Browsing by Author "Wada Eyasu"

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    Morphological and Molecular Characterization, Assessment of Nutritional Composition and Micropropagation of Cocoyam (Xanthosoma Sagittifolium (L.) Schott) from Ethiopia
    (Addis Ababa University, 2018-06-03) Wada Eyasu; Feyissa Tileye (PhD); Tesfaye Kassahun (PhD); Asfaw Zemede (Professor)
    Morphological and Molecular Characterization, Assessment of Nutritional Composition and Micropropagation of Cocoyam (Xanthosoma sagittifolium (L.) Schott) from Ethiopia Eyasu Wada Wachamo, PhD Dissertation Addis Ababa University, June 2018 Cocoyam (Xanthosoma sagittifolium (L.) Schott) is a tuberous root crop in the Araceae family. It is an exotic crop to Ethiopia that was introduced fairly recently but has spread widely and already become part of the agricultural and food systems of the people, wherein tuber and root crops play an important role as sources of food. However, cocoyam has not been given research attention commensurate to its importance as it is a neglected crop by research and development community. This study was conducted to characterize cocoyam diversity at morphological and molecular levels through documenting farmers’ knowledge, perceptions and management practices; determining nutritional composition; and developing a micropropagation protocol for this neglected crop. The present ethnobotanical survey results showed that the crop is given different local names by farmers and that it is locally used for food, fodder, medicine and other purposes. Furthermore, the results showed that the uses of cocoyam as a food crop and fodder are the most preferred traits as perceived by the farmers while hardness, sour taste, unpleasant smell and low market demand were the major constraits for cocoyam production. Green- and purple-colored cocoyam plants were observed during our survey. The field study helped to distinguish two classes of qualitative traits for petiole color, lamina orientation, color of veins on leaf surfaces, position of cormel apex and shape of cormels. Analysis of variance (ANOVA) revealed significant variation in 11(84.6%) of the 13 studied quantitative traits. Principal Component Analysis (PCA) reduced the 13 quantitative traits to 3 Principal components (PCs) with the eigen values >1, which explained 69.2% of the observed variations. In the genetic diversity analysis using 11 SSR markers, a total of 36 alleles were detected (mean 3.273). High SSR marker diversity was detected within populations (average Ho = 0.503 and He = 0.443) and when all collections were considered as single population (Ho: 0.508, He: 0.566). Supporting these results, genetic diversity analysis using AFLP markers revealed high Nei’s gene diversity (He) within populations (He = 0.349) and at the entire collection level (He = 0.389). SSR markers revealed strong genetic differentiation among populations and between green and purple cocoyam morphotypes by Fst values 0.196 and 0.463, respectively. However, unlike SSR markers, AFLP marker-based analysis showed low genetic differentiation among populations (Gst = 0.072) as well as between green and purple cocoyam morphotypes (Gst = 0.024). The nutritional composition analysis showed that both the green- and purple-cocoyam morphotypes can provide nutrient-rich products, albeit slight differences in the quantities of proximate, minerals and antinutritional factors. A micropropagation protocol was successfully developed in which the green- and purple-cocoyam shoot tip explants were best initiated on Murashige and Skoog (MS) medium containing 2.0 mg/l BAP, best multiplied on MS medium containing 2.5 mg/l BAP and 0.5 mg/l NAA and the best IBA concentration for rooting was MS medium supplemented with 2.0 mg/l IBA. Overall, a lot of useful indigenous knowledge exists within the farming communities in the rural areas, but cocoyam is poorly studied and underutilized crop in spite of its nutritional value & its potential as food crop. The findings of this study are very important to enhance the future use of cocoyam in the country. Collaborative research intervention involving the development of varieties, making available high quality planting material for farmers & promoting value chains and market opportunities are valuable for sustainable use of the exiting diversity & to safeguard the potential end users of cocoyam in the country.
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    Serological and Molecular Based Assay of Tomato (Lycopersicon Esculentum Mill.) and Cassava (Manihot Esculenta Crantz) Viruses in Ethiopia
    (Addis Ababa University, 2010-06) Wada Eyasu; Feyissa Tileye (PhD); Abraham Adane (PhD)
    Tomato as well as cassava yield is limited by virus diseases and which has been one of most important constraint for production of both crops. The genus Begomovirus belongs to family Geminiviridae and has emerged as more serious constraints to varieties of crops including tomato and cassava worldwide. In addition to it, other major tomato viruses infecting tomato plant in tropical Africa have been included in the genus Tobamovirus, Tospovirus, Potyvirus and Cucumovirus. African cassava mosaic virus also causes a devastating cassava yield. To determine the incidence and prevalence of begomoviruses on tomato and cassava in Ethiopia, 570 tomato and 250 cassava leaf samples were collected from 57 tomato and 25 cassava fields respectively from October 21, 2009 to December 21, 2009. Most of the tomato fields were surveyed at East Shewa in Rift Valley and western Ethiopia whereas most cassava fields were surveyed at southern Ethiopia. The tomato samples were tested in DAS-ELISA against seven tomato infecting viruses: Tomato yellow leaf curl virus, Tomato mosaic virus, Tomato spotted wilt virus, Tomato ring spot virus-Chickadee strain, Tobacco mosaic virus, Potato virus Y and Cucumber mosaic virus. Cassava samples were tested in TAS-ELISA against African cassava mosaic virus, using universal probe which can detect all African cassava mosaic virus species so far described. Molecular technique based assays were performed based on immunocapture PCR for detection of Tomato yellow leaf curl virus, using Begomovirus DNA-A specific degenerative primer pair, Begomo_146 and Begomo_672. Immunocapture-PCR and standard PCR techniques were used to test African cassava mosaic virus, using three pairs of primers: Begomovirus DNA-A specific, Begomovirus DNA-B specific and African cassava mosaic virus DNA-A specific. Tomato samples from Rift Valley areas provided weak positive test to Tomato yellow leaf curl virus and clear positive test to Tomato mosaic virus in DAS-ELISA. All tomato samples were negative for Tomato spotted wilt virus, Tomato Ring spot virus-Chickadae strain, Tobacco mosaic virus, Potato virus Y and Cucumber Mosaic virus. The expected 520 bp PCR product of Tomato yellow leaf curl virus was obtained from samples which gave weak positive test for this virus in DAS-ELISA test. TAS-ELISA test as well as molecular technique based assays based on both methods using three pairs of primers all provided negative results for African cassava mosaic virus. Research should be broadened to include more samples. Tomato yellow leaf curl virus and Tomato mosaic virus were detected at 24.6% and 47.37% of the study area respectively. These viruses showed a distinct pattern of distribution in the surveyed areas at incidence level varying from 20% to 70%. Considering the incidence and distribution, appropriate virus management programme should be sought. Key word: Begomoviruses, Cassava, ELISA, IC-PCR, Tomato