders
report that domesticated landraces are more palatable (Table2).
There are no data about the presence and genetics of secondary
products that may be eliminated during domestication. Several
authors have suggested that enset was rst cultivated by grow-
ing wild plants in the terminal Pleistocene or Early Holocene
(Brandt, 1984; Hildebrand, 2001). Although there is little evi-
dence for this, it would compete with, or pre-date, the rst evi-
dence of intense Musa cultivation (~6500years before present)
in the New Guinea Highlands (Denham etal., 2003). Evidence
from Uganda and Cameroon dates Musa cultivation in Africa
to at least 2500 years before the present (Mdiba et al., 2001;
Lejju et al., 2006), although these data have not met with uni-
versal acceptance (Neumann and Hildebrand, 2009). There is
limited evidence that enset, although not used today, may have
been historically consumed in northern Uganda (Thomas, 1940;
Hamilton etal., 2016). It has also been suggested that Ensete
once formed an ‘Ensete belt’ in East Africa from north-east
Lake Victoria south-east to the Usambara Mountains, Tanzania
(Langhe etal., 1994), and was used in times of food scarcity.
This is largely consistent with the data presented in Fig. 4,
and we note that genetic characterization of these populations
would provide crucial insights into their history. Furthermore,
among some communities (outside Ethiopia) enset is reported
to maintain a cultural signicance (Philippson, 1990). It has
been suggested that this ancient care of Ensete in Africa con-
tributed to the rapid and widespread adoption of the bananas
arriving from Asia, with the oldest names relating to banana
apparently derived from those in use for Ensete (Langhe etal.,
1994). Elsewhere outside Africa, Ensete is reported to have
been used as an emergency food source in Vietnam during the
Second World War, with the growing point used as a vegetable
(Oyen and Lemmens, 2002). Similarly, parts of E.glaucum are
consumed in New Guinea, particularly the ripe fruits which
are eaten raw (Kennedy, 2009), suggesting additional potential
among underexploited wild relatives.
THE DISTRIBUTION OF WILD AND DOMESTICATED
ENSETE
Ensete consists of three very widespread species (E.ventricosum
and E. livingstonianum in Africa; E. glaucum in Asia) and ve
AB
F. 3. Metaphase chromosomes of Ensete ventricosum ‘Maurelli’ 2n = 18.
Chromosomes appear blue with the DNA stain DAPI and show two distinct
5S rDNA loci (red) at the ends of a medium sized chromosome pair (A). The
simple sequence repeat AAC (green) is distributed along all chromosome arms
(B). Sequences were mapped by uorescence in situ hybridization (FISH)
using the method of Schwarzacher and Heslop-Harrison (2000, for details see
Supplementary Data Information). Scale bar= 5μm; ‘x’ denotes unspecied
soil/contamination in image.
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Borrell etal. — Enset in Ethiopia
6
other localized endemics or near-endemics (Fig.4). Three species
have been formally assessed for the IUCN red list, of which two
(E.ventricosum and E.livingstonianum) are ‘Least Concern’ and
one (E.perrieri) is ‘Critically Endangered’. Although not assessed,
E.superbum would probably meet the criteria for ‘Endangered’,
and all other non-cultivated species could be considered ‘Data
Decient’. Musella lasiocarpa may be extinct in the wild (Liu
et al., 2003). Ensete ventricosum is the only Ensete species in
Ethiopia (Brandt etal., 1997), occurring in the South and South-
West (Tsegaye and Struik, 2002) across the Southern Nations,
Nationalities and People’s Regional (SNNPR) region, as well as
the neighbouring regions of Oromia and parts of Benishangul-
Gumuz (Fig.5). Hereafter, we refer to E.ventricosum as enset and
we distinguish wild from domestic landraces. Spelling of regions,
zones and other place names follows Davis etal. (2018).
Wild enset in Ethiopia is considered by some researchers
to be range-restricted and declining (S. Demissew, pers. obs.)
although there is a paucity of data to support or refute this.
Birmeta et al. (2004) report that wild enset occurs mainly
around the city of Bonga (SNNPR region; Kaffa zone) and
in a smaller area by the Omo river (SNNPR region; Gamo
Gofa zone) whilst Garedew et al. (2017) report wild enset to
be widely distributed in Sheka forest (SNNPR region; Skeka
zone). Herbarium records indicate historical presence in
Metekel (Benishangul-Gumuz region), West Wellega (Oromia
region), Kefa and Sidama zones (SNNPR region). Observations
of wild enset are further complicated by escaped domestic enset
occurring on the periphery of villages or in neighbouring for-
ests (e.g. a cluster of 15 enset plants closely resembling domes-
tic varieties in Harenna forest, several hundred metres from the
nearest habitation; J.S.B., pers.obs.).
As a forest species, the wild enset distribution will be affected
by regional rates of forest loss. Ethiopia currently has less than
4 % forest cover, down from a potential climax vegetation max-
imum of 25–35 % (Reusing, 1998; Moat etal., 2018). It is pos-
sible that wild enset has become extinct in some areas, such as the
Rift Valley area around Hawassa (SNNPR region; Sidama zone),
where an estimated 82 % of forest has been lost since 1972 (Dessie
and Kleman, 2007). This area has a strong and diverse enset cul-
ture, and is considered by some the origin of enset domestication
(Simoons, 1965), yet there is no contemporary evidence of wild
enset. By comparison, domesticated enset is considerably more
widespread in Ethiopia, suggesting substantial niche expansion
for the cultivated crop. The distribution of domesticated enset
appears to reect both amenable ecological conditions, population
density (Yemataw etal., 2014b) and the presence of ethnic groups
for which it is a staple (Tsegaye and Struik, 2002; ethnobotanical
aspects also reviewed by Borrell etal., unpubl. res.). Enset is a
highland crop cultivated at altitudes ranging from 1200 to more
than 3100 m a.s.l. (Simoons, 1965; Brandt etal., 1997; Tsegaye
and Struik, 2001, 2002) and is reported to perform best at eleva-
tions of 2000–2750 m (Brandt etal., 1997). According to Bezuneh
and Feleke (1966) the soil type of enset cultivation areas is mod-
erately acidic to slightly basic (pH 5.6–7.3), with 0.10–0.15 %
total nitrogen and 2–3 % organic matter. Similarly, Shank (1994)
reported that enset often performs best in acidic, heavy clay soils
that retain high levels of organic matter when manured. Preferred
climatic conditions are reported to be an average air temperature
of 16–20°C and an annual rainfall of 1100–1500mm, evenly dis-
tributed throughout the year (Brandt etal., 1997).
