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Ghislain M.,International Potato Center | Tovar J.,International Potato Center | Prentice K.,International Potato Center | Ormachea M.,International Potato Center | And 9 more authors.
Acta Horticulturae | Year: 2013

African sweetpotato weevils (SPW), Cylas puncticollis and C. brunneus, pose a major threat to sweetpotato, which plays a vital role in food security and income generation for both the urban and rural poor in Sub-Saharan Africa (SSA). SPW can limit sweetpotato production causing total crop loss. Control methods such as integrated pest management and breeding have not succeeded satisfactorily in curbing out these pests thus opening the door for using biotechnology and genetic engineering to make transgenic sweetpotato that are resistant to weevil infestation. At least three protein samples from Bacillus thuringiensis (Bt) have been found to be toxic to both SPW species at less than 1 ppm (Cry7Aa1, CryET33/CryET34, and Cry3Ca1). Corresponding gene constructs were developed using sporamin and b amylase regulatory sequences to express and accumulate high Cry protein levels in the storage root. Approximately 100 transformed events from sweetpotato cultivars (including one African cultivar), were produced by Agrobacterium tumefaciens transformation of petioles and somatic embryos. Gene expression from leaf tissues using qRT-PCR revealed up to 20X difference among events. Protein accumulation using DAS-ELISA and storage roots exhibited even larger variation between events. However, so far only 18 of the 90 events have produced storage roots which could be bio-assayed. Most events accumulated Cry proteins below the LC50 level, two events accumulated Cry protein at the LC50 level and only one event accumulated Cry protein above the LC50 level (3 times the LC 50 level). Bioassays using transgenic tissues infested with SPW larvae are on-going but preliminary results reflect low toxicity as expected based on Cry protein content in the storage roots. Future steps include the screening of additional events, characterization of competitive binding of these Cry proteins and confined field trials of SPW-resistant events. Source


Zawedde B.M.,U.S. National Center for Biotechnology Information | Harris C.,Michigan State University | Alajo A.,National Crop Resources Research Institute | Hancock J.,Michigan State University | Grumet R.,Michigan State University
Economic Botany | Year: 2014

Factors Influencing Diversity of Farmers' Varieties of Sweet Potato in Uganda: Implications for Conservation. There is increasing concern that agricultural intensification is causing loss of crop biodiversity due to displacement of traditional farmers' varieties by a small number of improved cultivars. Using ethnobotanical surveys, we assessed the implication of adoption of new sweet potato (Ipomoea batatas) cultivars on the maintenance of farmers' varieties in Uganda. Other factors influencing varietal diversity were also assessed. A total of 102 farmer households distributed in the top three sweet potato production agro-ecological zones were interviewed. With the exception of released cultivars, very few varieties appeared in more than one region. The majority of the respondents indicated that they continue to plant some of the existing varieties when they adopt new cultivars. Loss of planting materials due to drought was a major constraint to maintaining varietal diversity for this vegetatively propagated crop. Limited land and lack of access to best management practices were also key constraints to maintenance of farmers' varieties. The primary criteria for adopting new cultivars were higher yield, taste, and duration to maturity. Yield stability, tolerance to native biotic and abiotic stresses, and good taste were important for maintenance of currently grown varieties. Overall, criteria for variety selection varied with household characteristics including farmer age and gender, uses of the crop, micro-climatic conditions in the farmers' fields, and level of access to agricultural extension. The observed heterogeneity in selection criteria, influence of social ties, and the role of environment in varietal maintenance have important implications for establishing breeding priorities and preservation of crop diversity. © 2014 The New York Botanical Garden. Source


Legg J.P.,IITA Tanzania | Jeremiah S.C.,IITA Tanzania | Jeremiah S.C.,Ukiriguru Agricultural Research Institute LZARDI | Obiero H.M.,Kenya Agricultural Research Institute | And 10 more authors.
Virus Research | Year: 2011

