Browsing by Author "Mwanga, Robert O.M."

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    An Online Database of Sweetpotato Germplasm Collection in Uganda
    (HortScience, 2010-01-01) Yada, Benard; Tukamuhabwa, Phinehas; Alajo, Agnes; Mwanga, Robert O.M.
    Sweetpotato [Ipomoea batatas (L.) Lam], the world's seventh most important crop, is widely grown and consumed as a staple food crop in Uganda. Uganda is the third largest global producer after China and Nigeria (Food and Agricultural Organization, 2007). It lies within the East African region, which is considered a secondary center of diversity for the crop where the farmers grow and maintain large numbers of different cultivars and landraces (Mwanga et al., 2001; Villordon et al., 2006). Genetic erosion threatens this diversity as a result of sweetpotato virus disease (SPVD) caused by dual infection of Sweetpotato feathery mottle virus (Potyvirus; Potyviridae) and Sweetpotato chlorotic stunt virus (Crinivirus; Closteroviridae) (Gibson et al., 1998), Alternaria bataticola blight, and African sweetpotato weevils, Cylas puncticollis Boheman and Cylas brunneus Fabricius. Farmers are also known to abandon poor-performing traditional cultivars in favor of newly developed ones released by the national breeding program (Bashaasha et al., 1995; Mwanga et al., 2001). The National Sweetpotato Program based at the National Crops Resources Research Institute (NaCRRI), Namulonge, Uganda, undertook a rigorous germplasm collection, characterization, evaluation, and conservation program to mitigate sweetpotato genetic erosion and also to find superior germplasm for cultivar development in hybridization schemes. A total of 1303 accessions of sweetpotato germplasm were collected from 21 major sweetpotato-producing districts of Uganda from January to July 2005. Information about farmers' indigenous knowledge of the cultivars was also collected. These accessions were assembled at NaCRRI and morphologically characterized using 40 standard root, vine, leaf, and flower descriptors of sweetpotato [International Potato Center (CIP), Asian Vegetable Research and Development Center, and International Board for Plant Genetic Resources, 1991] scored 90 to 100 d after planting in the field. A total of 946 morphologically distinct accessions were identified after removal of duplicates. Field evaluations were also conducted for SPVD, Alternaria blight, and yield at three sites for two seasons. Subsequently, 192 superior genotypes were selected from the germplasm evaluation of which 190 were genetically distinct on molecular characterization using 10 fluorescent-labeled simple sequence repeat markers, IB-R16 (VIC), IB-R19 (PET), IBCIP-13 (NED), IB-R03 (PET), IBCIP-9 (6-FAM), IB-S09 (NED), IB-R08 (PET), IB-R12 (NED), IB-S07 (6-FAM), and IB-S07 (PET), obtained from CIP, Lima, Peru. The database for sweetpotato germplasm collection in Uganda referred to as the “Uganda Sweetpotato Germplasm Database” (USGDB) is described. To our knowledge, the USGDB is the most comprehensive description of collected sweetpotato germplasm in the region. USGDB has all 946 morphologically distinct accessions fully described, including passport (accession identifiers and information recorded by collectors) data, morphological characterization, and evaluation data. This database has been made available online for public use at: http://www.viazivitamu.org/ugasp_db/index.php. The database contains the names, accession number as assigned by collectors, geographical location (longitude and latitude), form of maintenance, and a total of 40 morphological descriptors. It further contains the total root yield, SPVD, and Alternaria bataticola blight disease resistance values for each accession. This online database is an important resource for enhancing the global exchange of sweetpotato germplasm. An online web-accessible database developed for the sweetpotato germplasm collection in Kenya called the “Viazivitamu database” is also available at http://www.viazivitamu.org (Villordon et al., 2007). The Ugandan and Kenyan databases will eventually be merged and expanded to produce a comprehensive regional database of sweetpotato germplasm resources that is representative of the entire East African region after checking for duplicates in the two collections. This USGDB collection is being maintained in the screenhouse and field at NaCRRI. Some 30 accessions are being maintained in vitro at the CIP gene bank at Lima, Peru. Request for this germplasm should be directed to the National Sweetpotato Program, NaCRRI, P.O. Box 7084, Kampala, Uganda.