The suitability of environmental conditions for enset culti-
vation across the domestic distribution clearly differs, as yield,
T2. Wild and domesticated traits in E.ventricosum
Character Wild enset Domesticated enset
Morphology
Leaf colour Green/glaucous Green, red, yellow, purple
Midrib colour Green Green, red, yellow, purple, black
Petiole colour Green Green, red, yellow, purple, black
Pseudostem colour Green Green, red, yellow, purple, black
Pseudostem shape Conical Conical, basal enlargement possible in some varieties
Corm size Small Enlarged
Corm colour Dark (reported sometimes black) Cream to white
Wax Not present Present on ventral leaf blade
Discoloration of tissue after cutting Present Uncommon
Palatability
Pseudostem edibility Bitter Edible
Corm edibility Bitter, largely inedible Variable, generally sweet. Edible
Genetics
Genetic diversity High High
Chromosome number n=9 n=9
Ploidy Diploid Diploid
Reproduction
Reproduction method Sexual Asexual (sexual also possible)
Sucker production No In some varieties
Seed dormancy Unknown Unknown
Other uses
Medicinal use None reported Yes
Fibre None reported Ye s
Disease susceptibility
Bacterial wilt Unknown Highly susceptible (but some are tolerant)
Mealybug Unknown Highly susceptible
Frost Unknown, suspected intolerant Tolerant
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Borrell etal. — Enset in Ethiopia 7
age to maturity and maximum obtainable size vary considerably
(Tsegaye and Struik, 2001; J.Borrell and A.Davis, pers. obs.),
although this is probably confounded by agriculture practice and
landrace selection (Shumbulo et al., 2012). At the upper eleva-
tion limit, low temperatures and frost has been hypothesized as
a constraint; at the lower limit, water availability (Brandt etal.,
1997). Various authors have dened enset as drought-tolerant
(Shumbulo et al., 2012; Harrison et al., 2014) and it is widely
regarded as ‘drought-resistant’ in Ethiopia (Birmeta, 2004)
although there is a lack of rigorous evidence to demonstratethis.
The geographical range of wild enset (in Ethiopia) is more
limited, perhaps due to more specic ecological require-
ments or alternatively loss of habitat (Fig. 5). According to
several authors it is restricted to 1200–1600 m a.s.l. (Brandt
etal., 1997). Baker and Simmonds (1953) described enset as
a species of swamps, river banks or forest clearings, at mid-
dle altitudes, rarely or never in dense shade. Across its regional
distribution, they record altitudes ranging from 1300 to 2300
m. Contemporary wild populations have been reported in
humid forest, frequently along river banks, often consisting of
10–200 plants (Birmeta et al., 2004). It therefore seems that
distribution and environmental tolerance of domesticated enset,
relative to its wild progenitor, has been expanded through the
domestication process.
COMPARATIVE MORPHOLOGY OF WILD AND
DOMESTICATED ENSET
The vegetative morphology of domestic enset is highly variable
(Fig. 1). Pseudostem colours include red, green, purple, black
and many colour combinations (Yemataw etal., 2014b). Mature
height ranges from 2 m in dwarf variants to more than 10 m for
enset plants occurring in the Sidama area. According to farmers,
corm size, tissue quality for starch, root structure for harvestabil-
ity, drought, frost and disease tolerance are all variable among
clonal genotypes (Tsegaye and Struik, 2001; Bizuayehu, 2002;
Tewodros and Tesfaye, 2014). This indicates high phenotypic
diversity. By comparison wild enset is predominantly green (also
referred to as ‘white’ in Ethiopia). Hildebrand (2001) showed
that wild and domesticated enset differ in growth pattern, with
the former increasing girth more consistently with age and the
latter attaining larger girth earlier in development. This could
be evidence of farmer selection for earlier maturing genotypes.
Domesticated enset is also characterized by further traits that are
not observed in wild enset. Hildebrand (2001) recorded the pres-
ence of a wax bloom on the ventral leaf blade and hypothesized
that this is a water stress response to hotter conditions and sun-
light exposure in farms, as opposed to the conditions in the for-
ests where wild enset is found. Ageneral comparison of wild and
domestic traits is given in Table2.
Floral morphology
This is poorly known (Fig.6), largely due to the fact that enset
is harvested before owering to maximize starch yield and is
exclusively multiplied using vegetative propagation techniques.
Despite this, there appears to be variation in inorescence length,
fruit shape and size and some farmers may use fruit morphology
to differentiate landraces (S. Tamrat, pers. comm.). Whether all
cultivated varieties produce viable seed, or indeed whether all
varieties ower is currently unknown. Similarly, the mode of pol-
lination and seed dispersal has not been studied extensively, with
various authors suggesting self-pollination (Tabogie, 1999), nec-
tar-seeking insects (Shigeta, 1990), bats (Fleming etal., 2009) or
monkeys (Hildebrand, 2001) as vectors.
Seed morphology and germination
As with other Musaceae, seed germination is generally poor
and inconsistent, with a thorough understanding of germination
requirements not yet achieved. Desiccated seeds have success-
fully been used in germination tests (Tesfaye, 1992), suggesting
that storage behaviour is orthodox (Ellis and Roberts, 1980).
According to Priestley (1986), E. ventricosum seeds can be
maintained for 1–2years in commercial storage. The thick testa
with a cutinous inner integument (Graven etal., 1996) provides
considerable protection, and has led people to consider enset as
being physically dormant and requiring scarication (Tesfaye,
1992); however, it seems that enset seeds are able to imbibe
water without mechanical intervention to equilibrium in 4 d
3000
Elev
ation (m)
Species
E. ventricosum
E. livingstonianum
E. homblei
E. perrieri
2000
1000
0
F. 4. Three species of Ensete occur in mainland Africa, Ensete homblei, E.
livingstonianum and E. ventricosum, with a fourth, E. perrieri, restricted to
Madagascar. E.ventricosum is likely to be the most widespread species within
the Musaceae, occurring over much of central, south-east and east Africa. Whilst
the contemporary distribution reaches as far north as the Ethiopian Highlands, it
has been suggested that enset was historically known to the Egyptians (Simoons,
1965). By comparison, distribution records for E.homblei, E. livingstonianum
and their numerous synonyms are sparse. Ensete livingstonianum appears to be
a species of drier habitats and is reported to die back in the dry season. It has a
more westerly distribution than E. ventricosum, although they are likely to be
sympatric over at least a portion of their range (Baker and Simmonds, 1953).
Comparatively, E.homblei is recorded from only a handful of locations in the
south-eastern Congo, and neighbouring northern Zambia. This could represent
low sampling effort, rarity or both. Finally, E.perrieri is known from only three
mature individuals, and is likely to be the most endangered crop wild relative of
enset. Due to difculty in distinguishing species with varying morphology, of
different ages, and sometimes only from seed samples, it is possible that some
geographically disjunct records represent misidentication, particularly for
E.livingstonianum and E.ventricosum. Records presented here are collated from
the literature (Cheesman, 1947; Baker and Simmonds, 1953), online databases
(GBIF, 2018), herbaria (AAU, K) and personal observations.
