Recent surveys did not detect Ralstonia solanacearum and Clavibacter michiganensis subsp. sepedonicus in potato-growing areas in Lebanon
In Lebanon, potato cultivation covers around 11 000 ha with a production of approximately 300 000 tonnes per year. This production is mainly concentrated in the Bekaa valley in Central-Eastern Lebanon (70% of the total potato-growing area), and in the Akkar plain in Northern Lebanon (25-30%). In the past there had been reports of Ralstonia solanacearum (species complex) and Clavibacter michiganensis subsp. sepedonicus (both EPPO A2 List) in Lebanon, but outbreaks were considered to be rare and localized (Saad and Nienhaus, 1969). According to these old studies, R. solanacearum was reported in Akkar, only on the basis of symptoms, and this was not confirmed by diagnostic methods. C. michiganensis subsp. sepedonicus was reported in Bekaa valley where it was presumably isolated from symptomatic material. These old records were not confirmed during more recent studies, and are therefore considered to be doubtful. In the 2000s, studies conducted in some Lebanese potato-growing areas did not detected the two bacteria (Abou-Jawdah et al., 2001; Choueiri et al., 2004). Therefore, it was felt necessary to establish an extensive and reliable survey programme to assess the possible presence (or confirm absence) of both R. solanacearum and C. michiganensis subsp. sepedonicus. Over the longer term, the objectives were also to establish a monitoring programme, as well as a traceability system and contingency plan in case of positive findings.
From 2012 to 2015, extensive field surveys were carried out in the Bekaa valley and Akkar plain to assess the occurrence of R. solanacearum and C. michiganensis subsp. sepedonicus (Choueiri et al., 2017). A total of 232 potato samples were collected from the Bekaa valley and 145 samples from the Akkar plain. Composite samples of 200 potato tubers were randomly collected from each field, in accordance with EC Council Directive 93/85/EEC. Twelve potato demonstration fields, designed for export of early potatoes to European markets, were established in the Akkar plain and surveyed using the same methodology. A network of 40 sampling sites in the Bekaa valley and 19 sites in the Akkar plain was established to collect and test surface water. In addition, the largest potato storage, processing and distribution facility in Lebanon was monitored. Collected plant and water samples were tested for both R. solanacearum and C. michiganensis subsp. sepedonicus and all results were negative. It is concluded that continuous efforts should be made to ensure regular monitoring for these quarantine bacteria in Lebanese potato production fields and potato industrial premises, as this will allow certification of their absence from potato lots both for export and domestic use.
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