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    Characterization of Ugandan Sweetpotato Germplasm Using Fluorescent Labeled Simple Sequence Repeat Markers
    (HortScience, 2010-02-01) Yada, Benard; Tukamuhabwa, Phinehas; Wanjala, Bramwell; Alajo, Agnes; Mwanga, Robert O.M.
    The genetic relationships among 192 superior, high–yielding, and disease-resistant sweetpotato [Ipomoea batatas (L.) Lam] accessions from the Ugandan germplasm collection were analyzed using 10 fluorescent labeled simple sequence repeat (SSR) markers. Relatedness among the genotypes was estimated using the Nei and Li genetic distance coefficient, cluster analysis and principle component analysis methods of NTSYS-pc software. The polymorphic information content of the SSR markers used in this study ranged from 0.23 to 0.76 for loci IB-S07 and IB-R12, respectively, with a mean value of 0.62. The number of polymorphic alleles detected per locus ranged from two to six with a mean of four, a confirmation of the effectiveness of microsatellite detection on an automated ABI 3730 sequencer. The mean pairwise genetic distance among the 192 genotypes was 0.57, an indication of moderately high genetic diversity. Cluster analysis divided the accessions into four major groups with no relationship to the district of origin. Two sets of duplicates were identified through SSR genotyping in this study. Up to 190 distinct accessions for use as potential parental genotypes in hybridization schemes for cultivar development in the region were identified.
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    Genetic Variability for Yield and Nutritional Quality in Yam Bean (Pachyrhizus sp.)
    (HortScience, 2016-09-01) Agaba, Rolland; Tukamuhabwa, Phinehas; Rubaihayo, Patrick; Tumwegamire, Silver; Ssenyonjo, Andrew; Mwanga, Robert O.M.; Gr€uneberg, Wolfgang J.
    The amount of genotypic and phenotypic variability that exists in a species is important for selection and initiating breeding programs. Yam bean is grown locally in tropical countries of the Americas and Asia for their tasty storage roots, which usually have low dry matter content. The crop was recently introduced in Uganda and other East and Central African countries to supplement iron (Fe) and protein content in diets. This study aimed to estimate genetic variability for root yield and quality traits among 26 yam bean accessions in Uganda. A randomized complete block design was used with two replications across two ecogeographical locations and two seasons during 2012 and 2013. Near-infrared reflectance spectroscopy (NIRS) was used to determine quality of storage root samples. Significant differences among genotypes were observed for all traits except root protein, zinc (Zn), and phosphorus contents. Genotypic variance components (
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    Sweetpotato weevil (Cylas spp.) resistance in African sweetpotato germplasm
    (International Journal of Pest Management, 2012) Muyinza, Harriet; Talwana, Herbert L.; Mwanga, Robert O.M.; Stevenson, Philip C.
    Host-plant resistance could be a useful tool for managing the weevils Cylas puncticollis and C. brunneus, which are major insect pests of sweetpotato in Africa. There is currently little information on existing resistance mechanisms against Cylas spp. in African cultivars, except where lower levels of weevil damage were attributed to escape due to deep rooting and reduced soil cracking, limiting the exposure of roots to weevils. Here, we evaluate weevil resistance in 134 sweetpotato cultivars and landraces over two seasons in two agroecologically diverse locations. Several sweetpotato cultivars, including New Kawogo, expressed resistance to Cylas spp. The resistance characteristics have been demonstrated in previous laboratory experiments to be quantifiable and thus potentially useful in targeted plant-breeding against Cylas spp. We showed external root and stem base damage to be an accurate quantitative indicator of internal root damage, offering rapid and accurate evaluation of resistance in field trials for screening. Moreover, weevil resistance can be assessed earlier in plant development, so saving time in the selection of the progeny from breeding programmes.