Abstract

INTRODUCTION

Enset [Ensete ventricosum (Welw.) Cheesman] is a large perennial 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 inflorescence with banana-like fruits. However, unlike sweet and starchy banana (with the latter called plantain in some contexts, although there is no botanical 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 4–7 years after planting. Despite a widespread distribution in eastern, central and southern tropical Africa (Baker and Simmonds, 1953; Lock, 1993), enset has only been domesticated in Ethiopia (Brandt et al., 1997). Here, hundreds of landraces are found in diverse climatic and agroecological systems (Birmeta et al., 2002; Tesfaye and Lüdders, 2003; Yemataw et al., 2014a) where they provide the staple food source for approx. 20 million rural people (Supplementary Data, Fig. S1 – see Supplementary data Information for population estimation methods).

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Fig. 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) A typical 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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Fig. 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).

Enset has historically been ascribed as a ‘tree against hunger’ (Brandt et al., 1997), due to the domesticated plant having important attributes that support the food security of communities that cultivate it. These attributes were evident during the devastating famines of the 1980s, where enset-growing communities reported little-to-no food insecurity (Dessalegn, 1995). Most significant 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). Enset also provides fibres, medicines, animal fodder and packaging material (Brandt et al., 1997). It stabilizes soils and microclimates (Abate et al., 1996) and is culturally significant (Kanshie, 2002; Negash and Niehof, 2004; Tewodros and Tesfaye, 2014). Enset has a complex management system supported by extensive ethnobotanical knowledge (Borrell et al., 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 deficits, 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, relatively 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 (Table 1). Although first reported by Bruce (1790) during travels in Ethiopia (Fig. 1A, ​,B),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 et al., 2003; Li et al., 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 Table S1), some including genera known for their medicinal properties and ornamental use. APG IV (Chase et al., 2016) has confirmed 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 organization of Ensete as sister to Musa may provide novel insights into the evolution of the globally important Musaceae family.

Like the other Musaceae genera, Ensete originated in northern Indo-Burma during the early Eocene, probably followed by a single African colonization via gradual overland dispersal during a more mesic climate period (Janssens et al., 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 18 mm compared to 10 mm) and an apparent adaptation to cooler and drier environments than most Musa species (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 landraces are known to occur in Ethiopia (provenance unknown). In the field, 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 et al., 2003) and this is consistent with flow 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 620 Mb per haploid genome for E. livingstonianum (measured by flow cytometry, Bartoš et al., 2005) and 547 Mb 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 flow cytometry (Bartoš et al., 2005), and the lower estimates from whole genome sequencing of 523 Mb for M. acuminata (D’Hont et al., 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 sections 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. livingstonianum (Bartoš et al., 2005). The latter has been reported to have additional minor 5S sites, which are either lost in E. ventricosum, 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 et al., 2010; Janssens et al., 2016).

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Fig. 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 fluorescence in situ hybridization (FISH) using the method of Schwarzacher and Heslop-Harrison (2000, for details see Supplementary Data Information). Scale bar = 5 μm; ‘x’ denotes unspecified soil/contamination in image.

In Musa there are over 1000 landraces with high genetic diversity, indicating multiple origins from different wild M. acuminata 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 selection (by farmers) of spontaneously occurring mutants with parthenocarpic fruit production. These are brought under cultivation, multiplied and distributed by vegetative propagation. Extensive hybridization has occurred, including between diploid wild species 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 domesticated enset, it seems likely that there were also multiple domestication 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 studies of wild and domestic enset in Ethiopia are required to elucidate 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 domestication (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 (Table 2). 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 first cultivated by growing wild plants in the terminal Pleistocene or Early Holocene (Brandt, 1984; Hildebrand, 2001). Although there is little evidence for this, it would compete with, or pre-date, the first evidence of intense Musa cultivation (~6500 years before present) in the New Guinea Highlands (Denham et al., 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 universal 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 et al., 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 et al., 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 significance (Philippson, 1990). It has been suggested that this ancient care of Ensete in Africa contributed 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 et al., 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.

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Fig. 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 difficulty in distinguishing species with varying morphology, of different ages, and sometimes only from seed samples, it is possible that some geographically disjunct records represent misidentification, 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.

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 five 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 Deficient’. Musella lasiocarpa may be extinct in the wild (Liu et al., 2003). Ensete ventricosum is the only Ensete species in Ethiopia (Brandt et al., 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 et al. (2018).

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Fig. 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.

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 forests (e.g. a cluster of 15 enset plants closely resembling domestic 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 maximum of 25–35 % (Reusing, 1998; Moat et al., 2018). It is possible 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 culture, 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 reflect both amenable ecological conditions, population density (Yemataw et al., 2014b) and the presence of ethnic groups for which it is a staple (Tsegaye and Struik, 2002; ethnobotanical aspects also reviewed by Borrell et al., unpubl. res.). Enset is a highland crop cultivated at altitudes ranging from 1200 to more than 3100 m a.s.l. (Simoons, 1965; Brandt et al., 1997; Tsegaye and Struik, 2001, 2002) and is reported to perform best at elevations of 2000–2750 m (Brandt et al., 1997). According to Bezuneh and Feleke (1966) the soil type of enset cultivation areas is moderately 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 1100–1500 mm, evenly distributed throughout the year (Brandt et al., 1997).