The rapid geographical expansion of the cassava mosaic disease (CMD) pandemic, caused by cassava mosaic geminiviruses, has devastated cassava crops in 12 countries of East and Central Africa since the late 1980s. Region-level surveys have revealed a continuing pattern of annual spread westward and southward along a contiguous 'front'. More recently, outbreaks of cassava brown streak disease (CBSD) were reported from Uganda and other parts of East Africa that had been hitherto unaffected by the disease. Recent survey data reveal several significant contrasts between the regional epidemiology of these two pandemics: (i) severe CMD radiates out from an initial centre of origin, whilst CBSD seems to be spreading from independent 'hot-spots'; (ii) the severe CMD pandemic has arisen from recombination and synergy between virus species, whilst the CBSD pandemic seems to be a 'new encounter' situation between host and pathogen; (iii) CMD pandemic spread has been tightly linked with the appearance of super-abundant Bemisia tabaci whitefly vector populations, in contrast to CBSD, where outbreaks have occurred 3-12 years after whitefly population increases; (iv) the CMGs causing CMD are transmitted in a persistent manner, whilst the two cassava brown streak viruses appear to be semi-persistently transmitted; and (v) different patterns of symptom expression mean that phytosanitary measures could be implemented easily for CMD but have limited effectiveness, whereas similar measures are difficult to apply for CBSD but are potentially very effective. An important similarity between the pandemics is that the viruses occurring in pandemic-affected areas are also found elsewhere, indicating that contrary to earlier published conclusions, the viruses per se are unlikely to be the key factors driving the two pandemics. A diagrammatic representation illustrates the temporal relationship between B. tabaci abundance and changing incidences of both CMD and CBSD in the Great Lakes region. This emphasizes the pivotal role played by the vector in both pandemics and the urgent need to identify effective and sustainable strategies for controlling whiteflies on cassava. © 2011 Elsevier B.V. Source


Zawedde B.M.,Michigan State University | Zawedde B.M.,UBIC | Harris C.,Michigan State University | Alajo A.,National Crop Resources Research Institute | And 2 more authors.
Economic Botany | Year: 2014

Factors Influencing Diversity of Farmers’ Varieties of Sweet Potato in Uganda: Implications for Conservation. There is increasing concern that agricultural intensification is causing loss of crop biodiversity due to displacement of traditional farmers’ varieties by a small number of improved cultivars. Using ethnobotanical surveys, we assessed the implication of adoption of new sweet potato (Ipomoea batatas) cultivars on the maintenance of farmers’ varieties in Uganda. Other factors influencing varietal diversity were also assessed. A total of 102 farmer households distributed in the top three sweet potato production agro-ecological zones were interviewed. With the exception of released cultivars, very few varieties appeared in more than one region. The majority of the respondents indicated that they continue to plant some of the existing varieties when they adopt new cultivars. Loss of planting materials due to drought was a major constraint to maintaining varietal diversity for this vegetatively propagated crop. Limited land and lack of access to best management practices were also key constraints to maintenance of farmers’ varieties. The primary criteria for adopting new cultivars were higher yield, taste, and duration to maturity. Yield stability, tolerance to native biotic and abiotic stresses, and good taste were important for maintenance of currently grown varieties. Overall, criteria for variety selection varied with household characteristics including farmer age and gender, uses of the crop, micro-climatic conditions in the farmers’ fields, and level of access to agricultural extension. The observed heterogeneity in selection criteria, influence of social ties, and the role of environment in varietal maintenance have important implications for establishing breeding priorities and preservation of crop diversity. © 2014, The New York Botanical Garden. Source


Tembo L.,Makerere University | Tembo L.,University of Zambia | Asea G.,National Crop Resources Research Institute | Gibson P.T.,Makerere University | And 2 more authors.
Plant Breeding | Year: 2013

Maize cob rot caused by Fusarium graminearum and Stenocarpella maydis affects grain yield and quality. The objective of this study was to investigate the appropriateness of multiple infection as a selection and breeding strategy for multiple resistance to F. graminearum and S. maydis. Twelve tropical inbred lines with varying resistance to either or both pathogens were mated in a full diallel and the progeny and their parents evaluated for reaction to single or multiple infection. Under multiple inoculation, S. maydis suppressed colonization of cobs by F. graminearum. General combining ability (GCA) effects indicated that inbred WL 118-10 effectively transmitted resistance to both diseases. Hybrids' resistant to S. maydis was also resistant to F. graminearum, but the reverse was not true. Therefore, efficient screening should initially involve screening for S. maydis followed by F. graminearum. Overall, the suppression of F. graminearum by S. maydis shows that multiple infection cannot be used as an appropriate breeding strategy to obtain multiple resistance. The use of F. graminearum and S. maydis separately is, therefore, the best breeding strategy. © 2012 Blackwell Verlag GmbH. Source

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