Browsing by Author "Susan E. Seal"

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    Comparative evolutionary analyses of eight whitefly Bemisia tabaci sensu lato genomes: cryptic species, agricultural pests and plant-virus vectors
    (BMC Genomics, 2023-07-19) Lahcen I. Campbell; Joachim Nwezeobi; Sharon L. van Brunschot; Tadeo Kaweesi; Susan E. Seal; Rekha A. R. Swamy; Annet Namuddu; Gareth L. Maslen; Habibu Mugerwa; Irina M. Armean; Leanne Haggerty; Fergal J. Martin; Osnat Malka; Diego Santos‐Garcia; Ksenia Juravel; Shai Morin; Michael E. Stephens; Paul Visendi Muhindira; Paul J. Kersey; M. N. Maruthi; Christopher A. Omongo; Jesús Navas‐Castillo; Elvira Fiallo‐Olivé; Ibrahim Umar Mohammed; Hua‐Ling Wang; Joseph Onyeka; Titus Alicai; John Colvin
    Background The group of > 40 cryptic white y species called Bemisia tabaci sensu lato are amongst the world’s worst agricultural pests and plant‐virus vectors. Outbreaks of B. tabaci s.l. and the associated plant‐virus diseases continue to contribute to global food insecurity and social instability, particularly in sub‐Saharan Africa and Asia. Published B. tabaci s.l. genomes have limited use for studying African cassava B. tabaci SSA1 species, due to the high genetic divergences between them. Genomic annotations presented here were performed using the ‘Ensembl gene annotation system’, to ensure that comparative analyses and conclusions reflect biological differences, as opposed to arising from different methodologies underpinning transcript model identification. Results WepresentheresixnewB.tabacis.l.genomesfromAfricaandAsia,andtwore‐annotatedpreviously published genomes, to provide evolutionary insights into these globally distributed pests. Genome sizes ranged between 616—658 Mb and exhibited some of the highest coverage of transposable elements reported within Arthropoda. Many fewer total protein coding genes (PCG) were recovered compared to the previously published B. tabaci s.l. genomes and structural annotations generated via the uniform methodology strongly supported a repertoire of between 12.8—13.2 × 103 PCG. An integrative systematics approach incorporating phylogenomic analysis of nuclear and mitochondrial markers supported a monophyletic Aleyrodidae and the basal positioning of B. tabaci Uganda‐1 to the sub‐Saharan group of species. Reciprocal cross‐mating data and the co‐cladogenesis pattern of the primary obligate endosymbiont ‘Candidatus Portiera aleyrodidarum’ from 11 Bemisia genomes further supported the phylogenetic reconstruction to show that African cassava B. tabaci populations consist of just three biological species. We include comparative analyses of gene families related to detoxification, sugar metabolism, vector competency and evaluate the presence and function of horizontally transferred genes, essential for understanding the evolution and unique biology of constituent B. tabaci. s.l species. Conclusions These genomic resources have provided new and critical insights into the genetics underlying B. tabaci s.l. biology. They also provide a rich foundation for post‐genomic research, including the selection of candidate gene‐ targets for innovative white y and virus‐control strategies.
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    Detection of cassava brown streak ipomoviruses in aphids collected from cassava plants
    (Frontiers in Sustainable Food Systems, 2023-02-08) Sarah Nanyiti; Richard Kabaalu; Titus Alicai; Phillip Abidrabo; Susan E. Seal; Sophie Bouvaine; Andy M. Bailey; Gary D. Foster
    Cassava is an important staple food in Africa and a major source of carbohydrates for 800 million people globally. However, cassava suffers severe yield losses caused by many factors including pests and diseases. A devastating disease of cassava is cassava brown streak disease (CBSD) caused by the cassava brown streak ipomoviruses (CBSIs) (family Potyviridae), Cassava brown streak virus (CBSV), and Ugandan cassava brown streak virus (UCBSV). Spread of CBSD is mainly through planting infected stem cuttings used for propagation. Transmission of CBSIs by the insect vector (Bemisia tabaci) has been reported. However, experimental transmission efficiencies of CBSIs are usually low. Recent research has showed the occurrence of a DAG motif associated with aphid transmission in other potyviruses, within the coat protein gene of CBSV. Consequently this study aimed to explore the possibility that besides whiteflies, aphids may transmit CBSIs. Cassava plants were assessed during a survey for occurrence of CBSD and aphids as potential alternative CBSIs vectors. We collected aphids from CBSD-symptomatic and symptomless cassava plants within farmers’ fields in Uganda during April–July 2020. The aphids were analyzed for the presence of CBSIs by reverse transcriptase-polymerase chain reaction (RT-PCR) and to determine aphid species using mitochondrial cytochrome oxidase (mtCOI) barcoding. Unusual aphid infestation of cassava plants was observed at 35 locations in nine districts across Uganda and on 11 other plant species within or adjacent to cassava fields. This is the first report of aphids infesting cassava in Uganda. Molecular analysis of the aphid confirmed presence of three different aphid species in the surveyed cassava fields, namely, Aphis solanella, Aphis fabae mordvilkoi, and Rhopalosiphum sp. mtCOI nucleotide sequences for the aphids in which CBSIs were detected are deposited with Genbank under accession numbers OP223337-40. Both UCBSV and CBSV were detected by RT-PCR in aphids collected from cassava fields with CBSD-affected plants. The CBSIs were detected in 14 aphid samples collected from 19 CBSD- symptomatic cassava plants. These results suggest the ability of aphids to acquire CBSIs, but transmission experiments are required on their vector potential.