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Borrell etal. — Enset in Ethiopia
8
(Bezuneh, 1971; Karlsson et al., 2013). Furthermore, whilst
soaking can improve imbibition, it is not essential and numerous
chemical treatments have been applied to enset seeds with little
success (Tesfaye, 1992; Karlsson etal., 2013). Enset embryos
do not extend within the seed (Karlsson et al., 2013), so they
are not therefore morphologically dormant. Eco-physiological
germination tests have so far been inconclusive, and an area
of exploration could be the role of alternating temperatures,
as this is important for Musa seed germination (Stotzky etal.,
1962; Ellis etal., 1985; Chin, 1996), but has given inconclusive
results for enset (Bezuneh, 1971; Tesfaye, 1992).
Like Musa (Cox etal., 1960; Asif etal., 2001), in vitro ger-
mination of excised embryos has been used as an alternative
technique to provide access to enset plant regeneration and the
development of new genotypes (Negash etal., 2000; Diro etal.,
2003, 2004). Progress on this, and other in vitro techniques
(shoot tip culture, callus culture and somatic embryogenesis)
has been reviewed by Diro etal. (2004).
In a comparison of wild and domesticated enset, it is impor-
tant to note that wild enset, to the best of our knowledge, engages
exclusively in sexual reproduction, whilst in a farm setting domes-
tic enset is exclusively clonally propagated by farmers (J.S. Borrell,
pers. obs.). When permitted to ower (enset is normally harvested
before owering) seed production and fertility appears further
diminished in domesticated plants (Hildebrand, 2001), which may
pose challenges for germplasm conservation. Dissection of a small
number (n=4) of wild, naturalized and domestic enset showed a
marked difference in well-formed, viable seeds per fruit and per
infructescence. Wild enset tends to have thousands of seeds, whilst
domestic enset has few fruits with full-sized seeds, and low num-
bers of viable seeds in each fruit, possibly due to the absence of
suitable pollinators in the domestic environment, or reduced tness
resulting from a domestication bottleneck.
DIVERSITY OF WILD AND DOMESTICATED ENSET
Whilst enset has only been domesticated in a comparatively small
region of the species’ wild distribution, the reported phenotypic
diversity of cultivated enset landraces is exceptionally high (Shank,
1994; Brandt etal., 1997; Tsegaye and Struik, 2002; Bizuayehu,
2008). Farmers claim to maintain diverse enset varieties for sev-
eral reasons, including: different qualities that suit different food
products, alternative uses such as bre, fodder or medicine, and
different climatic and pest tolerance (Olango etal., 2014; Yemataw
etal., 2014a).The Areka Agricultural Research Centre (Wolayta
Zone, Ethiopia), for example, reports that it maintains 623 distinct
enset landraces from 12 major enset-growing areas of Ethiopia
(Yemataw etal., 2017). In our own literature survey, we recorded
1270 unique vernacular names for wild and domestic enset varie-
ties from 28 publications (Supplementary Data TableS2). After
clustering similar sounding names, we still recovered 475 phonetic
groups (Fig.7). Furthermore, there was remarkably low common-
ality between studies with the vast majority of enset landraces
being referenced in the literature onlyonce.
4000
Sidama
Gamo–Ari
Gurage–Wolayta
Oromo–Sheko
Wild enset
Elev
ation (m)
Major enset regions
14
12
10
8
6
4
35 40 45
0 100 200 300 km
3000
2000
1000
0
F.5. Distribution of major domesticated enset-growing regions (shaded polygons) and wild enset records (red points) in Ethiopia. Whilst domestic enset is
occasionally encountered in the wider area, these four enset farming areas represent the major centres of cultivation, where enset is frequently the most important
starch staple. The Sidama zone (SNNPR region) is predominantly high elevation, with enset sometimes grown together with crops such as coffee under sparse
shade trees. At the highest elevations, enset is subject to frost damage. The Gurage-Wolayta cultivation area encompasses (from north to south) adjacent zones
(Gurage, Hadiya, Kambata and Wolayta) in the SNNPR region. The northern part of Gurage is markedly drier than many other areas of enset cultivation. Here
enset is predominantly grown in dense stands with few other crops and no shade trees. Gamo (Gamo zone) and Ari (South Omo zone) are relatively poorly known
areas of enset cultivation, with high spatial variation in enset importance. Sheka and Dawro (SNNPR region) and adjacent areas in Oromia (Oromia region) are
also relatively poorly researched. Here domestic enset occurs in close proximity to wild enset.
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Borrell etal. — Enset in Ethiopia 9
Indigenous knowledge
Farmers use vernacular names for identication of enset
clones, with up to 26 landrace names being recorded from a
single farm (Yemataw etal., 2014a). Whilst vernacular names
are known to vary considerably based on region, language and
ethnic group, it is difcult to know if this represents distinct
diversity or vernacular duplication. Indeed, the true number of
landraces may be considerably less or more than we report: as
in many other crops, the same genotype may be given multiple
names (synonyms), or different genotypes given the same name
[homonyms; see for apple (Malus) Liang etal., 2015].
Phenotypes
Whilst the majority of studies rely on indigenous knowledge
for identication of differing landraces (Olango et al., 2014;
Yemataw et al., 2016), several authors have also attempted to
document and analyse enset landraces using phenotypic char-
acters (morphology). Initially, Zippel and Kefale (1995) devel-
oped a eld survey technique for the rapid identication of enset
clones based on morphological characters, principally colour.
In subsequent research, Tabogie (1997) reported signicant
variation among 79 enset accessions collected from different
parts of Ethiopia and attempted to associate yield with different
traits. Bekele et al. (2013) undertook a similar study and cat-
egorized 120 distinct enset landraces into 11 clusters. The most
important morphological descriptors included pseudostem cir-
cumference, corm weight and bre yield, with maturity period
and number of leaves also contributing useful information. This
suggests that there is indeed high diversity in desirable crop
traits. Other authors report similar morphological diversity in
eld surveys (Yemataw et al., 2012, 2014a, 2017). However
due to the vast number of landraces and considerable variability
between individuals, the degree of precision and consistency in
morphological studies is unclear.
Genotypes
In comparison with other important food crops, there are few
studies employing molecular markers for germplasm charac-
terization and evaluation of genetic diversity in enset (Table3).
ABC
DEF
F.6. Floral morphology and diseases of enset. (A) Ayoung inorescence (landrace: ‘Dima’). (B) Amature inorescence (landrace: Touzoma). (C) Ripe enset
fruits (landrace: ‘Lemat’). (D) Amealybug-infested corm. (E) Ayoung enset plant showing symptoms of bacterial wilt (Xanthomonas wilt of enset). (F) An enset
plant recently killed by bacterial wilt.
0 200 400 600 800 100
01
200
Number of enset landraces
Phonetically grouped landrace names
Unique landrace names
Frequency of reporting
40
30
20
10
0
F.7. Frequency of enset landrace vernacular names in the literature. In com-
parison with the high number of domesticated enset vernacular names, only
four names were reported for wild enset (E.ventricosum) in our survey.
