|Authors: ||V. Aritua, N. Parkinson, R. Thwaites, D.R. Jones, W. Tushemereirwe, J.J. Smith|
|Keywords: ||Gyrase B sequence, internal transcribed spacer (ITS) region|
Xanthomonas wilt of enset and banana was first described in Ethiopia in 1968 and is now a serious disease that is spreading in East and Central Africa.
Earlier studies identified Xanthomonas campestris pv. musacearum as the causal agent.
This paper describes the characterisation of strains of the bacterium that were isolated in four countries between 1968 and 2006. Phylogenetic analysis of partial nucleotide (nt) sequences of the gyrase B gene and internal transcribed spacer (ITS) region, and genomic amplicon fingerprints using repetitive sequence PCR and fatty acid methyl esters, showed that all strains of the pathogen belonged to the same genotype.
Twenty strains originating from Ethiopia, Uganda, the Democratic Republic of Congo and Rwanda had nt sequence identities above 98%. When compared to other species of bacteria, the pathogen was not found to be related to X. campestris, but to X. vasicola, a species that contains X. vasicola pv. holcicola, a sorghum pathogen.
Further, a group of sugarcane and maize pathogens that had been classified as X. axonopodis pv. vasculorum, but which were atypical of the species and had been proposed for reclassification as X. vasicola pv. vasculorum, were found to be most similar to the banana and enset strains.
The results support the reclassification of X. campestris pv. musacearum as X. vasicola pv. musacearum. In addition, the data reveal that the recent occurrence of Xanthomonas wilt in Uganda and other East African countries is a consequence of the spread of the pathovar first recognised on enset in Ethiopia.
Possible hypotheses to explain evolutionary pathways of the three strains of Xanthomonas that affect enset, banana, sorghum, sugarcane and maize are proposed.
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