The suitability of environmental conditions for enset cultivation across the domestic distribution clearly differs, as yield, 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 elevation limit, low temperatures and frost has been hypothesized as a constraint; at the lower limit, water availability (Brandt et al., 1997). Various authors have defined 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 demonstrate this.

The geographical range of wild enset (in Ethiopia) is more limited, perhaps due to more specific ecological requirements or alternatively loss of habitat (Fig. 5). According to several authors it is restricted to 1200–1600 m a.s.l. (Brandt et al., 1997). Baker and Simmonds (1953) described enset as a species of swamps, river banks or forest clearings, at middle 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 et al., 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 harvestability, 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 presence of a wax bloom on the ventral leaf blade and hypothesized that this is a water stress response to hotter conditions and sunlight exposure in farms, as opposed to the conditions in the forests where wild enset is found. A general comparison of wild and domestic traits is given in Table 2.

Floral morphology

This is poorly known (Fig. 6), largely due to the fact that enset is harvested before flowering to maximize starch yield and is exclusively multiplied using vegetative propagation techniques. Despite this, there appears to be variation in inflorescence 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 flower is currently unknown. Similarly, the mode of pollination and seed dispersal has not been studied extensively, with various authors suggesting self-pollination (Tabogie, 1999), nectar-seeking insects (Shigeta, 1990), bats (Fleming et al., 2009) or monkeys (Hildebrand, 2001) as vectors.

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Fig. 6.

Floral morphology and diseases of enset. (A) A young inflorescence (landrace: ‘Dima’). (B) A mature inflorescence (landrace: Touzoma). (C) Ripe enset fruits (landrace: ‘Lemat’). (D) A mealybug-infested corm. (E) A young enset plant showing symptoms of bacterial wilt (Xanthomonas wilt of enset). (F) An enset plant recently killed by bacterial wilt.

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 et al., 1997; Tsegaye and Struik, 2002; Bizuayehu, 2008). Farmers claim to maintain diverse enset varieties for several reasons, including: different qualities that suit different food products, alternative uses such as fibre, fodder or medicine, and different climatic and pest tolerance (Olango et al., 2014; Yemataw et al., 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 et al., 2017). In our own literature survey, we recorded 1270 unique vernacular names for wild and domestic enset varieties from 28 publications (Supplementary Data Table S2). After clustering similar sounding names, we still recovered 475 phonetic groups (Fig. 7). Furthermore, there was remarkably low commonality between studies with the vast majority of enset landraces being referenced in the literature only once.

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Fig. 7.

Frequency of enset landrace vernacular names in the literature. In comparison with the high number of domesticated enset vernacular names, only four names were reported for wild enset (E. ventricosum) in our survey.

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 important 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.

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 agriculture (Adhikari et al., 2015). Social changes through urbanization, mobility and labour are all threats, too, to traditional farming practices. Threats to germplasm diversity are compounded 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 confidentiality considerations limiting opportunities outside Ethiopia and public availability of knowledge. Climate change is projected to substantially impact all agricultural systems in East Africa, resulting in declining and more variable yields, with subsequently adaptation and transitions to new growing areas becoming necessary (Challinor et al., 2014; Adhikari et al., 2015; Rippke et al., 2016). Despite this, the projected impact on enset cultivation has not been assessed. Concurrently, several authors have suggested an overall decline in the diversity of enset landraces on farms in Ethiopia (Negash et al, 2002; Birmeta et al., 2004; Zengele, 2017), although there have been no systematically repeated surveys or clear empirical data to support this.

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 et al., 2011). In the latter half of the 20th century this has been largely met, not through substantial growth in 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 valuable crop attributes, as well as the dependency of 20 million Ethiopians, enset has been overlooked by modern crop improvement research. This therefore represents an opportunity 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 recommendations for short- and long-term development of enset as a key food security crop.

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Fig. 8.

Roadmap for the sustainable development and exploitation of the Ethiopian starch crop enset for food security and to support livelihoods.

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. ventricosum 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 tolerant crop could be further enlarged and it could potentially be introduced to new areas.

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 afield, a second project is exploring the potential introduction of enset to Zambia in an effort to combat hidden hunger (Cardenas et al., 2018). Future research effort should focus on characterizing the environmental requirements of enset to predict habitat suitability and assess the feasibility of introduction to novel areas.

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 office 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 finishing 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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Fig. 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.

SUPPLEMENTARY DATA

Supplementary data are available online at https://academic.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). Table S2: Landrace names for domesticated varieties of Ensete ventricosum, identified 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 methods used to prepare Figs 2, ​,33 and ​and77 and Supplementary Data Figs S1 and S2.

ACKNOWLEDGEMENTS

LITERATURE CITED