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Borrell etal. — Enset in Ethiopia
10
In the rst studies of their kind, random amplied polymorphic
DNA (RAPD) was used to measure the genetic diversity and
relatedness of 111 cultivated enset clones collected from nine
enset-growing regions (Birmeta etal., 2002) and 146 cultivated
enset clones collected from four regions, in Ethiopia (Negash
etal., 2002). The authors reported a high level of genetic vari-
ability among the tested germplasm as well as considerable
duplication of vernacular names (for landraces) among the col-
lection and suggested that full identity between two clones can
only be determined by more extensive genome comparison.
In a later study, domesticated enset was then compared to ve
wild enset populations by Birmeta etal. (2004), with the two
groups found to cluster separately in an UPGMA (unweighted
pair group method with arithmetic mean) analysis based on
RAPD markers.
Subsequently, 71 cultivated enset clones collected from two
different areas of south-western Ethiopia (Keffa and Dawro
zones, SNNPR region) were evaluated with inter simple
sequence repeat (ISSR) markers to estimate genetic variation
(Tobiaw and Bekele, 2011). Two ISSR markers produced 26
clear scoreable bands and clustered all the 71 cultivated enset
landraces in to two major groups, which aligned with their col-
lection regions. Olango etal. (2015) developed the rst set of
genomic microsatellite markers from pyrosequencing of an
enriched genomic library of E.ventricosum and examined their
cross-genus transferability to related taxa, using them to esti-
mate genetic diversity, as well as relationships between wild
and domesticated enset accessions. The analysis demonstrated
that intra-population allelic variation contributed more to gen-
etic diversity than inter-population variations. Phylogenetic
data combined with principal components analysis results
revealed that wild enset clustered together and were distinct
from domesticated enset landraces sampled across the region
(Olango etal., 2015).
More recently there has been an effort to enable enhanced
enset research through the publication of the E. ventricosum
draft genome sequence (Harrison etal., 2014), with an approxi-
mate size of 547Mb (GenBank accession number AMZH02).
Whilst the original ‘JungleSeeds’ assembly has unknown
provenance and is only distantly related to Ethiopian plants, the
subsequent assemblies of the Ethiopian landraces ‘Onjamo’,
‘Bedadeti’ and ‘Derea’ are likely to be of more use to research-
ers. Afurther 17 E.ventricosum accessions have subsequently
been re-sequenced using Illumina HiSeq and MiSeq platforms
and raw reads aligned against the published E. ventricosum
‘Bedadeti’ reference genome sequence (Yemataw etal., 2018).
Available genome sequences are reported in Table4.
Crop wild relatives (CWRs)
Of the studies reporting vernacular, phenotypic and genetic
diversity of enset, almost all exclusively address domesticated
enset landraces. Only two studies, by Birmeta etal. (2004) and
Olango et al. (2015), included formal analysis of wild enset
accessions in Ethiopia. Therefore, whilst wild and domesti-
cated enset are distinct, the relationship between domesticated
landraces and their wild crop progenitors, as well as their value
in breeding programmes, is unclear.
Spatial patterns of diversity
Without a clear understanding of enset diversity (and how
it is partitioned across vernacular taxonomies, phenotypic and
genetic components, and wild vs. domestic), it is difcult to
draw conclusions on the geographical distribution of diver-
sity in Ethiopia. Negash et al. (2002) documented 146 clones
from four enset-growing zones: Kefa-Sheka (western SNNPR
region), Sidama (eastern SNNPR region), Hadiya and Wolayta
(both in central SNNPR region) in Ethiopia. Birmeta (2004)
recorded 111 clones from nine enset-growing areas. Emerging
from these studies are a rst indication of regional patterns of
diversity; for example, Yemataw et al. (2014a) found Hadiya
(within the Gurage-Wolayta enset area; Fig. 5) to have the
highest landrace richness, as well as the greatest number of
unique landraces, whilst Sidama had the lowest (Fig. 5). In
Sidama, Tesfaye and Lüdders (2003) found enset diversity to
T3. Previous genetic and genomic studies of wild and domestic E.ventricosum in Ethiopia
Marker Aims No. of markers No. of genotypes Origin Reference
AFLP Genetic diversity and identity of cultivated enset clones 180 loci 146 domesticated clones Domesticated Negash etal.
(2002)
RAPD Genetic diversity among Ethiopian enset clones 97 loci 111 domesticated clones Domesticated Birmeta etal.
(2002)
RAPD Comparison of wild and cultivated gene pools in Ethiopia 72 loci 5 wild populations (48
plants), 9 domesticated
clones
Wild and
domesticated
Birmeta etal.
(2004)
ISSR Genetic diversity of cultivated enset clones 26 loci 71 domesticated clones Domesticated Tobiaw and
Bekele (2011)
SNP Genome sequence – 1 domesticated clone Domesticated Harrison etal.
(2014)
SSR Cross-taxa transferability of markers, genetic diversity
and phylogenetic relationship with Musa spp.
34 markers 6 wild and 64 domesticated
clones
Wild and
domesticated
Olango etal.
(2015)
SNP Genome assemblies, phylogenetics and SNP datasets 20 000 17 domesticated clones Domesticated Yemataw etal.
(2018)
AFLP, amplied fragment length polymorphism; RAPD, random amplied polymorphic DNA; ISSR, inter simple sequence repeat; SNP, single nucleotide
polymorphism.
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Borrell etal. — Enset in Ethiopia 11
be correlated with elevation, whilst in the Gamo Highlands
Samberg et al. (2010) found enset diversity peaked at 2500–
2800 m with an average of 15 landraces per farm, and only six
or seven per farm below 2000 m and above 3000 m, respectively,
thus hinting at important biogeographical patterns. Despite the
above studies, a national assessment of areas of enset diversity
is lacking.
NEAR-TERM THREATS: ENSET PESTS AND
PATHOGENS
Pests and diseases affecting enset growth and yield represent the
most serious short-term threat to enset production. The most im-
portant disease is Xanthomonas wilt of enset (XWE; Xanthomonas
campestris pv. musacearum), together with enset root mealy bug
(Cataenococcus ensete) infestation (Fig. 6). Additional pests
(nematodes, mole rat, porcupine, termites) and diseases (bacterial,
fungal and viral) currently cause moderate to limited damage.
Xanthomonas wilt of enset (XWE)
Caused by the pathogen Xanthomonas campestris pv.
