Plant Disease (2017) 101, 1481-1488

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Ronel Roberts, Glynnis Cook, Tim G. Grout, Fathiya Khamis, Ivan Rwomushana, Peterson W. Nderitu, Zuberi Seguni, Christopher L. Materu, Chanel Steyn, Gerhard Pietersen, Sunday Ekesi and Hendrick F. le Roux (2017)
Resolution of the identity of ' Candidatus Liberibacter' species from huanglongbing-affected citrus in East Africa
Plant Disease 101 (8), 1481-1488
Abstract: ' Candidatus Liberibacter asiaticus', the bacterium associated with citrus Huanglongbing (HLB), was reported from Uganda and tentatively from Tanzania, posing a threat to citriculture in Africa. Two surveys of citrus expressing typical HLB symptoms were conducted in Uganda, Kenya, and Tanzania to verify reports of ' Ca. L. asiaticus' and to assess the overall threat of HLB to eastern and southern African citrus production. Samples were analyzed for the presence of ' Candidatus Liberibacter' species by real-time PCR and partial sequencing of three housekeeping genes, 16S rDNA, rplJ, and omp. ' Ca. L. africanus', the bacterium historically associated with HLB symptoms in Africa, was detected in several samples. However, samples positive in real-time PCR for ' Ca. L. asiaticus' were shown not to contain ' Ca. L. asiaticus' by sequencing. Sequences obtained from these samples were analogous to ' Ca. L. africanus subsp. clausenae', identified from an indigenous Rutaceae species in South Africa, and not to ' Ca. L. asiaticus'. Results indicate a nontarget amplification of the real-time assay and suggest that previous reports of ' Ca. L. asiaticus' from Uganda and Tanzania may be mis-identifications of ' Ca. L. africanus subsp. clausenae'. This subspecies was additionally detected in individual Diaphorina citri and Trioza erytreae specimens recovered from collection sites. This is the first report of ' Ca. L. africanus subsp. clausenae' infecting citrus and being associated with HLB symptoms in this host.
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Link to article at publishers website
Database assignments for author(s): Sunday Ekesi, Glynnis Cook, Ivan Rwomushana

Research topic(s) for pests/diseases/weeds:
surveys/sampling/distribution
identification/taxonomy


Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.


Trioza erytreae Citrus (genus) Uganda
Diaphorina citri Citrus (genus) Uganda
Liberibacter africanus Citrus (genus) Tanzania
Liberibacter africanus Citrus (genus) Uganda