Distribution of Candidatus Liberibacter species associated with huanglongbing in Eastern Africa and first report of ‘Candidatus Liberibacter asiaticus’ in Kenya
In Africa, huanglongbing is mainly associated with the bacterium ‘Candidatus Liberibacter africanus’ (EPPO A1 List) principally transmitted by Trioza erytreae (EPPO A2 List). Several subspecies of ‘Ca. L. africanus’ have been reported, including ‘Ca. L. africanus subsp. capensis’, ‘Ca. L. africanus subsp. clausenae’, ‘Ca. L. africanus subsp. teclae’, ‘Ca. L. africanus subsp. vepridis’, and ‘Ca. L. africanus subsp. zanthoxyli’. ‘Ca. L. asiaticus’ (EPPO A1 List) was first reported in Africa in Ethiopa in 2010, and (another of its vectors) Diaphorina citri (EPPO A1 List) was first recorded in Tanzania and in Kenya in 2016 and 2017, respectively (EPPO RS 2017/166).
Surveys were conducted in Uganda (300 sites), Ethiopia (170 sites) and Kenya (9 sites) to assess the status of huanglongbing in these countries, identify the associated Liberibacter species in citrus plants and their psyllid vectors. In Ethiopia, huanglongbing symptoms were not seen at low altitudes (<1000 m; Oromia region) but were found at high altitudes (1 876–2 116 m; Gondar region). Symptoms were found in 26% of the Ugandan sites, 20.6% of the Ethiopian sites and 66.6% of the sites surveyed in Kenya. Trioza erytreae was found at 10 sites in Uganda and 7 sites in Ethiopia, but not in any of the sites in Kenya. Conversely, D. citri was found at all sites in Kenya at the time of the survey, but not in Uganda or Ethiopia. Sequencing showed that ‘Ca. L. africanus’ and ‘Ca. L. africanus subsp. capensis’ occurred together in the western region in Uganda, and that ‘Ca. L. africanus subsp. clausenae’ is the only species found in the eastern region. In Ethiopia, ‘Ca. L. africanus subsp. clausenae’ (75%), ‘Ca. L. asiaticus’ (25%) and ‘Ca. L. africanus’ (4%) occurred in the Gondar region while only ‘Ca. L. asiaticus’ was found in Tigray and Wollo regions. In Kenya, ‘Ca. L. asiaticus’ was present at the Coastal region, while ‘Ca. L. africanus subsp. clausenae’ was found in the western region. This is the first report of ‘Ca Liberibacter asiaticus’ in Kenya.
The situation of ‘Candidatus Liberibacter asiaticus’ in Kenya can be described as follows: Present, in the Coastal region.
Sources
Ajene IJ, Khami FM, van Asch B, Pietersen G, Seid N, Rwomushana I, Ombura FLO, Momanyi G, Finyange P, Rasowo BA, Tanga CM, Mohammed S, Ekesi S (2020) Distribution of Candidatus Liberibacter species in Eastern Africa, and the first report of Candidatus Liberibacter asiaticus in Kenya. Scientific Reports 10, 3919 https://doi.org/10.1038/s41598-020-60712-0