Detection of Ralstonia solanacearum biovar 1 in Portugal
In Portugal, potato brown rot caused by Ralstonia solanacearum (EPPO A2 List) was considered to be rather widespread at the beginning of the 20th century but eradication measures subsequently lead to its disappearance. In the late 1990s, R. solanacearum race 3 biovar 2 reappeared in potato and tomato fields (including solanaceaous weeds), and it was also detected in surface water used for irrigation. In late May 2007, potato plants showing symptoms of brown rot were observed in several irrigated fields in the Baixo Mondego region (Central Portugal). Laboratory analysis (isolation on semi-selective medium, IF, PCR, sequencing, bioassays) confirmed the presence of R. solanacearum biovar 1 in potato samples. However, the bacterium was not detected in water samples collected from infected fields and their vicinity. This is the first time that R. solanacearum biovar 1 is reported from Portugal.
The origin is this outbreak is not known, although it is suspected that the bacterium may have been introduced with imports of latently infected potato seeds from abroad. The use of the same agricultural machinery by different farmers may then have played an important role in disseminating the bacterium to neighbouring potato fields. It was also noted that infected potato fields were located near ornamental and forest nurseries which might have been possible sources of contamination. Specific phytosanitary measures were taken to eradicate the disease.
The situation of Ralstonia solanacearum in Portugal can be described as follows: Transient, biovar 1 strains detected in some potato fields (Baixo Mondego region), under eradication.
Sources
Cruz L, Eloy M, Quirino F, Carrinho H (2008) Ralstonia solanacearum biovar 1 associated with a new outbreak of potato brown rot in Portugal. Phytopathologia Mediterranea 47(2), 87-91.