Browsing by Author "Colvin, John"

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    African ancestry of New World, Bemisia tabaci-whitefly species
    (Scientific reports, 2018) Mugerwa, Habibu; Seal, Susan; Wang, Hua-Ling; Patel, Mitulkumar V.; Kabaalu, Richard; Omongo, Christopher A.; Alicai, Titus; Tairo, Fred; Ndunguru, Joseph; Sseruwagi, Peter; Colvin, John
    Bemisia tabaci whitefly species are some of the world’s most devastating agricultural pests and plant-virus disease vectors. Elucidation of the phylogenetic relationships in the group is the basis for understanding their evolution, biogeography, gene-functions and development of novel control technologies. We report here the discovery of five new Sub-Saharan Africa (SSA) B. tabaci putative species, using the partial mitochondrial cytochrome oxidase 1 gene: SSA9, SSA10, SSA11, SSA12 and SSA13. Two of them, SSA10 and SSA11 clustered with the New World species and shared 84.8‒86.5% sequence identities. SSA10 and SSA11 provide new evidence for a close evolutionary link between the Old and New World species. Re-analysis of the evolutionary history of B. tabaci species group indicates that the new African species (SSA10 and SSA11) diverged from the New World clade c. 25 million years ago. The new putative species enable us to: (i) re-evaluate current models of B. tabaci evolution, (ii) recognise increased diversity within this cryptic species group and (iii) re-estimate divergence dates in evolutionary time.
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    African Basil (Ocimum gratissimum) Is a Reservoir of Divergent Begomoviruses in Uganda
    (Plant disease, 2020) Mollel, Happyness G.; Ndunguru, Joseph; Sseruwagi, Peter; Alicai, Titus; Colvin, John; Navas-Castillo, Jesus; Fiallo-Oliv, Elvira
    Begomoviruses are plant viruses that cause major losses to many economically important crops. Although they are poorly understood, begomoviruses infecting wild plants may have an important role as reservoirs in the epidemiology of viral diseases. This study reports the discovery and genomic characterization of three novel bipartite begomoviruses from wild and cultivated African basil (Ocimum gratissimum) plants collected in Uganda, East Africa. Based on the symptoms shown by the infected plants, the names proposed for these viruses are Ocimum yellow vein virus (OcYVV), Ocimum mosaic virus (OcMV), and Ocimum golden mosaic virus (OcGMV). Genome and phylogenetic analyses suggest that DNA-A of OcGMV is mostly related to begomoviruses infecting tomato in Africa, whereas those of OcYVV and OcMV are closely related to one another and highly divergent within the Old World begomoviruses. The DNA-A of all characterized begomovirus isolates are of a recombinant nature, revealing the role of recombination in the evolution of these begomoviruses. The viruses characterized here are the first identified in O. gratissimum and the first in Ocimum spp. in the African continent and could have important epidemiological consequences for cultivated basils and other important crops.
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    African Cassava Whitefly, Bemisia tabaci, Resistance in African and South American Cassava Genotypes
    (Journal of integrative agriculture, 2012) Omongo, Christopher A.; Kawuki, Robert; Bellotti, Antony C.; Alicai, Titus; Baguma, Yona; Maruthi, M. N.; Bua, Anton; Colvin, John
    The whitefly, Bemisia tabaci, is a major pest of cassava, particularly in Africa where it is responsible both for the transmission of plant viruses and, increasingly, for direct damage due to feeding by high populations. To date, there have been no practical solutions to combat this emerging problem, due to the inability of the subsistence farmers that grow cassava to afford expensive inputs such as insecticides. A programme of research was carried out linking institutes in Africa, the UK and South America, to identify possible resistance sources in cassava to the whitefly, Bemisia tabaci. The South American genotype MEcu 72 and several Ugandan cassava landraces including Ofumba Chai, Nabwire 1 and Mercury showed good levels of resistance to B. tabaci. Field and screen-house experiments showed that all of the improved, high-yielding cassava mosaic disease (CMD) resistant cassava genotypes assessed were highly susceptible to B. tabaci and supported high populations of all life stages. These data support the hypothesis that the continuing high populations of cassava B. tabaci in Uganda are due, in part, to the widespread adoption of CMD-resistant cassava varieties during the CMD pandemic. They also show that the whitefly, Aleurotrachelus socialis, resistance present in the South American cassava genotypes could have broader applicability in the Old World.
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    Desmodium mottle virus, the first legumovirus (genus Begomovirus) from East Africa
    (Archives of virology, 2017) Mollel, Happyness G.; Sseruwagi, Peter; Ndunguru, Joseph; Alicai, Titus; Colvin, John; Navas-Castillo, Jesu´ s; Fiallo-Olive, Elvira
    A novel bipartite legumovirus (genus Begomovirus, family Geminiviridae), that naturally infects the wild leguminous plant Desmodium sp. in Uganda, was molecularly characterized and named Desmodium mottle virus. The highest nucleotide identities for DNA-A, obtained from two field-collected samples, were 79.9% and 80.1% with the legumovirus, soybean mild mottle virus. DNA-B had the highest nucleotide identities (65.4% and 66.4%) with a typical non-legumovirus Old World begomovirus, African cassava mosaic virus. This is the first report of a legumovirus in East Africa and extends the known diversity of begomoviruses found infecting wild plants in this continent.
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    Genetic diversity of whitefly (Bemisia spp.) on crop and uncultivated plants in Uganda: implications for the control of this devastating pest species complex in Africa
    (Journal of pest science, 2021) Mugerwa, Habibu; Colvin, John; Alicai, Titus; Omongo, Christopher A.; Kabaalu, Richard; Visendi, Paul; Sseruwagi, Peter; Seal, Susan E.
