Ralstonia solanacearum biovar 1 associated with a new outbreak of potato brown rot in Portugal

Abstract

In May 2007, potato plants exhibiting symptoms possibly of brown rot were collected in some potato fields in the Baixo Mondego region (Center), Portugal, as a part of a nationwide programme to monitor Ralstonia solanacearum. All laboratory procedures laid down in Commission Directive 2006/63/EC, including dilution plating on semi-selective medium SMSA, indirect imunofluorescence (IIF), polymerase chain reaction (PCR) using specific primers and bioassays on tomato plants, were strictly followed and the causal agent of the disease was identified as Ralstonia solanacearum. The identity of the pure cultures of the isolated organism was confirmed by PCR, IIF and pathogenicity tests on several other plant species (eggplant, tobacco, pelargonium and eucalyptus). In biovar determination, the failure of the isolates to utilise/oxidise certain carbon sources indicated that the isolates were all biovar 1. This biovar has a broader host range than biovar 2 strains, and affects several crops of economic importance including ornamental plants and forest trees. Comparative analysis of 16S rRNA and endoglucanase (egl) gene sequences of these isolates with sequences that have been deposited at the GenBank revealed a similarity higher than 99% for several Ralstonia solanacearum isolates from biovar 1, including isolate DAR 64836 (Accession number DQ011551). This is the first report of Ralstonia solanacearum biovar 1 in Portugal. All control measures specified in the Commission Directive are being implemented.