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Occurrence of Plant-Parasitic Nematodes on Enset (Ensete Ventricosum) in Ethiopia with Focus on Pratylenchus Goodeyi As a Key Species of the Crop

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Occurrence of Plant-Parasitic Nematodes on Enset (Ensete Ventricosum) in Ethiopia with Focus on Pratylenchus Goodeyi As a Key Species of the Crop Nematology 0 (2020) 1-13 brill.com/nemy Occurrence of plant-parasitic nematodes on enset (Ensete ventricosum) in Ethiopia with focus on Pratylenchus goodeyi as a key species of the crop Selamawit A. KIDANE 1,2,BeiraH.MERESSA 3,SolveigHAUKELAND 4,5, ∗ Trine HVOSLEF-EIDE 1, , Christer MAGNUSSON 4, Marjolein COUVREUR 6,WimBERT 6 and Danny L. COYNE 2,6 1 Norwegian University of Environmental and Life Sciences, NMBU, P.O. Box 5003, 1432 Ås, Norway 2 International Institute of Tropical Agriculture, IITA, PMB 5320, Ibadan, Nigeria 3 Jimma University College of Agriculture and Veterinary Medicine, P.O. Box, Jimma, Ethiopia 4 The Norwegian Institute of Bioeconomy Research, NIBIO, P.O. Box 115, 1431 Ås, Norway 5 International Centre of Insect Physiology and Ecology, P.O. Box 30772-00100, Nairobi, Kenya 6 Nematology Research Unit, Department of Biology, Ghent University, Campus Ledeganck, Ledeganckstraat 35, B-9000 Ghent, Belgium Received: 24 July 2020; revised: 6 September 2020 Accepted for publication: 7 September 2020 Summary – Enset (Ensete ventricosum) is an important starch staple crop, cultivated primarily in south and southwestern Ethiopia. Enset is the main crop of a sustainable indigenous African system that ensures food security in a country that is food deficient. Related to the banana family, enset is similarly affected by plant-parasitic nematodes. Plant-parasitic nematodes impose a huge constraint on agriculture. The distribution, population density and incidence of plant-parasitic nematodes of enset was determined during August 2018. A total of 308 fields were sampled from major enset-growing zones of Ethiopia. Eleven plant-parasitic nematode taxa were identified, with Pratylenchus (lesion nematode) being the most prominent genus present with a prominence value of 1460. It was present in each sample, with a highest mean population density per growing zone of 16 050 (10 g root)−1, although densities as high as 25 000 were observed in fields at higher altitudes in Guraghe (2200-3000 m a.s.l.). This lesion nematode is found in abundance in the cooler mountainous regions. Visible damage on the roots and corms was manifested as dark purple lesions. Using a combination of morphometric and molecular data, all populations were identified as P. goodeyi and similar to populations from Kenya, Uganda and Spain (Tenerife). Differences in population densities amongst cultivars indicate possible resistance of enset to P. goodeyi. Keywords – altitude, food security, lesion nematode, molecular data, morphology, prominence value. Ensete ventricosum, commonly known as enset, is on approximately 400 000 ha (CSA-Ethiopia, 2016). As a large perennial herbaceous plant belonging to the a key starch staple food source, enset provides food se- Musacea family, together with banana and plantain. Un- curity for over 20 million people, or at least 20% of the like banana and plantain, however, enset does not produce Ethiopian population. Furthermore, it is also used for ani- bunches but instead produces a large underground corm mal feed, fibre, construction and medicine (Brandt et al., that is harvested. The pseudostem is formed from a bun- 1997). The crop grows best at cooler, higher altitudes and dle of leaf sheaths and large leaves, which may reach up is found mostly between 1200-3100 m a.s.l., in the south to 10 m high and 2 m diam. (Westphal & Stevels, 1975). and southwestern areas of the country. Enset-based farm- Wild enset species are found distributed over sub-Saharan ing systems represent a traditional and sustainable form Africa and Asia, but in Ethiopia, where it has been domes- of agriculture, which includes a diverse range of crops ticated, it is cultivated as an important food crop grown that are cultivated alongside enset (Cheesman, 1947; Sim- ∗ Corresponding author, e-mail: [email protected] © The authors, 2020 DOI 10.1163/15685411-bja10058 This is an open access article distributed under the terms of the CC BY 4.0 license. Downloaded from Brill.com03/08/2021 07:47:20AM via free access S.A. Kidane et al. monds, 1962; Brandt et al., 1997). Enset is a perennial emphasis on the most prevalent nematode genus, Praty- crop that takes, on average, 7 years to mature; however, lenchus. This study also served to identify ‘hot spots’ as with most crops, the period to maturity is likely to where material could be collected for use in trials. be lengthened under challenge from biotic and abiotic threats. Identifying the biotic threats that challenge enset, and consequently addressing them, has received limited Materials and methods attention. A number of constraints challenge enset production, SURVEY AREA with bacterial wilt disease caused by Xanthomonas va- Enset root and soil samples were collected from the sicola pv. musacearum (Xvm) (previously named X. southern part of Ethiopia, from administrative zones campestris