    Over the past three decades, highly increased whitefly (Bemisia tabaci) populations have been observed on the staple food crop cassava in eastern Africa and associated with ensuing viral disease pandemics and food insecurity. Increased whitefly numbers have also been observed in other key agricultural crops and weeds. Factors behind the population surges on different crops and their interrelationships are unclear, although in cassava they have been associated with specific populations within the Bemisia tabaci species complex known to infest cassava crops in Africa. This study carried out an in-depth survey to understand the distribution of B. tabaci populations infesting crops and uncultivated plant hosts in Uganda, a centre of origin for this pest complex. Whitefly samples were collected from 59 identified plant species and 25 unidentified weeds in a countrywide survey. Identities of 870 individual adult whiteflies were determined through mitochondrial cytochrome oxidase 1 sequences (651 bp) in the 3′ barcode region used for B. tabaci systematics. Sixteen B. tabaci and five related whitefly putative species were identified based on > 4.0% nucleotide divergence, of which three are proposed as novel B. tabaci putative species and four as novel closely related whitefly species. The most prevalent whiteflies were classified as B. tabaci MED-ASL (30.5% of samples), sub-Saharan Africa 1 (SSA1, 22.7%) and Bemisia Uganda1 (12.1%). These species were also indicated to be the most polyphagous occurring on 33, 40 and 25 identified plant species, respectively. Multiple (≥ 3) whitefly species occurred on specific crops (bean, eggplant, pumpkin and tomato) and weeds (Sida acuta and Ocimum gratissimum). These plants may have increased potential to act as reservoirs for mixed infections of whitefly-vectored viruses. Management of whitefly pest populations in eastern Africa will require an integration of approaches that consider their degree of polyphagy and a climate that enables the continuous presence of crop and uncultivated plant hosts.
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    Influence of Cassava Morphological Traits and Environmental Conditions on Field Populations of Bemisia tabaci
    (Insects, 2021) Katono, Kasifa; Macfadyen, Sarina; Omongo, Christopher Abu; Lapaka Odong, Thomas; Colvin, John; Karungi, Jeninah; Otim, Michael Hilary
    High populations of species in the whitefly complex Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) were reported to cause severe damage to cassava in East and Central Africa. However, reasons for B. tabaci population increases are not well understood. We investigated the effect of cassava morphological traits, temperature, rainfall and relative humidity (RH) on the abundance of B. tabaci. Five cassava genotypes with varying levels of resistance to cassava mosaic disease, cassava brown streak disease, and B. tabaci infestation were planted in three Ugandan agro-ecological zones. The experiment was conducted in 2016 and 2017 in a randomized complete block design. Across all locations, the tallest genotype Alado alado supported the lowest number of B. tabaci adults. In areas with high B. tabaci prevalence, leaf area, leaf lobe width, and leaf lobe number exhibited significant positive effects (p < 0.001) on B. tabaci adult count. Positive effects of relative humidity and negative effects of temperature and rainfall on B. tabaci adult and nymph counts were observed in 2016 and 2017, resulting in low populations in Lira. Evidently, temperatures of 28–30 C, rainfall of 30–150 mm and RH of 55–70%, and deployment of cassava genotypes of low plant height, large leaf area, and lobe width significantly enhanced B. tabaci population growth.
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    A novel East African monopartite begomovirus-betasatellite complex that infects Vernonia amygdalina
    (Archives of virology, 2017) Mollel, Happyness G.; Ndunguru, Joseph; Sseruwagi, Peter; Alicai, Titus; Colvin, John; Navas-Castillo, Jesu´ s; Fiallo-Olive, Elvira
    The complete genomes of a monopartite begomovirus (genus Begomovirus, family Geminiviridae) and an associated betasatellite found infecting Vernonia amygdalina Delile (family Compositae) in Uganda were cloned and sequenced. Begomoviruses isolated from two samples showed the highest nucleotide sequence identity (73.1% and 73.2%) to an isolate of the monopartite begomovirus tomato leaf curl Vietnam virus, and betasatellites from the same samples exhibited the highest nucleotide sequence identity (67.1% and 68.2%) to vernonia yellow vein Fujian betasatellite. Following the current taxonomic criteria for begomovirus species demarcation, the isolates sequenced here represent a novel begomovirus species. Based on symptoms observed in the field, we propose the name vernonia crinkle virus (VeCrV) for this novel begomovirus and vernonia crinkle betasatellite (VeCrB) for the associated betasatellite. This is the first report of a monopartite begomovirus-betasatellite complex from Uganda.
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    Occurrence of Bondar’s Nesting Whitefly, Paraleyrodes bondari (Hemiptera: Aleyrodidae), on cassava in Uganda
    (Revista Brasileira de entomologia, 2018) Abu Omongo, Christopher; Namuddu, Annet; Okao-Okuja, Geofrey; Alicai, Titus; Brunschot, Sharon van; Ouvrard, David; Colvin, John
    Cassava is a valued calorific source to millions of Africans who eat it daily and a vital staple for their food security. One of the key constraints to this crop is white flies which are both a vector of viral diseases and a direct pest. Although the African cassava white fly is known to cause physical damage on cassava with considerable tuberous yield loss, a recent white fly outbreak caused unusually severe damage, which prompted the current reported investigation. Molecular identification of white fly adults sampled from the affected cassava field revealed the presence of a new white fly species, Paraleyrodes bondari. This communication is the first report of the occurrence of P. bondari on cassava in Uganda.