Browsing by Author "Ferguson, Morag"

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    Eleven years of breeding efforts to combat cassava brown streak disease
    (Breeding Science, 2016) Sezi Kawuki, Robert; Kaweesi, Tadeo; Esuma, Williams; Pariyo, Anthony; Kayondo, Ismail Siraj; Ozimati, Alfred; Kyaligonza, Vincent; Abaca, Alex; Orone, Joseph; Tumuhimbise, Robooni; Nuwamanya, Ephraim; Abidrabo, Philip; Amuge, Teddy; Ogwok, Emmanuel; Okao, Geoffrey; Wagaba, Henry; Adiga, Gerald; Alicai, Titus; Omongo, Christopher; Bua, Anton; Ferguson, Morag; Kanju, Edward; Baguma, Yona
    Cassava (Manihot esculenta Crantz) production is currently under threat from cassava brown streak disease (CBSD), a disease that is among the seven most serious obstacles to world’s food security. Three issues are of significance for CBSD. Firstly, the virus associated with CBSD, has co-evolved with cassava outside its center of origin for at least 90 years. Secondly, that for the last 74 years, CBSD was only limited to the low lands. Thirdly, that most research has largely focused on CBSD epidemiology and virus diversity. Accordingly, this paper focuses on CBSD genetics and/or breeding and hence, presents empirical data generated in the past 11 years of cassava breeding in Uganda. Specifically, this paper provides: 1) empirical data on CBSD resistance screening efforts to identify sources of resistance and/or tolerance; 2) an update on CBSD resistance population development comprising of full-sibs, half-sibs and S1 families and their respective field performances; and 3) insights into chromosomal regions and genes involved in CBSD resistance based on genome wide association analysis. It is expected that this information will provide a foundation for harmonizing on-going CBSD breeding efforts and consequently, inform the future breeding interventions aimed at combating CBSD.
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    Manual for Collection of Cassava Germplasm and Associated Farmer Knowledge in Eastern and Southern Africa
    (International Institute of Tropical Agriculture, Ibadan, Nigeria, 2014) Cox, T. Paul; Nakabonge, Grace; Ferguson, Morag
    Cassava germplasm and associated farmer knowledge from southern, eastern and central Africa is under represented in national and international germplasm collections. This germplasm consists mainly of farmer varieties (landraces) which have been grown for many years and harbor valuable adaptive gene complexes that have evolved under human and environmental selection pressures. The current situation of lack of a repository means that (1) local landraces are not readily available to breeders (2) some farmer landraces contain genetic variation and are not ‘clonal’ as researchers and breeders assume, and no ‘type specimen’ exists so breeders are often not sure of what they are breeding with, (3) disease-free farmer landraces are not available, preventing the movement and sharing of germplasm, (4) landraces and the adaptive gene complexes they harbor are vulnerable to genetic erosion from the spread of improved varieties with increased breeding activities in the region and in the face of devastating diseases such as cassava brown streak disease which may cause the total loss of susceptible landraces, and (5) there is no germplasm database concerning the various attributes of particular clones, geographical location and farmer perceptions for use as a decision-making tool. This lack of ‘farmer-centric’ information means that breeders may not fully understand the subtleties of farmer preferences with implications for varietal adoption of improved germplasm
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    Physiological and molecular characterization of drought responses and identification of candidate tolerance genes in cassava
    (AoB plants, 2013) Turyagyenda, Laban F.; Kizito, Elizabeth B.; Ferguson, Morag; Baguma, Yona; Agaba, Morris; Harvey, Jagger J. W.; Osiru, David S. O.
    Cassava is an important root crop to resource-poor farmers in marginal areas, where its production faces drought stress constraints. Given the difficulties associated with cassava breeding, a molecular understanding of drought tolerance in cassava will help in the identification of markers for use in marker-assisted selection and genes for transgenic improvement of drought tolerance. This study was carried out to identify candidate drought-tolerance genes and expression-based markers of drought stress in cassava. One drought-tolerant (improved variety) and one drought-susceptible (farmer-preferred) cassava landrace were grown in the glasshouse under well-watered and water-stressed conditions. Their morphological, physiological and molecular responses to drought were characterized. Morphological and physiological measurements indicate that the tolerance of the improved variety is based on drought avoidance, through reduction of water loss via partial stomatal closure. Ten genes that have previously been biologically validated as conferring or being associated with drought tolerance in other plant species were confirmed as being drought responsive in cassava. Four genes (MeALDH, MeZFP, MeMSD and MeRD28) were identified as candidate cassava drought-tolerance genes, as they were exclusively up-regulated in the drought-tolerant genotype to comparable levels known to confer drought tolerance in other species. Based on these genes, we hypothesize that the basis of the tolerance at the cellular level is probably through mitigation of the oxidative burst and osmotic adjustment. This study provides an initial characterization of the molecular response of cassava to drought stress resembling field conditions. The drought-responsive genes can now be used as expression-based markers of drought stress tolerance in cassava, and the candidate tolerance genes tested in the context of breeding (as possible quantitative trait loci) and engineering drought tolerance in transgenics.