School of Biosecurity, Biotechnolgy and Laboratory Sciences (SBLS) Collection
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Browsing School of Biosecurity, Biotechnolgy and Laboratory Sciences (SBLS) Collection by Author "Adero, Joanne"
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ItemIntegrated epidemiology, viral genomics and molecular host response mechanisms to sweet potato viruses(Makerere University, 2025) Adero, JoanneSweetpotato (Ipomoea batatas L.) is a critical food security and income crop in subSaharan Africa (SSA), especially for smallholder farmers, but its production faces severe constraints from Sweetpotato virus disease (SPVD), resulting from synergistic co-infection by Sweet potato feathery mottle virus (SPFMV) and Sweet potato chlorotic stunt virus (SPCSV), leading to yield losses of up to 98%. This study examined the epidemiology, genetic diversity and host resistance mechanisms of SPVD in Uganda through a multi-faceted approach. A socio-economic and disease survey of 95 households/fields across central (n=33), eastern (n=30), and western (n=32) regions revealed widespread SPVD incidence (up to 100% in some areas), with farmers identifying it as the primary constraint, yet nearly half lacked knowledge of symptoms, vectors (aphids and whiteflies), and management practices; adoption of controls like rogueing and clean planting material was low, influenced positively by education and symptom awareness but negatively by farming experience and land size, highlighting needs for gender-sensitive training and extension services. Next-generation sequencing (NGS) of diseased vines from 48 samples identified nine viruses, including first reports of Sweetpotato pakakuy virus (SPPV) and Sweetpotato symptomless virus-1 (SPSMV1) in Uganda, with frequent mixed infections; phylogenetic and recombination analyses showed high diversity in SPFMV and Sweetpotato virus C (SPVC), driven by mutations, recombination events (especially in coat protein and helper component proteinase genes), and purifying/diversifying selection, affirming East Africa as a viral evolution hotspot. An experimental transcriptomic study of three cultivars ('Beauregard' as susceptible, 'Tanzania' as moderately tolerant, and 'New Kawogo' as highly tolerant) infected with SPFMV, SPCSV, or SPVD at 3-, 6-, and 12-weeks postinoculation. Transcriptomic profiling uncovered cultivar-specific responses: 'New Kawogo' demonstrated robust resistance via early upregulation of redox regulation, transcriptional factors, hormonal signaling (e.g., salicylic acid and systemic acquired resistance), and detoxification, enabling full recovery; 'Tanzania' exhibited adaptive, delayed immune activation with partial tolerance through metabolic reprogramming and MAPK pathways; while 'Beauregard' showed susceptibility marked by transcriptional repression, immune suppression, and failure to recover. These results underscore knowledge gaps, viral diversity, and differential host defenses as key factors in SPVD persistence, providing candidate genes (e.g., oxidoreductases, ATP-binding proteins, SUMOylation regulators) for marker-assisted breeding and functional genomics to develop resilient varieties, ultimately enhancing sustainable sweetpotato production, food security, and livelihoods in SSA.
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ItemOccurrence of cassava mosaic geminiviruses and cassava brown streak viruses in cassava and wild plant species in Uganda(Makerere University, 2015) Adero, JoanneCassava (Manihot esculenta crantz) is an important food and cash crop worldwide. Currently cassava brown streak disease (CBSD) caused by Cassava brown streak ipomoviruses (CBSVs) and cassava mosaic disease (CMD) caused by Cassava mosaic geminiviruses (CMGs) are the major constraint to cassava production in East Africa. Occurrence of these viruses in alternative hosts is unknown and therefore potential risk posed to cassava cultivation. A survey was conducted in five agro ecological zones of Uganda, in 24 cassava growing districts to determine plant species that may be alternative hosts for these viral pathogens. Leaf samples plant species with virus-like symptoms found within or adjacent to cassava fields were picked and analyzed. Overall CBSD mean incidence for the 24 districts was 38.4%. Kayunga district had the highest incidence (100%), while Soroti had the lowest incidence at 4.7% and two districts did not have CBSD. CMD mean incidence was 13.4%, with Busia having the highest incidence at 46% while Kamuli had the lowest incidence at 0.7% and five districts did not have CMD. Nucleic acids were extracted from both cassava and suspected alternative plants, and tested for CMGs by conventional PCR and CBSVs by two-step RT-PCR and analyzed by agarose gel electrophoresis. Twelve (12) wild plant species were positive for CMGs with nine (9) plants positive with ACMV and three (3) plants positive for EACMV-UG. Ten (10) plants were positive for UCBSV and one (1) was detected with CBSV. PCR products were purified and quantification and Amplicons were sequenced in both directions. All nine ACMV sequences, three EACMV sequences and one CBSV sequence obtained from non-cassava host plants had significant similarities with sequences in the gene bank with sequence having 89–100% nucleotide sequence identity with cassava isolates from East and West Africa. Plant species identification was done for confirmed alternative host plants for CMGs and CBSVs, and plants were identified into seven species namely Ageratum conzyzoides, Asystasia gangetica, Solanum incanum, Leonotis nepetifolia, Hewettia sublobata, Erythrina abyssinica, and M. glaziovii. These results provide definitive evidence for the natural occurrence of cassava viruses in plant species besides cassava, acting as reservoirs for the viruses. This therefore demands appropriate measures to safeguard cassava production in Uganda.