Musacearum, XWE was rst observed on enset in Ethiopia in
the 1930s (Castellani, 1939), but only identied as X.campes-
tris pv. musacearum on enset in 1968 (Yirgou and Bradbury,
1968) and subsequently on banana in 1974 (Yirgou and
Bradbury, 1974). Various symptoms characterize the disease:
leaf yellowing, distortion and wilting/collapse, and pockets of
yellow or cream-coloured slimy ooze are visible in cut vascu-
lar tissues in leaf sheaths, leaf midribs and real stem (Blomme
et al., 2017). Vascular bundles often become discoloured,
although this symptom is not as conspicuous as the internal
discoloration observed in banana. Total yield loss is expected
once the disease takes hold, although plant recovery has been
observed in tolerant landraces (e.g. the landraces ‘Mazia’,
‘Badadeti’ and ‘Astara’, J.S. Borrell, pers. obs.; Hunduma
etal., 2015).
The main mode of spread of XWE is through cultivation
tools and contaminated planting material. However, por-
cupines, warthogs and mole rats often eat rhizomes and,
in the process, can transmit XWE (Brandt et al., 1997).
Insect-vector transmission via flowers does not occur in
cultivated enset as plants are harvested before or at flower
emergence. The incidence of XWE in wild enset is not
known. More broadly, the pathogen arrived in Uganda and
the Eastern Democratic Republic of Congo in 2001 and has
since spread across most of the highland banana production
zones of east and central Africa, probably from the disease
reservoir in enset (Blomme etal., 2017). Control measures
that could prevent, reduce or eliminate the spread of XWE
include the disinfection of tools between use on different
plants, preventing animals from browsing infected plants,
fencing infected sites and the rigorous removal of infected
plants (Quimio and Tessera, 1996). We also note concur-
rent genomic research on X. campestris pv. musacearum
which has identified evidence of two distinct sublineages,
suggesting more than one introductory event, and candidate
virulence factors that may facilitate host infection (Nakato
etal., 2018).
Pests affecting enset growth and yield
The enset root mealy bug (Cataenococcus ensete) is a major
pest of enset in southern Ethiopia, having been rst reported at
Wonago (Tsedeke, 1988; Addis etal., 2008). Enset root mealy-
bugs have an elongate-oval body covered with bright white wax
secretions on the dorsal and lateral sides. Although the insect
has been present in various parts of the enset-growing region, it
has only become a serious threat to enset production in recent
years (Addis et al., 2008). The insect attacks enset of all ages,
but particularly young plants, with symptoms including retarded
growth, dried out outer leaves (but with a green central shoot)
and eventual plant death, especially under moisture stress. Enset
plants attacked by root mealybugs have a signicantly lower
number of roots as compared to healthy plants. As a result,
mealy bug-damaged enset plants are more easily uprooted.
Mealy bugs are mainly spread through infested planting mater-
ials (Bizuayehu, 2002; Addis etal., 2008), and thus production
of mealy bug-free planting materials is a key control measure.
Although symptoms are often not clearly visible, root necro-
sis due to nematodes poses an increasing constraint to enset pro-
duction (Addis etal., 2006). Bogalel etal. (2004) carried out a
nematode survey at 25 enset cultivation sites, representative of
seven agro-ecological zones. The predominant nematode spe-
cies found was Pratylenchus goodeyi (5640 per 100g fresh root
weight), followed by Aphelenchoides ensete and Meloidogyne
spp. The nematode Aphelenchoides ensete was also isolated from
leaves that showed severe streak-like symptoms on young enset
plants. In a subsequent study, 294 enset plants across the enset-
growing region were assessed for root damage and sampled for
nematode identication. Twelve plant parasitic nematode taxa
were identied: P.goodeyi was the most common species, pres-
ent in about 90 % of samples, with Ektaphelenchoides spp. and
Meloidogyne spp. also observed (Addis etal., 2006).
Minor diseases caused by bacterial, fungal and viral pathogens
The fungal disease Sclerotium root and corm rot of Enset is
characterized by a gradual rotting of roots and leaf sheaths at
the soil level and stunted plant growth (Quimio and Tessera,
1996). The causal agent was identied as a Sclerotium sp.
which can gain entry to enset plants through damaged roots and
corms. The pathogen survives in disintegrating root and corm
tissue present in the soil (Quimio and Tessera, 1996). Asecond
fungal disease, Cephalosporium inorescence spot of enset,
causes extensive necrosis of ower bracts and necrotic spots
on leaf sheaths of mature plants (Tessera and Quimio, 1994).
Finally, Enset streak is believed to be caused by a badnavirus
(Tessera etal., 1996) and chlorotic and yellow mosaics, streaks
and stripes are characteristic leaf symptoms of the disease.
Severely affected plants have also narrow distorted leaves and
become stunted. Early infection results in a signicant reduc-
tion in yield. The major means of dissemination of the disease
is through infected corms or suckers arising from an infected
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Borrell etal. — Enset in Ethiopia
12
corm. Acomplete overview of enset bacterial, fungal and viral
diseases is provided in Jones (2000).
LONG-TERM THREATS: CLIMATE CHANGE AND
DECLINING DIVERSITY
In the longer term, shifting environmental conditions due to
climate change and declining farm diversity of landraces are
likely to be increasingly important threats to enset agricul-
ture (Adhikari et al., 2015). Social changes through urban-
ization, mobility and labour are all threats, too, to traditional
farming practices. Threats to germplasm diversity are com-
pounded by a lack of nationally and internationally secure
germplasm collections, including both in vivo and long-term
storage as seeds or through cryopreservation, with the strong
restrictions on germplasm movement and condentiality con-
siderations limiting opportunities outside Ethiopia and pub-
lic availability of knowledge. Climate change is projected to
substantially impact all agricultural systems in East Africa,
resulting in declining and more variable yields, with sub-
sequently adaptation and transitions to new growing areas
becoming necessary (Challinor etal., 2014; Adhikari et al.,
2015; Rippke etal., 2016). Despite this, the projected impact
on enset cultivation has not been assessed. Concurrently, sev-
eral authors have suggested an overall decline in the diversity
of enset landraces on farms in Ethiopia (Negash etal, 2002;
Birmeta et al., 2004; Zengele, 2017), although there have
been no systematically repeated surveys or clear empirical
data to supportthis.
Enset susceptibility to climate change
Ethiopia’s mean annual temperature increased by 1.3°C
between 1960 and 2006 at an average rate of 0.28 °C per
decade (McSweeney et al., 2010). Nationally, mean annual
temperature is projected to increase by 1.3–3.1 °C by the
2060s and 1.5–5.1°C by the 2090s (McSweeney etal., 2010).
Historical precipitation patterns are less clear due to strong
inter-annual and inter-decadal variation, but appear to have
declined slightly overall (Jury and Funk, 2013; Mekasha
et al., 2014). Future projections indicate increasing annual
precipitation but are highly variable (McSweeney etal., 2010;
Mekasha etal., 2014).
Despite these past and future climatic changes, there have
been no studies assessing the projected impact on enset. In
studies on Coffea arabica, for which there is substantial envir-
onmental niche overlap with enset, Moat etal. (2017) showed
that 39–59 % of the current growing area could experience
climate changes large enough to render them unsuitable for
coffee farming, and Davis et al. (2012) report a 38–90 %
reduction in climatically suitable areas for wild populations.
