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dc.contributor.advisorHvoslef-Eide, Trine (A.K.)
dc.contributor.advisorGedebo, Andargachew
dc.contributor.advisorSpetz, Carl Jonas Jorge
dc.contributor.authorBuko, Dereje Haile
dc.coverage.spatialEthiopia, Hawassaen_US
dc.date.accessioned2020-12-02T14:07:53Z
dc.date.available2020-12-02T14:07:53Z
dc.date.issued2019
dc.identifier.isbn978-82-575-1657-4
dc.identifier.issn1894-6402
dc.identifier.urihttps://hdl.handle.net/11250/2711545
dc.description.abstractThe initiative to improve sweet potato production and productivity in Ethiopia began in the 1980s and so far, there are 26 improved sweet potato varieties made available for farmers. Lack of a rigorous quarantine scheme during exchanges of sweet potato germplasm for improvements may have been the main routes for introduction of sweet potato viruses into Ethiopia. Subsequently, the viruses have been disseminated with high infection levels in the country as a result. Viral diseases has been stated as the main reason for the declining productivity of sweet potato in Ethiopia during the last two decades. In spite of this, there have been few efforts to document the damage it causes, little knowledge on farmers’ perception of the viruses, no efforts in generating high yielding varieties free from economically important viruses and no plan for such virus tested material for dissemination to end users. Furthermore, the tissue culture protocols to generate virus-free plant are often genotype specific and have not been optimized for a wider diversity of genotypes to use for virus elimination and further large-scale propagation. This PhD thesis was generated as a subproject under a NORHED project. It has been designed to increase production and productivity of sweet potato in Ethiopia by addressing five specific objectives. The first objective was to review and document previous research findings that have been conducted on virus detections and eliminations in Ethiopia and bring it to further attention (Paper I). Through literature review and personal communication, we found few virus surveys and sweet potato virus elimination trials undertaken in Ethiopia for the last two decades. We found that Sweet potato feathery mottle virus (SPFMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato virus G (SPVG), Sweet potato virus II (SPV2) and Cucumber mosaic virus (CMV) have been identified through surveys and that little virus elimination methods have been applied in Ethiopia. We concluded that intervention and actions are needed, and this is recommended in this review. We hope that this review paper will facilitate further actions by the authorities, research centers and extension workers, together with the universities. The second objective was to investigate farmers’ perception of virus (es), virus transmission, insect pests and their management in order to improve prevention and eradication of the sources for infections in the future (Paper II). The majority of the farmers (64.7%) and a high proportion of the extension workers (41.2%) interviewed had low perception of sweet potato diseases caused by viral infection and its associated symptoms. A majority of the interviewed farmers know that insects feeds on sweet potato plants, but did not know if insects could transmit viruses from an infected plant to a healthy one. We conclude that neither the farmers nor extension workers have received adequate training related to sweet potato diseases and insect pest management. Training farmers and extension workers is highly advisable in order to enhance the management of virus diseases in Ethiopia. The third objective was to optimize a rapid multiplication method for various many genotypes through tissue culture, as this would facilitate rapid propagation of cleaned stock plants (Paper III). Here we looked at 1) concentrations and combinations of cytokinin (6-benzylamino purine (BAP) and auxin)) and auxin (Naphthalene Acetic Acid (NAA)) for initiation of meristems of four high yielding sweet potato varieties, and 2) varying concentrations of BAP combined with Gibberellic acid (GA3) for better shoot multiplication from single nodal cuttings of five Ethiopian sweet potato high yielding varieties. Concentrations and combinations of NAA and BAP significantly affected the initiation of shoot from meristems and the weight of callus produced per culture (p< 0.05). Moreover, there was a significant genotype x environment interaction. The highest success rate on average over all genotypes was 54% and was obtained with 0.1 mg/L NAA combined with 1 mg/L BAP. The number and height of shoot obtained per nodal cuttings was also significantly affected by the concentrations of BAP, the varieties and the interaction (all at p< 0.05). The highest number of shoot per plants was obtained with ½ concentration Murashige and Skoog’s (MS) medium salts, supplemented