Agricultural and Veterinary Sciences

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Browsing Agricultural and Veterinary Sciences by Author "Abaca, Alex"

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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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    Evaluation Of Cassava Genotypes For Resistance To Cassava Brown Streak Disease (Cbsd) In Uganda
    (Makerere University, 2013) Abaca, Alex
    Cassava (Manihot esculenta Cranz) production in Uganda is being constrained by the devastating effects of cassava brown streak disease (CBSD). CBSD is caused by cassava brown streak virus (CBSV), which affects all parts of the cassava plant, causing characteristic above and below ground symptoms. The economically damaging symptoms occur on the roots as a yellow/brown-corky necrosis. In terms of control, the most economically viable method for CBSD management is the use of host-plant resistance. This implies that development of cassava varieties that are resistant to CBSD is an important component in the CBSD management. Thus, the specific objectives of this study were to: (i) evaluate local and elite cassava genotypes for resistance to cassava brown streak disease, (ii) assess the genetic relatedness of these selected cassava genotypes using the simple sequence repeat (SSR) markers and (iii) quantify CBSD root symptom development stages among selected cassava varieties. To achieve this, 116 local and elite cassava genotypes were evaluated at Namulonge, a hotspot for CBSD. Foliar data were collected at monthly interval for a period of 12 months and root data was collected at harvest. Fresh leaves were collected and DNA was extracted from these genotypes and assayed with 30 SSRs, using the ABI 3730 DNA sequencer (Applied Biosystems). Nine other cassava genotypes classified as 5 tolerant and 4 susceptible were also tested at NaCRRI in a factorial split plot design for the determination of root necrosis development critical stages. Foliar and root CBSD incidence and severity were collected starting at 4 MAP for root necrosis progression up to 12
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    Evaluation of Newly Released Cassava Varieties for Yield Performance, Reactions to Cassava Diseases and Farmers’ Preference in Adjumani District of Uganda
    (Journal of Agricultural Science, 2021) Abaca, Alex; Odama, Emmanuel; Komakech, Alfred; Asiku, Baron; Andema A. Andrews
    Cassava viral diseases particularly cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) have put pressure on cassava breeders to develop varieties that are resistant/tolerant to them. Several cassava varieties have been rolled out to farmers with the latest being NAROCASS series that are tolerant to these diseases. The yield performance of these new varieties have not been documented in some sub zones like Adjumani district that falls within a major West Nile agro-ecology of Uganda. Therefore this study sought to established yield performances of, reactions to major diseases, and farmers’ preference to these newly released cassava varieties in Adjumani. Results showed significant (P ≤ 0.05) differences among cassava varieties and experimental sites for all the parameters evaluated. Average yield performance by varieties were in the order of a local cassava—Alifasia (8.7 t/Ha) lowest, NAROCASS 2 (18.55 t/Ha), NASE 14 (33.97 t/Ha), NASE 19 (41.26 t/Ha), and NAROCASS 1 (41.71 t/Ha) highest. CMD foliar symptom was present at all sites on a local cassava—Alifasia, and on NAROCASS 1 in Ayiri parish, Ukusijoni sub-county. CBSD foliar symptoms were observed on off-types (TME 14) in the plot of NASE 14 in Miniki Parish only whereas CBSD root necrosis was observed at all sites on the local cassava—Alifasia, and on NASE 19 in Maaji parish, Ukusijoni sub-county. Cassava root rot disease was localised in Ukusijoni sub-county only. Farmers’ preferences to these newly released cassava varieties were in the order of NASE 19 (40.96%), NAROCASS 1 (24.86%), NAROCASS 2 (15.82.28%), NASE 14 (15.54%), and a Local cassava—Alifasia (2.83%). Result from this study strengthens the information gap in the breeding process towards developing a cassava variety with farmer-preferred attributes, and can also inform the utilisation of these improved cassava varieties in Adjumani district. Keywords: cassava varieties, cassava brown streak disease, cassava mosaic disease, farmers’ preference, yield performance, new varieties, Adjumani
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    Genetic Relationships of Cassava Genotypes That are Susceptible or Tolerant to Cassava Brown Streak Disease in Uganda
    (Journal of Agricultural Science, 2013) Abaca, Alex; Kawuki, Robert; Tukamuhabwa, Phenihas; Baguma, Yona; Pariyo, Anthony; Alicai, Titus; Omongo, C. Christopher; Abidrabo, Phillips; Katono, Kasifa; Bua, Anton
    A total of 99 cassava genotypes whose field reaction to cassava brown streak disease (CBSD) was known, were assayed with 30 simple sequence repeat (SSR) markers to establish their genetic parallels. Two categories of CBSD reaction were considered: CBSD-susceptible genotypes (characterized by > 60% root and foliar CBSD incidence), and CBSD-tolerant genotypes (characterized by < 15% root and foliar CBSD incidence). DNA was extracted from leaf samples using the miniprep method and genotyped using ABI 3730 DNA sequencer. The test genotypes at 0.02 similarity coefficient, CBSD-tolerant and CBSD-susceptible genotypes clustered into 5 main sub-clusters. When data were subjected to principle component analysis (PCA) irrespective of the CBSD reaction grade, the first three principal components accounted for 68% of the total genetic variation. Despite having different number of individuals, the observed heterozygosity (Ho) for CBSD-susceptible (Ho = 0.58) and CBSD-tolerant (Ho = 0.66) were comparable and provide scope for long-term CBSD breeding and/or gene tapping.
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    Grain Hermetic Storage Adoption in Northern Uganda: Awareness, Use, and the Constraints to Technology Adoption
    (Agricultural Sciences, 2022) Okori, Francis; Cherotich, Sam; Abaca, Alex; Baidhe, Emmanuel; Adibaku, Francis
    Post-harvest storage losses (PHLs) remain significant in Sub-Saharan Africa (SSA) due to several factors mainly insect pests and molds. Hermetic storage technologies (HSTs) are being promoted to address these storage losses. In Uganda, HSTs were first introduced in 2012. However, its use among farming households remains low today. Data were collected from 306 smallholder farmers from four districts of Northern Uganda using a pre-tested semistructured questionnaire to understand their knowledge, use, and constraints to the adoption of hermetic storage. A multivariate Logit regression model was used to find the significance of the factors affecting adoption. Results showed low awareness and use of hermetic storage among smallholder farmers. Only 53.3% of the interviewed farmers were aware of the use of hermetic storage for grain storage. The SuperGrain bag was the most known form of hermetic storage (35.3%), followed by the Purdue Improved Crop Storage (PICS) bag (34.9%), metallic silo (15.5%), and plastic silo (14.4%). Hermetic storage use was even lower as only 17.6% of the surveyed farmers were using one or more forms of hermetic storage to store their grains. Insect pest management without chemical insecticides was the main reason (83.1%) for hermetic storage use. About 75.5% of those aware of hermetic storage had received training in the technology. Hermetic storage use in farming households led to improved food availability, household income, and nutrition.