Coffee requires the correct environmental conditions at spe-
cic times of the growing cycle for successful owering and
fruiting (Moat etal., 2017). By contrast, enset is less suscep-
tible to short-term temperature or precipitation variation that
can detrimentally impact coffee crops, and is not reliant on a
sexual reproduction cycle for food production (DaMatta and
Cochicho Ramalho, 2006).
Enset germplasm collections
Whilst empirical evidence of declining enset diversity is
lacking, systematic collection and maintenance of diverse
crop germplasm is important to maximize use and availabil-
ity in sustainable agricultural development, and guard against
the erosion of genetic diversity. Bioversity International (a
CGIAR Research Centre) is currently committed to the long-
term preservation of the entire banana genepool. This has
been achieved through the collection and maintenance of
4928 Musa germplasm accessions, encompassing numerous
crop wild relatives, including a handful of Ensete spp. (Ruas
etal., 2017). Collected accessions are preserved as living col-
lections across numerous partner organizations, as well as
in vitro under slow growth conditions and using cryopreser-
vation. To facilitate this, the Musa Germplasm Information
System (MGIS) was developed (https://www.crop-diversity.
org/mgis/) which has served to accelerate Musa research (e.g.
MusaNet, 2016). Virus-free Musa germplasm is now freely
available for international distribution upon request through
the MGIS website; between 1985 and 2014 the Bioversity
International Musa Germplasm Transit Centre (ITC) distrib-
uted over 17 000 samples among 109 countries worldwide.
However, to date only six Ensete accessions are available
through the MGIS database (Table5), of which only two are
E.ventricosum. Of these two, one is termed the ‘red mutant’
which is most likely a commonly available horticultural cul-
tivar named ‘Maurelii’, the other – arguably the most import-
ant accession – is of unknown provenance, but reported to
be wild. Therefore, it is possible that despite 5000 Musaceae
accessions, domesticated landraces of this important tropical
crop are not conserved internationally.
Two comparatively very large living collections of domes-
ticated enset exist at eld sites in Ethiopia. The rst, Areka
eld station (part of the Southern Agricultural Research
Institute), reports to maintain a collection of approx. 600 land-
races (Harrison etal., 2014) from several regions of Ethiopia,
with four clonal replicates of each. Second is a newer collec-
tion at the University of Wolkite (Fig.1C), which maintains
approx. 110 landraces from the Gurage region with up to 15
replicates of each. Information on these collections, such as
the landraces they contain, is not publicly available. Finally,
Guzzon and Muller (2016) conducted a review of the avail-
ability of stored and fresh seeds of E.ventricosum, E.hom-
blei and E.livingstoninum. Of the 27 African genebanks, 42
botanic gardens and four researchers contacted, only one col-
lection was available: one accession of E. ventricosum col-
lected in Tanzania maintained at the Millennium Seed Bank,
RBG Kew, UK, stored in orthodox conditions (15 % relative
humidity, −20°C).
FUTURE RESEARCH PRIORITIES
Global food demand is increasing, and is likely to continue
to increase into the second half of this century (Godfray
et al., 2010). By 2050, a projected 100–110 % increase in
global crop demand, relative to 2005 levels, will be required
(Tilman etal., 2011). In the latter half of the 20th century
this has been largely met, not through substantial growth in
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Borrell etal. — Enset in Ethiopia 13
cropland, but by improvements in crop productivity often
dubbed the ‘Green Revolution’ (Evenson and Gollin, 2003).
In this article we have shown that despite unique and valu-
able crop attributes, as well as the dependency of 20 mil-
lion Ethiopians, enset has been overlooked by modern crop
improvement research. This therefore represents an oppor-
tunity for sustainable exploitation to support livelihoods and
improve food security in the region. Here, building on the
literature examined in this review, we identify our ten priority
areas for research (summarized in Fig.8) and make recom-
mendations for short- and long-term development of enset as
a key food securitycrop.
1. Coordination of research and methods
Whilst enset has only been domesticated in Ethiopia, enset
research encompasses researchers from at least 40 institutions
in 11 countries. Currently, despite positive national and interna-
tional collaborations (e.g. Brandt et al., 1997; Yemataw et al.,
2018), enset research is still disconnected with many interest-
ing and important research programmes running in isolation.
Partly, the aim of this review is to draw together many disparate
aspects of enset research to facilitate discoverability and col-
laboration by researchers.
In addition, we relate the experience of the Global Musa
Genomics Consortium (http://www.musagenomics.org) which
sought to bring together expertise and enable close collabor-
ation, the sharing of materials, resources, data and technology
to accelerate Musa breeding efforts (Roux et al., 2011). It is
our view that enset research and food security in Ethiopia could
benet from such an approach, with equitable and appropriate
access and benet sharing agreements in place. Here, we pres-
ent and make available the resource www.enset-project.org,
which will act as an open repository for data emerging from our
current research programme.
2. Experimental evaluation of enset agronomic practices
There are numerous cultural practices employed in enset cul-
tivation that are reported to signicantly inuence growth and
yield, but few of these have been empirically evaluated in robust,
replicated and controlled experiments (reviewed by Borrell
et al., unpubl. res.). Akey practice, for instance, involves sys-
tematic transplanting of enset at specic ages, which appears to
have a dramatic impact on the resulting pseudostem and corm
size (Yemataw et al., 2016), perhaps by delaying maturity. In a
study by Tsegaye (2007), transplanting treatments signicantly
affected height, pseudostem circumference and dry matter yield,
and increased partitioning of dry matter to harvestable parts. To
our knowledge a similar practice has not been reported in any
other crop. Other practices include aeration of the soil, mulching
with discarded plant material, companion plants, the use of fertil-
izer, various rhizome preparation practices for vegetative multi-
plication, as well as treatments for pests and diseases. However,
the efcacy of these practices is largely unknown and they repre-
sent an important rst step in optimizing enset agriculture.
3. Disease characterization and development of disease-free
tissue culture protocols
Whilst several pests and pathogens are known to affect enset
cultivation in Ethiopia, their impact on regional yields is yet to
SHORT-TERM GOALS LONG-TERM GOALS
Coordination of
research and methods
Remote sensing
monitoring under current
and future climates
Exploration of genetic
diversity and local
adaptation
Experimental
evaluation of agronomic
practices
Investigation of crop
wild relatives
Disease
characterization and
development of tissue
culture protocols
Systematic banking of
germplasm and
development of genetic
resources
Understanding the enset
microbiome and
endogenous yeast
cultures
Exploring the potential
for enset cultivation in
Ethiopia and Africa
Exploring alternative
uses and by-products
F.8. Roadmap for the sustainable development and exploitation of the Ethiopian starch crop enset for food security and to support livelihoods.