pv. musacearum (Xcm)) (Studholme et al., where enset is most commonly grown (Sidama, Hadiya, 2020) receiving most attention (Addis et al., 2004, 2008; Kembata and Keffa) in August 2018. Based on the Nakato et al., 2018). The enset root mealy bug (Cataeno- Ethiopian administrative structure a total of 308 fields coccus ensete) can cause severe damage to the roots and were sampled; 72 fields were selected randomly from corm, reducing crop vigour and production (Addis et al., each of the four zones and an additional ten fields each 2010). Also, fungal diseases such as a Sclerotium sp. root from Guraghe and Jimma zones (Fig. 1). In some fields and corm rot, and Acremonium inflorescence spot, causing where multiple cultivars were present, samples were necrosis on flower bracts and leaves, can affect produc- collected separately from different cultivars. For each tion, although they appear not to be widespread (Tesera & sample, the location, geographical coordinates, altitude Quimio, 1994; Quimio & Tesera, 1996). A newly reported and enset cultivar were recorded. Enset thrives best in leaf streak disease, caused by a new Badnavirus species, slightly acidic, well-drained and fertile soils (Brandt et al., has also recently been identified (Abraham et al., 2018; 1997). Specific soil characteristics were not assessed for Abraham, 2019). Plant-parasitic nematodes, well known each site; however, we have observed that in each farm as major production constraints to banana and plantain enset was grown in soils rich in organic matter. Root and production (Sikora et al., 2018), have received only lim- soil samples were removed using a spade by excavating a ited attention on enset (Coyne & Kidane, 2018; Coyne hole ca 0.5 m distance from the stem, from 3-4 plants of et al., 2018). A few studies have associated various ne- each cultivar per field and placed in plastic bags, labelled matode species with the crop, with the lesion nematode and stored in a cooler box for transport to the laboratory. Pratylenchus goodeyi appearing to be the most prevalent Additional P. goodeyi populations were collected from (Peregrine & Bridge, 1992; Tesera & Quimio, 1994; Spei- Kenya and Uganda, and others supplied from Canary jer & Fogain, 1998; Mandefro & Dagne, 2000; Swart et Islands (courtesy of Javier López-Cepero), which were al., 2000; Bogale et al., 2004). The root-knot nematodes included in the molecular assessment for comparison with Meloidogyne incognita, M. javanica and M. ethiopica, Ethiopian populations. and Aphelenchoides ensete have also been reported as po- tential production constraints (Mandefro & Dagne, 2000; PROCESSING OF SAMPLES Swart et al., 2000). Compared to other pathogens, nematodes are, in gen- Soil and root samples were processed separately. En- eral, poorly recognised in sub-Saharan Africa (Coyne et set roots were carefully washed, cut longitudinally and al., 2018) and Ethiopia in particular (Abebe et al., 2015). chopped into ca 0.5 mm-sized pieces and a 10 g sub- Despite a handful of studies associating nematode species sample was used for nematode extraction. For soil sam- with enset, there has been no concerted effort to estab- ples, a 100 ml sub-sample was extracted after fully mixing lish the pest potential of nematodes on enset. The current the soil for each sample. Nematodes were extracted from study serves to provide a basis for more focused studies both soil and roots using a modified Baermann method towards understanding the pest potential of nematodes on over a period of 48 h (Hooper et al., 2005). Nematode the crop. A comprehensive sampling of nematodes was suspensions were decanted and nematodes collected on a undertaken in southern Ethiopia to establish the current 38 μm sieve, rinsed into beakers, reduced to 10 ml and situation regarding nematode incidence across the region, densities counted from 1 ml aliquots under a compound in relation to commonly cultivated cultivars and the influ- microscope. Nematode densities were calculated for each ence of altitude (temperature) on their occurrence, with root and soil sample and expressed as the number of ne- 2 Nematology Downloaded from Brill.com03/08/2021 07:47:20AM via free access Plant-parasitic nematodes on enset Fig. 1. Map showing nematode survey fields in southern Ethiopia. matodes in 10 g root or 100 ml soil. The extracted nema- MOLECULAR CHARACTERISATION todes were subsequently heat-killed, with half the quan- tity preserved in triethanolamine formalin (TAF) to pre- The ethanol-preserved nematodes were washed three pare permanent slides for morphological analyses and the times in 400 μl of sterile water for 10 min. DNA ex- remainder preserved in ethanol (97%) for molecular anal- traction was done by cutting an individual specimen and ysis. transferring the two pieces to an Eppendorf tube contain- ing 20 μlofWLB(50mMKCl;10mMTrispH8.3; 2.5 mM MgCl2; 0.45% NP-40 (Merck Life Sciences); MORPHOLOGICAL CHARACTERISATION 0.45% Tween-20). The samples were frozen for at least 10 min; 1 μl proteinase K (1.2 mg ml−1) was added and Nematodes fixed in TAF were processed to anhy- the samples were incubated for 1 h at 65°C and 10 min at drous glycerin for permanent slides, following a modified 95°C.
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