First report of Candidatus Liberibacter asiaticus in Bhutan
Mandarin (Citrus reticulata) is an important crop in Bhutan with approximately 1.8 million trees. Since the mid-1990s, symptoms of decline have been observed in the Punakha Valley and Wangdue districts (sparse yellow foliage, shoot die-back). Considering symptomatology and presence of Diaphorina citri (Homoptera: Psyllidae – EPPO A1 quarantine pest), the occurrence of citrus greening was suspected. In summer 2002, surveys were carried out in the Punakha Valley and Wandue districts. Symptoms were observed in most mandarin orchards (at altitudes ranging from 700 to 1450 m), and were most severe near Punakha (centre of the valley). They were also observed on Citrus aurantifolia, C. medica and tangelos. PCR tests revealed the presence of Candidatus Liberibacter asiaticus. It is suspected that the disease was introduced via infected planting material (although the source could not be identified) and that natural spread is occurring as D. citri is present. This is the first report of Candidatus Liberibacter asiaticus in Bhutan.
The situation of Candidatus Liberibacter asiaticus in Bhutan can be described as follows: Present, found in Punakha Valley and Wangdue districts.
Notes
1) The EPPO Secretariat had previously no information on the presence of Diaphorina citri in Bhutan.
2) Citrus greening disease has two forms in Asia and Africa which were respectively characterized as Candidatus Liberobacter asiaticum and Candidatus Liberobacter africanum. The names of the two bacterial species have corrected as follows Candidatus Liberibacter asiaticus and Candidatus Liberibacter africanus.
Sources
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Ahlawat, Y.S.; Baranwal, V.K.; Thinlay, Doe Doe, Majumder, S. (2003) First report of citrus greening disease and associated bacterium ‘Candidatus Liberibacter asiaticus’ from Bhutan.
Plant Disease, 87(4), p 448.
Doe Doe, Namgay Om, Chencho Dorji, Thinlay, Garnier, M.; Jagoueix-Eveillard, S.; Bové, J.M. (2003) First report of ‘Candidatus Liberibacter asiaticus’, the agent of citrus Huanglongbing (ex-greening) in Bhutan.
Plant Disease, 87(4), p 448.
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