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Borrell etal. — Enset in Ethiopia
14
be quantied. Similarly, geographical patterns in disease inci-
dence are not yet available. In the medium term, it is likely that
different degrees of disease tolerance may be identied across
enset landraces and crop wild relatives. This genetic diversity
will provide the long-term basis for crop breeding to generate
disease-resistant genotypes. The generation of disease-free tis-
sue culture protocols (e.g. Tripathi etal., 2015) is also likely to
play an important role. Concurrently, ongoing surveillance to
identify newly emerging pathogens, or the potential for trans-
mission from related species (e.g. the widely cultivated Musa),
is an important safeguard for enset sustainability.
4. Remote sensing under current and future climates
Estimates of the land area under enset cultivation (e.g.
Shank; 1994; Central Statistical Agency, CSA, Government
of Ethiopia, 2004), and associated yields (Pijls et al., 1995;
Tsegaye and Struik, 2001; Sahle etal., 2018) are highly vari-
able and have been historically hampered by difcult access to
remote areas. The long-term nature of enset cultivation, local
differences in cultivated landraces, plant growth rates, agro-
nomic practice and dependency on co-staple crop productivity
in any given period make estimating enset production difcult
(Cochrane and Adam, 2017). Therefore, standardized empirical
analyses of the land area under enset cultivation, yield compo-
nents and inter-annual trends are lacking.
Advances in the resolution and availability of satellite data
(e.g. MODIS, Sentinel 2) are increasingly being applied to
vegetation and crop surveys (Hütt etal., 2016; Immitzer etal.,
2016; Moat etal., 2017). Thus, in the near term there may be the
potential to use freely available satellite data to directly moni-
tor annual enset production. Furthermore, this approach could
be applied to mapping bacterial wilt outbreaks. Concurrently,
improved regional bioclimatic datasets (e.g. Worldclim2) and
an enhanced network of climate stations and data loggers
across the enset-growing region will allow better characteriza-
tion of the enset environmental niche and stress conditions. The
impact of climate change under a range of future scenarios is
yet to be quantied for enset and will form an important part
of any future development strategy, as undertaken for coffee in
Ethiopia (Moat etal., 2017; Davis etal., 2018).
5. Exploration of genetic diversity and local adaptation
High enset genetic diversity distributed over a wide range of
environmental conditions suggests that the domestication process
may have facilitated adaptation of landraces to local conditions,
and indeed to a wider range of conditions than its wild progeni-
tor. Because enset is a clonally reproducing and distributed plant,
this represents a powerful system to investigate the genomic
basis of adaptive traits. Key steps to achieve this would be the
characterization of existing enset genetic diversity using high-
resolution genomic markers, standardized methods to measure
tness and yield as well as robust monitoring of environmental
conditions. Concurrently, assessing the risk of erosion to enset
genetic diversity through the loss or decline of landraces should
be a priority for future enset monitoring strategies. In the medium
term this could similarly be extended to monitoring of crop wild
relative diversity. In the long term, with the prerequisite knowl-
edge of germination biology, novel sexual breeding utilizing
mapping populations and pan-genomic sequencing may enable
the development of improved landraces, tolerant of disease, bet-
ter adapted to current and future climates, or with desirable yield
or by-product attributes (Tester and Langridge, 2010).
6. Investigation of crop wild relatives
During the process of domestication, crops typically experi-
ence a genetic bottleneck resulting in reduced variation when
compared to wild progenitors. CWRs are therefore an impor-
tant source of genetic diversity for crop improvement (Jarvis
etal., 2008), and may possess desirable traits that have been
lost in domesticated landraces. The susceptibility of wild enset
to pathogens such as XWE, for example, is currently unknown,
and they may harbour important genetic diversity for disease
tolerance or resistance (see for example in wheat, Ali et al.,
2016; Rasheed etal., 2018). Wild enset is also reported to have
a higher seed set and germination rate than domesticated enset,
so understanding the reasons why this is diminished in the latter
will be important in developing seed-based germplasm collec-
tions for breeding.
Whilst CWRs have been used extensively for breeding in
other species (Tester and Langridge, 2010), such as improv-
ing drought tolerance in wheat (Farooq, 2004), their use is
anticipated to further increase due to advances in molecular
technology (Hajjar and Hodgkin, 2007). Therefore, long-term
conservation of wild diversity is a key foundation for the sus-
tainable exploitation of enset. Asimilar approach has already
been undertaken in Ethiopia through the formation of biosphere
reserves for wild populations of Arabica coffee (Coffea ara-
bica) (Davis etal., 2012; Aerts etal., 2016).
7. Exploring alternative uses
In addition to being a major dietary starch source, ensetalso
has the potential to produce other valuable by-products. Fibre
can be extracted from the pseudostem and leaves, and is compa-
rable with other natural bres such as ax, sisal and hemp (Teli
and Terega, 2017). High value wax is currently extracted from
closely related banana species (Yanagida etal., 2003) and several
authors have identied the importance of enset as animal fodder
(Fekadu and Ledin, 1997; Mohammed etal., 2013). Enset is also
widely considered as an important medicinal plant in Ethiopia,
and is used in particular to treat individuals with fractured or bro-
ken bones, as well as for placental discharge in humans and live-
stock (Tsehaye and Kebebew, 2006; Assefa and Fitamo, 2016).
The chemical basis of these uses has not been explored.
8. Understanding the enset microbiome and endogenous yeast
cultures
The plant microbiome is probably in the order of tens of
thousands of species, and its relevance to plant health and yield
is only beginning to be understood (Berendsen et al., 2012).
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Borrell etal. — Enset in Ethiopia 15
T5. Internationally available Ensete germplasm accessions
Species Landrace Accession
number
Institute code Field
collection
In vitro Lyophilized
leaves
Cryopreserved Available for
distribution
Origin Origin
E.gilletii (livingstonianum) – ITC1389 BEL084 (ITC) No Yes No Ye s No Wild NGA_Jos,
Plateau
State,
Nigeria
E.glaucum Pisang Pidak IFRI-001 IDN150 (ICHORD) Yes No No No No Wild Indonesia
E.glaucum subsp. glaucum Vudu Vudu ITC0775 BEL084 (ITC) No Yes Ye s Yes Yes Wild Papua New
Guinea
E.ventricosum subsp ventricosum – ITC1387 BEL084 (ITC) No Yes Ye s No Yes Wild Unknown
E.ventricosum subsp ventricosum red mutant ITC1388 BEL084 (ITC) No Yes Yes No Ye s Wild Unknown
E. unknown Chuoi Nguon VNIO60 VNM007 (FAVRI) Yes No No No No Landrace Vietnam
T4. Comparison of available E.ventricosum genome sequences and assemblies, with related Musa species
Landrace E.ventricosum
‘Bedadeti’
E.ventricosum
‘JungleSeeds’
E.ventricosum
‘Onjamo’
E.ventricosum ‘Derea’ M.acuminata subsp.