with 2 mg/L BAP. This should be the first medium to try when new varieties are to be taken into tissue culture propagation. Paper IV has two objectives: 1) detect the viruses infecting five selected high yielding sweet potato varieties from Ethiopia and 2) compare the elimination efficiency of meristem culture alone or meristem cultures combined with thermotherapy. We applied the following virus detection methods: a) infection test using indicator plant, b) enzyme linked immune sorbent assay (ELISA), and c) reverse transcriptase polymerase chain reaction (RT-PCR). This was combined with virus elimination treatments (meristem culture alone or thermotherapy combined meristem culture) for the chosen five varieties. We found that grafting shoot tips of symptomless test plants on an indicator plant (Ipomea setosa) facilitates an easy detection of SPFMV using ELISA. Sweet potato feathery mottle virus (SPFMV) and Sweet potato chlorotic stunt virus (SPCSV) have been previously reported, and were also detected in this study. We further report of Sweet potato virus C (SPVC) for the first time in Ethiopia. Heat-treating donor plants before meristem culture is more efficient for virus elimination than meristem culture alone. This method generated the highest number of plants free from the virus. The efficiency of each of these methods varied with the cultivars tested. A clean stock of five sweet potato varieties have been obtained to be used as further multiplication and use of virus free planting materials. In the last paper (Paper V), we compared the efficiency of using reverse transcription PCR (RT-PCR) and Next Generation Sequencing (NGS) as a method to verify efficient elimination of viruses and detection of potential novel viruses in plants before and after virus elimination using VirusDetect software. NGS has confirmed the presences of SPFMV, SPVC and SPCSV previously detected in plants before virus elimination treatment by RT-PCR. Moreover, the NGS method detected some of the common viruses in some of plants before virus elimination where these viruses had not been detected using RT-PCR. In addition, NGS confirms the presence of three viruses in Genus badnaviruses all collectively belongs to species known as Sweet potato pakkakuy virus (SPPV) and Sweet potato symptomless mastrevirus-1 (SPSMV-1) previously unknown to be present in Ethiopia in most of plants before virus elimination treatment and in some of plants after the treatment. Therefore, the use of NGS in virus certification schemes is more reliable than RT-PCR and can be used in the developing country like Ethiopia in the future, as the cost is getting lower and lower.en_US
dc.description.abstractDet ble tatt flere initiativ på 1980-tallet for å forbedre søtpotetproduksjon og øke avlingene i Etiopia. Så langt har det fremkommet 26 forbedrete sorter av søtpotet, og som er tilgjengelig for bønder. Mangel på strenge karantenebestemmelser ved utveksling av nytt foredlingsmateriale av søtpotet kan være årsaken til spredning av virus på søtpotet i Etiopia. Som en følge av dette, har alle deler av landet som dyrker søtpotet høy grad av virusinfeksjoner. Virussykdommer har oppgitt som hovedårsaken til at avlingene har gått tilbake de siste tyve årene. Likevel, har det vært liten innsats for å dokumentere skadene, liten kunnskap om hvordan bøndene opplever situasjonen i forhold til virusinfeksjoner, ingen innsats for å rense høytytende sorter for virusinfeksjoner og heller ingen plan for å starte rensing med etterfølgende tilbud om virusrenset materiale til bøndene. I tillegg til dette, er de vevskulturoppskriftene som finnes kun utviklet for noen få genotyper, og de er oftest svært genotypespesifikke. Det finnes ingen medier som er brukbare for en større bredde av sorter og med god mulighet for påfølgende masseformering, slik at bøndene kan få tilgang til rensede sorter.en_US
dc.description.sponsorshipNorwegian Agency for Development Cooperation (Norad) funded project ‘‘Controlling disease in sweet potato and enset in South Sudan and Ethiopia to improve productivity and livelihoods under changing climatic conditions using modern technologies’’ under the NORHED program, Agreement No ETH-13/0017, 2013-2019.en_US
dc.language.isoengen_US
dc.publisherNorwegian University of Life Sciences, Åsen_US
dc.relation.ispartofseriesPhD Thesis;2019:94
dc.rightsAttribution-NonCommercial-NoDerivatives 4.0 Internasjonal*
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/deed.no*
dc.subjectSweet potatoen_US
dc.subjectVirusesen_US
dc.subjectDetectionen_US
dc.subjectEliminationen_US
dc.subjectmanagementen_US
dc.titleSweet potato virus in Ethiopia : detection, characterization, elimination and managementen_US
dc.title.alternativeVirus i søtpotet i Etiopia : påvisning, karakterisering, rensing og forebyggingen_US
dc.typeDoctoral thesisen_US


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