Browsing by Author "Smith, Julian"

Now showing 1 - 4 of 4
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    Comparative pathogenicity studies of the Xanthomonas vasicola species on maize, sugarcane and banana
    (African Journal of Plant Science, 2015) Karamura, G.; Smith, Julian; Studholme, David; Kubiriba, Jerome; Karamura, E.
    Previous biochemical and molecular sequence analyses of Xanthomonas campestris pathovar musacearum, the etiological agent of banana Xanthomonas wilt, suggest that it belongs within the species Xanthomonas vasicola (X. vasicola pv. vasculorum and X. vasicola pathovar holcicola. However, the X. vasicola pathovar names were considered invalid according to pathovar naming standards and placed as one X. vasicola species; this was also not helped by the lack of sufficient comparative pathogenicity studies. Hence the proposal to rename X. campestris pathovar musacearum was no longer further supported. This study therefore carried out large scale comparative pathogenicity trial studies on the X. vasicola strains and X. campestris pathovar musacearum on 112 plants for banana and maize, and 84 plants for sugarcane, to establish or support the proper X. vasicola pathovar designations. The study also included nine common plant pathogenic Xanthomonas pathovars and one non-Xanthomonas strain. The six strains of X. campestris pathovar musacearum used in the study caused disease in sugarcane and banana but not on maize. 2 and 4 strains of X. vasicola pathovar vasculorum and X. vasicola pathovar holcicola, respectively were not only pathogenic on maize and sugarcane but each also caused distinct symptoms on maize. X. vasicola pathovar vasculorum caused deformation of the plant while X. vasicola pathovar holcicola caused stunted growth.
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    Evaluation of a lateral flow device for in-field detection of Banana Xanthomonas Wilt and its application in tracking the systemicity of Xanthomonas campestris pv. musacearum
    (African Journal of Agricultural Research, 2016) Karamura, Georgina; Ochola, Dennis; Smith, Julian; Kubiriba, Jerome; Karamura, Eldad
    Early detection of Banana Xanthomonas Wilt (BXW) in the field and immediate destruction of infected plants or plant tissue are key control methods to prevent the introduction and spread of BXW. This requires rapid, cost-effective and an on- site diagnostic tool to detect the bacterium, Xanthomonas campestris pv musacearum (Xcm). Polymerase chain reaction (PCR) detection technique for BXW is efficient but requires expensive equipment and knowledgeable expertise; this limits PCR application to the laboratory. This study therefore was carried out to evaluate the enzyme-linked immunosorbent assay (ELISA) tool configured as a lateral flow device (LFD) for detection of Xcm. Studies on the systemicity of Xcm in banana were carried out using the BXW-LFD in a field trial of 300 banana plants of Pisang Awak inoculated with the Xcm at Kiifu Forest, Mukono District, Uganda. Pseudo-stem samples from symptomatic and asymptomatic suckers were collected and tested with the LFD and the results compared with conventional PCR using the GspDm BXW primers. The LFD was able to detect Xcm 3 days post inoculation (dpi), 2 cm above and below inoculation site, 15 to 35 days in the pseudo-stem, 35 to 42 days to reach the corm and 81 days in the lateral roots. The rate of Xcm movement in banana was found to be sigmoid in nature, leveling off as the bacteria moved down the pseudo-stem towards the corm. Conventional PCR was only 24% more sensitive than the LFD. The use of the BXW LFD can therefore boost BXW control measures through improved surveillance and quarantine services to arrest the introduction and spread of the disease within and between national borders.
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    Genome Sequencing of Xanthomonas vasicola Pathovar vasculorum Reveals Variation in Plasmids and Genes Encoding Lipopolysaccharide Synthesis, Type-IV Pilus and Type-III Secretion Effectors
    (Pathogens, 2014) Wasukira, Arthur; Coulter, Max; Al-Sowayeh, Noorah; Thwaites, Richard; Paszkiewicz, Konrad; Kubiriba, Jerome; Smith, Julian; Grant, Murray; Studholme, David J.
    Xanthomonas vasicola pathovar vasculorum (Xvv) is the bacterial agent causing gumming disease in sugarcane. Here, we compare complete genome sequences for five isolates of Xvv originating from sugarcane and one from maize. This identified two distinct types of lipopolysaccharide synthesis gene clusters among Xvv isolates: one is similar to that of Xanthomonas axonopodis pathovar citri (Xac) and is probably the ancestral type, while the other is similar to those of the sugarcane-inhabiting species, Xanthomonas sacchari. Four of six Xvv isolates harboured sequences similar to the Xac plasmid, pXAC47, and showed a distinct Type-IV pilus (T4P) sequence type, whereas the T4P locus of the other two isolates resembled that of the closely related banana pathogen, Xanthomonas campestris pathovar musacearum (Xcm). The Xvv isolate from maize has lost a gene encoding a homologue of the virulence effector, xopAF, which was present in all five of the sugarcane isolates, while xopL contained a premature stop codon in four out of six isolates. These findings shed new light on evolutionary events since the divergence of Xvv and Xcm, as well as further elucidating the relationships between the two closely related pathogens.
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    Genome-Wide Sequencing Reveals Two Major Sub-Lineages in the Genetically Monomorphic Pathogen Xanthomonas Campestris Pathovar Musacearum.
    (Genes, 2012) Wasukira, Arthur; Tayebwa, Johnbosco; Thwaites, Richard; Paszkiewicz, Konrad; Aritua, Valente; Kubiriba, Jerome; Smith, Julian; Grant, Murray; Studholme, David J.
    The bacterium Xanthomonas campestris pathovar musacearum (Xcm) is the causal agent of banana Xanthomonas wilt (BXW). This disease has devastated economies based on banana and plantain crops (Musa species) in East Africa. Here we use genome-wide sequencing to discover a set of single-nucleotide polymorphisms (SNPs) among East African isolates of Xcm. These SNPs have potential as molecular markers for phylogeographic studies of the epidemiology and spread of the pathogen. Our analysis reveals two major sub-lineages of the pathogen, suggesting that the current outbreaks of BXW on Musa species in the region may have more than one introductory event, perhaps from Ethiopia. Also, based on comparisons of genome-wide sequence data from multiple isolates of Xcm and multiple strains of X. vasicola pathovar vasculorum, we identify genes specific to Xcm that could be used to specifically detect Xcm by PCR-based methods.