malaccensis
M.itinerans M.balbisiana
BioSample SAMN02854351 SAMN01797775 SAMN05751581 SAMN05729394 SAMEA2272344 SAMN04505257 SAMN02333823
GenBank assembly GCA_000818735.2 GCA_000331365.2 GCA_001884845.1 GCA_001884805.1 GCA_000313855.2 GCA_001649415.1 –*
Coverage 30 40 21 18.4 20.5 92 41.4
Scaffold count 45 745 52 692 51 525 – 7 512 28 415 –
Scaffold N-50 21 097 13 866 16 208 – 1 311 088 195 772 –
Contig count 46 254 71 088 54 038 60 129 29 249 55 966 180 175
Contig N-50 20 943 11 721 15 546 12 314 28 326 35 438 7 884
Size (Mb) 451.3 437.3 444.8 429.5 472.2 455.0 402.5
Total gap length 10 455 286 734 46 732 0 81 753 624 39 952 266 61 115 757
*Assembly is available at: http://banana-genome-hub.southgreen.fr/organism/Musa/balbisiana [18 October2018].
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Borrell etal. — Enset in Ethiopia
16
Importantly, there are indications that the microbiome may
have a role in the suppression of plant diseases. Therefore, in
the long term, characterization of the enset microbiome across
different agroecological environments, combined with whole
genome and population genomic studies, may provide novel
pathways to crop improvement. Concurrently, a signicant
component of enset agriculture is fermentation of the pseu-
dostem and corm tissue using endogenous yeasts. This practice
is currently performed by farmers and is thus highly variable.
Development of improved fermentation cultures may result in
rapidly improved product quality, as well as provide an oppor-
tunity to improve micro-nutritional content.
9. Systematic germplasm banking and development of genetic
resources
Given their economic and food security value, Ensete spe-
cies, and particularly domesticated enset landraces, are cur-
rently severely underrepresented in global ex situ germplasm
collections. This chronically limits the potential for plant
breeding and crop improvement. In the long term, under
scenarios of habitat loss, agricultural intensication, disease
spread, climate change and introduction of high-yielding geno-
types, both wild and domestic enset are at risk of losing genetic
diversity, and with it potentially important adaptive traits.
Whilst a large number of landraces are present in two col-
lections in Ethiopia, germplasm management of vegetatively
propagated plants species such as enset is costly, time-con-
suming, vulnerable to poor documentation and requires a large
land surface area for proper maintenance. Therefore, a key
research goal should be further exploration of the potential for
germplasm banking as seeds, together with a strategy to collect
germplasm from a wide range of spatial and ecological condi-
tions. Conventional breeding and ex situ conservation by seed
also requires an understanding of seed desiccation tolerance,
longevity in storage and, essentially, germination require-
ments. As with Musa, much of this is not well understood.
Similarly, access to domestic enset germplasm outside of
Ethiopia is challenging and historically limited. If (with appro-
priate access and benet sharing agreements) additional domes-
ticated germplasm could be admitted in to the ITC genebank
(Leuven, Belgium) it will not only be more readily accessible
to the scientic community (beneting research and sustainable
exploitation), but would also safeguard a critically important
tropical crop.
F. 9. Mark Anthony John Goodwin: 9 August 1960 to 25 August 2018 (left) and in Hawassa, Ethiopia with enset in May 2012 (right). Images Pat
Heslop-Harrison.
BOX 1. In memoriam Mark Goodwin
We are deeply saddened to write that our co-author, colleague and friend, Mark Goodwin (Fig.9), passed away suddenly in
his University ofce on 25 August 2018, aged just 58. During the day, he had held many discussions related to enset, including
ways to connect researchers and build collaborations. Mark’s particular expertise was in the delivery of impact from research
projects, linking with pedagogy and the importance of advanced training. After nishing his PhD, Mark worked for the UK
Government’s Overseas Development Administration and The Open University, before joining the University of Leicester in
2006. Within the Department of Genetics and Genome Biology, he was a leader in the Centre for Excellence in Teaching and
Learning (CETL), led the Virtual Genetics Education Centre project, managed the Leicester-Gondar PhD programme and
was an Academic Partner for British Council programmes in Afghanistan and Bangladesh. Mark was a co-investigator for the
GCRF Foundation project on enset leading to the work presented in this publication. Mark was taken from us much too soon,
and we will greatly miss his input to the delivery of impact from research programmes.
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Borrell etal. — Enset in Ethiopia 17
10. Exploring the potential for enset cultivation in Ethiopia and
Africa
Within Ethiopia, domesticated enset appears to occupy a
range of conditions distinct and somewhat broader than wild
enset. Similarly, the wild distribution outside Ethiopia of E.ven-
tricosum extends as far as South Africa, encompassing a range
of environmental conditions not found in Ethiopia. Therefore,
it seems likely that the climatic envelope of this already toler-
ant crop could be further enlarged and it could potentially be
introduced to newareas.
In Ethiopia, a current research programme has collected
four landraces from Dilla (Gedio zone; SNNPR region) and
introduced these to a novel enset cultivation area near Ankober
(North Shewa; Amhara region), north of Addis Ababa, to
investigate performance. An equally important component is
the concurrent introduction of enset harvesting and processing
cultural knowledge (see Borrell et al., unpubl. res.). Further
aeld, a second project is exploring the potential introduc-
tion of enset to Zambia in an effort to combat hidden hunger
(Cardenas etal., 2018). Future research effort should focus on
characterizing the environmental requirements of enset to pre-
dict habitat suitability and assess the feasibility of introduction
to novel areas.
SUPPLEMENTARY DATA
Supplementary data are available online at https://aca-
demic.oup.com/aob and consist of the following. Table S1:
Species and associated GenBank accession numbers for ITS
sequences included in the phylogenetic analysis (Fig. 2 and
Supplementary Data Fig.S2). TableS2: Landrace names for
domesticated varieties of Ensete ventricosum, identied in the
review of available literature. Fig. S1: Estimated population
size of the major enset-growing regions. Fig.S2: Phylogenetic
relationships of Ensete species within the Zingerberales.
Supplementary Information: Detailed information on meth-
ods used to prepare Figs2, 3 and 7 and Supplementary Data
FigsS1 andS2.
ACKNOWLEDGEMENTS
The authors wish to acknowledge collaborators from Wolkite
University, Hawassa University, Addis Ababa University, the
Ethiopian Biodiversity Institute and the Southern Agricultural
Research Institute for enabling and facilitating research on enset
in Ethiopia. This work was supported by the GCRF Foundation
Awards for Global Agricultural and Food Systems Research,
entitled, ‘Modelling and genomics resources to enhance exploit-
ation of the sustainable and diverse Ethiopian starch crop enset
and support livelihoods’ [Grant No. BB/P02307X/1].
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